Mercury in fish seems not to harm older brains

Eating moderate amounts of fish - and its added ingredient, mercury - appears to pose little danger to the brains of older adults, according to new study findings released Tuesday.

Among a group of older adults between 50 and 70, those with more mercury in their blood appeared to perform equally well in multiple tests of mental functioning as people with lower blood mercury levels.

In fact, according to the Journal of the American Medical Association report, older adults with higher mercury levels tended to outperform others on tests of manual dexterity involving finger tapping.

Older adults are often advised to eat fish for its omega-3 fatty acids, as well as its cardiovascular benefits. Overall, these findings suggest that moderate amounts of fish are okay for aging brains, lead author Megan Weil of Johns Hopkins University in Baltimore, Maryland told Reuters Health.

However, she noted that more than half of the adults included in the study had blood mercury levels far below what the U.S. Environmental Protection Agency (EPA) considers potentially harmful. Consequently, it's still too soon to tell whether it's safe for fish-lovers to continue their dietary preference into old age, when our brains become more sensitive to toxins, Weil noted.

"Is it causing a problem? That is the question," she said in an interview.

Weil recommended that older adults follow current U.S. government guidelines for eating fish, found at http://www.epa.gov/waterscience/fish/MethylmercuryBrochure.pdf. Although these guidelines were designed for women of childbearing age and young children, older adults may be equally "sensitive" to the effects of mercury, said Weil, also based at the Association of State and Territorial Health Officials in Washington, DC.

During the study, Weil and her team analyzed blood samples from 474 older adults, then asked them to complete 12 tests of mental functioning.

Half the adults had a blood mercury level at or below 2.1 micrograms per liter - significantly lower than the government's cutoff of 5.8, above which experts fear mercury may damage the brain.

When the researchers compared individuals to others with blood mercury levels that fell one unit below, they found that people with higher blood mercury levels performed equally well or better in most tests of mental functioning, although they struggled more with a test of visual memory.

Given that people with higher blood mercury levels fared equally well in most tests, it's possible that their poorer performance in one test is due solely to "chance," rather than an effect of mercury on the brain, Weil suggested.

SOURCE: Journal of the American Medical Association, April 20, 2005.