5 Reasons Why Concerns About Mercury in Fish Are Misguided | Chris Kresser
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5 Reasons Why Concerns About Mercury in Fish Are Misguided

by Chris Kresser

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In 2004 the EPA and FDA published new guidelines suggesting that pregnant women (and those who might become pregnant) limit their consumption of fish to 12 ounces (340 g) per week due to concerns about mercury exposure.

These guidelines, which were only intended for pregnant women for the sake of their developing children, have quickly become an accepted fact among the mainstream media, the medical establishment, and the general public. They have also been indiscriminately extended to other populations, including men and women who are not pregnant. I frequently have patients that tell me they’re limiting seafood consumption due to concerns about mercury, and it seems like there’s a new study or media story on this topic every week.

But is it really true that eating fish increases the risk of harm from mercury—either for the developing children of pregnant women, or anyone else? Should pregnant women be limiting their consumption of fish for this reason? And is it possible that that pregnant women might actually be harmed by following the FDA/EPA guidelines?

Are you limiting fish intake due to concerns about mercury? Find out why you might be doing more harm than good.

I answer these questions in detail below. This article will be longer than usual; it’s an important topic and I want to give it the attention that it deserves. For the time challenged among you, here are the key points:

  • There’s no evidence that pregnant women or children (or anyone else) will be harmed by eating more than 12 ounces (340 g) of the most commonly consumed varieties of fish.
  • In fact, there’s a lot of evidence that eating less than 12 ounces a week of fish could cause significant harm to both pregnant women and young children.
  • Most pregnant women need to eat more fish, rather than less.

That’s the summary. Now let’s look more specifically at 5 reasons why you shouldn’t take conventional advice about mercury in fish at face value.

#1: Studies of mercury exposure in fish consistently ignore the important role of selenium

We’ve known about the role of selenium in preventing mercury toxicity for at least 45 years, with the first research report on this topic appearing in 1967. (1) Since then several studies have shown that selenium consistently and predictably counteracts the adverse effects of mercury exposure. (2)

How does selenium do this? Exposure to mercury is harmful because it deactivates special selenium-dependent enzymes—called selenoenzymes. Since the brain consumes nearly 25% of the oxygen we breathe, it continuously produces oxygen by-products that can damage the fats and proteins that make up the brain. Selenoenzymes are extremely important in the brain because several of them prevent oxidative damage while others actually reverse it.

In the past, researchers thought selenium was protective because it binds to mercury and prevents mercury from harming other molecules. This led to the mistaken idea that mercury causes harm in the body until selenium binds it. But our current understanding is almost the reverse: it’s not that selenium prevents mercury toxicity by binding to mercury, but that mercury interferes with selenonzyme function by binding to selenium. In fact, mercury cannot cause harm until it occurs in high enough amounts to inhibit a significant percentage of selenoenzyme activities. Mercury is only harmful because it binds to selenium and prevents it from performing its vital roles in the brain.

As long as you are eating fish that contains more selenium than mercury, the amount of selenium in the body will always be in plentiful excess of mercury. That means that these essential selenoenzymes are never inhibited to a meaningful degree. Fortunately, the vast majority of fish most people consume have more selenium than mercury. The exceptions are pilot whale, shark, tilefish, king mackerel and swordfish.

Unfortunately, the well-documented protective effect of selenium is consistently ignored in both the medical community and the media when reporting on potential harms from fish consumption. This is almost certainly causing harm, as it has led to advising pregnant women and young children to eat less fish, when we should instead be telling them to eat more.

#2: The evidence suggesting harm from consuming seafood is weak, and doesn’t apply to the fish most people consume

There’s no question that mercury is a potent neurotoxin, and that significant exposure can lead to problems in both children and adults. For example, catastrophic pollution from a chemical plant in Minamata Bay in Japan caused severe toxic effects in the local population during the 1950s and 1960s. (3)

But does that mean that eating seafood which contains mercury is harmful? This idea comes primarily from a study performed in the Faroe islands, which are located approximately halfway between Norway and Iceland, and another performed in New Zealand. (4, 5)

The Faroes study is problematic for several reasons. First, it examined the neurological and developmental effects of maternal consumption of pilot whale meat, (the source of the bulk of their total mercury exposure), and found that eating ocean fish actually protected against the adverse effects that were noted. Even if the blood levels of mercury observed in this study were associated with harm in developing babies (which is debatable, as I argue below), such low exposures were not expected to be harmful to adults and no harms were observed in adults. This is because adults have plentiful reserves of selenium throughout their bodies and in their brains that help protect their brain selenium levels from being depleted. It is only when these reserves are depleted that oxidative damage can begin to occur. Developing babies are more vulnerable because they have no stockpiles of selenium to protect against mercury.

Second, the “adverse effects” observed in this study were extremely subtle. The magnitude of the effects noted were on the order of one finger tap slower than an unaffected child in a test which measured how many times the child could tap in ten seconds. (Tap one finger as fast as you can on your computer keyboard or mobile device and you’ll get a clear idea of just how subtle this effect was.) What’s more, the children who had the highest whale meat exposures were primarily from rural areas, whereas the unaffected kids were from urban areas. It is possible that factors other than mercury exposure may have differed between the two groups (e.g. socioeconomic status, home environment, having to wake up earlier and drive a long distance to the test site, etc.), and those factors may have influenced the results instead of their mercury exposures.

Third, over 85% of the seafood consumed by pregnant women in the Faroe Islands study was pilot whale meat. Earlier in the article I mentioned that pilot whale meat is one of the few species of seafood that contains more mercury than selenium, and thus would be expected to cause harm. Pilot whale meat is also much higher in other environmental toxins like cadmium, PCBs, and dioxins. A lot of toxins can accumulate in a 5,000 lb. whale during its 45–60 year life at the top of the oceanic food chain.

The New Zealand study was also problematic. Its results were highly dependent on whether or not a single child was included or excluded. (6) That child had by far the highest blood mercury content, but also was a high achiever. Including that child made the study results insignificant, but excluding the child made the study results significant. When the results of a study depend significantly on a single subject, that throws the findings into doubt. In addition, selenium deficiency was quite common in New Zealand at the time this study was performed—they were one of the most selenium-deficient nations on earth at that time—and the take-out “fish and chips” consumed by New Zealanders in the late 1970s included fish such as sharks—which like pilot whale, are one of the few species of seafood which contain far more mercury than selenium. (7)

What these studies tell us is that consumption of seafood that is high in mercury and low in selenium by pregnant women is potentially harmful for their children, especially if overall selenium intakes are low. They do not indicate that consumption of commonly eaten seafood with more selenium than mercury cause harm to pregnant women, children, or anyone else.

#3: Studies of pregnant women consuming seafood show benefits, not harm—as long as the fish contain more selenium than mercury

There are four major studies that have evaluated the effects of maternal mercury exposure from seafood on subsequent child development. I discussed two of them above, and showed why they do not apply to most people who eat fish. That leaves two studies: one performed in the Seychelles Islands (northeast of Madagascar), and another in the UK. (8, 9)

The Seychelles and UK studies found no adverse effects from consuming seafood. On the contrary, the UK study indicated substantial benefits from increasing maternal fish consumption, and noted neurological and developmental impairments among children whose mothers had avoided fish consumption. These studies are better indicators of the effects of seafood consumption for pregnant women, because outside of a few areas like the Faroes, most seafood that is commonly consumed in the U.S. and around the world contains far more selenium than mercury.

At least one US study confirms the beneficial impact of maternal seafood consumption. Researchers examined the effects of prenatal mercury exposure in a group of women living in Manhattan at the time of the World Trade Center disaster. The women who ate more seafood did have higher levels of mercury in their umbilical cord blood, but that did not translate into worse outcomes for their children. On the contrary, consumption of seafood during pregnancy was associated with significant benefits in motor development and verbal and total IQ. (10)

Once again, we see that the effects of consuming seafood that contains less mercury than selenium are not comparable to those of consuming seafood with more mercury than selenium.

#4: Advising pregnant women (and everyone else) to reduce their fish consumption is NOT harmless

If eating fish only exposed us to mercury without offering any benefit, we wouldn’t be having this conversation. Unfortunately, that’s far from the truth.

In the UK study I mentioned above, while the researchers did not find harm in consuming more than 12 ounces (340 g) of fish per week, they did find that consuming less than that amount was associated with significant impairments of communication skills and verbal IQ at six and eighteen months of age, and continued on throughout their adolescence (these children are now ~20 years old). This study was by far the largest (14,000 mother-child pairs), best designed (multiple evaluations performed and repeated throughout life), and best controlled for other factors such as socioeconomic, educational, and a host of other potentially pertinent factors. They found the worst effects were observed in children whose mothers ate no seafood at all during their pregnancy (about 12% of the study population).

This should not come as a surprise. A large number of studies indicate that lower intake of long-chain omega-3 fats (found in fish) during pregnancy is associated with growth retardation, delayed or suboptimal depth perception, lower scores in tests which measure neurodevelopment, deficits in fine motor skills, speed of information processing in infants, and irreversible deficits in the release of key neurotransmitters like serotonin and dopamine. (11)

What’s more, it’s likely that both the benefits (from consuming more seafood) and harms  (from consuming less seafood) that were observed in the UK study would be amplified if it was repeated here in the US. The ratio of omega-6 to omega-3 fats in the US is significantly higher than it is in the UK. A high intake of omega-6 fats limits the conversion of short-chain omega-3 fats into their longer-chain—and far more important, from a health perspective—derivatives like EPA and DHA. This makes it even more necessary for pregnant women (and others) in the US to obtain these beneficial long-chain omega-3 fats directly from food. And guess what the only significant dietary source of these fats is? That’s right: seafood.

Finally, in addition to the data I mentioned above linking higher intake of omega-3 fats to better neurological and developmental outcomes in children, there is evidence that fish consumption is beneficial for adults. Studies have shown that even modest fish consumption (1-2 servings of cold-water, fatty fish like salmon per week) are associated with a 36 percent decrease in deaths from heart disease, and a 17 percent reduction in deaths from all causes. (12) For more on the benefits of eating fish, see my article “Is Eating Fish Safe? A Lot Safer Than Not Eating Fish!”.

#5: Ignoring the protective effects of selenium underestimates the risk of eating some fish

Although most ocean fish contain far more selenium than mercury, the selenium status of freshwater fish is much more variable. Mercury tends to accumulate in fish in lakes where selenium availability is limited. That leads to a double-whammy where some freshwater fish have relatively high mercury levels along with low selenium levels. This may explain why adverse effects were observed in a study of freshwater fish consumption in Finland, a country notorious for its poor selenium status, and was so low that it became the first nation to add selenium to its fertilizers. (13)

It’s important to note that even when total mercury levels in fish are below the recommended safety limit, consuming these high mercury, low selenium fish may still cause harm to consumers. In other words, it’s the ratio of selenium to mercury in the fish (known as the “selenium health benefit value or; HBVSe”)—rather than the absolute amounts of either—that determine whether it is safe to eat.


