Study: Consuming Fish During Pregnancy Carries Both Benefits and Risks.

Findings suggest that pregnant women should eat fish to encourage fetal brain development — but not fish that are high in mercury.

Attention-deficit/hyperactivity disorder (ADHD) affects as many as one in 10 children worldwide, yet its causes are not well understood.

Now, a study by a BU School of Public Health researcher links low-level prenatal mercury exposure with a greater risk of ADHD-related behaviors. The study, published in the Archives of Pediatrics & Adolescent Medicine, also found that maternal fish consumption during pregnancy can help reduce the risk of ADHD-related behaviors in children.

The dual findings are possible because many types of fish have extremely low levels of mercury, so it is possible for a pregnant woman to eat nutritionally beneficial fish without exposure risks.

Sharon Sagiv“Women need to know that nutrients in fish are really important for brain development, but they also need to be aware that high mercury levels in some fish pose a risk,” said Sharon Sagiv, PhD, assistant professor of environmental health at BUSPH, who conducted the study with Susan Korrick, MD, of Brigham and Women’s Hospital.

“The message is, ‘Eat fish — but don’t eat fish high in mercury,’ ” such as swordfish, shark, fresh tuna or king mackerel. Fish that are low in mercury include flounder, haddock and salmon.

The U.S. Environmental Protection Agency and the U.S. Food and Drug Administration have recommended that pregnant women limit their total fish intake to no more than two, six-ounce servings per week. However, fish also is a source of nutrients, including omega-3 fatty acids, which have been shown to benefit brain development.

The new study suggests there may be a “protective effect” from fish consumption above the recommended limit. The researchers found a reduced risk of ADHD-related behaviors in children whose mothers reported eating more than two servings per week. The study did not examine what types of fish are best for a pregnant woman to eat.

The developmental neurotoxicity of mercury is known but the findings from prior epidemiological studies are inconsistent, with some studies showing associations between mercury exposure and ADHD-related behaviors, and others reporting no associations.

“These findings underscore the difficulties pregnant women face when trying to balance the nutritional benefits of fish intake with the potential detriments of low-level mercury exposure,” said Dr. Korrick.

The analysis involved approximately 400 children born in New Bedford, Mass., between 1993 and 1998. Shortly after their mothers gave birth, researchers collected hair samples from the mothers and analyzed them for mercury. They also gave the mothers a questionnaire to determine their fish consumption during pregnancy. Eight years later, researchers followed up with the children and administered standardized tests to determine behaviors related to ADHD.

The researchers found an increased risk of childhood ADHD-related behaviors with increasing maternal hair mercury levels. The mercury levels were lower than levels shown to be potentially harmful in most previous studies. “These are not very highly exposed populations,” Sagiv said.

Statistical analysis indicated that mercury exposure appeared to be associated with inattention and impulsivity/hyperactivity. At 1 microgram/per gram or more of mercury, the study found a 40 percent higher risk for mild to marked atypical inattentive behavior, and a 70 percent higher risk for impulsive/hyperactive behavior.

The researchers said further investigation is needed on the links between mercury and ADHD. “This is just one study,” said Sagiv. “More needs to be done.”

The study was supported by grants from the National Institute of Environmental Health Sciences of the National Institutes of Health.

Submitted by: Lisa Chedekel

chedekel@bu.edu