The Scary Reason Why Pregnant Women Should Avoid Fish

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Why Pregnant Women Should Avoid Tuna

All fish contain small amounts of methylmercury, the most toxic form of mercury, and “fish consumption represents the main source of methylmercury exposure.” In my videos Nerves of Mercury and Fish Fog, I discuss how mercury exposure through fish consumption, even within the government’s safety limits, can have adverse neurological and behavioral effects on child development. Severe exposure can cause overt structural brain abnormalities like microcephaly, a shrunken brain disorder. But we didn’t know whether low exposure could also affect brain size until recently.

Autopsy studies suggest mercury preferentially affects the developing cerebellum, so researchers used ultrasound to measure cerebellum size in newborns of mothers who had high body levels of mercury.

Let’s put those levels into practical terms. In the video, Fish Intake Associated with Brain Shrinkage, you can see the results of a study measuring mercury concentration in human hair. Just one can of tuna a week raises human hair mercury concentration to levels nearly three times as high as the “high” group in the ultrasound study. So the bodies of the women suffering high mercury contamination were considered heavily contaminated, but even just a little canned tuna once in a while could bump our levels even higher. So the high really wasn’t that high. But what did they find?

The researchers demonstrated that babies born to mothers with higher hair mercury levels had cerebellums up to 14% shorter than those born to mothers with lower hair mercury levels. They conclude that prenatal exposure to what may be considered low-levels of methylmercury does indeed influence fetal brain development as evidenced “by decreased size of a newborn’s brain.”

But what about the long chain omega-3 DHA in fish—isn’t that necessary for healthy brain development? That’s the topic of my video Mercury vs. Omega-3s for Brain Development.

For more on canned tuna in particular, check out:

Michael Greger, M.D.

PS: If you haven’t yet, you can subscribe to my videos for free by clicking here and watch my full 2012 – 2015 presentations Uprooting the Leading Causes of Death, More than an Apple a Day, From Table to Able, and Food as Medicine.


Michael Greger M.D., FACLM

Michael Greger, M.D. FACLM, is a physician, New York Times bestselling author, and internationally recognized professional speaker on a number of important public health issues. Dr. Greger has lectured at the Conference on World Affairs, the National Institutes of Health, and the International Bird Flu Summit, testified before Congress, appeared on The Dr. Oz Show and The Colbert Report, and was invited as an expert witness in defense of Oprah Winfrey at the infamous "meat defamation" trial.

18 responses to “Why Pregnant Women Should Avoid Tuna

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  1. “cerebellums up to 14% shorter”

    “Up to” is a lousy way to summarize a distribution. It’s common in advertising, but not consistent with a scientific frame of mind.

    (Disclaimer: I am a subscriber to this site and I don’t eat fish.)

    1. Agreed with the “up to 14%” comment.

      And what about the selenium intake….i’ve read selenium prevents the detrimental effects of the mercury. Is there truth in this theory?

  2. Dr. Greger, or any other Dr.’s or knowledgeable folks here… about transdermal iodine? Safe? Effective? Prudent? Both vegans and non-vegans claim it is an awesome source of iodine but does it work, and is there reason for concern? Having hard time tracking down literature on this, in regards to “science”. Thanks.

    1. All fish contain methylmercury, none of which is good for pregnant women, fetuses, or anyone else. Fish also contain other accumulated toxins, cholesterol, saturated fat, parasites, etc.

      Why needlessly subject yourself or your children to health hazards? All of the nutrients derived from fish -and other animal products- can be obtained more healthfully, humanely and environmentally responsibly from plant sources. Do the responsible thing: be vegan, for everyone’s sake.

      1. My son and his wife went trout fishing. I’m wondering how much mercury is in trout because she’s pregnant. I am a vegan but they are not. Spare me the lecture.

  3. But what about this study??

    The SCDS has shown that Seychellois children have a normal range of development when compared to children in developed countries. So far, we have not found clear evidence of abnormal or delayed development in children as a result of their mother’s consumption of fish during pregnancy.