As the evidence above indicates, aside from the warnings to avoid shark, swordfish, tilefish, and king mackerel (varieties which can contain far more mercury than selenium), the EPA/FDA advice to limit fish consumption during pregnancy is not only unfounded, it is potentially harmful. From a public health perspective, pregnant women should be eating more fish—not less.

There is one reason, however, that I’m concerned about advising people to increase their fish intake: the environmental and social impact. To meet even the EPA/FDA guidelines for maternal fish intakes—which as I’ve argued in this article, are likely too low—would require a doubling of per capita fish intake in the US. Yet ecologists have warned for years that the exploitation of global fisheries at the current rate is not sustainable without massive conservation efforts. (14) Many fisheries are either completely exhausted or in significant decline, and pressure to increase fish consumption may exacerbate this problem if it’s not done in a sustainable manner.

This is a big problem—the elephant in the room when it comes to discussions about the health benefits of seafood consumption. As with many similar predicaments, there is no easy solution. I’m continuing to research the issue and will report back soon. In the meantime, I suggest using guides such as those published by the Marine Stewardship Council and The Monterey Bay Aquarium to choose only the varieties of fish that are being harvested sustainably. Fortunately, many of the most sustainable choices (e.g. sardines, anchovies, mackerel, wild-caught salmon, etc.) are also the fish that are highest in the beneficial long-chain omega-3 fats.

Now I’d like to hear from you. Have you been limiting fish consumption due to concerns about mercury? If so, how has the information in this article affected you? Are you concerned about the environmental impact of eating fish? Share your thoughts with me in the comment section below. (And please share this article with your friends and family, especially women that are pregnant and/or have young children.)

I’d like to thank Dr. Nick Ralston for his generous guidance and contributions to this article.


Join the conversation

  1. Thanks, this means I can eat my tuna without trepidation. Your article is very convincing.

    One question: drinking tea has been shown to increase mercury in the blood. I wonder if this is a significant issue. The Japanese, who drink green tea every day (and a lot of fish), have the highest life expectancy, so maybe not.

  2. Chris,

    I consumed a can (two) per day of sardines, everyday, and what do know, why hair analyses showed mercury and arsenic through the roof. So, no sardines for me.

    Now, my ND put me on chlorella which I can’t tolerate to get these toxins out. I can’t take chlorella and I’m stick with these toxins. So, heavy metals in seafood DO get absorbed by your system.

      • hah that article criticizing hair analysis is b.s. … A person that constantly gets updated on hair testing every three months or less will show hair levels rise and decrease depending on how well the body is removing mercury. So its quite simple to understand, if a person detoxes correctly … the hair level of mercury starts to drop which is a sign concentrations in the body are dropping and you can also back this up through blood work analyzing Homo-cysteine/DHT levels and seeing this level drop as mercury is removed from the body. Therefore a person that has a consistent lifestyle/diet with minimal mercury exposure while constantly getting hair analysis done will have a relatively consistent level of mercury show up in the hair but when a person starts to add fish to the diet… mercury levels in the hair shoot up … fortunately the person is able to detox this mercury because some people have a hard time… no matter how much selenium is in the body and when a person has a hard time removing mercury… the hair test will show a very low level which means the body is armoring it… the lower the reading… the worse the toxicity

  3. Mercury been on this earth long before man walked it’s surface. If as environmentals say is true then we should all be dead or at the very least loosing our hair and running around crazy
    Asians, have been eating fish daily from the San Francisco bay for a couple of century’s, Native Americans for 1000s of years
    Selenium is natural and abundant
    use some common sense
    Mercury is the cashcow for environmentals, Tax payers are being hosed

  4. When I was a competitive athlete I ate several cans of albacore tuna most days (every day if I could). I did this for years and years. Never once did I experience any of the side effects associated with mercury poisoning. The only side effect is that I felt fantastic, I became a great athlete, and I looked like Hercules. Truth

  5. For the past five years, I’ve gotten terrible headaches whenever I consume any quantity of ocean-caught fish. As I understand it, these headaches are the result of the presence of methylmercury in the fish. I have no scientific evidence to back this up other than reading I’ve done on the subject and the headaches, which are quite intense.

    • Right Michael. Studies are often full of more holes than swiss cheese, I have seen hundreds of people poisoned by ONLY eating fish, no other exposures, and it was NOT the fish this article is indicating (ie, Tuna is a huge offender, yet this article says it is okay, baloney)

  6. I am sorry, but this post is just not true. I have methy-lmercury poisoning due to my love for sushi not to forget the terrible amount of mercury in the atmosphere and soil due to coal burning. It is a real problem that cannot be nonchalantly dismissed as bunk. Please be respectful of the science and responsible with your blog.

    • He didn’t “dismiss” anything. He provided a long and well-cited blog post, explaining the errors with the sources of where the fish-mercury scare was coming from, and provided evidence that contradicted the EPA’s concerns. Disagreeing or countering established opinions is not “dismissing” anything. Blinding writing off a blog post as “simply not true” and saying “don’t disagree with science” is a form of dismissal since you aren’t providing any countering evidence or arguments.

  7. You have allayed my concern. I eat salmon for lunch and dinner nearly every day and have done so for months in an endeavor to lose weight and live a heart healthy lifestyle. I probably consume on average about 5lbs a week so I was getting a bit concerned that I might be acquiring mercury toxicity.

  8. Hi Chris,

    Very interesting topic. I am especially interested in measuring levels of mercury in humans after consumption of fish as well as measuring selenium. Chris are there studies available that have done or at least attempted to do this?

    As a treatment of mercury high toxicity levels – are there any studies about people with high mercury content – then having reduced levels after ingesting selenium?



    • The Harbor Branch Institute in Fort Pierce, Florida just did a study with a Florida University on the mercury levels of local Treasure Coast Saltwater Fish sportsmen and others who enjoy local caught seafood. You might be interested to check out their research.

  9. “Decadal Declines of Mercury in Adult Bluefish (1972-2011) from the Mid-Atlantic Coast of the U.S.A.”

    “Concentrations of total mercury were measured in muscle of adult bluefish (Pomatomus saltatrix) collected in 2011 off North Carolina and compared with similar measurements made in 1972. Concentrations of mercury decreased by 43% in the fish between the two time periods, with an average rate of decline of about 10% per decade. This reduction is similar to estimated reductions of mercury observed in atmospheric deposition, riverine input, seawater, freshwater lakes, and freshwater fish across northern North America. Eight other studies between 1973 and 2007 confirm the decrease in mercury levels in bluefish captured in the Mid-Atlantic Bight. These findings imply that (1) reductions in the release of mercury across northern North America were reflected rather quickly (decades) in the decline of mercury in adult bluefish; (2) marine predatory fish may have been contaminated by anthropogenic sources of mercury for over 100 years; and (3) if bluefish are surrogates for other predators in the Mid-Atlantic Bight, then a reduction in the intake of mercury by the fish-consuming public has occurred. Finally, with global emissions of mercury continuing to increase, especially from Asia, it is important that long-term monitoring programs be conducted for mercury in marine fish of economic importance.”

  10. I love fish and would eat it everyday if not for the warnings against it, so I find this article very intriguing. I do hope there is more research done, because unfortunately some of the opposing comments sound like they’re also based on some pretty sound evidence. I’d especially like to learn more about whether a selenium supplement would make it safer to eat wild caught fresh water fish such as Trout, Bass, and the like.

  11. I found this very beneficial. A friend linked me to this article from Facebook when I complained about keeping with my doctor’s fish in-take requirements during my pregnancy. I love albacore tuna and eat at least two cans a week. I also love salmon, crab, halibut and shrimp and just recently started liking Tilapia. I would eat it once a day when not pregnant but my doctor was stating this was too much. This article and similar ones I have researched since has given me the confidence to eat fish as I see fit. Also helps me from worrying about my toddlers consumption as they generally eat what I eat. This is my third pregnancy and this one I have gone a little off doctors advice on fish and on vitamin requirements (increasing Vitamin D per NW living recommendations) and this has been my healthiest pregnancy. As many have stated in their previous comments, it is all in moderation and keeping nutrients coming into your body at a steady level so never too much at once so your body can absorb all it needs. Thank you for the informative article.

  12. Hi!
    You have given great information about mercury/selenium ratio…you have warned of the older fish consumed like shark and swordfish…the older the fish the longer it has lived in the environment…thus creating the warnings of high mercury! You touched on freshwater fish…and gave a warning, again the freshwater fish are more likely to contain high levels of mercury!.. My question now is farming!!! There is a lot of ocean fish farming and I know to stay clear! Why have you decided to promote ocean fish but not warn against the farmed ocean fish?

  13. I have lost 85lbs in the last year. I have stuck with a good diet of good natural food. I eat 6 cans of albacore tuna a week for lunch. During the week for dinner I will consume a pound of wild salmon. Its all in moderation and depends on ones body cause everyone is different. The research I have done about murcury has lead me to stay away from root veggies like carrots, parsnips, potatoes, and asparagus. Most big company farmers plant these veggies because they absorb the heavy metals from the ground which cleans it up to grow other things the next year. Moderation is the key. Grow what you can, if you can’t, buy from local small farmers. Eat wild or grass fed meat. Stay away from farm raised fish and Walmart type meat. Big key……Thank the Lord for the food you eat and to bless it to your body! 🙂

  14. This is fascinating. I have been eating a fish diet for the past two years (previously I was vegan) and I just had a Trace Mineral Tissue test, and a Quicksilver mercury speciation test confirming total mercury levels of 21.2. Higher than my doctor, or the labs have ever seen! I was taking 200mcg of selenium for a few months before realizing this. I had hypothyroidism and was looking for my ‘root cause.’ Id say the warnings are legit. Nobody is talking about the severity of this situation. There are many sources of mercury getting into our food, but for me, I consumed fish every other day for weeks as my primary protein. Heavy intake….. sure, but it is a significant problem worth worrying about.

    • Yeah I’m not sure about this…have you come in contact with any of Dr. Chris Shade’s work? He’s an expert on Mercury and says fish and amalgams are the two biggest sources we face. As someone who suffers from Mercury toxicity and knows the difficulties of getting it out when it’s there, I don’t think you should encouraging people to think that selenium is a built in detox for any mercury that’s in the fish. From what I’m learning, that’s just not the case.

      • Currently having all my metal fillings removed and replaced with white ones. Its not cheap but I think its worth it.

    • I agree, I was eating a high fish diet for the past year, focusing on low mercury fish, wild cod and flounder and dover sole.. I just tested high for Methyl Mercury toxicity from a hair test and have many of the symptoms of it.. My poor liver function could not detox the mercury from fish !!!

  15. What comes to mind is the Seventh Day Adventist Church. It seems that their diet (protein) consist mostly of things like nuts, fish, small amounts of chicken, and legumes. No beef, or pork and very little or no fried foods. Yes, they watch their sugar, alcohol, and caffeine levels. But they live the longest of any major denomination. I think their fish eating habits come into play…

    • One of the few good things about religion is the support network that it creates which no doubt helps with health and longevity. It is a pity that it was invented by man to control men and in particular women and not for its primary benefit which is a network of support.

