When it comes to preventing Alzheimer’s disease (search), the old saying that “an apple a day keeps the doctor away” might be good advice, according to a new study.

Apples contain a compound called quercetin (search) that appears to protect rat brain cells from free radicals — unstable molecules that damage cells and are known to play a role in some diseases such as Alzheimer’s disease.

Quercetin is an antioxidant. Antioxidants (search) are known to counteract free radicals (search).

The study was conducted by researchers including Chang Yong Lee, PhD, head of Cornell University’s food science and technology department.

The scientists soaked rat brain cells in quercetin for two hours and then exposed the cells to hydrogen peroxide, a molecule similar to free radicals that can damage cells.

For comparison, the scientists did a similar test using another antioxidant — vitamin C — instead of quercetin.

Quercetin did a better job than vitamin C at protecting the brain cells.

The results suggest that quercetin “contributes significantly” to the protection of brain cells from free radicals in conditions like Alzheimer’s disease, say the researchers, whose study is scheduled to appear in the Dec. 1 issue of the Journal of Agricultural and Food Chemistry.

It’s a long way from lab tests on rat brain cells to treatments for humans, so it’s too soon to call apples (or quercetin) the key to avoiding Alzheimer’s disease.

However, there’s no downside to eating apples.

“People should eat more apples, especially fresh ones,” says Lee in a news release. “Eating at least one fresh apple a day might help.”

Fresh apples are best, says Lee, because quercetin is mainly found in apple skins, with red apples generally having more of the antioxidant than green ones.

If apples don’t appeal, load up on cranberries this Thanksgiving. Quercetin is found in berries — especially cranberries and blueberries — and onions.

By Miranda Hitti, reviewed by Brunilda Nazario, MD

SOURCES: Heo, H. Journal of Agricultural and Food Chemistry, Dec. 1, 2004. News release, American Chemical Society. Reuters.