    The Seychelles Child Development Study (SCDS) is a research project involving the Ministries of Health and Education in Seychelles, the University of Ulster in Northern Ireland, and the University of Rochester in the United States. The study began in the mid-1980s with two main objectives:

    To study child development in the Republic of Seychelles

    To study factors, such as diet, that may modulate associations between mercury exposure and child development

    To study effects of prenatal and postnatal mercury exposure

    To study exposure to organic and inorganic mercury

    To study factors that modulate associations between mercury exposure and child development

    To study the relation between mercury exposure and disabilities such as Autism

  4. This is giving me a scare. My husband and I are planning to have our first baby. As I have been reading posts and articles about the path to pregnancy, but it seems difficult to cope with. For instance, I am thinking how difficult it would be to go through the 9 months. Other than chicken, fish is not just my father’s, but my favorite as well. Are there any alternative source for omega 3 other than the food supplement such as fish oil I am taking?

    1. Andrea: If you are OK with taking pills, then how about using an algea based DHA (omega 3) pill? The vegan omega 3 pills are completely safe. There are several companies out there now that sell fish-free omega 3. I’ve even seen one in my local health food store. Here is an on-line example (I’m not promoting any particular brand. Just giving you an idea):

      Also, I thought you might be interested in the following page which does a good job of explaining *safe* nutrition options for pregnant women, infants, on up through teens.

      1. Hi Thea, thanks for sharing me this. I am enlightened. I know I can’t win my friends with salad, but I don’t mind. Perhaps, people will know what a wonderful life is with all these veggies. My husband is trying to cooperate, he plans to have an all veggie week this week.

        1. Andrea: Good luck! Eating healthy can be a learning curve, but when you get over it, you will look back and think that it’s really not all that hard.

          I did want to point out one little thing: You mentioned “veggies” twice. I just want to make sure that is your short-hand for “whole plant foods”. The point is: You don’t have to *just* eat vegetables/salad. If you tried that, I imagine you would be hungry a lot. And you might miss out on some important nutrition. So, don’t forget all of the other foods that are so good (and filling) to have in your diet: whole intact grains (barley, rice, quinoa, millet, farro, wheat berries, steel cut oats, etc), legumes (all those beans and pea varieties), fruit (especially berries), and nuts and seeds (in moderation = 1-2 ounces a day).

          If you are new to this, I recommend some good cookbooks that will give you some good ideas and are delicious! A new one I just got attached to is Vegan Casseroles. And some old favorites (all available on Amazon) are: Everyday Happy Herbivore, Let Them Eat Vegan, and Vegan On The Cheap. Some friends of mine are swearing by the new book, Thug Kitchen (and you can get a lot of their recipes for free on-line.) But the book has too much swearing for me to get myself.

          Hope that helps. I’m keeping my fingers crossed for both you and your husband!

          1. Hi Thea! I have to say thank you from the bottom of my heart. It’s been almost a month now that we’re having brown rice and considering oat meal and peanut butter for breakfast. Perhaps, I wouldn’t notice the change, but my friends and my husband did.
            The whole vegetable thing for lunch and dinner is really helping. As far as I know I need to keep a healthy body before we are having our first baby. (that rhymes, eh?) And that means, I have to lose these extra pounds. I hope next year would be a good year for us.

    2. if your worried about autism let me guess you have autism relative in your family?

      i notice a lot of ppl worried about “vaccines” have a crapton of relatives with autism and want something convenient to blame when its about to happen to them cuz of poor genetics

  5. so mercury digested in tuna is dangerous to a pregnant woman and her baby. How about the thimerasol/mercury in the adult dose of the flu vaccine injected into women? How about the trace amounts of thimerasol in the DaPT shot injected into pregnant women? How about the aluminium in the DaPT shot given to pregnant women? How about the aluminium in the Hep B shot and in the vitamin K shot given to newborns on the first day of life?

    There are NO SCIENTIFIC, DOUBLE BLIND, CONTROLLED, LONG TERM STUDIES that show that pumping pregnant women full of poison and toxins is safe. Pregnant women are being treated as guinea pigs, and they have been for over 80 years. Look at the DES fiasco, the “Wonder Drug” that ruined an entire generation. Where are they now? Dead. That is why you do not hear from them. Look at Thalidomide. How many mistakes must be made before we start putting modern medicine on the defensive to prove something is safe before we die from it?

    1. Don’t like my comments you obviously don’t understand sarcasm I said women who have more than one autistic kid should be thrown in jail for destruction of society people like you are a plague for children stay out of our lives get your balls or vag cut up an go live in a desert

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