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Prenatal mercury exposure linked to ADHD behaviors

Monday October 8, 2012
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Low-level prenatal mercury exposure may be associated with a greater risk of attention-deficit/hyperactivity disorder related behaviors, according to a study.

However, fish consumption during pregnancy may be associated with a lower risk of these behaviors, researchers reported Oct. 8 on the website of the Archives of Pediatrics & Adolescent Medicine. Because many types of fish have low levels of mercury, a pregnant woman potentially can eat nutritionally beneficial fish without being exposed to significant levels of harmful mercury.

ADHD is one of the most common neurodevelopmental disorders of childhood and affects 8% to 12% of children worldwide, although its cause is not well understood, according to information in the study background. The developmental neurotoxicity of mercury is known, but findings from epidemiological studies are inconsistent, with some studies showing associations between mercury exposure and ADHD-related behaviors and others reporting no significant association.

Nonoccupational methylmercury exposure comes primarily from eating fish, and the Environmental Protection Agency and the Food and Drug Administration have recommended pregnant women limit their total fish intake to no more than two 6-ounce servings per week. However, fish is also a source of nutrients, such as omega-3 fatty acids, which have been shown to benefit brain development, potentially confounding mercury-related risk estimates.

Methodology and findings

Sharon K. Sagiv, PhD, MPH, of the Boston University School of Public Health, and colleagues analyzed data from the New Bedford, Mass., birth cohort, a group of infants born between 1993 and 1998, to investigate the association of peripartum maternal hair mercury levels and prenatal fish intake with ADHD-related behaviors at age 8.

"Hair mercury levels were consistently associated with ADHD-related behaviors, including inattention and hyperactivity/impulsivity," the researchers wrote. "We also found that higher prenatal fish consumption was protective for these behaviors."

Mercury exposure appeared to be associated with inattention and impulsivity/hyperactivity, and some outcomes had an apparent threshold with associations at 1 microgram per gram or greater of mercury, according to the researchers’ statistical analysis. There also appeared to be a protective association for fish consumption of greater than two servings per week with ADHD-related behaviors, particularly impulsive/hyperactive behaviors.

"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 Susan Korrick, MD, MPH, a study coauthor from Brigham and Women’s Hospital.

The study abstract is available at http://archpedi.jamanetwork.com/article.aspx?articleid=1377487.


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