Pregnancy

In 2004, U.S. government food and environment regulators cautioned pregnant women not to eat more than 340 grams or 12 ounces of fish a week, the amount in two normal servings. The aim was to reduce their exposure to mercury, which contaminates fish worldwide. A Harvard University study in the Faroe Islands in the North Atlantic that year had found that pregnant women who had consumed a lot of fish and whale meat and blubber bore children with irreversible damage to certain brain functions.

However, the U.S. fish consumption advisory can also lead to poor fetal brain development, says the new research from the government's own National Institutes of Health.

"We find that the net effect of the advisory is exactly the opposite of its intended effect," said Joseph Hibbeln.

Joseph Hibbeln is National Institutes of Health psychiatrist and biochemist. He evaluated the results of a British study that tracked the diets of 12,000 pregnant women and the neurological development of their babies. He found that children whose mothers ate less than 340 grams of fish each week, the recommended U.S. government limit, had lower intelligence, worse fine motor control, and poorer communication and social skills than children of mothers who ate more fish.

"If you avoid seafood, you are avoiding a critical dietary source of nutrients that are known to be important for the baby's developing brain," he said. "You create something of a nutritional deficiency if you don't eat seafood or you don't take supplements."

Hibbeln reports in the journal Lancet that the key nutrients fish supply are omega 3 fatty acids, which are essential for optimum brain development.

A commentary in the journal says no one knows how much mercury exposure is toxic. It was written by pediatric neurologist Gary Myers of the University of Rochester, New York, who has conducted his own study of fish consumption among pregnant women in the Seychelles Islands. They consume a lot of seafood - about 12 fish meals a week - and they had mercury levels about 10 times higher than American women. Yet Myers found no link between the metal and their children's cognitive test scores.

He thinks the oils in fish may protect against mercury's toxicity, and he is conducting research to test this notion.

In the meantime, he questions whether the U.S. government fish dietary guideline is wise, especially since surveys show that many Americans have reduced their seafood intake because of it.

"One can not look at just one aspect of child development and child health," said Gary Myers. "You have to look at the whole picture. When you protect children against one possible risk by limiting fish consumption, you may actually be causing more harm than good."

Myers says the Lancet study should be of great interest to government authorities pondering the risks and benefits of fish consumption.