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 above video, 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. We can see an MRI of what a normal brain looks like when we 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:

In health,
Michael Greger, M.D.

PS: If you haven’t yet, you can subscribe to my free videos here and watch my live year-in-review presentations Uprooting the Leading Causes of Death and More Than an Apple a Day.

Fukushima and Radioactivity in Seafood
Mercury Testing Before Pregnancy
The Effects of Cow’s Milk on Babies


Jeanne Rogers
Jeanne R7 months ago

Thank you for sharing.

Julianna D.
Juliana D1 years ago

So I'll stick with DHA and avoid actual fish.

Janice Thompson
Janice Thompson2 years ago

I meant HAT making, not with the E.

Janice Thompson
Janice Thompson2 years ago

Mercury was used in hate making. Hence the Mad Hatter.

Carol P.
Carol P2 years ago

More scare tactics. It has been common knowledge for decades that pregnant women should avoid consuming large fish like tuna because of the mercury contamination so I don't know why Greger felt the need to make it out to be some big discovery that he's bringing to us.

But rather than work to get people to stop eating fish, wouldn't it be better to shut down coal-burning power plants that are spewing mercury into the air that we breath and polluting the water that we drink, even before it makes its way into the fish that pregnant women aren't eating anyway?

Danuta Watola
Danuta W2 years ago

Thanks for sharing!!

heather g.
heather g2 years ago

The real problem is the 2,000 chemicals used and over-used, that all run from the farms into the rivers and sea with every rainfall.

Oleg Kobetz
Oleg Kobetz2 years ago

Thank you

Helga Ganguly
Helga Ganguly2 years ago

They should do a study of pregnant women in West Bengal where the people are primarily vegetarian but love fish so much that they call fish "fruit of the sea." At least that's what my husband says. My mother loved herring. I was a 9 lb baby. Of course,I was a 10 month baby.All my children are intelligent but I rarely ate fish.I love crab,shrimp,and lobster and salmon.

Chad Anderson
Chad A2 years ago

I really dislike fish except for the occasional king mackeral (or some Korean sardine dishes) so I have a dilemma.