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5 Reasons Why Concerns about Mercury in Fish Are Misguided


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selenium mercury, mercury in fish
Mercury content in fish has been a health concern for many years.

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?

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.

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#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.

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

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Join the conversation

  1. 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?

  2. 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.

  3. 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!

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

  5. 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.

  6. 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.

  7. 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.

  8. 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.

  9. 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.

  10. “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.

  11. 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.

  12. 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.

  13. 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.

  14. 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….

  15. 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.

        • I just found the list of symptoms way too long. Seems to cover the whole of ICD.

    • 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.

    • Brazil nuts. Loaded with selenium to the point of only needing to eat 3/day.

      • ….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.

  16. 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?