How Seafood Can Impact Brain Development

Image Credit: Dion van Huyssteen / Flickr. This image has been modified.

How Seafood Can Impact Brain Development

In my video Fish Intake Associated With Brain Shrinkage, I discussed evidence suggesting that mercury exposure through fish intake during pregnancy may decrease the size of the newborn’s brain. However, just because fish-eating mothers may give birth to children with smaller brains doesn’t necessarily mean their children will grow up with neurological defects. In the video, Mercury vs. Omega-3s for Brain Development, you can see real-time functional MRI scans of teens whose moms ate a lot of seafood when pregnant. Because these kinds of scans can measure brain activity, as opposed to just brain size, we can more accurately determine if exposure to mercury and PCBs affected these kids. You can see an MRI of what a normal brain looks like when you flash a light in someone’s eyes, but the MRI is significantly different for the mercury and PCB exposed brains, suggesting toxicant related damage to the visual centers in brain. (For more on the effect of mercury on teens, see Nerves of Mercury). Fish consumption may also increase the risk of our children being born with epilepsy.

So does maternal fish consumption have an effect on how smart our kids turn out? The DHA in fish—a long chain omega 3 fatty acid—is good for brain development, but mercury is bad for brain development. So a group of researchers looked at 33 different fish species to see what the net effect of these compounds would have on children’s IQ. For most fish species, they found that “the adverse effect of mercury on the IQ scores of children exceeded the beneficial effects of DHA.” In fact, so much brainpower may be lost from fish consumption that the United States may actually lose $5 billion in economic productivity every year.

For example, if pregnant women ate tuna every day, the DHA would add a few IQ points. But the mercury in that very same tuna would cause so much brain damage that the overall effect of eating tuna while pregnant would be negative, wiping out an average of eight IQ points. The only two fish that were more brain-damaging than tuna were pike and swordfish.

At the other end of the spectrum, the brain boosting effect of DHA may trump the brain damaging effects of mercury in salmon by a little less than one IQ point. Unfortunately, IQ only takes into consideration the cognitive damage caused by mercury, not the adverse effects on motor function and attention and behavior deficits. We think that attention span may be particularly vulnerable to developmental mercury exposure, probably due to damage to the frontal lobes of the brain.

And the IQ study didn’t take into account the relatively high levels of PCBs in salmon and the accompanying concerns about cancer risk. Sustainability concerns are another wrinkle, as farm-raised salmon are considered a “fish to avoid.” While king mackerel is considered a best choice for sustainability, the mercury levels are so high as to warrant avoiding consumption—exceeding both the FDA and EPA action levels for mercury contamination. But why risk any loss in intelligence at all when pregnant women can get all the DHA they want from microalgae supplements without any of the contaminants? We can then get the brain boost without the brain damage.

More on PCBs in:

-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.

9 responses to “How Seafood Can Impact Brain Development

Comment Etiquette

On, you'll find a vibrant community of nutrition enthusiasts, health professionals, and many knowledgeable users seeking to discover the healthiest diet to eat for themselves and their families. As always, our goal is to foster conversations that are insightful, engaging, and most of all, helpful – from the nutrition beginners to the experts in our community.

To do this we need your help, so here are some basic guidelines to get you started.

The Short List

To help maintain and foster a welcoming atmosphere in our comments, please refrain from rude comments, name-calling, and responding to posts that break the rules (see our full Community Guidelines for more details). We will remove any posts in violation of our rules when we see it, which will, unfortunately, include any nicer comments that may have been made in response.

Be respectful and help out our staff and volunteer health supporters by actively not replying to comments that are breaking the rules. Instead, please flag or report them by submitting a ticket to our help desk. is made up of an incredible staff and many dedicated volunteers that work hard to ensure that the comments section runs smoothly and we spend a great deal of time reading comments from our community members.

Have a correction or suggestion for video or blog? Please contact us to let us know. Submitting a correction this way will result in a quicker fix than commenting on a thread with a suggestion or correction.

View the Full Community Guidelines

  1. Are you labeling all fish as having a greater negative ratio of mercury to DHA, or are there sources of fish and shellfish where the DHA positive effect is far higher than the negative mercury effect (level)?

    What about some species of wild caught shrimp, virtually void of mercury, as well as cold water mussels and clams, all showing very little if any mercury at times? And what about the Japanese fish eaters? There are lots of them.

    To my knowledge not all fish and shellfish contain PCB’s and mercury at levels that negate the positive DHA benefits, as well as natural B12, but please someone correct me if I am wrong. We deserve clarity here, and we need it!!!!…….I want to be plant-based and vegan as much as possible, but I also would like to know the big picture for this issue, and not just assume that there are not fish and shellfish out there that can be of benefit for people who struggle with digestion issues/nutrient depletion,absorption/amino acid absorption on a vegan diet…… well as being able to handle B12 supplements without
    adverse effects.

    1. From my understanding, if you don’t get DHA sources from animal products, your body converts ALA (the main source of Omega 3 in flaxseed) to DHA more efficiently.

    2. According to an article in Nutrition Reviews (Vol. 66, pp. 326-332), between eight and 20 per cent of ALA is converted to EPA in humans, and between 0.5 and nine percent of ALA is converted to DHA. In addition, the gender plays an important role with women of reproductive age reportedly converting ALA to EPA at a 2.5-fold greater rate than healthy men.

      At 0.5-9%, you’d have to consume a lot of ALA to reach your daily dose.

    1. Johnb: Here’s my understanding: There are different types of algea. Spirulina is a type that is associated with becoming contaminated and having problems. However, the “microalgea” DHA pills you can buy are made from special algea that is grown in highly controlled sterile environments. No worries (all else being equal) about contamination.

      Make sense?

Leave a Reply

Your email address will not be published. Required fields are marked *

Pin It on Pinterest

Share This