Fish consumption during pregnancy is a complex scientific topic. On the one hand, fish are rich in nutrients essential for brain development, including polyunsaturated fatty acids, selenium, iodine, and vitamin D. On the other hand, fish contain methylmercury, a known neurotoxin. This has led the U.S. Food and Drug Administration to recommend that expectant mothers limit their consumption, inadvertently leading many women to forgo fish consumption altogether during pregnancy.
Fish consumption is a major route of exposure to methylmercury. However, efforts to understand the health risk of mercury are further complicated by the fact that the nutritional benefits of fish can modify or reduce the toxicity of mercury. A new study appearing in the American Journal of Epidemiology Based on data from a cohort of residents of a coastal Massachusetts town, a new framework is being created that can untangle these questions, reduce confusion, and provide clearer guidelines for pregnant mothers' fish consumption.
“We propose an alternative modeling approach to address the limitations of previous models and thereby contribute to better, evidence-based advice on the risks and benefits of fish consumption,” said the authors, including Sally Thurston, PhD, of the University of Rochester Medical Center, Susan Korrick, MD, MPH, with Harvard TH Chan School of Public Health and Brigham and Women's Hospital, and David Ruppert, PhD, with Cornell University. “In fish-eating populations, this can be addressed by separating mercury exposure into fish intake and the average mercury content of fish consumed.”
The new research comes from an analysis of data from the New Bedford Cohort, which was created to assess the health of children born to mothers living near the New Bedford Harbor Superfund site in Massachusetts. The current study included 361 children from the cohort who were born between 1993 and 1998 and who underwent neurodevelopmental assessments at age 8, including tests of IQ, language, memory and attention.
The researchers were able to measure mercury exposure during the third trimester of pregnancy through hair samples collected from the mothers after birth. Although hair samples are the traditional method of studying maternal mercury exposure, this approach alone cannot distinguish between mothers who regularly ate low-mercury fish and mothers who ate a smaller amount 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 type and frequency of fish and shellfish consumed during pregnancy. The authors estimated average mercury levels by type of fish, and when combined with information about the mothers’ diet, they were able to create a more accurate and detailed method for estimating the joint associations of fish intake during pregnancy and mercury levels in fish on neurodevelopment.
Using this model, the researchers found that the relationship between fish consumption during pregnancy and subsequent neurodevelopment varied depending on the estimated average mercury levels in the fish. Specifically, consuming fish with low mercury content was beneficial, while consuming fish with higher mercury content was detrimental.
“Given the methodological limitations of previous analyses, future research extending our alternative modeling approach to account for both the average mercury content and nutrient content of fish could better assess the risk-benefit trade-off of fish consumption, an important component of many healthy diets,” the authors said.
The authors are in the process of applying this model to other large studies of maternal fish consumption, including the Seychelles Child Development Study, on which Thurston is a researcher.
The American Journal of Epidemiology study was supported with funding from the National Institute of Environmental Health Sciences.
