The fatty acids found in fish, such as omega 3, are essential for good brain development
The Food and Drug Administration (FDA) and international agencies are in the process of revising guidelines concerning fish consumption in an attempt to better reflect the nutritional benefits of fish.
Currently, the FDA recommend that pregnant women should eat fish no more than twice a week. The reason for limiting fish consumption is because much of the mercury in the environment ends up in the world's oceans, so fish contain small amounts of the chemical.
Although a link between consumption of fish and childhood developmental problems has never been conclusively proved, experts have previously been concerned about the consequences of elevated mercury levels in pregnant women.
However, fish contain many beneficial nutrients. For example, their fatty acids are essential for good brain development.
A partnership between the University of Rochester Medical Center, NY, Ulster University in Belfast, UK, and the Republic of Seychelles Ministry of Health and Ministry of Education yielded the Seychelles Child Development Study - one of the longest and largest population studies of its kind.
As the 89,000 residents of the Seychelles islands in the Indian Ocean consume approximately 10 times as much fish in their diet as people in the US or Europe, the region was considered to be an ideal location for measuring the public health impact of low-level mercury exposure over a long period.
Omega-3 may counteract the inflammatory effect of mercury
More than 1,500 mothers and children participated in the study. The development of the children was assessed using a variety of communication skills, behavior and motor skills tests. The tests started at 20 months after birth and the children were followed into their 20s. Hair samples were also collected from the mothers while they were pregnant so that the team could measure levels of prenatal mercury exposure.
Prenatal mercury exposure was not linked with lower test scores, the researchers found. As the children were followed into adulthood, it was established that there was no association between consumption of fish among pregnant mothers and impaired neurological development in their offspring.
Levels of polyunsaturated fatty acids (PUFA) were also measured in the women while pregnant. The researchers found that the children of mothers with higher levels of the omega-3 (n3) fatty acid found in fish performed better on some tests.
Another PUFA, n6, which comes from meats and cooking oils, is more prevalent in the US and Europe than it is in regions like the Seychelles. However, n6 is known to promote inflammation - unlike n3, which has anti-inflammatory properties.
In the study, the children of mothers with higher levels of n6 were found to perform less well on the motor skills tests than children with higher levels of n3. This finding supports a theory among some scientists that n3 counteracts the inflammatory effects of mercury.
Philip Davidson, PhD, the principal investigator of the Seychelles Child Development Study, a professor emeritus at the University of Rochester and senior author of the study, says:
"It appears that the relationship between fish nutrients and mercury may be far more complex than previously appreciated. 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."