One Fish, Two Fish, Go Low-Mercury Fish

Mercury in pregnant women linked to inattentive or hyperactivity symptoms in children

(RxWiki News) One of the foods pregnant women need to watch out for is fish. They are advised to avoid fish with too much mercury. But eating fish with lower mercury levels might be a good idea.

A recent study found that women eating more fish tended to have children with fewer symptoms of inattention and hyperactivity. But the boys of women who had higher mercury levels shortly after birth tended to have more of these symptoms.

"Eat only low-mercury fish while pregnant."

The study, led by Sharon K. Sagiv, PhD, MPH, of the Department of Environmental Health at Boston University School of Public Health, looked at pregnant women's mercury exposure and fish intake and compared these to inattention and hyperactivity behaviors of their children.

The data for the study included 607 children born between 1993 and 1998 in New Bedford, Massachusetts.

The children received neuropsychological assessments at about 8 years old to assess whether they showed inattentive, hyperactive or combined symptoms.

The study did not look at whether the children met the clinical definition of attention deficit hyperactivity disorder (ADHD). It also did not consider whether children in the study had been diagnosed with ADHD.

For 421 of these children, the researchers used a hair sample from their mothers, taken about 10 days after birth, to test for mercury levels.

Hair samples have been shown to provide reasonable information about the amount of organic mercury in a person's body.

For 515 of the children (including overlap with those who had hair samples), the researchers collected information from the mothers about their average weekly fish intake while pregnant.

Some fish are known to have high levels of mercury, and pregnant women are advised to avoid too much mercury-containing fish while pregnant because of its possible negative effects on the baby's brain development.

The average amount of mercury found among the women's hair samples was 0.45 μg/g.

Women who had over 1 μg/g of mercury in their hair sample were somewhat more likely (1.4 times) to have children who showed mild or moderate symptoms of attention difficulties. The link was mostly associated with boys.

These boys were also about 1.7 times more likely to exhibit impulsive or hyperactive behavior. The link between mercury exposure and inattentive or hyperactive behaviors was less apparent for girls.

However, women who ate more than two servings per week were less likely to have children showing inattentive or hyperactive behaviors.

It's not clear why the women who ate more fish had children with fewer symptoms of behavior similar to ADHD behavior.

It may be related to the omega-3 fatty acids (which promote brain development) in the fish. It may also relate to the types of fish the women ate.

According to the U.S. Department of Agriculture, women should avoid eating fish containing high levels of mercury during pregnancy, such as shark, swordfish, tilefish and mackerel.

The USDA also recommends that pregnant women do not eat more than 6 ounces of canned white tuna per week.

However, eating fish types that are low in mercury may be beneficial. These include salmon, flounder, tilapia, trout, pollock and catfish.

In general, this study found that a higher level of organic mercury in the women's hair samples was related to a higher number of symptoms related to inattention and hyperactivity. Women who ate more fish tended to have children with a lesser amount of these symptoms.

The study did not find that children of mothers with higher mercury levels were necessarily at a higher risk of developing ADHD or that these children had ADHD. Any conclusions about ADHD or its risk were beyond the limits of the study.

The study was published October 8 in the Archives of Pediatrics & Adolescent Medicine. The study was funded by the National Institute of Environmental Health Sciences at the National Institutes of Health. The authors declared no conflicts of interest.

Review Date: 
October 7, 2012