It’s well known advice for pregnant women — don’t eat fish while you’re expecting, since the mercury they contain could harm a developing brain.
Fish are among the most common sources of exposure to mercury, which accumulates in streams and rivers from natural erosion and industrial waste and can spill out into the oceans as well. According to the Natural Resources Defense Council, tilapia contains among the lowest amounts of the heavy metal, while swordfish harbors enough that the group advises avoiding the fish altogether. These dangers are especially relevant to pregnant women, since studies connected mercury to neurological deficits in developing fetuses.
But a new study from researchers at the University of Bristol questions whether seafood is the primary contributor of mercury accumulation in the body. In fact, according to their latest data, fish may account for only 7% of dietary mercury in the human body.
The researchers analyzed 103 food and beverage items consumed by 4,484 women during pregnancy. Altogether, these items accounted for less than 17% of total mercury levels in the women’s bodies. Based on these findings, the researchers say policies that advise against eating fish during pregnancy may need to be revisited, since limiting women’s seafood intake may not reduce their mercury levels significantly.
After fish, the foods and drinks with the highest mercury contamination were herbal teas and alcohol. It’s possible that some traces of mercury get into teas during preparation. “Our findings suggest that although seafood is a component of dietary mercury exposure, it may contribute to less than half of the mercury intake from dietary sources,” the authors write.
The Environmental Protection Agency (EPA) maintains that fish and shellfish are an important part of a healthy diet for women and children, and the 2010 Dietary Guidelines for Americans encourages everyone to eat more fish weekly. But public health officials warn that because nearly all fish contain traces of mercury, meeting those requirements, especially for women who may become pregnant, are pregnant, or nursing mothers and young children, may take some additional research into choosing fish at the lower end of the mercury spectrum. Light tuna, for example, is a better choice than chunky white, and sticking to shrimp and salmon can also lower exposure to mercury without sacrificing the benefits of fish.
The EPA did not respond to requests for comment on the study and whether the data warrants any change in the advice to pregnant women.
While it turns out that a large proportion of the total blood mercury levels found in women did not come from any dietary source, the researchers say it’s critical to find out where the rest of the metal contamination originates. Finding out that answer is critical since it could revise what women are told about how to protect their unborn children from mercury exposure. They may be able to get pregnant and eat their fish too.