Knowing which fish to eat during pregnancy is very important

Scientists have been grappling with the subject of fish consumption during pregnancy for a long time. While fish are laden with nutrients like polyunsaturated fatty acids, selenium, iodine, and vitamin D, essential for brain development, they also contain methyl mercury, a neurotoxicant.

It’s a tricky balance to navigate, prompting the US Food and Drug Administration to recommend expectant mothers to limit fish consumption. This, however, has an unintended consequence: many women completely avoid fish during their pregnancy.

Dilemma with fish consumption during pregnancy

A recent study took on this complex issue, producing a novel framework based on data from a Massachusetts coastal community.

“For patients who are seeking guidance about fish consumption, public advisories can be confusing and lead to decreased fish intake,” said senior author Susan Korrick, MD, of the Brigham’s Channing Division of Network Medicine and Division of Pulmonary and Critical Care Medicine.

The researchers believed that understanding the health risks of mercury should factor in the nutritional benefits of fish that might reduce or counterbalance mercury toxicity.

Along with Dr Korrick, leading the charge were Sally Thurston, PhD, from the University of Rochester Medical Center and David Ruppert, PhD, from Cornell University.

They proposed an innovative modelling approach to improve evidence-based advice on the risks and benefits of fish consumption.

Thurston, Korrick, and Ruppert suggested that in fish-eating populations, mercury exposure could be dissected into fish intake and the average mercury content of the consumed fish.

Mercury mystery

The scientists drew their data from the New Bedford Cohort, a group assembled to assess the health of children born to mothers residing near the New Bedford Harbor Superfund site in Massachusetts.

The study included 361 children who underwent neurodevelopment assessments at eight years of age, measuring IQ, language, memory, and attention.

The researchers measured mercury exposure during the third trimester of pregnancy using hair samples from mothers collected after birth.

A significant drawback, however, was that this method couldn’t discern between mothers who frequently ate low-mercury fish versus those who consumed smaller quantities of high-mercury fish.

New angle to an old problem

The scientists broke new ground by devising a model that incorporated estimates of mercury exposure per serving of fish.

They drew upon a food questionnaire completed by the mothers, which outlined the type, frequency, and mercury content of fish and shellfish consumed during pregnancy.

With these details, the researchers could estimate the joint effects of fish intake and fish mercury levels on neurodevelopment.

“We propose an alternative modelling approach to address limitations of previous models and to contribute thereby to improved evidence-based advice on the risks and benefits of fish consumption,” said the authors.

Fish, pregnancy, and neurodevelopment

The results were intriguing: the relationship between pregnancy fish consumption and subsequent neurodevelopment pivoted on the estimated average mercury levels in the fish.

Specifically, eating low mercury-containing fish was beneficial, while consuming fish with higher levels of mercury was detrimental.

“Our study finds that eating more fish was generally beneficial for neurodevelopment when pregnant individuals consumed fish containing low levels of mercury but detrimental when individuals consumed fish with the highest average mercury levels. It’s important for people to think about what kind of fish they are consuming rather than simply cutting down on fish intake entirely,” said Thurston. 

“Our goal is for our study to help facilitate better estimation of the risk-benefit tradeoffs of fish consumption, a key component of many healthy diets,” added Korrick. 

The team hopes that future work will expand on this modeling approach, taking both the average mercury and nutritional content of fish into account.

Clarity amid confusion

These hopeful findings could be the key to demystify public advisories on fish consumption and avoid inadvertently reducing fish intake.

There’s a general consensus that more work needs to be done to refine this model, taking into account differences in the beneficial nutrients in the fish consumed, like PUFA or selenium content.

However, the study marks an essential step forward in understanding the risks and benefits of fish consumption during pregnancy.

The study is published in the journal American Journal of Epidemiology.

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