Consumption of fish may have little effect on mercury levels in pregnant women

A new study suggests pregnant women may not need to worry so much about eating fish, even those varieties that are reportedly high in mercury.

Fish consumption may make up only 7 percent of the mercury levels found in the human body, according to new research published Sept. 30 in Environmental Health Perspectives. That suggests eating fish likely won't present a major health risk to mom and baby. The food might even offer benefits, according to the study's authors.

"We were pleasantly surprised to find that fish contributes such a small amount to blood mercury levels," author Jean Golding, professor at the University of Bristol in England, said in a press release. "We have previously found that eating fish during pregnancy has many health benefits for both mother and child. We hope many more women will now consider eating more fish during pregnancy."

Fish has been linked to some benefits for pregnant women. They are a source of iodine, and mild iodine deficiencies during pregnancy have been associated with lower IQs and reading abilities for the children. Fish also contain iron, zinc and protein, as well as omega-3 fatty acids, which can help in brain development according to the Mayo Clinic.

But some fish can contain higher mercury levels, which have been linked to problems with growth and development. The National Academies' National Research Council estimated that about 60,000 U.S. children are born with neurological problems each year due to overexposure to mercury while in the womb.

The Food and Drug Administration (FDA) and the Environmental Protection Agency (EPA) advise pregnant women against eating shark, swordfish, king mackerel and tilefish because of their high mercury content. They also remind women to check local advisories about the safety of fish caught by family and friends in local lakes, rivers and coastal areas.

Shrimp, canned light tuna, salmon, pollock, and catfish have low levels of mercury, and pregnant women can eat up to 12 ounces (2 average meals) a week of these items, the government health agencies said. They also point out that albacore "white" tuna has more mercury than canned light tuna, so pregnant women should limit their consumption of white tuna to 6 ounces per week.

Researchers for the new study analyzed information from the Children of the 90s study, which included data on 103 food and drink items eaten by 4,484 U.K. women during pregnancy.

Overall, less than 1 percent of the women had mercury levels higher than recommended by the National Research Council and the EPA, which is less than 0.1 micrograms per kilogram of body weight per day. Women who had the highest mercury levels were on average older, college-educated, had a professional or managerial job, owned their own home and were expecting their first child.

All the 103 food items together made up only 17 percent of the mercury found in the women, the analysis showed.

After white and oily fish, the food items that had the most mercury content were herbal teas and alcohol. Wine had higher levels than beer. But, researchers were more surprised by the herbal teas, and believed this could suggest that teas might contain some toxins.

The researchers concluded that current advice to limit seafood intake probably would not have an effect on mercury levels in pregnant women.

Another study published in October 2012 in the Archives of Pediatric and Adolescent Medicine showed that while low levels of mercury consumption by pregnant women raised their children's risk of ADHD-related behaviors, eating more fish was found to decrease the risk of those same behavioral problems. The finding was still true even if the mothers were eating some fish that had high mercury content.

Golding said while fish might be beneficial, nothing beats getting all your nutrients during pregnancy.

"It is important to stress, however, that pregnant women need a mixed balanced diet," he said. "They should include fish with other dietary components that are beneficial including fruit and vegetables."