Folates appear to have more impact on reducing Alzheimer's risk than vitamin E, which is known for its antioxidant properties, and other nutrients considered useful in deterring brain-aging, the study found.

Maria Corrada and Dr. Claudia Kawas of UC Irvine's Institute for Brain Aging and Dementia led the effort.

More Beneficial Than Other Nutrients

The researchers analyzed the diets of non-demented men and women age 60 and older and then compared the food nutrient and supplement intake of those who later developed Alzheimer's disease to the intake of those who did not. This is the largest study to date to report on the association between folate intake and Alzheimer's risk, and to analyze antioxidants and B vitamins simultaneously, the authors note.

"Although folates appear to be more beneficial than other nutrients, the primary message should be that overall healthy diets seem to have an impact on limiting Alzheimer's disease risk," says Corrada, who like Kawas started with the study while at Johns Hopkins University in Baltimore.

Study volunteers provided detailed dietary diaries, which included supplement intake and calorie amounts, for a typical seven-day period. Ultimately, 57 of the original 579 participants developed Alzheimer's disease.

Many Diets May Lack Enough Folates

Those with higher intake of folates, vitamin E and vitamin B6 had lower comparative rates of the disease, the researchers found. When the three vitamins were analyzed together, only folates were associated with a significantly decreased risk.

No association was found between vitamin C, carotenoids ( such as beta-carotene ) or vitamin B-12 intake and decreased Alzheimer's risk.

"The participants who had intakes at or above the 400-microgram recommended dietary allowance of folates had a 55-percent reduction in risk of developing Alzheimer's," says Corrada, an assistant professor of neurology. "But most people who reached that level did so by taking folic acid supplements, which suggests that many people do not get the recommended amounts of folates in their diets."

Reduce Birth Defects

Folates already have been proven to reduce birth defects, and research suggests that they are beneficial to warding off heart disease and strokes.

Although folates are abundant in foods such as liver, kidneys, yeast, fruits ( like bananas and oranges ), leafy vegetables, whole-wheat bread, lima beans, eggs and milk, cooking or processing often destroys them.

Because of their link to reducing birth defects, folates have been added to grain products sold in the US since 1998. But even with this supplement, it is thought that many Americans have folate-deficient diets.

Recent research is beginning to show relationships between folates and brain aging. Earlier this year, Dutch scientists showed that adults who took 800 micrograms of folic acid daily had significant improved memory test scores, giving evidence that folates can slow cognitive decline.

Unmeasured Factors

"Given the observational nature of this study, it is still possible that other unmeasured factors also may be responsible for this reduction in risk," said Kawas, the Al and Trish Nichols Chair in Clinical Neuroscience.

"People with a high intake of one nutrient are likely to have a high intake of several other nutrients and may generally have a healthy lifestyle," she noted. "But further research and clinical studies on this subject will be necessary."