    • The health and life expectancy of Mormons are almost identical to SDA, but they have no such dietary restrictions.

  16. I eat way more fatty fish than mot people, at least once a day. I usually don’t believe what I’m told, because I’ve found most science experts appear to lie, but I check things out for myself. In this case a mercury test ordered by the Doctor. It came back very low in mercury. If I don’t have a problem I’d like to meet the person who does. The interesting issue that came up though confirmed the problem is a hoax. The result from the lab took a very long time so my wife went in to the Doctor’s office to find out why. Turns out the test came back, low mercury but high arsenic! It turns out that if you want to test a seafood eater for contamination you must order a special test which is rarely ordered. This test separates the two arsenic’s, organic and inorganic where the standard test dies not. If you eat lot of seafood you absorb a lot of organic arsenic which isn’t toxic. But the standard test doesn’t distinguish. Since the seafood eater test is a special order and rarely ordered this tells us there is little problem with toxic seafood since the toxic seafood test is rarely ordered. An essential skill in this world is to be able to identify the few practitioners in science who don’t habitually tell lies.

      • That’s the key take-away. Not everyone can detoxify efficiently. The one’s who can eat fish at that level and not see any mercury accumulation are the ‘perfect fish eaters.’ Lucky!

        • This article is very concerning – leading people to believe that mercury is not a problem in seafood. A few of these people are hitting on the key issue – methylation. Some people are not good natural detoxifiers due to genetic methylation issues such as the MTHFR SNP. MTHFR is more common than people realize. I have dealt with mercury toxicity for the last three years due to my dental amalgams and subsequently was subjected to more mercury exposure because they weren’t removed with all the safety precautions. I didn’t know then about any of this, but I certainly know now. When your adrenals go into near failure, your thyroid is low, and your hormones just about quit to function all because of toxicity, you get a crash course in learning all about how genetics and environment determine exactly if you will have issues with mercury. “Your genes load the gun and your environment pulls the trigger.” Chris Shade, Mercury Expert. You really owe it to your readers to add information to this article about genetic methylation issues. I don’t know if you have ever suffered from mercury toxicity or not. It’s not something to mess around with with.

  17. Chris I have to absolutely disagree with you on this article. In my office I see people with a variety of conditions that show up as mercury toxic, which I can tell using Applied Kinesiology (AK). And while it is easy to say (AK) is not scientifically valid, etc, I have found that it finds answers with far more accuracy than any lab test does. But in terms of mercury toxicity and science, here is what is known:

    1. The new science on genetic susceptibilities to mercury toxicity (see PubMed 24420334) means that individuals may have widely varying abilities to excrete versus retain mercury.

    2. Mercury’s toxic mechanism is unusually insidious. It blocks sulfur, which is found in tens of thousands of different, important biomolecules, including metabolic enzymes, cofactors, receptors, signaling molecules, and structural proteins. One result of this sulfur blockage is that mercury blocks the glutathione system, which, ironically, is the body’s detoxification system for mercury and other
    toxicants. Thus, a healthy person may be able to handle some mercury, but a person who already has a body burden may not.

    As Chris notes, mercury does not cause harm until it occurs in high enough amounts to inhibit a significant percentage of a target enzyme. Unfortunately, by the time symptoms become noticeable, much damage has been done. If the affected biomolecules are deep inside the
    cells, such as inside the mitochondria (an area for which mercury has a strong affinity), or in the fragile neuronal tubulin of the long axons, the damage may be irreversible.

    3. Mercury also binds irreversibly to selenium, which is a cofactor in several key enzymes. Although an adequate selenium intake may protect these enzymes to some degree, it does not protect against mercury’s main toxic mechanism — sulfur blockage.

    4. Data on mercury concentrations in fish show that average levels vary by about ten-fold across species. So, it is prudent to know where your favorite species lie on this continuum. In addition, the raw data show wide variability among individual fish even of the same size and species. Finally, the fish mercury concentration measurements used by regulatory agencies to develop dietary recommendations are many years old, and the world has become more polluted, particularly regarding mercury.

    5. Toxic risks to the developing fetus and child should be taken seriously because, to quote the title of a book by Harvard fish-mercury expert Philippe Grandjean, a baby has “only one chance” for proper development. Even for adults, once mercury is stored in the brain or other tissues, it may be impossible to remove it, particularly for those who are genetically predisposed for poor excretion.

    The local Bay Area Chronic Mercury Poisoning Support Group is replete with horror stories (some with ample scientific documentation) of individuals who became disabled with illness via mercury exposures that experts claimed were harmless. San Francisco physician, Jane Hightower,
    wrote the book, Diagnosis Mercury, as well as a peer-reviewed journal article on mercury poisoning from dietary fish, after many of her patients developed mercury poisoning while pursuing a supposedly healthy diet.

    6. Given that mercury toxicity is so difficult to study in humans (for example, blood, urine, and hair levels do not necessarily reflect body
    burden), it is prudent to view the results of mercury studies in the context mercury’s known toxic mechanisms. In other words, mercury is a known neurotoxin that accumulates in some individuals, and this may be difficult to detect in typical studies, thus, such studies should not be used as evidence that certain levels of mercury exposure are “safe”.

    Chris opines that the decrease in finger-tap-speed associated
    with mercury is trivial. Yet by the time a change in neurological function is clinically detectable in such a test, much damage has been done that is probably irreversible.

    The history of mercury appears to be unfolding like that of other toxicants including asbestos and lead, in which a commercially valuable product was believed to be safe until improved research eventually revealed tragically irreversible harm even at levels once thought to be low.

    • Wow, Srinika, you definitely did your homework! I suspect that Chris wasn’t aware of all this research and data when he wrote this post. If he had been, I suspect he wouldn’t feel so comfortable in making these claims. But I could be wrong. Chris, what do you think of Srinika’s post? Would you amend your statements in light of new research that conflicted with them?

      • Mr. Kresser, I notice that you haven’t responded to these comments. They strike me as extremely important. I’d be interested to read your response, if you’d be willing to share.

    • Srinika,

      Thanks for your thoughtful comment. I’ll address point by point, with input from Dr. Ralston.

      1. The new science on genetic susceptibilities to mercury toxicity (see PubMed 24420334) means that individuals may have widely varying abilities to excrete versus retain mercury.

      That is an important point and you will be interested in knowing that dietary selenium greatly enhances mercury excretion.

      (Li, Y.-F., Dong, Z., Chen, C., Li, B., Gao, Y., Qu, L., Wang, T., Fu, X., Zhao, Y., Chai, Z. (2012) Organic selenium supplementation increases mercury excretion and decreases oxidative damage in long-term mercury-exposed residents from Wanshan, China. Environmental Science and Technology. 46(20):11313-11318.)

      2. Mercury’s toxic mechanism is unusually insidious. It blocks sulfur, which is found in tens of thousands of different, important biomolecules, including metabolic enzymes, cofactors, receptors, signaling molecules, and structural proteins. One result of this sulfur blockage is that mercury blocks the glutathione system, which, ironically, is the body’s detoxification system for mercury and other
      toxicants. Thus, a healthy person may be able to handle some mercury, but a person who already has a body burden may not.

      The concentrations of sulfur in the body are ~100,000 times higher than the toxic concentration of mercury (~1-2.5 µmol/L ~200-500 mg/L), however, mercury’s affinity for selenium is on the order of a million times higher than its affinity for sulfur. Since the concentration of selenium in the body is 1 µmol/L, it is not surprising that toxic mercury exposures are able to irreversibly inhibit selenoenzymes. Mercury is currently the only toxicant we are aware of that can inhibit brain selenoenzyme activities.

      As Chris notes, mercury does not cause harm until it occurs in high enough amounts to inhibit a significant percentage of a target enzyme. Unfortunately, by the time symptoms become noticeable, much damage has been done. If the affected biomolecules are deep inside the
      cells, such as inside the mitochondria (an area for which mercury has a strong affinity), or in the fragile neuronal tubulin of the long axons, the damage may be irreversible.

      The entire point of this article is that the damaging effects you describe only occur after mercury concentrations become high enough to impair selenoenzyme function.

      3. Mercury also binds irreversibly to selenium, which is a cofactor in several key enzymes. Although an adequate selenium intake may protect these enzymes to some degree, it does not protect against mercury’s main toxic mechanism — sulfur blockage.

      Early toxicologists that studied mercury issue thought sulfur was the target, but this is because they were not aware of selenium metabolism. Sulfur molecules are acted on by selenoenzymes, and although mercury binds to these sulfur molecules first, they deliver the mercury to the selenium at the enzyme active site. Sulfur molecules are not the target of mercury toxicity, they are the messenger that deliver mercury to its actual target; the selenium in the active site of the selenoenzymes.

      4. Data on mercury concentrations in fish show that average levels vary by about ten-fold across species. So, it is prudent to know where your favorite species lie on this continuum. In addition, the raw data show wide variability among individual fish even of the same size and species. Finally, the fish mercury concentration measurements used by regulatory agencies to develop dietary recommendations are many years old, and the world has become more polluted, particularly regarding mercury.

      Actually, studies of mercury levels in fish are continually underway, and there has not been an indication of any notable trend demonstrating increases in the mercury contents of ocean fish (I can send some citations if you need them).

      Freshwater fish are a different story, but the risks related to their consumption is also inversely related to their selenium content.

      5. 5. Toxic risks to the developing fetus and child should be taken seriously because, to quote the title of a book by Harvard fish-mercury expert Philippe Grandjean, a baby has “only one chance” for proper development. Even for adults, once mercury is stored in the brain or other tissues, it may be impossible to remove it, particularly for those who are genetically predisposed for poor excretion.

      The concept that there is just “one chance” for proper neurodevelopment is the entire reason for this article. Children born to mothers that avoid eating ocean fish are without the benefits of omega-3 and other nutrients essential for healthy brain development. If that does prove to be the case, children may be shortchanged by as much as 5 IQ points-some studies indicate that in the U.S., the actual loss may be even greater.

      The mercury which is retained in brain and other tissues is almost exclusively in the form mercury selenides. Since this highly insoluble retained form has already stolen a selenium, it cannot steal another.

      The local Bay Area Chronic Mercury Poisoning Support Group is replete with horror stories (some with ample scientific documentation) of individuals who became disabled with illness via mercury exposures that experts claimed were harmless. San Francisco physician, Jane Hightower, wrote the book, Diagnosis Mercury, as well as a peer-reviewed journal article on mercury poisoning from dietary fish, after many of her patients developed mercury poisoning while pursuing a supposedly healthy diet.

      The study by Dr. Hightower documents that people that eat fish contain more mercury than those that do not. However, since her work does not compare the incidence of illness among those that do vs do not eat fish. In an oversimplified example, this is analogous to proving that since virtually all people that have ever died were known to have consumed water in the 24 hour period preceding their death, that proves that water exposure is what caused their deaths.

      As I’m often reminding people, correlation is not causation.

