Children born to women who ate more seafood during pregnancy have higher IQs compared to those whose mothers ate little or no fish, according to a new study.

Seafood is the main source of omega-3 fatty acids, which the fetus needs for optimal brain development. But women of childbearing age have been advised to limit their intake of seafood to avoid exposing a fetus to trace levels of neurotoxins such as mercury, which can inhibit brain development in young children.

Salmon is high in omega-3 fatty acids and tends to be low in mercury contamination.
(CBC)

Joseph Hibbeln of the National Institutes of Health in Bethesda, Md., and colleagues at the University of Bristol analyzed data from more than 8,000 British women.

The researchers compared how children performed on developmental tests measuring communication, social and fine motor skills depending on how much seafood their mothers ate.

At age seven, children born to mothers who ate more than 340 grams of seafood or three portions per week showed a lower risk of having low verbal IQ scores compared to those whose mothers ate less.

No evidence found

"We recorded no evidence to lend support to the warnings of the U.S. advisory that pregnant women should limit their seafood consumption," the study's authors concluded.

"In contrast, we noted that children of mothers who ate small amounts [less than 340 grams per week] of seafood were more likely to have suboptimum neurodevelopmental outcomes than children of mothers who ate more seafood than the recommended amounts."

Health Canada guidelines for mercury in fish call for a concentration of no more than 0.5 parts per million — about half the limit considered safe in the United States.

Most fish fall under the limit, but swordfish, shark and fresh or frozen tuna may exceed it and consumption of these should be limited. For young children and women of childbearing age, Health Canada recommends a limit of one meal per month of swordfish, shark or fresh and frozen tuna.

Mercury may build up in fish living in polluted water. Large predatory species such as shark tend to accumulate more mercury in their tissues than species farther down the food chain.

"People are perhaps best served by advisories that follow science and are conservative in the absence of compelling scientific evidence of harm," Dr. Gary Myers and Philip Davidson of the University of Rochester Medical Center in New York wrote in a journal commentary.

"These results highlight the importance of including fish in the maternal diet during pregnancy and lend support to the popular opinion that fish is brain food."