Mercury Toxicity, Kids & Fish Consumption

Mercury Toxicity, Kids & Fish Consumption

by Chris Kresser

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Recent research suggests that kids may be more sensitive to mercury than adults and that toxic effects may occur at blood levels that are significantly lower than the conventional upper limit. But does that mean kids shouldn’t eat fish at all?

I pay special attention to any research that concerns health risks to children. As a parent and a clinician, there are few things more important to me than protecting the well-being of our future generations.

There’s no shortage of studies indicating that mercury is toxic to both adults and children. Thus far, however, virtually all environmental policy in the US regarding exposure to mercury (and other toxins) has been based on risk to the “average adult.” Policy makers have paid little attention to the unique risks that toxins pose to infants, children, and other vulnerable populations.

This is a serious mistake because there are at least four differences between children and adults that suggest children are far more vulnerable to the effects of toxic chemicals:

  1. Children have greater exposures to chemicals for a given body weight. Kids drink seven times more water, eat three to four times more calories, and breathe twice as much air per pound of body weight than adults. Studies have shown that both low weight and short stature increase the toxicity of mercury and other compounds.
  2. Children’s ability to metabolize and eliminate toxic compounds is significantly lower than that of adults, because they lack the enzymes needed to break down and remove these chemicals from the body.
  3. Children’s early developmental processes are easily disrupted. We now understand that children have “windows of vulnerability” where exposures to even minute doses of toxins can disrupt organ function and cause lifelong dysfunction.
  4. Children have more time to develop chronic disease. Some diseases, like cancer and neurodegenerative conditions, can take decades to develop. This makes causality less obvious and difficult to track in studies. For example, at Minamata Bay in Japan, impaired cognition and dysfunctions in mood and behavior were found in adults who did not exhibit any clinical effects as children following developmental, early-life exposures. (1, 2, 3)

Fish consumption and mercury toxicity in kids: a growing concern?

These differences may explain the findings in a study called “Fish consumption, low-level mercury, lipids, and inflammatory markers in children.” (4) Researchers studied 100 kids in Oswego County, New York, between the ages of nine and eleven.

Not surprisingly, they found that the kids who ate fish had better lipid profiles, with higher levels of HDL cholesterol and lower levels of triglycerides. This is consistent with a large body of evidence linking fish consumption with improved cardiovascular health.

Less expected was the finding that the fish-eating children had a blunted cortisol response and higher levels of inflammatory markers. Cortisol is a hormone that plays a crucial role in our ability to respond to and tolerate stress. The researchers speculated that mercury from the fish increased the production of inflammatory proteins, which in turn eventually suppressed cortisol levels. This was the first study to document an association between blood mercury levels, systemic inflammation, and endocrine disruption in children.

Kids may experience toxic effects of mercury at doses lower than previously thought.

Disturbingly, these harmful effects were observed at blood mercury levels far below the current safe limit of 5.8 μg/dL established by the WHO and the US National Academy of Sciences and National Research Center. The kids in this study had an average mercury level in the blood of 0.77 μg/dL, and, with one exception, all affected kids had a mercury level below 3.27 μg/dL.

This is not the first study to show that mercury can have toxic effects in children at levels that are below the current safety threshold. Researchers in Granada, Spain, found declines in cognitive function, memory, and verbal processing in preschool age children at levels below the conventional limits. (5)

Not so fast! Other studies show that kids benefit from fish consumption

After reading that last section, you might be ready to pull fish and seafood out of your children’s diet entirely. But before you do that, consider the following:

  • Fish consumption may only make up about 7 percent of the mercury levels in the body, according to a study published in the journal Environmental Health Perspectives. (6)
  • A large body of evidence suggests that maternal consumption of seafood during pregnancy protects against mercury-associated impairments in cognitive function, attention, and behavior. (7, 8, 9, 10, 11, 12)
  • Fish and seafood contain nutrients that are vital to proper brain development in children, including the long-chain omega-3 fats EPA and DHA, selenium, zinc, and highly absorbable protein. (13)
  • Studies on the impact of public health advisories to limit fish consumption suggest that they may mask the nutritional value of fish and lead to a greater reduction in fish intake than is desirable. (14, 15)

There’s no one-size-fits-all approach when it comes to fish consumption and mercury!

So far we’ve reviewed studies suggesting that mercury may be toxic in children at levels much lower than the established cutoffs, as well as studies that consistently indicate benefits from consumption of seafood by pregnant mothers and during early childhood. How do we resolve this apparent contradiction?