      6. Given that mercury toxicity is so difficult to study in humans (for example, blood, urine, and hair levels do not necessarily reflect body burden), it is prudent to view the results of mercury studies in the context of mercury’s known toxic mechanisms. In other words, mercury is a known neurotoxin that accumulates in some individuals, and this may be difficult to detect in typical studies, thus, such studies should not be used as evidence that certain levels of mercury exposure are “safe”.

      That is what is done in the current article, and is actually the point of the entire article. Methylmercury irreversibly inhibits selenoenzymes. Evidence which has disproved the earlier assumptions about mercury toxicity have consistently supported this biochemical mechanism.

      Chris opines that the decrease in finger-tap-speed associated with mercury is trivial. Yet by the time a change in neurological function is clinically detectable in such a test, much damage has been done that is probably irreversible.

      The history of mercury appears to be unfolding like that of other toxicants including asbestos and lead, in which a commercially valuable product was believed to be safe until improved research eventually revealed tragically irreversible harm even at levels once thought to be low.

      I don’t argue with the asbestos and lead issues being initially misunderstood. Certainly, the mercury issue was misunderstood for a number of years. However, in this case, the tragically irreversible harms may be arising from fears based on mistaken assumptions that have since been proven to be false.

      As always, I will continue to review the literature and consult with people on both sides of the issue. If I encounter convincing evidence that the harms of consuming seafood outweigh the benefits, I will revise my recommendation. So far, I haven’t seen such evidence.

      I had a conversation with Dr. Mark Hyman last weekend in which he raised many of the same concerns that Srinika raised, and he shared some of his experience with patients in his clinic that he believes suffered from mercury toxicity from eating fish. I am continuing a dialog with him and may have him on my podcast eventually to discuss the other side of the issue.

      It’s certainly an important topic and we should continue to explore it as deeply as possible.

      • Thank you for the response, although I believe it missed the point.

        You claim that selenium prevents mercury poisoning, and you dismiss mercury’s well-known toxic mechanism — it binds sulfur and thus impairs important detoxification pathways, — yet you offer no references aside from Li et al. (which only showed that selenium helps eliminate some mercury, not that it prevents mercury poisoning).
        Regarding mercury’s binding to sulfur, Stephanie Seneff has written for the Weston A. Price Foundation about local functional sulfate deficiency as a cause of chronic illness, noting that some people over-excrete
        sulfate even though they are deficient at the cellular level. Suchpeople who have abnormal sulfur metabolism may be particularly susceptible to the toxic effects of mercury.
        As discussed in her book, Diagnosis Mercury (if not in her 2003 study, which you describe), Jane Hightower undertook her study on mercury levels in fish-eating patients because so many of her patients had
        mysterious health complaints consistent with mercury poisoning and most if not all of these patients were found to have a high fish intake and high blood mercury levels — and most felt better after discontinuing
        fish. You may view this as insufficient evidence of cause and effect, but most sick people do not.
        The ocean’s mercury levels have already risen about 30% over the last 20 years and are expected to continue to rise.
        Based on the above, as well as the new science on genetic susceptibilities to mercury toxicity, the picture is far too complicated to claim that everyone can eat fish without consequence.

        • Please read one more time Chriss comment he explain you sulfur assocation yet you in next comment wrote the same and claim he dont understand but to be honest you dont understand

    • Excellent comment, and I totally agree. Mercury is difficult (if not impossible) to accurately gauge levels of in organs, such as the brain. Mercury toxicity is not something to be taken lightly.

    • mercury has been our waterways long before man walk the earth. the rivers of the Sierra Nevada have been purging the mercury into the bay area, long before the 49ers started mining and if the toxic nature of mercury is true,( in regards to Selenium offset) then how is it the Native Americans don’t have mad hatter disease, or Asian Americans fishing the bay for a couple of centuries, we should by all accounts have a epidemic

  18. Hi

    Slightly off topic but I have just discovered the interesting theories behind Vit K2. It seems a very plausible explanation for the French paradox given that the french seem to eat foods high in vit K2 eg cheese, pate etc. As a result I now supp with K2 and have started consuming Guida cheese and Duck liver pate. Kind of ironic that these foods are still baulked at by your average UK GP. Changing tack I am interested in making a trip to the USA to hopefully get a VAP test and maybe a consultation with a specialist who has a more holistic view instead of the typical UK dug company stranglehold view most UK practitioners have here. Can anyone advise ?

  19. Wow, such an impressive and detailed article! I watched a documentary about mercury recently and it was recommended to avoid eating to much fish especially for pregnant women. It was said see fish have the highest concentration of this dangerous chemical element. It’s higher in sees and oceans that in lakes and rivers. However I didn’t really believe this. If we’ll listen to everything then it will turn out it’s dangerous to eat, drink and breath at all…

  20. Tuna fish in cans hasn’t tasted right for the past 2 or 3 years at least. Something changed. I can’t eat it. It is contaminated with ammonia. This is probably part of the processing. Some also has soy. I stopped buying it. There may be less known brands where the tuna isn’t contaminated. If one eats tuna on occasion then it shouldn’t be an issue for most people. In the end, it
    s about the total toxic load on your body.

    If one is pregnant, one should be on a more healthy clean diet. Either buy good quality or avoid it. Take supplements also.

  21. Where do molluscan (clams/oysters/mussels) and crustacean (shrimp/crab/lobster) shellfish fall on this spectrum, compared to some of the fish species mentioned? Thanks!

  22. Dear chris,
    Thank you so much for all your great articles, love your approach and your heart integrity,,,do u have a news letter ? how one can ask a question from time to time?
    thank u so much

  23. Thanks for mentioning the sustainability issue, the elephant in the room indeed. It’s not just fish that has ecological implications–I don’t think the planet can support 7 billion humans eating a Paelo diet high in animal protein.

    • Nor can the planet support 7 billion humans eating monocropped grains and other low nutrient-density foods. The global population explosion and distribution of food is a challenging predicament with no easy answers.

      • You are right about this – if nothing else, we are reaching, or have reached, the water limits in many places. We need to drink the water, and we need it for farming. Besides – the intensive clearing necessary to feed all these people -especially the vegetarians – just exacerbates the problem by disrupting local water cycles.

        On the subject of fish – all of you who are concerned about the state of our fisheries should learn about and then (hopefully) loudly oppose the proposed Pebble Mine in Western Alaska’s Bristol Bay region. This will be a gigantic open pit, heavy metal mine smack in the middle of the spawning and nursery grounds of the last intact American fishery – the wild Alaskan salmon that are so healthy for us, and prized for their quality and abundance. It’s destructive from the outset, and only gets worse along the way.

        I think that being Paleo – in whatever form – brings with it the ancient responsibility of connecting with, cherishing, and sustaining our food sources and the environment we all share. Otherwise – too many babies, too much greed, Darwin is vindicated, and we all lose.

        There is no free lunch.

        • “Besides – the intensive clearing necessary to feed all these people -especially the vegetarians – just exacerbates the problem by disrupting local water cycles”

          This as well as Chris’s comment is very antagonistic and avoids the point of the original comment on sustainability. Chris’s comment on monocrops doesn’t fit with sustainability either and is rather inappropriate.

          All the land, water and resources we need to feed and raise the animals we eat is exactly what we SHOULD put towards growing diverse crops that supply the most nutrition for HUMANS. Think of how much MORE food we can grow directly for humans if it weren’t for the high demand of meat. Meat can’t be expected to feed our growing world population. The point is more towards responsibly using the land and reducing our meat consumption.

  24. This discussion opens up a can of worms and brings to the for front the need for a sustainable organic food supply.
    Our Canadian ecological icon (Dr David Suzuki) has once again taken a step back and reassessed the impact of fish farming on our health and the environmental impact it has caused for our coastal waters. He has devised a way to use our food waste to make our farmed fish and poultry more nutritious. Since every town and city has a waste disposal the ecological impact to our planet would be astronomical. When or if his ideas are implemented in fish/poultry farming, that will be when I begin to eat farmed fish.


  25. Hi Chris, I’m 34 and I’ve been feeling sick for the past 4 years. Recently I did a urine toxic metals test and it showed 20 µg/L of mercury and 10 µg/L of lead. I have never had any metal amalgams in my mouth and I eat a very healthy diet (organic fruits/veggies, natural chicken/beef and wild fish). I live in DC suburbs with very clean air in a 1995 colonial with zero VOC pain. I drink only spring water and do not take any medication. I also haven’t been vaccinated since I was a kid.

    Where did this toxic junk come from? The only possible explanation I have is farmed fish. Last year I had grilled farmed Costco salmon for dinner and tuna salad with rye crisps for snack nearly every day. Maybe I’m wrong and that is not the source, but SOMETHING is? Why is my body full of heavy metal sludge that causes fungus and yeast and some other opportunistic bug to prosper inside of me as I’m writing this? What do you suggest I do? Maybe eat MORE fish?

    I’m 34 and I haven’t felt healthy in 4 years. I’m going to be 35 in a few month and I’m scared to get pregnant. No, actually I WON’T be getting pregnant until my body is healthy, because I refuse to take this risk. The problem is – there’s no cure. Detox protocols contradict each other other. Cilantro/chlorella is awesome until it’s a total scam and should be avoided. Maybe DMSA/DMPS/EDTA will help? Oh stop it, silly…..
    Because the ultimate truth is – WE MUST EAT MORE FISH!
    Finally an answer that makes sense!!!

    I’m bitter because I’m sick of being sick. Because apparently mercury causes anger and hostility. Because I’m tired of causes and treatments that contradict each other. And, most importantly, because nobody cares about anything but profits.

    • I sympathize completely. As I said in my comment anything that IS healthy for us is almost cost prohibitive and I agree with you probably also cannot be trusted. Profits before people. 🙁

    • Jenna,

      I feel for you and have been in that place of feeling ill and not knowing what is causing it myself. Unfortunately, it’s all too easy to attribute illness to a test result when it “makes sense” without any specific proof that the two are connected (i.e. the positive test result and the symptoms).

      There’s a famous study that was done at UCLA on back pain and structural problems like slipped discs. The brought a bunch of people into the clinic, some with pain, some without. Then they gave them MRIs. As you might expect, some of the people had slipped discs and other structural problems, while others didn’t. But here’s the catch: there was no correlation between structural problems and pain. Some people with pain had structural problems, others did not. And some with structural problems had pain, while others did not.

      I just mention this because if you test with mercury levels slightly above the EPA limit (which is 1/10th the level shown to *possibly* cause subtle harm in developing children), and you have symptoms that *could* be associated with mercury toxicity, it’s natural to assume that these findings are connected. But that doesn’t mean that they are.

      We need to constantly guard against this as patients and clinicians.

      • Oh well. Spoken like a true western doctor. You should also add that there’s a disease called “hypochondria” and that I should google it.

        Chris, my test results are not “slightly above”. My mercury is 4 times the upper limit and my lead is 5 times that. Unless, of course, the lab chart lies?

