The study adds strength to the theory -- bolstered by recent animal studies -- that the risk of developing Alzheimer's and similar diseases may be reduced by dietary intervention, particularly by increasing one's intake of antioxidant-rich foods. It is scheduled to appear in the Dec. 1 issue of the Journal of Agricultural and Food Chemistry, a peer-reviewed publication of the American Chemical Society, the world's largest scientific society.
"On the basis of serving size, fresh apples have some of the highest levels of [the antioxidant] quercetin when compared to other fruits and vegetables and may be among the best food choices for fighting Alzheimer's," says study leader C.Y. Lee, Ph.D., professor and chairman of the Department of Food Science & Technology at Cornell University in Geneva, N.Y.
"People should eat more apples, especially fresh ones," Lee says. He cautions that protection against Alzheimer's using any food product is currently theoretical and adds that genetics and environment are also believed to play a role in the disease. Despite these caveats, the researcher predicts that "eating at least one fresh apple a day might help." But Lee also points out that results so far are limited to cell studies and that more advanced research, particularly in animals, is still needed to confirm the findings.
Previously Lee and his associates have shown that apples may help protect against cancer too.
For the current study, the researchers exposed groups of isolated rat brain cells to varying concentrations of either quercetin or vitamin C. The cells were then exposed to hydrogen peroxide to simulate the type of oxidative cell damage that is believed to occur with Alzheimer's. These results were then compared to brain cells that were similarly exposed to hydrogen peroxide but were not pre-treated with antioxidants.
Brain cells that were treated with quercetin had significantly less damage to both cellular proteins and DNA than the cells treated with vitamin C and the cells that were not exposed to antioxidants. This demonstrates quercetin's stronger protective effect against neurotoxicity, according to the researchers.
Scientists are not sure of quercetin's mechanism of action, but some suspect it might work by blocking the action of highly-active chemicals called free radicals, an excess of which are thought to damage brain cells as well as other cell types over time. Further studies are needed, they say.
Even though quercetin is relatively stable during cooking, fresh apples are better sources of quercetin than cooked or processed apple products because the compound is mainly concentrated in the skin of apples rather than the flesh, Lee says. Products such as apple juice and apple sauce do not contain significant amounts of skin. In general, red apples tend to have more of the antioxidant than green or yellow ones, although any apple variety is a good source of quercetin, he adds.
For those who don't like apples or may have difficulty eating the whole fruit, there are some promising alternatives, Lee suggests. Other foods containing high levels of quercetin include onions, which have some of the highest levels of quercetin among vegetables, as well as berries, particularly blueberries and cranberries. Like other antioxidants, quercetin has been associated with an increasing number of potential health benefits, including protection against cancer.
Alzheimer's is a chronic form of dementia that primarily strikes the elderly and causes severe memory loss and, eventually, death. The disease is characterized by the overproduction of a protein, beta-amyloid, that accumulates in the brain of its victims. Although normal brains contain beta-amyloid, those with the disease have comparatively large amounts. The protein is thought to produce free radicals (oxidants) that appear to cause cumulative damage to brain cells, according to some researchers.
Although there's no cure for the disease and no one is sure of its exact causes, some researchers are increasingly optimistic that dietary intervention using antioxidant-rich foods might help reduce the risk of developing the disease. Other foods rich in antioxidants include blueberries, red wine, red grapes and dark chocolate.
Alzheimer's affects an estimated 4.5 million people in the United States, according to the National Institute on Aging. That figure is expected to rise dramatically as the population ages, experts predict.
The U.S. Department of Agriculture, the U.S. Apple Association, New York State Apple Research and Development Program, and Korea Science and Engineering Foundation provided funding for this study.
The American Chemical Society is a nonprofit organization, chartered by the U.S. Congress, with a multidisciplinary membership of more than 159,000 chemists and chemical engineers. It publishes numerous scientific journals and databases, convenes major research conferences and provides educational, science policy and career programs in chemistry. Its main offices are in Washington, D.C., and Columbus, Ohio.
-- Mark T. Sampson
EDITOR'S NOTE: November is National Alzheimer's Disease Awareness Month.
The online version of the research paper cited above was initially published Nov. 10 on the journal's Web site. Journalists can arrange access to this site by sending an e-mail to firstname.lastname@example.org or calling the contact person for this release.