Americans are conflicted about fish. Some of us like to catch them, some of us like to release them and many of us eat them. Health professionals say that fish is good for us (it’s high in protein, most varieties are low in fat and many have heart-healthy properties), that we should eat more. Others take care to note that some varieties of fish are particularly prone to toxic exposure to mercury.
So what’s a pregnant woman to do, especially in light of a new study that shows that a prospective mom’s fish-rich diet can offer protection against the child later developing behaviors associated with attention-deficit/hyperactivity disorder (ADHD)? Especially in light of the Journal of the American Medical Association’s advice (JAMA) that for pregnant women, mothers who are breastfeeding and women of childbearing age, fish consumption is important for its DHA, an omega-3 fatty acid that aids infant brain development?
The new study, published in the Archives of Pediatric and Adolescent Medicine, involved children born during the 1990s in Massachusetts; 515 women who had just given birth completed a dietary survey and about 420 provided samples of their hair for mercury testing. About eight years later, researchers tested the kids to assess behaviors associated with ADHD.
The results, as reported on ScienceNews.org, ranged from children with almost no ADHD-related behaviors to some with clear clinical disease. The mother’s hair-mercury level related to where her child fell along the spectrum.
The data, the researchers said, demonstrate that a woman can eat fish regularly, but also maintain a low-mercury diet. “It really depends on the type of fish that you’re eating,” one of the authors told ScienceNews. Some study participants had been eating more than two servings of fish weekly but tested for relatively little mercury.
Like lead, mercury is a potent neurotoxin that has been linked to many health problems, including delays in neural development. To see our post about the toxic nature of lead, click here.
In the study, children of women with hair mercury levels in the top 20 percent of those tested showed a 50 to 60 percent increased risk of ADHD-related behaviors. But the kids with ADHD-related traits “were still considered to be within the normal range,” the researcher said, “and not maladaptive.” (On some components of the childrens’ assessment for attention, boys showed a greater sensitivity to mercury than girls.)
Other studies have reached similar results. One based in Canada, according to ScienceNews, found an association between elevated mercury concentrations in children at birth and at school age, and an increased risk of ADHD by about age 11. That study also confirmed earlier evidence suggesting a link between lead and ADHD.
Some studies, however, indicate a genetic susceptibility to ADHD in some people. Environmental pollutants, too, are considered by some people to be risk factors. They include tobacco smoke and possibly polychlorinated biphenyls (PCBs), certain pesticides and bisphenol A (BPA).
The new study didn’t collect data on the species of fish the mothers ate. But its researchers said that previous studies have shown that tuna, swordfish and shark can be particularly high in mercury; salmon and cod tend to be relatively low in the toxic metal.