There are two primary answers. First, mercury content is highly variable across different species of freshwater and ocean fish and shellfish. Not surprisingly, many studies suggest that consumption of seafood species that are lower in mercury (and higher in selenium) leads to better outcomes than consuming those that are higher in mercury. (16, 17, 18)

Second, we now know that there are a variety of genetic, epigenetic, and environmental factors that collectively determine susceptibility to mercury toxicity in a given individual. For example:

  • Several genes have been identified that affect the toxicokinetics of mercury. These include genes that affect mercury uptake (LAT1, LAT2, OAT1, OAT2), biotransformation (particularly glutathione-related genes like GS, GCL, GR, GPx, GGT, GST), distribution (SEPP1, GPX1, GPX4, MT1A, MT1E), and elimination (MRP1, MRP2, MDR1). (19, 20) Our current understanding is that genes account for about 30 percent of the variability observed in mercury levels in individuals with similar exposure.
  • Research indicates that polymorphisms in other genes, such as BDNF, COMT, and 5-HTTLPR can amplify the toxic effects of mercury. (21, 22, 23)
  • Epigenetic markers such as urinary porphyrin excretion, MMP-9 and MMP-2 protein levels, nitric oxide production, and low birth weight have been shown to modify the effects of mercury exposure. (24)
  • Males appear to be more adversely affected by mercury than females, possibly because of greater retention in tissues and organs and lower excretion via urine and stool. (25, 26, 27)
  • Methyl mercury, the primary form found in fish, is eliminated in the bile as a glutathione conjugate. This means that anything that affects glutathione will affect mercury clearance. A wide variety of genetic and environmental factors influence glutathione levels, including polymorphisms (aka SNPs) in glutathione-related genes, diet (glutathione itself is present in foods, as are glutathione precursor nutrients like selenium, copper, zinc, magnesium, B6, B12, folate, and vitamin E), chronic stress, chronic disease, physical activity, advanced age, toxins, and oxidative stress—to name a few!

This is just a partial list; there are many other factors, both known and likely unknown, that influence mercury’s effect on both children and adults.

The important takeaway is that we can no longer simply designate a particular blood level of mercury as “harmful” or “safe.” That is far too simplistic. As the authors of a review of the genetic influences on mercury toxicity stated:

These reports acknowledge that tremendous interindividual and interspecies variation exists in exposure and hazard and that complex gene-environment interactions may underlie such variation but as yet remain unresolved. With no resolution to such variability, decision-making is hampered and uncertain. (28)

In other words, it’s hard for policy makers and clinicians to make recommendations about mercury exposure when there’s so much variability in how people respond to it.

What this means for your children

In the not-too-distant future, we’ll be able to run a battery of tests that quickly determine individual susceptibility to mercury (and other toxins) and make customized diet and lifestyle recommendations based on those results.

In fact, we’ve been working to create a diagnostic algorithm with exactly that purpose at California Center for Functional Medicine. Unfortunately, this approach is in its infancy and we still have a lot to learn. Another challenge is that the amount of testing that is required to identify all of the factors that influence how an individual responds to mercury is extensive—and expensive.

In the meantime, here are the recommendations that I can make based on my current understanding of the science:

  • Give your children seafood at least twice a week, but restrict to species that are lowest in mercury. These include anchovies, sardines, clams, North Atlantic mackerel, herring, and salmon. Conveniently, many of these species are also highest in the beneficial omega-3 fats EPA and DHA. Another option is to avoid seafood but give your children cod liver oil or fish oil. However, although the marine oils do contain EPA and DHA (and vitamins A & D in the case of cod liver oil), they do not contain other beneficial nutrients found in seafood, such as selenium, zinc, and copper. This may not be an issue if your children are eating a diet that is nutrient-dense overall (see below).
  • Have your kids avoid or significantly limit consumption of species that are higher in mercury. These include yellowfin and canned albacore tuna, Spanish and king mackerel, Chilean sea bass, marlin, orange roughy, shark, swordfish, and bigeye/ahi tuna.
  • If your children develop cavities, take them to a dentist that uses composite resin fillings instead of mercury amalgams. Dental amalgams have consistently been shown to be a source of mercury exposure in both children and adults. (29) Mercury from amalgams readily crosses the blood brain and placental barriers, where it is oxidized to inorganic mercury. Many experts in mercury toxicity believe that inorganic mercury presents a greater challenge to the body than methyl mercury from fish.
  • Feed your children a nutrient-dense diet with plenty of glutathione, selenium, copper, zinc, magnesium, B6, B12, folate, and vitamin E.
  • Ensure that your children are doing other things that support glutathione pathways, such as getting adequate sleep, exercising regularly, and minimizing exposure to other environmental toxins.

