The benefits of eating fish may do more than just offset the risks of mercury exposure to unborn babies. Research shows that nutrients in fish may actually shield the brain from the potentially toxic effects of the chemical.
The findings are based on a study that spans three decades. The results show that high levels of fish consumption by pregnant mothers in the Seychelles—an average of 12 meals per week—did not result in developmental problems in their children.
Researchers have previously equated this phenomenon to a kind of biological horse race, with the developmental benefits of nutrients in fish outpacing the possible harmful effects of mercury also found in fish.
However, the new research, published in the American Journal of Clinical Nutrition, indicates that this relation is far more complex. Compounds present in fish, specifically polyunsaturated fatty acids (PUFA), may also actively counteract the damage that mercury causes in the brain.
“These findings show no overall association between prenatal exposure to mercury through fish consumption and neurodevelopmental outcomes,” says co-author Edwin van Wijngaarden, associate professor of public health sciences at University of Rochester.
“It is also becoming increasingly clear that the benefits of fish consumption may outweigh any potentially adverse effects of mercury.”
“This research provided us the opportunity to study the role of polyunsaturated fatty acids on development and their potential to augment or counteract the toxic properties of mercury,” says lead author Sean Strain, professor of human nutrition at Ulster University in Northern Ireland.
“The findings indicate that the type of fatty acids a mother consumes before and during pregnancy may make a difference in terms of their child’s future neurological development.”
Benefits Versus Risks
The new study comes as the U.S. Food and Drug Administration (FDA) and international agencies are in the process of revisiting fish consumption advisories to better reflect the health benefits of nutrients found in fish.
The FDA’s current guidance—which recommends that pregnant women limit their consumption of certain fish to twice a week—was established because of the known risk of high-level mercury exposure on childhood development.
Mercury is found in the environment as a result of both natural and human (for example, coal plant emissions) activity. Much of it ends up being deposited in the world’s oceans and, as a result, fish harbor the chemical in very small amounts.
This has given rise to concerns that the cumulative impact of prenatal exposure to mercury through fish consumption may have negative health outcomes, despite the fact that a link between low-level exposure and developmental consequences in children has never been definitively established.
At the same time, fish are rich in a host of beneficial nutrients, including fatty acids, which are essential to brain development, leading to a long-standing exchange among scientists, environmentalists, and policymakers over the risk versus benefit of fish consumption.
The debate has significant consequences for global health, as billions of people across the world rely on fish as their primary source of protein.
Mothers in Seychelles
The National Institute of Environmental Health Sciences and the Government of Seychelles provided funding for the study.
The Seychelles Child Development Study—a partnership between the University of Rochester, Ulster University, and the Republic of Seychelles Ministry of Health and Ministry of Education—is one of the longest and largest population studies of its kind.
The Seychelles, a cluster of islands in the Indian Ocean, has proven to be the ideal location to examine the potential health impact of persistent low-level mercury exposure. The nation’s 89,000 residents consume fish at a rate 10 times greater than the populations of the United States and Europe.
The new study followed more than 1,500 mothers and their children.
At 20 months after birth, the children underwent a battery of tests designed to measure their communication skills, behavior, and motor skills. Researchers also collected hair samples from the mothers at the time of their pregnancy to measure the levels of prenatal mercury exposure.
Results show that mercury exposure does not correlate with lower test scores. The finding tracked with the results of previous studies by the group—some of which have followed children in the Seychelles into their 20s—that also have shown no association between fish consumption and subsequent neurological development.
Researchers also measured the PUFA levels present in the pregnant women. They found that children of the mothers with higher levels of fatty acids, known as omega 3 or n3 (the kind found in fish), performed better on certain tests.
Another common form of PUFA, called n6, comes from other meats and cooking oils and is found in greater abundance in the diets of residents of developed countries.
The fatty acids in fish (n3) are known to have anti-inflammatory properties, compared to n6, which can promote inflammation. One of the mechanisms by which mercury inflicts its damage is through oxidation and inflammation.
This has led researchers to speculate that not only does n3 provide more benefit in terms of brain development, but that these compounds may also counteract the negative effects of mercury.
This was reflected in the study’s findings, which show that the children of mothers with relatively higher levels of n6 did poorer on tests designed to measure motor skills.
“It appears that relationship between fish nutrients and mercury may be far more complex than previously appreciated,” says Philip Davidson, the principal investigator of the Seychelles Child Development Study, professor emeritus at University of Rochester, and senior author of the study.
“These findings indicate that there may be an optimal balance between the different inflammatory properties of fatty acids that promote fetal development and that these mechanisms warrant further study.”
*Image of “salmon” via Shutterstock