        I’ve been diagnosed with hypothyroidism (Hashimoto’s) with antibodies and all the good stuff. I have full-blown Fibromyalgia, CFS, chronic migraines, extremely low energy and libido, anxiety, depression, mood swings, irritability, brain fog, memory problems, difficulty concentrating, night sweats and tremors.

        If you’re going to suggest that this autoimmune/neurological bouquet is not related to the toxic heavy-metal build-up, then I’ll be on my way.

        As and old Russian proverb says “Full will never understand the hungry”. Perhaps in order to really understand the disease one must overcome it himself…


        • Jenna, I am sorry to hear about all of your health problems. I completely understand because my mother was chronically ill with all kinds of problems for decades before we were able to finally get her healthy. I also cured my son of autism through lots of detoxification and extreme nutrition.

          I wanted to make a few suggestions, and please dont be offended if you have already tried all of these and they have not helped. I do a lot of nutrition research and these are things I have seen change peoples lives. These may or may not be helpful.

          1. First have complete bloodwork done for as many things as possible. Dr. J.E. Williams has a really good program for what blood tests to get and how to interpret them and what to do about them (http://www.renegadehealth.com/bloodtestblueprint/about.html). It may reveal such things as hormone/chemical imbalance, toxicity, vitamin or mineral deficiency (e.g. what are your D levels, magnesium levels, B vitamin levels), methylation problems, omega 3/omega 6 imbalances, allergies, gut flora imbalance, etc. You should try to get help doing this from a qualified naturopathic doctor, I would avoid conventional doctors, they will just try to give you a coctail of drugs.
          2. Make sure your environment is not part of the problem. Such as mold or EMF. Things like this can be subtle and can devastate a persons health.
          3. Yeah, get off the farmed fish and start taking krill oil – some wild caught fish would probably be good. If you are trying to detox the mercury out, there are two good protocols that I know of: Dr. Chris Shade’s program and Dr. Andrew Hall Cutler’s program. Dr. Mark Hyman has a good protocol as well. I would also suggest a thorough and gentle detox of your entire system, starting with your colon. Then your kidneys, liver, intestines. Then a thorough parasite/microorganism cleanse. You could consider some kind of fasting detox. In your condition of health, i would be very careful with any kind of detox and be very gentle and if possible work with a naturopathic doctor.
          4. Keep up the good diet and organic foods. Avoid GM foods. Eliminate all processed sugar. Eliminate all wheat. Probably eliminate dairy unless it is raw and fermented.
          5. Consider adding herbs into your diet. In particular medicinal mushrooms to build up your immune system. e.g. Reishi, Chaga, Cordyceps, Maitake, Shiitaki, Lions Mane, Agaracus Blazei, Agarikon, Turkey Tail, and Meshima These can change your life. There are also several other magical herbs that can help support your overall healing, e.g. gynostemma.
          6. Consume fermented foods on a regular basis. Build your gut flora strong and healthy. They are your greatest ally!!
          7. Avoid toxic chemicals. Like make sure your shower is filtered, and your not using a lot of toxic lotions, perfumes, toothpaste, detergents, etc.
          8. Consider adding in more superfoods into your diet. Like sprouts, colostrum, moringa, coconut oil, palm fruit oil, blackseed oil, aloe vera, noni. Make sure you are getting enough healthy fats like coconut oil and olive oil in your diet. You could even consider a short term ketogenic diet to reverse your poor health, though I would not advise this for the long term. Maybe try some juicing as well.
          9. make sure you are not chronically dehydrated and are getting plenty of water and raw sea salt – like celtic sea salt.
          10. some kind of exercise program would be good. yoga would probably be great. dont over do it.
          11. try to manage your stress.
          12. grounding and a hulda clark zapper. You should not do both at the same time because grounding will nullify the zapper. The zapper is for removal of unwanted parasites and microoganisms. I would suggest sleeping grounded and zapping during the day for several hours (for several months).
          13. You could visit a specialized clinic (expensive) such as the Hippocrate’s Health Institue or the Gerson Institute to both diagnose what is going on and to aid in your healing. I also think a Dr. like Dr. Mark Hyman may be able to help you – in other words a doctor that will really look under the hood to find out what is going on.

          I hope that helps and I hope you get better. Best.

          • Does the Hulda Clark zapper really work? If so, why don’t alternative practitioners use or recommend it? The closest therapy to this used in alternative care is Frequency Specific Micro current (FSM).

            It would be interesting to hear Chris Kresser’s opinion of this device.

            • Absolutely it works. I have to use it to get rid of parasites once in a while and it always works. I also know of people personally who have “cured” herpes with it. Others do recommend it, e.g. David Wolfe – not really a practitioner, but definitely a very knowledgeable nutritionist. There are lots of alternative practices not commonly recommended by practitioners I think mostly because of unfamiliarity or a lack of studies. Sometimes it takes things like this to get someone better because nothing else works.

        • Jenna, I have pretty much all of the symptoms that you mentioned, and I have been told I can’t even go to a regular dentist because of mercury exposure. Very frustrated and confused, but nice to find someone who can understand what this feels like!! Totally agree with you about mercury, totally disgusted with doctors!

        • Jenna, urine and blood level tests have been found to be very lacking in correlation with tissue levels and with toxic effects. So these results are not worth taking any notice of. As AHC explains, copper tox can be extremely like merc tox. You could easily have got copper overload, especially if you have a relevant gene for Wilson’s or Wilson or whatever it’s called disease.

          • Hi Robin, I’ve also done Doctor’s Data hair test. It showed elevated mercury and lead as well as extremely off-the-chart aluminum. No copper. And I don’t have any symptoms of Wilson’s disease. I’m quite familiar with Andy Cutlers protocol. I’m also in his FB and Yahoo groups.

  26. Your view that over-avoidance of seafood may be an ongoing negative
    factor in our ioverall health picture is likely on target – but this whole area
    is heavily laced with iffiness.
    In my own experience…I started taking selenium supplements in 1980 –
    17 years before mainstream medicine+media announced that selenium
    signiifcantly reduced risk of heart and cancer problems. Nevertheless,
    dental mercury brought me ino the world of mercury poisoning…with
    mercury almost off the chart. It might be that my positive selenium intake
    kept the results from being…even worse than they were.
    One more factor from my personal experience. Mercury poisoning MIMICS
    Lou Gehrig’s disease. My brother, whp died some 10 years ago, began
    just collapsing…leg muscles gave out “for no reason” as he would say.
    Every day, I mean seven days a week…for I guess a decade…he had a
    tuna-melt (strictly albacore) sandwich for lunch. Do I think it contributed
    mightily to his demise” Yes I do. Can I prove it? No I can’t.
    Given my related personal experience, the chart showing that albacore is
    high in selenium…will NOT even slightly tempt me to hop back on the
    tuna express. I loved tuna…enjoyed it when I visted my bother. And maybe
    his “addiction” was simply too much of a not-so-safe food.
    All that said…the points you make are interesting and well worth
    thinking about. However…as one who is living with the permanent
    residual damage mercury does to the brain and nerves…thanks, but
    no thanks.

  27. Excellent article as per usual Chris!

    I have done thousands of hair tissue mineral analyses and the most consistent pattern for elevated mercury levels is fish consumption, regardless of location in the world. More consistent than dental amalgam. It is particularly distressing to see elevated levels in New Zealand (NZ), associated with fish consumption, because we are just about as far away from the industrialised North as can be!

    By the way, shark is seldom served as fish and chips nowadays in NZ.

    Yes, NZ’ers are consistently low in selenium which is easily corrected with supplementation. While there may be selenium in fish I don’t see evidence from my testing that it is nearly enough – not for NZ anyway because our soils are generally very low. We are even more deficient in zinc and molybdenum by the way.

    A word of caution when interpreting a hair tissue test for elements like mercury: Elevated levels on the test may indicate toxicity, or can indicate that the body is efficiently excreting the toxin (therefore high in the hair sample). Low levels in the hair may indicate that one is accumulating rather than excreting! Easy to get the interpretation completely around the wrong way! So, if you are using this test to measure toxins, please consult a practitioner who is thoroughly trained and experienced in the application of this test, including matching test results with history, signs and symptoms.

    With regards to blood tests for mercury and other toxins: A blood test will only show what is circulating in the blood at that moment. The body will do all it can to whisk that toxin out of the body. If it can’t, due to too much toxin or, say weak liver function, then it will be sequestered in “safe” places like the fat and bone, later to be mobilised and excreted.

    The combination of hair and blood tests are the most useful for a clinician when it comes to determining toxic exposures.

  28. Very interesting, but like many others I am wondering about
    canned tuna? Also, I think there are large populations here and in other countries that live inland and are not true
    fish eaters. It doesn’t seem reasonable that these people with long histories of not eating much fish would be at risk health wise? Thanks for replying to so many questions.

  29. I have been limiting fish because I am concerned about fish coming from other countries, who don’t have the same safety guidelines as the US.
    What are your thoughts on fish from China, Vietnam, etc.?

  30. Another great article/discussion, thanks! My concern is not so much the mercury, I am now scared of radiation (from Japan) and the polluted quality of plastic eating fish.

  31. Thanks for this.

    Is there a reason to avoid wild caught pacific fish because of Fukushima? I keep hearing this, but I only eat wild fish, mostly Pacific, so this limits any fish I can find. What are your thoughts on effects from Fukushima on fish?

  32. This is utter nonsense. There is absolutely no provable scientific analysis behind any claims about safety. Do you understand how to actually create a scientific experiment and then how to interpret the results?

    I like some of your writings but you are way out of your league on some of the others. This is one such example. Citing other inconsequential research or falsified research doesn’t make any statement accurate.

  33. I think this is an excellent topic of discussion because of the significant importance of omega 3 EFAs in the body and especially during pregnancy. However I believe there is some misinformation in this article and some important missing information as well. I believe the issue is made out to be not eating enough fish when the real issue is not this at all, it is being sufficient in omega 3 essential fatty acids.

    Is the statement that “In fact, mercury cannot cause harm until it occurs in high enough amounts to inhibit a significant percentage of selenoenzyme activities. Mercury is only harmful because it binds to selenium and prevents it from performing its vital roles in the brain.” really true? I have my doubts. First mercury not only targets the brain, but also the central nervous system, the kidneys, the liver, the heart, the pituitary, the thyroid, and the GI tract. There is plenty of evidence that mercury can cause harm to many places in the body not just the brain as this statement implies and mercury binds to other biologically active components of the human body than just selenoenzymes. For example mercury can also bind to cell membranes and disrupt cellular function in that way. So, I dont think this statement is correct, though I am not 100% sure.

    Mercury is the second most toxic metal known to man (right after plutonium) and comes in four forms: Elemental Mercury (Hg), Inorganic Mercury (Hg2+) (when elemental mercury is oxidized and loses two electrons, it is a salt), Methyl Mercury (MeHg) (comes from bacterial synthesis of inorganic mercury), and Ethyl Mercury (EtHg) (a synthetic man made organomercurial form similar to MeHg). These all have very different reactions in the body in the way they are absorbed, where they are absorbed, and the types of damage they inflict. The type found in fish is Methyl Mercury or more correctly Methyl Mercury Cysteine. This is important to know in this discussion.