If you’re working with a functional medicine provider, another step you can take is to have your children tested to determine how much mercury they are absorbing from fish consumption.

In our clinic, we prefer and use the Quicksilver Mercury Tri-Test. I recently interviewed Dr. Christopher Shade, the director of Quicksilver Scientific, about the various test methods available for mercury and the shortcomings of the “mercury challenge tests” that have been popular in the alternative medicine community. Check that out if you haven’t already.

I would also recommend reading a guest post entitled “Could Mercury Toxicity Be Causing Your Symptoms?” by my staff physician, Dr. Amy Nett. This may help you to recognize potential effects of mercury exposure in your children (and yourself).

I’ll continue to review new research on this topic as it is published and report back with any important developments.

Happy safe fish eating!

32 Comments

Join the conversation

  1. Hello there Chris,
    I am currently detoxing from Mercury using Andy Cutler’s Chelation method. He speaks evil of Dr Shade, and how he makes de detoxification protocol more expensive, when everything you really need to detox is ALA as a chelator, and Vit E, Mag, Zinc, Selenium, Fish Oil, Vit C, Vit D as supports.

    Have you read about Andy?

  2. Hello there Chris,
    I am currently detoxing from Mercury using Andy Cutler’s Chelation method. He speaks evil of Dr Shade, and how he makes de detoxification protocol more expensive, when everything you really need to detox is ALA as a chelator, and Vit E, Mag, Zinc, Selenium, Fish Oil, Vit C, Vit D as supports. Have you read about Andy?

  3. I used to eat lots of fish, especially wild-caught salmon, rich in nutrients and omega 3. However reading lots of articles on the matter, I’m now trying to limit my fish consumption as I don’t see how we can find a trusted source of really clean fish.

    I have started playing with organic gardening and I’m now producing my own natural organic fruits an vegetables, but unfortunately don’t have a solution for growing my own clean ocean fish unfortunately… still searching 🙂

  4. I’m not a very big fish eater (actually I’m not a fish eater at all, as I do not like it) so I’ve never really considered much about mercury consumption – adult, child, or otherwise. This is good information to be aware of though, and to pass along to those who are fish-eaters, especially those with children.

  5. I’ve always been worried about my fish consumption. Mercury is bad enough, but there are so many other contaminants in the ocean that can easily enter your body through fish consumption.

    • I agree, I was thinking the same thing. Nowadays, not all the vaccines contain mercury but in the past all of them contained incredible amounts.

  6. Thanks for this article! I have long suspected that children are more susceptible to chemicals than adults. I work at a pre-school and I can see the differences Diet makes in our students.

  7. Hi Chris –

    Thank you for sharing! I had no idea that children were so much more prone to mercury than adults. I really appreciate the tips you provided at the end. At what age would you say it’s okay to start eating more mercury fish?

  8. Chris, I always appreciate your refreshingly balanced presentation of the science. That said, in this case I wonder about putting so much credence in a relatively small, short-term study, when far larger, longer-term studies focused on this issue have failed to find only positive correlation between maternal seafood consumption and child health. (ALSPAC – 14,000+ mother-child pairs studied for more than 20 years, SCID – 700 mother-child pairs observed more than 20 years). The authors of the UK ALSPAC study found the association between seafood consumption and child developmental outcome so positive they concluded that advice counseling pregnant and nursing women to limit seafood could actually be detrimental. (Lancet, 2007). While possible, it strains credulity to think that seafood consumption during the fetal stage would confer net benefit, while posing a hazard after birth.
    How great it will be when we can all be tested and told precisely what to eat for optimal health. In the meantime I suggest that sticking with natural foods that humans have been consuming for nearly as long as we’ve been on this planet is probably a pretty safe bet

    • Hi Randy,

      I mentioned that in the article and provided several references supporting the positive association between maternal seafood consumption and cognitive/behavioral scores in children:

      “A large body of evidence suggests that maternal consumption of seafood during pregnancy protects against mercury-associated impairments in cognitive function, attention, and behavior.”

