Folates best at preventing Alzheimer's disease

Aug 15 2005

According to results from a long-term study on aging, adults who eat the daily recommended allowance of folates significantly reduce their risk of developing Alzheimer's disease.

Folates are B-vitamin nutrients found in oranges, legumes, leafy green vegetables and folic acid supplements.

The major observational study demonstrates the importance of healthy diet for long-term brain health and found that folates appear to have more impact on reducing Alzheimer's risk than vitamin E, a noted antioxidant, and other nutrients considered for their effect as a brain-aging deterrent.

In the study, Maria Corrada and Dr. Claudia Kawas of UC Irvine's Institute for Brain Aging and Dementia, analyzed the diets of non-demented men and women age 60 and older.

They then compared the food nutrient and supplement intake of those who later developed Alzheimer's disease to the intake of those who did not develop the disease.

To date this is the largest study to report on the association between folate intake and Alzheimer's risk and to analyze antioxidants and B vitamins simultaneously.

Both Corrada, and Kawas started the study while at Johns Hopkins University in Baltimore, and they say that, 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 the risk of Alzheimer's disease.

In their work the researchers used data from the Baltimore Longitudinal Study of Aging, to identify the relationship between dietary factors and Alzheimer's disease risk.

During the years 1984 to 1991, study volunteers provided detailed dietary diaries, which included supplement intake and calorie amounts, for a typical seven-day period.

Of the original 579 participants, 57 ultimately developed Alzheimer's disease, but the researchers found that those with a higher intake of folates, vitamin E and vitamin B6 shared lower comparative rates of the disease.

However when the three vitamins were analyzed together, only folates were associated with a significantly decreased risk.

The researchers found no association between vitamin C, carotenoids, such as beta-carotene, or vitamin B-12 intake, and decreased Alzheimer's risk.

Corrada, who is an assistant professor of neurology, says that 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.

But it seems that 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.

Folates have already 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, they are often destroyed by cooking or processing.

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

Recent research by Dutch scientists also supports the relationships between folates and brain aging, when they 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.

Kawas, who is the Al and Trish Nichols Chair in Clinical Neuroscience, says that due to the observational nature of this study, it is still possible that other unmeasured factors also may be responsible for this reduction in risk, as 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 says that further research and clinical studies on this subject will be necessary.

Collaborators on the study were Judith Hallfrisch of the U.S. Department of Agriculture, Denis Muller with the National Institute on Aging and Ron Brookmeyer at Johns Hopkins.

The study was originally undertaken at the Gerontology Research Center of the NIA and the Department of Neurology at Johns Hopkins.

Funding for the study came from the Extramural Programs of the NIA.

The Baltimore Longitudinal Study of Aging, which was begun in 1958 by the NIA is America's longest-running scientific study of human aging.

BLSA scientists are discovering what happens as people age and how to separate changes due to aging from those due to disease or other causes.

As many as 1,400 men and women are study volunteers.

The study results appear in the inaugural issue of the quarterly peer-reviewed research journal, Alzheimer's & Dementia: The Journal of the Alzheimer's Association.