    Unlike other forms of mercury, methyl mercury cysteine is 95% absorbed in the gut and because it is bound to cysteine (which is a mimic of methionine) it can get everywhere in the body crossing the blood brain barrier and the placental barrier. MeHg is highly toxic to cells and causes massive cellular dysregulation and malfunction. It can also break down into toxic inorganic mercury, Hg2+, and do its damage in that form. This is of course if MeHg is not stopped by something like selenium, or chlorella, or alpha-lipoic acid.

    There are recent studies that show selenium rich fish do cause mercury toxicity harm. Here is one such study: http://www.hindawi.com/journals/bmri/2012/681016/. It is a study on mice, but is still concerning. I looked at some of the studies chris references and cannot tell who sponsored them, but studies are never perfect, they are sometimes wrong, sometimes not done well, and sometimes are influenced by money, profits, corporations.

    When consuming fish it is important to note the difference between farm raised fish versus wild-caught fish. There is a big difference and people should avoid farm raised fish for many reasons I wont go into, there is plenty of info on the web about this.

    Although fish and fish eggs are probably the best source of omega 3’s, there are good effective supplemental forms, including krill oil, distilled pharmaceutical grade fish oil (e.g. carlsons), fermented fish oil, and concentrated algae forms. Although there is some evidence that krill oil can be contaminated with arsenic, so may not be the best choice. If Krill is clean, however, it is probably even better than fish for omega 3s and is in fact probably the best bioavailable source in existence. And, though somewhat debatable, krill is almost certainly a sustainable source. Also, there are very rich vegetarian sources (flax, chia, sacha inchi) of ALA, which can be converted up to about 10% into DHA/EPA. I know some people thrive on ALA sources of omega 3s, but for most people, ALA sources will not result in omega 3 sufficiency. So it is simply not correct to say fish is “the only significant dietary source of these fats”.

    In my opinion, pregnant women should absolutely limit fish, but not omega 3s and I think that distinction should have been made here. Why would a woman want to consume something that is potentially harmful (there is always a possibility because MeHg does cross the placental barrier)? Studies arent perfect. A pregnant woman can get all the omega 3’s she needs from clean fish oil or clean krill oil. Moreover, omega 3’s from any source should always be consumed with antioxidants and coconut oil for greater effectiveness and oxidation prevention. Krill oil will actually not oxidize in the body, unlike fish oil.

    I think the bottom line here is that the real issue for a pregnant woman is to make sure she is consuming plenty of omega 3 oils (especially DHA and EPA) not that she is consuming plenty of fish. Fish is one source and a very good source, but the fact that fish contain not only mercury but can also contain PCB’s and dioxins means they pose a potential risk of causing damage to the fetus. And moreover, the mercury toxin level is increasing, it is not decreasing. Even if the risk is small with selenium rich fish, why take that risk unnecessarily? I think advising anyone (especially a pregnant woman) to eat lots of fish is just not a good idea. On the other hand advising everyone (especially pregnant women) to consume sufficient omega 3 oils is what should be being advised.


    • Thanks for your thoughtful comment.

      I am familiar with the study you linked to and have discussed it with Dr. Ralston, who made several of the observations I’m sharing in this response. Though at first glance it does seem to suggest harm from mercury in seafood, upon closer inspection it raises more questions than it answers. The diets which where supplemented with fish contained slightly less (~7%) less mercury, than the “MeHg” diets, but the mercury levels in all brain tissues were 35 +/-10% lower in mice that were fed diets supplemented with fish.

      In Figure 1, you can see that there was no observed effect of MeHg on the outcome they monitored, but those fed fish were adversely affected. If the harmful effects were due to mercury, we’d expect to see higher levels of mercury in the brain tissues of affected animals. Yet this is not the case; in fact, there was more MeHg in the brain tissues of animals that were less affected.

      There’s a rule of thumb in toxicology: “the dose makes the poison.” Either it’s true that the mercury in the fish caused the adverse effects, in which case we have to ignore this fundamental tenet of toxicology, or there is some other reason that animals eating the fish were harmed.

      What could that reason be? More investigation is needed, but we know that mercury the H. aimara (wolf fish) is an ambush predator that grows to body weights as big as 40 kg. It’s one of the “river monsters” that appears in the TV series of the same name. Like all apex predators, it bioaccumulates persistent bioaccumulative toxicant (PBT) agents that enter its ecosystem. These include mercury, but also many other organic and inorganic toxins. It seems more likely that one of these toxins accounted for the harm, since mercury levels were lower in the brains of affected animals than those that weren’t affected.

      As I mentioned in the article, so far the major studies that have been done on the effects of maternal seafood consumption involving species with a positive selenium/mercury ratio have found only benefit to the developing baby (and mother). As always, I’ll continue to evaluate the research as it is published and if I see a need to change my recommendation, I will.

      Finally, there are nutrients in fish (like vitamin D, selenium, and highly absorbable protein) that are not found in fish oil. I do not think they are equivalent.

    • i had Mercury toxicity in 2004 due to my 5 amalgam fillings. I was very ill from them. My legs were like stones and very heavy, I had no energy, headaches, knee and shoulder pain. And the pains travelled around my body from jaw to shoulder and turned up at a different place every day! After save removal I was treated by a natural holistic doctor in Germany. He used electro acupuncture according to dr. Voll. And we also detoxified using bears garlic (high amounts of sulphur). Neprorella algeas and a few other things plus liver and kidney support as we strengthened the detox organs. Yes Mercury crosses the blood brain barrier and I made the huge mistake in taking algeas while I still had filings in the mouth. My short term memorie was completely gone and I could not retain anything what people said to me 5 seconds after someone said something, this was very scary, however this only lasted for a few days.
      So we detoxified my body over several months and the machine was telling us how much Mercury was still in my body. In the end it was all gone. The arrow on the machine went lower and lower each time I saw him. I saw him every 2 weeks flying there from England, where I lived at the time. I just want people to know that it is definitely all reversible, so to not get scared. My brain is better then anyone’s I know of. I also take a lot of flax seed oil which really helps my brain too. I’m 38 now and look like 25. I only eat organic and no grains, sugars, pasteurized diaries… and cook my own food. That natural doctor was brilliant. 3 years ago I came to the U.S. and now I’m in a dilemma with having to eat all this US pseudo organic produce which is neither real raw nor organic. All eggs are put into bleach which is forbidden in Europe. I import my nuts from Germany as I can’t digest the (same) nuts here. The honey here even if it says raw is not raw. The word raw and natural are only marketing tools. I’m also convinced that organic here is not organic. Because I lived in 3 countries in Europe and we also had a big garden. Real organic food smells much stronger, and gets very wrinkly and withers away within 2 or 3 days!
      I came here 2012 and I heard that my natural (very successful) doctor, who healed a lot of people, died within 3 months!!! He was very healthy when I saw him last, which was in November and he was death by March! I’m sure he was killed.
      There was a doctor once found hanging (plus his secretary) because they found a cure for something. I’m sure the medical system is like the Mafia, like my 80 year old German elder friend told me. He saw over the last 30 something years all the things which helped him and his wife slowly be taken off the market!
      Same happens here too. Just that the USA is far more worse when it comes to food and much more corrupted!
      Anyway, he healed me from mercury poisoning and yes definitely you can get it out of your body and brain !!

  34. Great article. I would like to advise people that are interested in this topic to watch the award winning documentary FISH, MERCURY, AND FISH: THE NET EFFECTS. The documentary and other useful information can be viewed at http://www.undeerc.org/fish/.

  35. Hi Chris,

    Your podcasts and posts are amazing! But while mercury is a concern, PCBs and other toxins stored in fat that are also a major issue. See Marion Nestle’s book “What to Eat” as a reference – her chapter on fish is amazing and has pretty much 100% convinced me that it is neither sustainable, nor healthy to eat most species of fish. It goes far beyond just mercury, from my understanding, especially if you care about environmental sustainability…

    • I addressed PCBs and other toxins in fish in a previous article: http://chriskresser.com/is-eating-fish-safe-a-lot-safer-than-not-eating-fish

      Here’s an excerpt:

      While it makes perfect sense to try to avoid these toxins to the greatest extent possible, abstaining from fish isn’t a particularly good strategy.

      The highest dietary sources of PCBs and dioxins are not fish, but beef, chicken and pork (34%), dairy products (30%) and vegetables (22%). Fish constitute only 9% of our dietary intake of these chemicals.

      The primary concern with PCBs and dioxins is cancer. Animal studies and some evidence in humans suggest that both are carcinogenic.

      However, an analysis has shown that, per 100,000 individuals, consumption of farmed vs. wild salmon would result in 24 vs. 8 excess cancer deaths, respectively, while consumption of either farmed or wild salmon would result in 7,125 fewer coronary heart disease (CHD) deaths.

      Another analysis of the same data suggested that, for all ages evaluated (25-35 to 85 years), CHD benefits outweighed cancer risks by 100- to 370-fold for farmed salmon and by 300- to more than 1000-fold for wild salmon.

      It’s important to note that the benefits of fish consumption are based on prospective studies and randomized trials in humans, whereas estimated cancer risks include a 10-fold safety factor and are based on experimental data in animals and limited studies in humans at extremely high doses.

      Cancer estimates also assumed lifetime salmon consumption of 1,000 mg/d of EPA & DHA (four 6-oz servings of wild salmon every week for 70 years). Of course virtually nobody in the U.S. currently eats this much salmon.

      On the other hand, CHD mortality reduction may be achieved with lower intake (i.e. 250 mg/d – one 6-oz. wild salmon serving per week). At this intake, CHD benefits would be the same (7,125 fewer deaths) while lifetime cancer risk would decrease by 75% (6 and 2 estimated deaths per 100,000 for farmed and wild salmon respectively). The CHD benefits would outweigh cancer risks by more than 3500-fold in the case of wild salmon.

  36. Hi Chris

    Super interesting article! I also liked the fact, that you widened the scope a bit and talked about the ecologic and social impact. This really often is my concern when I think about eating more fish. Also thanks for the insight on freshwater fish. I live in a region in Germany where we have a good supply of rainbow trout, can you say anything about the selenium/mercury ration of trout?



  37. I’m pregnant and I haven’t reduced my seafood intake at all. In fact, I am trying to INCREASE it by making sure that I eat sardines for lunch at least twice a week (in addition to fish and shellfish for dinner a few times a week). My whole life my mom called fish brain food, and ate a ton of fish when she was pregnant with me. I, obviously, am brilliant, so there you go 😉

    • Same here. I eat a good canned sardine a couple of times a week, brazil nuts, canned Atlantic wild caught salmon every week or so and call it done. Getting all wrapped up in every detail and worry about this and other health details, frankly, has become soul-sucking (FOR ME–if you have issues, go for it with a bang so don’t go off on me here. LOL) but life awaits and I am partaking and backing off from all this in the future. 66 YO granny, feel great now, eat the best I can and don’t worry about it. I know what to do, will have an ear cocked for changes in Paleo (which is changing and that is good!!–Vegans seem stuck, doctrinaire and desperately searching for corroboration–which turned me off years ago when I was searching.) But these are MY own opinions. I had to stop and evaluate just how much time and money I was spending on obsessing on all this. People should decide for themselves–and I have. Chris does a super job and I respect what he is doing. About the “studies” you have to pick something, or you are just whipped around in confusion and worry and obsession. I am not a scientist–but in my years I have decided to trust what I feel and think, along with what I know already. I have to–I want to sleep at night. LOL. At 66 I do know that feeling good and good health is important and makes the rest of my life more fun and strong. That is the goal. The rest of my life outside of my diet and exercise being worthy and accountable and productive . Best and regards to all here!

