The antioxidant beta carotene may help prevent mental decline in men, a new study reports, but only with long-term use.

Using data from the same study that established the benefits of low-dose aspirin in reducing the risk of heart disease, researchers followed almost 4,000 men for an average of 18 years. Half of them received 50 milligrams of beta carotene every other day -- the equivalent of four carrots a day -- and half were given a placebo pill.

When that part of the study ended in 1998, an additional 2,000 generally healthy men with an average age of 73 were recruited and randomised in the same way: Half got beta carotene and the rest took a placebo. All 6,000 continued in the study, which went on for another three years. The paper appears in the Nov. 12 issue of The Archives of Internal Medicine. Men who took the antioxidant for three years or less had no improvement on standard tests of memory, but those who took it for 15 years or more scored consistently higher on all tests.

The differences were small, but the authors pointed out that even modest improvements in verbal memory predict substantial differences in rates of dementia. "The broader message," said Francine Grodstein, the lead author and an associate professor of medicine at Brigham and Women's Hospital in Boston, "is that this is the first study that has shown that there are ways, through fairly straightforward lifestyle modifications, that we can help memory as we get older."

New York Times