When fish is not contaminated, moderate consumption of the protein-rich food source by pregnant women and young children appears to boost the children's neurological development, a new study shows.

"Our research adds to the literature suggesting that fish contains nutrients that may enhance early brain development," said Dr. Julie Daniels, assistant professor of epidemiology at the University of North Carolina at Chapel Hill School of Public Health. "We cannot say that we have proven that eating fish will have long-lasting effects in making people smarter, since we have only looked at early development markers through an observational study."

More research is needed to corroborate the findings, Daniels said.

A report on the study appears in the July 2004 issue of the journal Epidemiology.

Conducted in Bristol, England, the research involved evaluating the association between mothers' fish intake during pregnancy and their offspring's early development of language and communication skills, Daniels said.

The team evaluated 7,421 English children born in 1991 and 1992. They studied the children since much has been learned about contaminants in fish, but little research has been done on the potential developmental benefits of eating fish, she said.

"We measured mothers' and children's fish intake by questionnaire," Daniels said. "Later, we assessed each child's cognitive development using adaptations of the MacArthur Communicative Development Inventory at 15 months and the Denver Developmental Screening Test at 18 months."

Researchers also measured mercury levels in umbilical cord tissue for a subset of 1,054 children.

"We found total mercury concentrations to be low and not associated with neurodevelopment," she said. "Fish intake by mothers during pregnancy, and by infants after birth, was associated with higher mean developmental scores. For example, the adjusted mean MacArthur comprehension score for children whose mothers consumed fish four or more times a week was 72, compared with 68 among those whose mothers did not consume fish.

While this may not be a major difference clinically, the statistically significant results were consistent across related subtests that could be important across a large population."

Scientists found that there was a subtle but consistent link between eating fish during pregnancy and children's subsequent test scores, even after adjusting for factors such as the age and education of the mother, whether she breastfed and the quality of the home environment.

The largest effect was seen in a test of the children's understanding of words at age 15 months. Children whose mothers ate fish at least once a week scored 7% higher than those whose mothers never ate fish.

A similar pattern, although less marked, was seen in tests measuring social activity and language development. Developmental scores were also higher among children who also ate fish at least once a week before their first birthdays.

The study suggests that if a woman eats moderate quantities of fish -- about two to three servings per week, or 12 ounces, of noncontaminated species -- her child might benefit, the scientist said. There is no evidence that the more fish a woman eats, the higher that benefit would be.

"Women should definitely avoid shark, swordfish, king mackerel and tilefish, according to the U.S. Environmental Protection Agency and Food and Drug Administration," Daniels said. "Those fish are higher on the food chain and have greater accumulation of pollutants."

Depending on the region where they are caught, many of the most commonly eaten fish are low in pollutants while still being high in critical long-chain fatty acids and other nutrients, she said. They include salmon, herring, pollock, canned light tuna and sardines.

Daniels said she is pursuing similar work in a group of U.S. children to confirm the results in other populations.

"We also need to follow the children longer to determine whether any benefits from fish intake are permanent or transient," she said.

Fish intake during pregnancy has the potential to improve fetal development because it is a good source of iron and long-chain omega fatty acids, which are necessary for proper development and function of the nervous system, Daniels said. Fish, especially oily fish, is a dietary source of eicosapentaenoic and docosahexaenoic acids (DHA), which are important in the structural and functional development of the brain before birth and through a child's first year. The concentration of DHA in fetal brain increases rapidly during the last three months in the womb.