  38. Hello Chris, this is a great article however, for many of us it is impossible to get or afford ocean fish. Most of the fish available in our area is farmed and farmed fish has been analyzed to have very low levels of Omega-3 fatty acids; farmed salmon are fed artificial Axtaxanthin which is toxic; and the chemical soup that farmed fish swim around in because of the waste material given off by the high concentrations of the fish in the cages is dangerous. It’s the same conundrum as with organic foods. We all know that they are better for us but who can afford them on a continuous basis? Ocassionally I buy them along with ocean fish but I’m sticking with eating mainly herring which is the highest in Omega-3 and the lowest in mercury and is also affordable. I also take a well distilled Omega-3 oil with independent lab analysis and eat brazil nuts and lots of onions for selenium. Thanks again for the great article. I will try to eat more wild caught salmon if I can.

  39. Chris – Love your articles! It’s awesome how you cut through the BS that reigns on other sites.

    Question – so if my selenium levels are adequate I DON’T need to have my amalgam fillings removed?


    • Laure,

      This is probably the first time I have disagreed with Chris’s assessment. Mercury is toxic, period. Amalgams are the worst. Your fillings MUST be removed by a properly trained dentist (search IAOMT), with proper detox protocol, as well…

    • My mom is 89 and in pretty good health. She’s had amalgam fillings since she was a teenager, and has had lots of other dental work besides. She also cooks in aluminum pots sometimes. What else can I say except that you can’t argue with success?

  40. Chris, you mention sardines, mackarel, wild salmon but what about tuna? Do most varieties of tuna have more selenium than mercury? Also what about the tuna and other seafood substitutes. I read an article that tested sushi restaurants across US and over half the fish they stated on menu (tuna, snapper etc) were actually another lower quality fish.

    Sushi is my favorite but my trust in most sushi establishments is low. Almost all of them use farmed salmon which is terrible and even when they tell me I can pay more for wild, I question it. I can usually tell when salmon is wild by the color and texture but now they are even using dyes to make it look like wild etc. When I order crab on the menu, I get pollock.

    • Tuna is high on the food chain, so its mercury levels are high as well. I’m not sure about the ratio, but given the high mercury levels, I would guess the ratio wouldn’t be too great. This Wikipedia article links to a bunch of articles you can read for more info: http://en.wikipedia.org/wiki/Tuna#Mercury_levels
      If the sushi you eat is from large predator fish, then it will be high in mercury too.

      Re salmon. I remember reading an article on Mark’s Daily Apple about different types of salmon farming. Farmed salmon wasn’t as good as wild, but there were definitely some types that were pretty good quality. I’ve actually found that farmed salmon looks and tastes better than frozen, though I eat mostly eat wild, for the health benefits. So I’m not sure how you are able to tell the difference between wild versus farmed, because by taste and look alone, the farmed actually seems to be much better quality, probably because they can manipulate feed and use dye to improve taste and texture. I definitely wouldn’t trust taste and appearance to guess whether salmon was wild or farmed.

  41. Thank you Chris for the great article! But I’m still a little confused…. isn’t there a problem with mercury accumulating in the body?

  42. Oh Chris, I can’t STAND the taste of seafood. Give me some good news…please? Is there any other way to get the nutrition?

    Thank you for your article! 🙂

  43. I totally agree that eating fish is a good idea and safe. But to add to the conversation – my dad is a deep sea fisherman who lives on Nantucket Island. He argues that politics have totally overtaken the fishing industry and some particular industries (particularly tuna) have influenced the numbers as far as the amount of mercury to selenium. He says that if they want good numbers, they just use small fish to get the numbers and ignore the large fish that have much higher mercury. He would still eat any fish – mercury or no mercury – but it is something to consider. He understands how fish pick up mercury and can see how that happens – but do you know how fish pick up selenium? We are not sure about that – and it would make a difference if the fish pick them both up at the same time. If you would like to talk to him about this in the furthering of your research – he would be delighted – as fishing is his life and his favorite topic of conversation. 🙂

  44. Hi Chris,
    What about the Fukushima Daiichi nuclear disaster and the levels of radioactive materials now in fish? Wouldn’t this be more of a problem than mercury levels and why we would advise to reduce fish consumption from these areas?

  45. Hi Chris,

    What would you say is a “safe level” of mercury?

    My Doctor’s Data test revealed a level of 21 for me, 11 for my daughter, both well above the 4 that the lab notes as the upper limit of “normal”. After removing the last couple of mercury fillings I will be doing a chelation but just wondering what you consider to be the normal range.


  46. Thank you, Chris, for the very informative article. Is there any data to show that the way in which organic methylmercury from seafood causes toxicity, ie by interfering with selenium, is similar for mercury that emanates from dental fillings (which is not all organic methylmercury, I think), or might more direct means of toxicity apply here?

  47. Great article Chris. I think many people will have a difficult time “swallowing” substantive changes to dietary recommendations because they have heard certain things their entire lives (e.g., sunlight causes cancer, cholesterol causes heart disease) and it is fully integrated into their way of thinking and doing. Unraveling certain habits is very difficult.

    My partner and I recently celebrated the birth of our daughter. We did not use any supplementation, rather, we sought high-nutrient content foods. Prior to conception, during pregnancy, and now through breastfeeding, seafood is a major emphasis of our diet. Certainly, we have avoided (or severely restricted) certain foods (high-trophic level predators), but in no way have we followed any FDA recommendations (raw seafood such as shellfish and roe were high on our list to acquire). We have a beautiful, alert, healthy, and fast growing (95th to above 100th percentile for size metrics) daughter who appears to me to be happy and enjoying life.

    Given that we recognized the importance of seafood in supplying several important vitamins, minerals, and omega-3 fatty acids, we did not completely throw caution to the wind. We often consume seafood with chelators (such as chlorella, there are others) to help bind to heavy metals that may be present in food. Certainly, I don’t consider chlorella to be the panacea that some dieticians do (and am concerned about B12 analogues–but we get lots of active B12 in our diet). There is good evidence from Asian studies that chlorella also limits other fat-soluble toxins (e.g., dioxins, PCBs) in the body and keep these lower in breast milk than mothers not consuming chlorella. I think there are strategies, such as one we used, that will allow people to consume seafood with greater confidence and know they are limiting absorption of mercury and other potentially harmful items. Seeking selenium-rich foods (not supplementing) would be another one that would seem quite valuable. Again, thank you for your writing. Ktankeyasin (take care of yourself).

    • Interesting. I’ve read about the concerns with eating raw fish during pregnancy, so I was wondering what you did to lower possible risks of microbial contamination? Congrats on your daughter, btw.

  48. I enjoy your articles. This one, I paid considerable interest to since I have been treated over the last few years to treatment for mercury poisoning. My mercury levels were very high, and I was losing hair and had almost every symptom imaginable. My homeopath put me on a cleanse with tablets to help remove the mercury. My mercury fillings were removed some time ago, so I don’t know if it was fish, or the build up of mercury from things like fillings, etc. and time that caused this. What I do know, is that even a year after the cleanse, I ended up losing my sense of smell. When we did another round of tablets to cleanse the final bits of mercury, my levels finally went down, and my sense of smell returned. I am now slightly paranoid about eating any fish with mercury…and I like fish! What I have been doing is occasionally having things like salmon, and avoiding Ahi or swordfish, two of my favorites. I have also started taking fermented cod liver oil and capsules with pasture raised butter (k2) to help support the cod liver. I am beginning to feel better. Any other thoughts are appreciated, this was a nightmare to figure out medically, and has been a long journey to cure. How long, in your opinion, would mercury from fillings stay in the body? Do you think it was just being personally more sensitive to the mercury that caused this? I ask, with absolute sincerity…I do not want this to happen to me again, thanks!

  49. I’m more concerned about the radioactive contamination of Pacific seafood today than mercury … can you do an article on that?

  50. Would you say eating 20 ounces of canned tuna daily be safe?

    Would you recommend increasing the amount of selenium via diet/supplementation in this scenario?


      • Wild Planet brand of canned tuna claims lower mercury because they only catch small sized tuna. The package states an average of 3,350mg omega 3 per can including 2,200 mg DHA/750 mg EPA. Pole and troll caught.

  51. Chris,
    Great article. Left me wondering though, since shrimp is a favorite of mine, what is the mercury to selenium ratio there? Is consumption of wild caught shrimp still a good idea?

    • Shrimp has a positive selenium health benefit value, which means that it has more selenium than mercury.

  52. Thanks Chris, as always, for being the voice of reason. I wanted to second the question above: for those of us who can’t afford wild caught salmon twice a week (and can’t stomach sardines or mackerel), is farmed salmon better than nothing?

    • Probably, but there are other choices too. And not all fish farming is equal; some methods are much worse than others in terms of health and environmental impacts.

  53. Dr. Brownstein, in an interview with Sean Croxton seems to differ with–possibly closer to Wendy Myers’ point of view as expressed in her post here.

    Personally, I find your point about the mercury in hair samples coupled with adequate selenium more compelling.

    • Dr. Brownstein has made some, errrr, far-fetched claims in the past. For example, he claimed that iodine can protect the entire body from Fukushima radiation. Nothing, except maybe a lead-lined room, can protect the entire body from ionizing radiation.

    • There are two issues with canned tuna: it is not particularly high in EPA/DHA, which is the primary benefit we get from eating fish; and it is often one of the most over-fished species.

  54. Chris, thank you – this article is very timely as my 10 month old son recently underwent a new genetic test (by MercuryWise) that determined he was very high risk for mercury sensitivity. As I am still breastfeeding, I thought that I should limit my fish consumption – or is this too paranoid? Do you have any tips for avoiding mercury aside from fillings and risky fish? I have informed my dr, and requested that he receive thimerosal free vaccines.

  55. “Safe” levels of Mercury? Ahhhh, no thanks… I’ll stick with my mercury free fish oil capsules.

    Problem solved.

    • Yes, there are safe levels of mercury—and several other toxins that you already have in your blood from breathing air, drinking water, eating food, and living on Earth in the year 2014.

      Fish oil capsules do not contain selenium, or vitamin D, or other nutrients that fish contain. And since selenium and selenoenzymes play a crucial role in preventing mercury toxicity and oxidative damage in the brain in general, and since supplementing with selenium long-term may not be safe (http://chriskresser.com/important-update-on-selenium-supplementation), fish oil capsules are not the equivalent of fish.

