Sharon K. Sagiv of the Boston University School of Public Health and colleagues analyzed data from a New Bedford, Mass., group of infants born from 1993 to 1998 who were tested for ADHD-related behaviors at age 8 and their mother's level of mercury after they gave birth.
"In this population-based prospective cohort study, hair mercury levels were consistently associated with ADHD-related behaviors, including inattention and hyperactivity/impulsivity," Sagiv said in a statement. "We also found that higher prenatal fish consumption was protective for these behaviors."
Non-occupational methyl mercury exposure comes primarily from eating fish and the U.S. Environmental Protection Agency and the U.S. Food and Drug Administration recommend pregnant women limit their total fish intake to no more than two, six-ounce servings per week. Fish are the main source of mercury, especially the large fish such as swordfish, but exposures can also come from the air of coal-fired power plants or plants grown near coal-fired power plants.
Fish is also a source of nutrients, such as omega-3 fatty acids, which have been shown to benefit brain development, potentially confounding the mercury-related risk estimates, Sagiv said.
The study, published online first in the Archives of Pediatrics & Adolescent Medicine, found there also appeared to be a lower risk association for fish consumption of greater than two servings per week with ADHD-related behaviors, particularly impulsive/hyperactive behaviors.
"In summary, these results suggest that prenatal mercury exposure is associated with a higher risk of ADHD-related behaviors, and fish consumption during pregnancy is associated with a lower risk of these behaviors," the study authors concluded.