The findings fly in the face of earlier reports. Those reports -- from whale-eating Faeroe Islanders and shark-eating New Zealanders -- linked pregnant women's seafood eating to brain toxicity in their children.
This time, researchers looked at women who ate the same kinds of fish you'd find in the grocery store. Gary J. Myers, MD, University of Rochester, N.Y., and colleagues followed 779 mother/infant pairs living in the Republic of Seychelles. Seychelles is a group of islands off the east cost of Africa. The well-nourished people there eat fish about 12 times per week.
"What we studied were people who ate ocean fish every day that have the same amounts of mercury as commercial fish," Myers tells WebMD. "They have mercury levels six to eight times higher than the average U.S. resident. Yet over nine years and evaluations with 50 endpoints, we find no pattern of adverse effects on these children."
Accompanying the study in the May 17 issue of The Lancet is a commentary by Constantine G. Lyketsos, MD, co-director of geriatric psychiatry and neuropsychiatry at Baltimore's Johns Hopkins Hospital. He notes that there's now no reason for pregnant women to avoid eating fish.
"The Seychelles data are very reassuring that concerns from earlier studies of mercury in fish eaten by pregnant women don't translate into effects on kids," Lyketsos tells WebMD.
Mercury is very dangerous to children. Relatively low concentrations keep a child's brain from developing normally. Kids with mercury poisoning have problems with thinking, language, memory, motor skills, perception, and behavior.
A 1997 study of people living in the Faeroe Islands found serious brain problems in 7-year-old children born to women who ate seafood during pregnancy. These problems were linked to mercury. The Faeroe Island women didn't have much higher mercury levels than the women in Myers' study. But they ate a lot of whale meat. Whales contain much more mercury than ocean fish. Myers suggests these large doses of mercury may be more harmful than mercury concentrations over time.
An earlier, smaller study from New Zealand linked mercury in fish eaten during pregnancy to brain problems in children. However, much of this seafood was fast-food fish and chips made from shark meat. Shark contains 10 times more mercury than the average ocean fish, Myers says.
"Swordfish and tuna probably are OK. They probably won't affect the fetus," Lyketsos says. "I might, however, advise pregnant women to hold off on whale meat and shark."
Moreover, Myers notes, fish is good for you. Large fish, in particular, are rich in omega-3 fatty acids that have multiple health benefits.
Ironically, the findings come on the heels of a report in the May 15 issue of Nature showing that overfishing has killed off 90% of the world's large fish. These are the fish people eat the most: Tuna, swordfish, marlin, cod, halibut, skates, and flounder. The study suggests that unless drastic cuts are made in commercial fishing, today's large fish will be tomorrow's dinosaurs.