New framework provides clearer guidance on fish consumption for pregnant women

Fish consumption during pregnancy is a complex scientific topic. On the one hand, fish is rich in nutrients essential for brain development, such as polyunsaturated fatty acids, selenium, iodine and vitamin D. On the other hand, fish contains methylmercury, a known neurotoxin. For this reason, the US Food and Drug Administration recommends that pregnant women limit their fish intake, and many women unconsciously avoid it completely during pregnancy.

Although fish consumption is an important pathway of exposure to methylmercury, efforts to understand the health risks posed by mercury are further complicated by the fact that the nutritional benefits of fish may buffer or reduce mercury toxicity. American Journal of Epidemiology Based on data from a coastal population in Massachusetts, a new framework has been developed that may clarify these questions, reduce confusion, and produce clearer guidance on fish consumption for pregnant women.

“We propose an alternative modelling approach to address the limitations of conventional models and contribute to improved evidence-based advice on the risks and benefits of fish consumption.“The authors, who include Dr. Sally Thurston of the University of Rochester Medical Center, Susan Corrick, MD, MPH, of the Harvard T.H. Chan School of Public Health and Brigham and Women's Hospital, and Dr. David Rupert of Cornell University, said: “For people who eat fish, this issue can be addressed by separating mercury exposure into fish intake and the average mercury content of the fish consumed.”

The new study emerged from an analysis of data from the New Bedford Cohort, a study created to evaluate the health of children born to mothers living near the New Bedford Harbor Superfund site in Massachusetts. The study included 361 children from the cohort who were born between 1993 and 1998 and underwent a neurodevelopmental assessment at age 8, including tests of IQ, language, memory, and attention.

The researchers were able to measure mercury exposure during the third trimester through hair samples taken from the mothers after birth, which has been the traditional method for studying maternal mercury exposure, but this method alone cannot distinguish between mothers who frequently consume low-mercury fish and those who only consume small amounts of high-mercury fish.

To overcome this limitation, the researchers instead created a model that included estimates of mercury exposure per serving of fish. This was possible because mothers in the cohort also completed a food questionnaire, reporting the types and frequency of seafood they consumed during pregnancy. By estimating average mercury levels by fish type and combining this with information on the mother's diet, the authors were able to create a more precise and detailed way of estimating the joint relationship between fish intake during pregnancy and fish mercury levels on neurodevelopment.

Using this model, the researchers found that the relationship between fish consumption during pregnancy and later neurodevelopment varied depending on the estimated average mercury level in the fish: specifically, consumption of fish with low mercury content was beneficial, whereas consumption of fish with high mercury content was detrimental.

“Because previous analyses had methodological limitations, future studies that extend alternative modeling approaches to consider both the average mercury content and nutrient content of fish may enable more precise estimates of the risk-benefit trade-offs of fish consumption, an important component of many healthy diets.” the authors said.

The authors are applying the model to other large-scale studies of maternal fish intake, including the Seychelles Child Development Study, in which Thurston is an investigator.

of American Journal of Epidemiology The research was funded by the National Institute of Environmental Health Sciences.