WEDNESDAY, Jan. 21, 2015 (HealthDay News) -- Despite concerns over mercury exposure, pregnant women who eat lots of fish may not harm their unborn children, a new study suggests.
Three decades of research in the Seychelles, the islands in the Indian Ocean, found no developmental problems in children born to women who consume ocean fish at a much higher rate than the average American woman, the study concluded.
"They eat a lot of fish, historically about 12 fish meals a week, and their mercury exposure from fish is about 10 times higher than that of average Americans," said study co-author Edwin van Wijngaarden, an associate professor in the University of Rochester's department of Public Health Sciences in Rochester, N.Y. "We have not found any association between these exposures to mercury and developmental outcomes."
The omega 3 fatty acids found in fish oil may protect the brain from the potential toxic effects of mercury, the researchers suggested.
They found mercury-related developmental problems only in the children of women who had low omega 3 levels but high levels of omega 6 fatty acids, which are associated with meats and cooking oils, van Wijngaarden said.
"The fish oil is tripping up the mercury," he said. "Somehow, they are interacting with each other. We found benefits of omega 3s on language development and communications skills."
The new findings come amid a reassessment regarding the risks and rewards of eating fish during pregnancy.
High levels of mercury exposure can cause developmental problems in children, the researchers noted. Because all ocean fish contain trace amounts of mercury, health experts for decades have advised expecting mothers to limit their fish consumption.
For example, current guidance from the U.S. Food and Drug Administration recommends that pregnant women limit consumption of fish to twice a week.
But in June, the FDA announced that it plans to update those recommendations and advise that pregnant women eat a minimum of two to three servings a week of fish known to be low in mercury. The FDA says these include shrimp, canned light tuna, salmon, pollock and catfish.
"It's not clear that the current recommendation of limiting your fish intake is actually warranted, based on the current data," said Dr. Laura Riley, medical director of labor and delivery at Massachusetts General Hospital in Boston. "This study is again raising that same question. Is this really that bad? Do you need to take into consideration the beneficial effects of eating fish?"
However, Riley isn't convinced that fish oil might protect against mercury. "More study needs to be done before you can convince me that the fish is actually protective," she said. "I want to see the data."
The new study focused on the Seychelles, a cluster of islands east of Africa, where fish is a dietary staple.
Researchers followed more than 1,500 mothers and their children. At 20 months after birth, the children underwent a battery of tests designed to measure their communication, behavior and motor skills. Mothers provided hair samples during pregnancy to measure levels of prenatal mercury exposure.
Mercury exposure did not correlate with lower test scores, the researchers concluded, and some of the Seychelles children now have been observed living healthy, normal lives into their 20s.
The latest findings suggest that the oil in fish might counteract damage caused by mercury, van Wijngaarden said.
Mercury ended up associated with developmental damage only in children whose mothers had high levels of meat-related omega 6 fatty acids but low levels of omega 3s from fish oil, researchers found.
"The theory is that mercury exposure confers toxicity because it induces oxidation in the human body, which often results in inflammation," van Wijngaarden said. "These omega 3s are more anti-inflammatory. The idea would be that they would reduce the level of inflammation in the mother, softening any effect that mercury might have on the unborn child."
Riley said pregnant women should continue to avoid fish known to have high levels of mercury, including shark, swordfish and king mackerel.
But, she said the takeaway message from this study is simple: "Go ahead and eat fish."
Avoiding fish known to be high in mercury "would be reasonable," Riley said. "But I wouldn't limit the amount of fish and shellfish."
The study -- funded by the U.S. National Institutes of Health and the Seychelles government -- was published Jan. 21 in the American Journal of Clinical Nutrition.
More information
For more information on eating healthy while pregnant, visit the March of Dimes.