  56. Dr. Michael Greger just posted a video based upon his own research that fish consumption of 2 servings or more can cause diabetes. He blames omega 3 fatty acids (?) and heavy metal toxins. http://nutritionfacts.org/video/fish-and-diabetes/?utm_source=rss&utm_medium=rss&utm_campaign=fish-and-diabetes&utm_source=NutritionFacts.org&utm_campaign=2d1d76a9d3-RSS_VIDEO_DAILY&utm_medium=email&utm_term=0_40f9e497d1-2d1d76a9d3-23455225

    He is a vegan and all of his research seems to disparage any diet that isn’t organic plant based. Is this an example of cherry picked data perhaps?

    • To say the least. The idea that fish consumption causes diabetes is preposterous and completely unsupported by the evidence.

    • When it comes to our health, I am increasingly concerned about opinions backed up with scientific data, because it is all too easy to cherry pick and slant research to fit an agenda. My advice is to always do your own research. No one is really going to look out for your health but you. Especially people making money from their point of view.

      There are some very good reporters out there who have a balanced perspective — and no personal stake in the game.

    • ALL Omega-3 foods/supplements raise blood sugar–Hubby’s BG monitor says so, and is backed up by the PDR for herbs/supplements.

      Along with Omega-3, NSAIDS, any kind of opioid pain-killer, and any kind of steroid can raise BG levels–some quiite high (as Hubby’s now learning with prednisolone for treating patella bursitis).

      • Thank you for this information. I have not heard or read about this before, however I really appreciate the tip to look into for further understanding.

    • Uh, yeah. This is ridiculous. I think many in the vegan community go to great lengths to support claims that eating animal protein is detrimental to health. They have to because it’s not supported by properly done and interpreted scientific research.

  57. This was an interesting article. One thing I would like to mention is that you say the main benefit of eating fish comes from it’s Omega 3 content and the main disadvantage is environmental aspect. However, there are other ways to get Omega-3’s in the diet – foods such as grass fed organic meats and wild game for example – these would not have the mercury problem and also takes pressure away from fish stocks. Personally, I have two potions of small oily fish such as sardines a week and I also have wild venison and grass pastured lamb every week.

  58. I underwent a year plus of IV chelation to remove heavy metals (lead, mercury, aluminum, iron, cadmium, and arsenic). Of course in the course of my lifetime I took antibiotics countless times, ate mostly processed foods, and loved sugar. The leaky gut that resulted left me (like many others) vulnerable to toxins of all sorts. I believe most Americans who eat SAD do not have the advantage of normal, healthy gut ecosystems. To assume the body will work as it was designed to work is optimistic.

  59. There are many flaws and ommissions here. First, you claim that “adults have plentiful reserves of selenium throughout their body”. As a clinician, I have seen many tests showing low selenium. Also, as a blanket statement, this is a huge generalization for all people, all continents.
    You acknowledge higher mercury in cord blood but say no effects to baby were found. A classic example of testing one result and not looking for effects in other areas.
    Mercury is the second deadliest poison on Earth, after radioactive plutonium. This article treats it too lightly and cherry-picks studies.
    Thank you.

    • I agree Beverly. Most of my clients test low in selenium. It’s really deficient in the soils. I’ve been talking selenium for two years and my selenium levels are still low! It seems to be challenging to raise this mineral level.

      But I do find it an interesting concept that mercury ingestion can be reduced if one eats fish that also have adequate selenium. I like this point of view because I love my sushi!

    • Mercury isn’t even close to the second-deadliest poison on earth, and radioactive Plutonium isn’t on the top-fifty list.

      Alt-med quacks like you would be wise to avoid making easily-falsifiable claims not central to your main claims. You’d retain a little more credibility that way.

      • Chill man. There is no reason to be rude because you disagree.

        While I disagree with some points Beverly and Wendy make and tend to agree with Chris’ more “neutral” approach, they do have data to support their statements. When Wendy says that “[a]lmost everyone has low level mercury toxicity”, she is not incorrect. While I feel her assumption that the low level toxicity most people have means that most of us will develop symptoms of mercury toxicity is flawed, SHE IS NOT WRONG that many of us have “higher than optimal” mercury levels (what is “optimal” is debatable and dependent on individual biology).

        When Beverly states that Chris is cherry-picking studies, he is in a way. He is attempting to show a more balanced attitude toward fish consumption and offer supporting research for that attitude, not say “mercury isnt important”, which is what I think some people took away from this article.

        It is possible to disagree with someone without being rude. Being rude diminishes your ability to get your point across clearly and makes even the people who agree with you not want you to speak. Don’t be the guy that even your teammates wish would quit the game….

  60. I have to say I don’t entirely agree with Chris’s position on mercury. I’ve done hair mineral analysis on all my clients and the ones that eat lots of fish have high mercury levels in their hair in addition to suffering the physiological effects of mercury toxicity. The ones that stick to very low mercury fish like sardines, anchovies and salmon have low or nonexistent levels in their hair. I think it’s about eating fish with low mercury levels. Of course I have all my clients supplement selenium and eat selenium-rich blue corn chips and take fish oil extracted from small fish. For me personally, I’m sticking to low mercury fish and avoiding the others even though I take selenium daily.

    Learn why everyone is mercury toxic and why fish is only one source of mercury. There are many other sources from which we ingest mercury so it’s wise to avoid larger fish since we can control ingestion from this source: http://www.liveto110.com/everyone-is-mercury-toxic/

    Check out my seafood survival guide: http://www.liveto110.com/seafood-survival-guide/

    • Statements like “everyone is mercury toxic” cannot be supported by the peer-reviewed evidence, ignore the role of selenium, and are a disservice to people that are already not eating enough seafood.

      Finding mercury in the hair is not relevant if selenium levels are adequate, and mercury levels are not above the amount shown to cause toxicity in adults. Furthermore, it’s not possible to determine that the symptoms you are seeing in your patients are attributable to “mercury toxicity”.

      Taking selenium supplements daily is also probably not a good idea over the long term, as I explained here: http://chriskresser.com/important-update-on-selenium-supplementation

      • I agree with Wendy. I got mercury toxicity from eating fish once per week. I also have several hundred hair tests on patients and the amount of mercury present in hair perfectly correlates with fish consumption, unless it is salmon or some other low mercury fish.

        Chris is correct though, high mercury in hair does not always correlate with symptoms of mercury toxicity. It is mostly those who have poor genetics for excreting mercury who have problems with it. My educated guess is that it is somewhere around 20-25% of the population who can’t excrete it. I don’t think the mercury is doing the other 75-80% of the population any favors though.

        I don’t want to encourage my patients to take the gamble that they are in the 75-80% category either. Mercury is too neurologically, immunologically and hormonally disruptive to want any of it around anyone.

      • When I say “Everyone is mercury toxic” I’m referring to low-level chronic toxicity, not serious toxicity requiring immediate medical attention. Fish is one source of mercury, but we also ingest it breathing air as mercury is released into the air with coal burning, etc. Many also have inorganic mercury in their body from amalgam fillings. Almost everyone does have low level mercury toxicity. Just wanted to clarify.

        • I have to agree with Wendy. My friend is a top MD in NYC- Integrative Medicine, and he sees a lot of mercury issues in his practice.

    • This is where you think and act for yourself because you have seen the effects of too much fish. I’ve encountered mercury toxicity with people eating too much fish as their primary source of protein.

      *** Methylmercury neurotoxicity is associated with inhibition of the antioxidant enzyme
      glutathione peroxidase ***

      …the mechanism of mercury toxicity in the adult brain may be related to proteins involved in mercury excretion, including glutathione, glutathione transferase, metallothionine and ApoE. Mercury depletes glutathione, selenium, and ascorbate (vitamin C), as well as inhibiting thiamine (B1) and pyridoxine (B6).

      Mercury exposure is the second-most common cause of toxic metal poisoning.

      Revised Protocol for Detoxifying Your Body from Mercury Exposure

      In summary, depletion of GSH increases MeHg accumulation and enhances MeHg-induced oxidative stress, and conversely, supplementation with GSH precursor protects against MeHg exposure in vitro.

      Can’t believe that CK is recommending more fish.

      • ….and much tastier than a powder filled gelatine cap!

        Now we can all enjoy our pilot whale, with a brazil nut batter 😉

        Thanks for making mention of this Wenchypoo.. I forget sometimes how rich these little guys are in Selenium.

  61. Informative and very helpful. But I noticed you did not discuss any of the published “safe” guidelines for blood levels of mercury. Is that due to your argument that selenium is protective, thus mercury blood levels are somewhat irrelevant?

    If your patients consumed more fish (ie, fish with good selenium/mercury ratio) and blood mercury levels went up above the govt recommended levels, is this actually less of a concern for a given patient than the government has made it out to be?

    I eat more good ocean fish than the average American so my question is of personal interest. Also, I eat one or two Brazilian nuts per day to add more selenium – is that selenium overkill, so to speak?


    • I was going to discuss this but at 2,500 words the article is already extremely long. But since you asked, I’ll take the opportunity to do it here!

      The “safe” limit for blood mercury established by the EPA is 5.8 µg/L. This is 1/10th of the blood level that was associated with the subtle adverse effects in prenatally exposed children in the Faroes that I mentioned in the article. What is missed in the discussion of this issue is that this “safe limit” is 1/10th of the level that might have caused slight harm in prenatally exposed children–not adults. There is no evidence whatsoever that a blood mercury level of 5.8 µg/L is harmful in adults, especially those with adequate intake of selenium.

      This is why a recent study showing that fish consumption leads to mercury levels higher than the 5.8 µg/L limit in adults, which generated a lot of media “scare” articles about mercury in fish, should not be a concern. The assumption in that study (and many others) is that the EPA limit is the point at which toxicity starts to occur, but as I explained above that is not the case—-even without any consideration of the role of selenium. You can see how one mistaken belief can lead to a series of other misconceptions. Unfortunately, this happens all-too-often in scientific research.

      I think one or two Brazil nuts a day is probably overkill. 2-3 times a week is fine if you’re eating other foods that contain selenium.

      • So if 5.8 ug/L in blood might not be a concern for adults, how does my recent testing of twice that with 12.43 ug/L (62 nmol/L) give reason to be extra careful with mercury in food/environment, increase selenium intake and suspect metal metabolism issues?

        This was back in January, and working with my functional medicine doc we’ve lowered the blood value to 3.0 ug/L (15 nmol/L “dentist levels”). We’re now working on gut flora etc in preparation for mercury chelation. I’ve been suffering with post-viral fatigue (ME/CFS) since mononucleosis back in March 2012, and these last months of lowering mercury levels have been significant in reducing headaches, fatigue and more symptoms – or at least it is presumed to be related to the mercury reduction.

        Thanks for all the good information and discussions you put forth 🙂

      • I’d suggest taking brazilnuts whenever fish, esp. shrimp is served. Is that a good policy do you think?

    • Same here. Very informative article. I guess we can supplement selenium or rise its intake through brazilnuts or must it come in the fish itself?

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