The Super-Confusing Truth About Mercury in Fish and ADHD in Children

One of the most precarious minefields for pregnant women often turns out to be the simple question: “What’s for dinner?”

Moms are told that fish is good for them and their developing babies because it’s believed that Omega-3 fatty acids benefit brain development. But worries over contaminants, particularly mercury, have scared plenty of moms-to-be off fish entirely. A new report released today in JAMA publication Archives of Pediatrics & Adolescent Medicine may not do much to alleviate the angst.

Researchers found that exposure to low-levels of prenatal mercury may be associated with a higher risk of attention-deficit hyperactivity disorder (ADHD) related behaviors. But the same study also points out that fish consumed during pregnancy may actually lower the risk of those behaviors.

Wait. What?

“The public health message is complicated,” lead author Sharon Sagiv tells TakePart.

What the scientists found is that methymercury exposure comes primarily from eating fish. And indeed, since 2004, the U.S. Environmental Protection Agency and the U.S. Food & Drug Administration have recommended that pregnant women eat up to 12 ounces of fish a week, but that they should avoid shark, swordfish, king mackerel and tilefish which are known to be high in mercury. But that specific warning, and plenty of press since then, has frightened many pregnant women away from fish entirely, and away from the benefits that eating fish provides for their developing babies -- now including protection from ADHD-related behavior.

Sagiv says that mercury found in the hair of mothers around the time of birth showed a greater risk of the children developing ADHD behaviors which included inattentiveness, hyperactivity and impulsiveness. But the study also found that women who ate more than the FDA recommended two servings of fish a week actually protected their babies from ADHD-behaviors.

Strip the study down and the takeaway for pregnant women is this: Eat fish, just not those high in mercury.

“Exposure to [swordfish, tilefish, king mackerel and shark] is already minimal in this country, not just in pregnant women,” says Gavin Gibbons, spokesperson for the National Fisheries Institute. “The universe of seafood that is open and encouraged by researchers for pregnant women are vast. There is a burden on the researchers to communicate this the right way.”

He’s right on that. In 2010, the WHO and FAO said governments around the world need to do a better job in communicating the risks associated with not eating seafood.

But when we get past the swordfish, tilefish, king mackerel and shark, the message still gets muddled. For example, we know tuna contains mercury, but those levels can vary when we’re talking about canned albacore or a piece of sushi made with fresh bluefin. And while the study doesn’t come right out and tell moms which specific fish to eat, we asked Dr. Nicholas Fisher, who studies mercury contamination in seafood at Stony Brook University to tell us which fish are known to be low in mercury. His list includes: flounder, tilapia, sardines, shrimp, and shellfish like clams oysters, mussels. Other low-mercury fish would include salmon, haddock and cod, and all are tasty ways to keep fish in the diets of worried moms.

How often do you put fish on your table? Let us know in the comments

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Clare Leschin-Hoar covers seafood, sustainability and food politics. Her work has appeared in Scientific American, The Wall Street Journal, Grist, Eating Well and many more. @c_leschin |