Fish Mercury May Not Harm Older Adults

Aging baby boomers hooked on fish may have cause for cheer. Results from a new study in the Journal of the American Medical Association suggest that higher levels of mercury in the blood from fish consumption do not adversely affect an older person's behavior or learning abilities.

Mercury is ubiquitous in the environment. Cars and heavy industry, as well as medical and other waste, all contribute. Microorganisms convert the mercury to methylmercury, which can easily enter an organism's blood and become lodged in the brain, causing a host of neurological problems. The primary source of mercury in humans is seafood. Because seafood also contains omega-3 fatty acids, which are known to be beneficial to the heart, older Americans are encouraged to eat more of it. That's worrying because this older population could be at a greater risk of experiencing the harmful effects of mercury.

To evaluate the risk, Megan Weil, an environmental health scientist at the Johns Hopkins University in Baltimore, Maryland, and colleagues correlated factors such as age and fish consumption with behavior and learning ability. The team analyzed the amount of mercury in the blood of 474 people aged 50 to 70. "Most mercury advisories are based on women of child-bearing age and children," says Weil. "But we forget about the aging population, which is more sensitive to toxic substances." The subjects were next given a series of 12 neurobehavioral tests. The researchers found that increased levels of blood mercury were associated with a worse score on tests of visual memory but better scores on tests for manual dexterity. In addition, "We saw no decrease in cognition," says Weil.

"This is a nice study because of its large sample size and the rigor of data collection," says Michael Shannon, a medical toxicologist at Children's Hospital in Boston. But he says it's too early to reassure older adults, because the results are "methodologically flawed and lack a clear take-home message." Because someone's fish consumption may vary over time, the authors acknowledge, a single measure of mercury in the blood may not be enough to make long-term conclusions.

Related site
NIH info on mercury consumption

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