(Agencies)
Updated: 2007-11-14 07:53

WASHINGTON -- Beta carotene taken as a dietary supplement for many years may protect against declines in memory, thinking and learning skills that often precede Alzheimer's disease, researchers said on Monday.

A split-view image showing PET scans of a normal brain (L) and a brain with Alzheimer's disease. Beta carotene taken as a dietary supplement for many years may protect against declines in memory, thinking and learning skills that often precede Alzheimer's disease, researchers said on Monday. [Agencies]

The study, published in the Archives of Internal Medicine, pointed to a protective effect against cognitive decline in healthy men who look beta carotene for about 18 years, but not in men who took the supplements for an average of a year.

The findings indicate beta carotene may be an important weapon in warding off memory problems that may foreshadow Alzheimer's and other forms of dementia, the researchers said.

"This is the first trial that has found any way to help your memory if you're healthy. I think it does tell us that we can change how our memory improves or worsens," Francine Grodstein of Brigham and Women's Hospital in Boston, who led the study, said in a telephone interview.

Taking beta carotene may have risks for some people such as raising lung cancer risk in smokers, Grodstein said.

Beta carotene is one of the antioxidants -- substances that prevent some of the damage from unstable molecules known as free radicals -- created when the body turns food into energy. Some experts think antioxidants can lower the risk of cancer, heart disease and other ailments.

"Beta carotene is an antioxidant vitamin. So the reason we thought it might help your brain is because there is now a lot of evidence that oxidative damage harms your brain. And that may be one of the initiating factors which leads to memory problems," Grodstein said.

In this study, researchers examined the effects of beta carotene on cognitive ability in two groups of men.

Those in a group of 4,052 men were randomly assigned in 1982 to take either 50 milligrams of beta carotene or a placebo every other day. Another 1,904 men between 1998 and 2001 were also randomly assigned to take either the same amount of beta carotene or a placebo every other day.

The men in the long-term group took the supplements for an average of 18 years. The men in the short-term group did so for an average of a year, with the longest being three years.

Men who took beta carotene in the long-term group recorded significantly higher scores on several cognitive tests -- particularly tests of verbal memory -- compared with those who took a placebo, the study found. In the short-term group, the men taking beta carotene did no better in cognitive tests.

In an editorial accompanying the study, Dr. Kristine Yaffe of the San Francisco Veterans Affairs Medical Center and University of California at San Francisco sounded a note of caution, saying studies have yielded mixed results about antioxidant supplements and better cognitive outcomes.

"For the clinician, there is no convincing justification to recommend the use of antioxidant dietary supplements to maintain cognitive performance in cognitively normal adults or in those with mild cognitive impairment," Yaffe wrote.

Another study also examined the link between diet and dementia. French researchers, writing in the journal Neurology, tracked the diets of 8,085 men and women over age 65. They were followed for four years, during which 183 of the participants developed Alzheimer's and 98 developed some other dementia.

Risk for developing dementia was found to be lower in those with diets heavy in fish, omega-3 oils, fruits and vegetables.