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. #fertility #pregnancy #kidshealth #myths #truths
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?
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
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)
#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.
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#4: Advising Pregnant Women (And Everyone Else) to Reduce Their Fish Consumption Is Not Harmless
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)
Conclusion
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.
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.
I’d like to thank Dr. Nick Ralston for his generous guidance and contributions to this article.
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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?
Cheers
Robyn
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.
“Decadal Declines of Mercury in Adult Bluefish (1972-2011) from the Mid-Atlantic Coast of the U.S.A.”
http://www.ncbi.nlm.nih.gov/pubmed/26148053
“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.”
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.
Well, Kevin, if you’re avoiding your love for daily fish then you can live vicariously through this guy:
https://www.youtube.com/channel/UCLoEIgWoth8VyJS3eeXSPlw
His entire diet is Fish. Yogurt. Water.
He posts weekly updates on his weight, condition, and basic metrics.
Note: You might have to tune in to see if he takes any selenium supplements.
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.
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?
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! 🙂
Amen brother
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 !!!
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.
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.
you may be a very good mercury detoxifier. doesnt mean everyone is.
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.
Genetics have nothing to do with it, Deanna. The selenium binds to the mercury, no matter what.
I think it’s pretty fishy when some of these posters say that they consume a lot of selenium and they still got mercury poisoning.
Scratch that. You are correct.
I had high hopes after reading Chris’ article, but he didn’t get it right. And he didn’t even edit it to put in the info.
This will be the last article I’ll read from this guy.
http://drhardick.com/genetics-detox-methylation
Edit your article, you moron.
and was this a blood test or a urine test?
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
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 ?
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…
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.
Don’t forget about the BPA in those cans! Another reason to avoid…
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!
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
Vishva
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.
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.
http://blogs.vancouversun.com/2013/10/16/david-suzukis-idea-leads-to-insect-based-fish-feed/
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…
http://drhyman.com/blog/2010/05/20/mercury-get-this-poison-out-of-your-body/
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.
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.
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.