People who consume high levels of the nutrient folate may have a reduced risk of developing Alzheimer's disease.

The prevalence of Alzheimer's is expected to quadruple by 2047. The neurodegenerative disease slowly leads to memory impairment, behavioural changes and dementia, affecting how people understand, think, remember and communicate.

Scientists suspect that higher levels of the amino acid homocysteine in the blood, which is linked to a higher risk for cardiovascular disease and stroke, may also increase the risk for Alzheimer's disease.

Since folate, vitamin B12 and vitamin B6 help the body to process homocysteine, it's thought that deficiencies may contribute to cardiovascular disease and dementia.

Clinical trials necessary

"The decision to increase folate intake to prevent Alzheimer's disease should await clinical trials," the researchers concluded in the January issue of Archives of Neurology.

Folate is a B vitamin that the body uses to make healthy new cells. It is found naturally in leafy green vegetables such as spinach, citrus fruits and beans. Dietary supplements offer the vitamin in the synthetic form of folic acid.

Dr. Jose Luchsinger of Columbia University Medical Center in New York and his team studied the diets of 965 people age 65 and older who did not have dementia when the study began.

B12, B6 didn't show same benefits

Those with higher levels of folate, whether from diet or supplements, were less likely to develop Alzheimer's, over the six years of the study. Vitamin B12 and vitamin B6 did not show the same benefits.

There was also a weak link between higher folate levels and lower homocysteine levels, "indirectly suggesting that a lower homocysteine level is a potential mechanism for the association between higher folate intake and a lower Alzheimer's disease risk," the researchers wrote.

The folate findings contrast with those of other studies, and other compounds such as hormones that were thought to reduce the risk of Alzheimer's based on observational studies have not panned out in randomized trials, Luchsinger cautioned.

Folate deficiency has also been linked to neural tube defects, in which the central nervous system fails to develop fully in the fetus, leading to defects such as spina bifida.

The Canadian government introduced mandatory fortification of some foods with folic acid in 1998. Since then, the rate of birth defects such as spina bifida has declined.