Pros and Cons of Eating Fish While Pregnant

A new study found that low-level mercury exposure though consumption of contaminated fish during pregnancy increased the risk of behaviors related to attention-deficit hyperactivity disorder (ADHD) in children. Eating the right types of fish, however, decreased that risk. Photo by Joey Rozier

To eat fish or not to eat fish during pregnancy?

The answer is complicated, according to a new study that found links between pregnant women’s exposure to low-level mercury, primarily from eating fish, and an increased risk of their children exhibiting behaviors related to attention-deficit hyperactivity disorder (ADHD).

However, the study, by Sharon Sagiv, a School of Public Health assistant professor of environmental health, and Susan Korrick, an internist at Brigham and Women’s Hospital in Boston, also found that eating fish during pregnancy had a protective effect, reducing the risk of ADHD-related behaviors in children.

These dual findings, published last month in the Archives of Pediatrics & Adolescent Medicine, are not as contradictory as they sound, because many types of fish have extremely low levels of mercury, so pregnant women could eat nutritionally beneficial fish without exposure risks.

Sagiv talked with BU Today about the study’s findings, which have made headlines nationally.

BU Today: How did you conduct the study?

Sagiv: Our analysis involved approximately 400 mothers and children born between 1993 and 1998 in New Bedford, Mass., a coastal community. Shortly after the mothers gave birth, samples of their hair were collected and analyzed for mercury. The mothers also were questioned about their fish consumption during pregnancy.

Eight years later, we followed up with the children to look at behaviors related to ADHD, using teacher reports and neuropsychological tests. We used those findings as the basis for the analysis.

What can pregnant women learn from the study—should they eat more fish or stay away from fish because of concerns about mercury?

To eat fish—absolutely—as long as it’s not fish containing high levels of mercury. There are certain fish that fall into the high-mercury category, such as swordfish, shark, fresh tuna, or king mackerel. Fish that are low in mercury include flounder, haddock, and salmon. It’s important to think about what kind of fish you are eating.

One of the interesting findings of the study was that eating fish above the levels recommended by the Food and Drug Administration (FDA) and the U.S. Environmental Protection Agency (EPA) had protective associations with ADHD-related behaviors. In a joint advisory, both agencies have recommended that pregnant women limit their total fish intake to no more than two, six-ounce servings a week. But we found that women who ate more than two servings a week had children with lower risks for ADHD-related behaviors—60 percent lower for impulsive hyperactivity behaviors, and a 50 percent decrease in risk for all behaviors. That certainly suggests that eating low-mercury fish can be beneficial. Fish are a source of nutrients, including omega-3 fatty acids, which have been shown to benefit brain development.

Do your findings mean those EPA and FDA guidelines are wrong?

I would never question guidelines based on data from only one study. But our findings do suggest that the recommendations may be too stringent. If we see consistency across other studies, then maybe these limits should be reconsidered—with a major footnote that we’d be talking about fish that are low in mercury.

Ob-gyns routinely refer to these guidelines when they’re advising pregnant women, so these studies are important for informing dietary recommendations for pregnant women.

Other studies have indicated a correlation between high mercury levels and the risk of ADHD-related behaviors. How is your study different?

There have been several studies that have looked at mercury cohorts, but they’ve involved populations that consume incredibly high levels of mercury. Our study looked at mercury levels at a much lower magnitude.

The two seminal studies were in the Seychelles Islands, off Africa, and in the Faroe Islands, near Iceland. One study found no association between mercury and neurodevelopment outcomes; the other did find an association. So these were two studies with very inconsistent findings. One possible reason why the Seychelles study found no association with neurodevelopmental outcomes is that the population there eats a lot of fish. Associations with adverse neurodevelopment may have been masked by the beneficial aspects of the fish they were consuming.

Other studies have reported the benefits of fish, or the detrimental effects of mercury on neurodevelopment. We think that being able to assess both, the way we did, is as an important step.

What do we know about the effects of mercury on brain development? Is there more to learn?

We know that exposure to very high levels of mercury is neurotoxic. Extreme mercury poisoning of seafood in Minamata Bay, Japan, in the 1950s led to severe neurologic effects in exposed adults and in offspring of exposed pregnant women. Evidence is mounting for associations between mercury and adverse neurodevelopment at much lower levels, in the range found in New Bedford. In addition, animal studies have shown that mercury induces changes in dopaminergic function, providing a biologic basis for effects on ADHD.

More studies are needed that account for the effects of fish contaminants and nutrients on neurodevelopment. In addition, further study of the protective association of fish, with respect to current FDA/EPA recommended guidelines, is needed. I’m glad to have been part of the beginning stages of that inquiry.

Lisa Chedekel can be reached at chedekel@bu.edu.