Nature Medicine | Spoonful of Medicine

Tossing back mercury

Seafood lovers, pregnant women and lobbyists for the fishing industry heard some startling news this week from a study in The Lancet.

Offspring of women who ate a lot of seafood during pregnancy scored higher on tests of verbal and social ability than offspring of women who at little or none—despite concerns about high mercury levels in seafood. Even the study’s authors were surprised.

The take-home message of the study may seem positive, but it comes with ominous undertones: “The benefits of eating seafood outweigh the risks.” Somehow, I’m not fully comforted.

What the study did not address was how the seafood-reared children would have fared if their mothers had eaten mercury-free fish—a thing about as rare as coelacanth caviar. It’s a tough question, but it’s worth asking — given that mercury at the concentrations found in many fish is likely harmful to fetal development, as The National Academy of Sciences has concluded.

The new study didn’t take the bite out of mercury — it just suggests that omega-3 fatty acids and other substances in seafood are really good for the developing nervous system. The findings will certainly put pressure on US regulatory agencies to change their advisories limiting fish intake for vulnerable populations. Pregnant women in the study had to eat more than the level advised by the agencies, 340 grams per week, for the beneficial effect.

So what is fish lover to do — believe this one study and start chowing down on tuna fish sandwiches? Carefully parse lists of fish species with high and low mercury content, or just eat a lot of omega-3 containing flax seed?

There’s only one sure way to make things simpler — and safer. And that is to get rid of mercury in our waterways.

The Bush administration is notoriously backward on this front. The US Environmental Protection Agency — the same agency that issues advisories on fish consumption — has ruled that coal-fired power power plants have almost 20 years to cut their emissions by 70 percent. That stands in contrast to an overturned Clinton-era ruling calling for a 90 percent reduction by 2008.

The EPA has received hundreds of thousands of letters protesting the Bush-era ruling — so a single study from The Lancet is unlikely to change anything. But those letters show how strongly people feel that there should be only benefit, but no risk, to eating a basic food item.


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    Alan Dove said:

    It is an interesting finding, but it ignores some important variables. For one thing, it looks only at a British population, where the demographics of fish-eating and the geography of pollution are certainly different from the States.

    American fish consumption splits along class lines. The poor, new immigrants, and rural people eat a lot more locally-caught fish, while affluent suburbanites tend to buy imported fish at the supermarket. The pregnant bond trader may benefit her baby by eating more wild-caught Scottish salmon, but the pregnant maid should probably eat less of the mercury-and-PCB-loaded shad her husband hauled out of the Hudson River.

    In any case, cleaning up the water would certainly be a step in the right direction.