      This is why I continue to recommend fish consumption to pregnant women and young children, but do suggest limiting to low mercury species as a precaution. Given some of the research indicating possible harm to susceptible children, and the fact that most people don’t have access to the testing necessary to determine susceptibility, I think a cautious approach designed to obtain the benefits from seafood consumption while avoiding the potential harms makes sense.

  9. Chris, I always appreciate your relatively balanced presentation of the science. That said, in this case I wonder about putting so much credence in a relatively small, short-term study, when far larger, longer-term studies have failed to find anything but positive correlation between maternal seafood consumption and child health. (ALSPAC – 14,000+ mother-child pairs studied for more than 20 years, SCID – 700 mother-child pairs observed more than 20 years). The authors of the ALSPAC study in the UK found the association so positive they concluded that advice counseling pregnant and nursing women to limit seafood could actually be detrimental to the child’s health and well-being. (Lance at 2007).

  10. Was the connection between mercury and the blunted cortisol response and higher inflammatory markers purely speculation, or was there some other reason to believe mercury was the cause despite the low levels? Was there anything else that could have been an alternate cause?

    • There was a clear correlation between the mercury levels, cortisol response, and inflammatory markers, but studies like this are not able to prove causality conclusively. The authors speculated on mechanisms that would explain the association (which I described in the article), and a plausible mechanism is one of the criteria that would strengthen the chances of a causal relationship between two variables.

  11. I’m not really concerned with the amount of mercury levels in fish (although I don’t eat fish any more) What I’m concerned about is the glaring absence of any reporting of radioactivity in fish. With the Fukushima pandemic disaster engulfing the world I don’t think anybody should eat fish.

  12. This is a great article. Looking out for our children’s health is always important, but Chris pointing out that kids are especially vulnerable to mercury poisoning and elimination is very important. I didn’t realize how many ways they are more vulnerable than adults until I read this.

    Many of the things he mentions for protecting kids are of course important to remember for adult protection also.

    Hidden at the end of Chris’ list of the “variety of genetic, epigenetic, and environmental factors that collectively determine susceptibility” to mercury poisoning was the factor of diet. It’s actual importance though may rate it a higher location in that list.

    Later, in his list of recommendations for safeguarding your child Chris mentioned the diet factors more obviously. I really feel that diet is no small factor. For many of us, even in spite of some genetic tendencies toward troubles with toxins, the most powerful move we can make to protect ourselves and our children is to take Chris’s recommendations to heart.

    According to Dr. Russell Jaffe, who has worked with methylation and toxic issues for over 30 years, by the time one is an adult, with proper nutrition, they should be able to protect their system from heavy metals. This doesn’t mean that children are going to be safe, but as an adult, without eating excess of toxic foods, you may be well protected just by your normal metabolism. Jaffee stress the same vitamins and minerals as Chris does, but also concentrates on Ascorbate and sulfur rich foods containing cysteine that are essential for making the enzymes and amino acids like metallothionein and glutathione that help eliminate toxins.

    For a little more on Jaffe,

    http://highintensityhealth.com/russell-jaffe-glutathione-metallothionein-vitamin-c-detox-molecules/

    The link includes both a video, but also notes tied to the video so you can jump quickly to items of interest or just read a quick summary of what Jaffe’s experience has been.

    Cheers, and remember to guard yourself, not just your kids! Mercury can be found almost everywhere these days. It’s not just the fish.

  13. Living downwind from a Pulp & Paper Mill or Coal fired Power Plant will also increase levels of mercury. They Chelate Heavy Metals from pulp fiber but the Chelation agent and heavy metals vent off to atmosphere. 1000 tradesman were exposed to pulp mill emissions. On our Hair Samples recommended by Dr. Harrada who studied the people around Minamata Bay our Nurtrional Minerals were depleted except for manganese and potassium which we were inhaling.
    A co-worker was told his mercury level was high from eating fish, but his wife cooked the fish and had a negligible mercury level. And this was upstream from the Grassy Narrows mercury poisoning of native people living on the watershed downstream from the Pulp Mill. Dr. Harrada has worked with them also.
    Sadly mercury contamination can be airborne. I do not know if mercury uptakes in plants, but very likely it uptakes in trees.

