Older adults with high intakes of the B vitamin folate may have a faster rate of mental decline than others their age, researchers reported Monday.

The finding is unexpected, and it’s not completely clear that folate caused the quicker cognitive deterioration seen in some study participants, according to the investigators.

However, the study’s lead author told Reuters Health, the results do suggest that older men and women should “use caution” in supplementing their diets with folic acid - the synthetic form of folate used in vitamin pills and added to foods such as cereals and other grains.

The study, which followed more than 3,700 adults age 65 and older, found that those whose daily folate intakes were near or higher than the recommended level generally had a faster rate of mental decline than those with lower folate intakes.

Experts recommend that adults get 400 micrograms of folate a day, through supplements, fortified foods or natural sources such as spinach and other leafy greens, beans and oranges. In this study, participants in the top fifth of folate intake - who typically consumed more than 700 micrograms in a day - had twice the rate of mental decline over six years as those who with the lowest folate intake.

Rates of decline were also faster among men and women who got more than 400 micrograms of folate a day specifically in the form of supplements, and among those whose typical intake of folate from food was nearly 400 micrograms.

The results, published in the April issue of the Archives of Neurology, were not what the researchers expected to find, according to study leader Dr. Martha Clare Morris of Rush University Medical Center in Chicago.

Folate is an important nutrient needed to produce and maintain healthy cells. Along with vitamins B12 and B6, folate also helps the body break down a protein called homocysteine, a byproduct of metabolism that, at high levels in the blood, is thought to be a risk factor for Heart disease and Stroke . Studies are looking into whether the three B vitamins can lower the risk of cardiovascular disease by cutting homocysteine levels.

“We don’t know yet what’s going on,” Morris said of the new findings.

A possible explanation, she noted, is that high folate intake is “masking” a deficiency in vitamin B12 in some people. Older adults are at greater risk of B12 deficiency because they tend to have problems absorbing the vitamin from its natural food sources, which include red meat, fish and poultry. Left untreated, the deficiency can cause mental function to deteriorate.

Folate can treat the anemia that often serves as a sign of vitamin B12 deficiency - but it cannot treat the nerve damage low B12 stores cause. So high folate intake could cause B12 deficiency to go undetected and untreated, which could in turn contribute to mental decline.

On the other hand, Morris and her colleagues found, high B12 intake was associated with slower mental decline among the oldest study participants. The rate of decline for the average 80-year-old who consumed 20 micrograms of B12 through supplements each day was 25 percent lower than that of those who got the recommended level of B12 for adults - 2.4 micrograms.

It’s too soon to make any broad dietary recommendations for older adults, according to Morris. However, she said, the study “calls into question folate supplementation of older people.”

Because adequate folate intake during a woman’s reproductive years is known to cut the risk of birth defects of the brain and spine, U.S. health officials require folic acid to be added to many grain products. This, along with widespread multivitamin use, means that many people may be getting much more than the recommended amount of folate in their diets, Morris and her colleagues point out.

Yet, Morris noted, very little is known about the potential health effects of this trend for older people. More research, she said, is needed to investigate the questions raised by this study.

SOURCE: Archives of Neurology, April 2005.