Researchers have developed a new and improved model to assess the risks and benefits of fish consumption

The model developed by the researchers could help inform recommendations and improve the evidence base on the risks and benefits of fish consumption, particularly during pregnancy.

In a paper published in The American Journal of Epidemiology, researchers from Brigham and Women's Hospital, Harvard T.H. Chan School of Public Health, the University of Rochester Medical Center, and Cornell University present a new framework that takes into account the estimated average mercury content of fish consumed. This helps weigh the harmful effects of mercury against the potential benefits of the nutrients in fish.

Applying this approach to a fish-eating population in Massachusetts, the team found that overall, consuming increasing amounts of low-mercury fish during pregnancy was beneficial, while consuming more high-mercury fish was detrimental to neurodevelopment.

“For patients seeking advice on fish consumption, public recommendations can be confusing and lead to decreased fish consumption,” said lead author Susan Corrick, MD, of the Division of Network Medicine and the Division of Pulmonary and Critical Care Medicine at Brigham and Women’s Hospital. Corrick is also a member of the Harvard-NIH Center for Environmental Health.

"Our study shows that fish consumption was generally beneficial for neurodevelopment when pregnant women ate fish with low mercury levels, but harmful when they consumed fish with the highest average mercury levels. It's important to think about what fish you eat, rather than just cutting back on fish overall," said lead author Sally Thurston, PhD, of the University of Rochester Medical Center.

Exposure to methylmercury (MeHg) can cause neurodevelopmental toxicity. However, many nutrients in fish are beneficial for neurodevelopment, including polyunsaturated fatty acids, selenium, iodine, and vitamin D.

Many studies examining the relationship between mercury exposure and health measure mercury based on its accumulation in hair. However, using only hair makes it impossible to separate the potentially harmful effects of mercury from the beneficial effects of fish consumption. For example, eating a large amount of low-mercury fish or a small amount of high-mercury fish may result in the same level of mercury in a hair sample but have different potential health risks.

Results from analyses using common statistical approaches to this problem can be difficult to interpret. To address these limitations, the researchers proposed a new model that takes into account the expected average mercury content of fish consumed.

The team looked at data from participants in the New Bedford Cohort (NBC), a study that followed 788 children of mothers living near a Superfund site in New Bedford, Massachusetts.

In addition to examining hair samples, the team used survey data from a food frequency questionnaire that mothers completed about 10 days after giving birth. Participants filled out details about the different types of fish they consumed during pregnancy.

The researchers looked at the association between fish consumption — categorized as low, medium, and high average mercury levels — and neurodevelopment in children in the cohort. The team measured neurodevelopment using tests of IQ, language, memory, and attention.

For children whose mothers consumed the most fish with the lowest mercury content, fish consumption was positively (favorably) associated with neurodevelopmental outcomes; in contrast, for children whose mothers consumed the highest mercury content fish, the association between fish consumption and neurodevelopmental outcomes was negatively (harmfully).

The authors note several limitations of the study, including that the estimates of mercury content in fish and the dietary survey data are imperfect. The study population included only participants from the New Bedford area and only looked at neurodevelopment. The study also does not account for variations in beneficial nutrients in the fish consumed, such as PUFA or selenium content.

"Our goal is to help our study contribute to a better assessment of the risk-benefit tradeoffs of consuming fish, a key component of many healthy diets," said lead author Susan Corrick, MD, of the Brigham and Women's Hospital's Division of Network Medicine and the Division of Pulmonary and Critical Care Medicine.

The team hopes that future studies will expand this modeling approach to take into account both the average mercury and nutrient content of fish.