  14. Great info. While there are many factors that could be associated with the blunted cortisol levels seen in the participants in the referenced study (4) (which weren’t accounted for, or revealed in the write up of the investigation). Nonetheless, their findings lead to valid concern given the clinical importance of chronic inflammation and impaired detoxification pathways in children. Ultimately, it is imperative for consumers to understand: not all fish are created equal. The synergy of nutrients consumed from seafood can be both beneficial or toxic depending on the health state of the individual. In addition to exploring phenotypes associated with detoxification Selenium (Se) found in varying levels in seafood is worth noting for its role in antioxidant and metabolic properties. Ralston and Raymond (2010) suggest a more reliable index for evaluating methylmercury exposure related to fish consumption include the molar ratio of Se:Hg as Selenium is understood to bind to MeHg, effectively blunting potential toxic affects and tissue accumulation. Perhaps eating a brazil nut or two when consuming seafood (especially fish higher on the food chain and thus containing higher levels of MeHg) might offset at least some of the toxicity associated with mercury exposure?!

    Ralston, N. & Raymon, L. (2010) Dietary selenium’s protective effects against methylmercury toxicity. Toxicology, 278(Functional Nutraceuticals in Chronic and Acute Diseases: Molecular Approach to Mechanisms of Action), 112-123. doi:10.1016/j.tox.2010.06.004

  15. “Feed your children a nutrient-dense diet with plenty of glutathione, selenium, copper, zinc, magnesium, B6, B12, folate, and vitamin E.”

    A list of foods would be much more useful than a list of nutrients.

    • Good point, Viola!

      Sometimes people then break into an exhaustive list of foods which itself is overwhelming.

      But I think I can make this quite simple, after reading what Jaffe says on the subject:

      If you eat greens from the garden, fresh and organic and grown on nutritious soil, expecially the cruciferous veggies like cabbage, collard, kale, and mustard greens you will be getting copper, zinc, and magnesium in about the right proportions to keep you healthy and allow your body to make glutathione. The crucifers, and also onions and garlic happen to concentrate selenium, and all the greens have fairly ample B vitamins, including folate, except for the B12.

      So that’s everything right there in the color green, except for B12 and vitamin E which you can get from many animal products or supplements.

      Last is glutathione, but that is best made in your body, cell by cell, from all the other ingredients.

      You didn’t mention, but I’ll add, that the amino acids glycine and cysteine are also important to build metallothionein which is part of the process of capturing an nullifying heavy metals. These 2 amino acids are in most animal products, with glycine being especially prevalent in bone broth.

    • You can google “foods high in selenium,” “foods high in zinc,” etc., and come up with your own list. This seems like a far more efficient way of doing things rather than expecting Chris to needlessly lengthen the article for his excessively lazy readers.

  16. Thank you for the article. We do eat wild salmon when I prepare it at home, but my 2 boys love sushi – mostly commonly salmon. Either salmon nigiri or salmon avocado roll. I’m unable to find a sushi restaurant in the area that serves wild salmon. Should I limit their intake of the salmon at sushi restaurants because it is farmed? We usually go twice/wk.

  17. I was under the impression that yellowfin (canned) was much lower in mercury than albacore. I recently looked it up on the EWG site, I think. It could have possibly been the one from the Monterey Bay Aquarium, though. I found a good buy on yellowfin on amazon. Unfortunately, our son loves it. I’ve already been restricting his consumption, which is difficult, as it’s so much healthier than eating crackers or other types of foods. It sounds like I’ll need to make salmon cakes more often instead. Thanks, Chris.

  18. So interesting you published this today b/c this has been on my mind lately. My 4 year old’s newfound favorite food is Tonnino tuna fillets packed with olive oil in a glass jar. He’s pretty picky so this is one of his few sources of really good fats (both the fish and the oil). At $7 a jar (2 servings), I think to think this is a high quality tuna but I have no idea how “quality” correlates with the amount of mercury or if being in a jar makes it closer to fresh or canned tuna? So far, I’m limiting him to 1 jar per week, but am worried that could be too much given what you typically hear about kids and mercury. thoughts?

  19. Chris, do you have any feedback/opinion on the RegActiv probiotic that contains bacteria (L. Fermentum ME-3) that produces glutathione in the gut? I am especially interested in information about its use in children.
    Thanks!

  20. I noticed you left off canned light tuna (from Skipjack) which is the lowest canned tuna in terms of mercury. It is readily available and cheaper than the albacore that is higher in mercury so I don’t understand why you left that off as a dietary source of canned tuna. I use it about 1-2 times a week for tuna salad with grated radishes and mashed avocado as a mayo sub plus green onions. Seems fine to me re” mercury even for children who eat significantly less than adults do.

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