Low B12 tied to faster mental decline with age

NEW YORK (Reuters Health) - Low levels of vitamin B12 could speed mental decline in older people, a new study suggests.

Among a group of men and women aged 65 and older, those whose levels of two B12 activity markers indicated higher blood levels of the vitamin had a slower drop-off in cognitive function over 10 years than their peers, researchers found.

Folic acid and vitamin B12 supplements can reduce levels of homocysteine, a protein that has been tied to Alzheimer's disease, suggesting that supplementing with these B vitamins could ward off dementia, the researchers explain in the American Journal of Clinical Nutrition. However, folic acid can mask B12 deficiency, and some studies have linked low levels of B12 and high folic acid consumption with faster mental decline.

To better understand the relationship among homocysteine, folic acid, B12 and cognitive function, Dr. Robert Clarke of the University of Oxford in the United Kingdom and colleagues followed 1,648 men and women 65 and older whose mental function was tested at least three times over a 10-year period.

The researchers checked levels of the biologically active portion of vitamin B12, holotranscobalamin, as well as methylmalonic acid, a marker for B12 function. Testing for B12 itself has a "poor predictive value," they note.

There was no association between homocysteine or folate levels and cognitive function, the researchers found. However, lower holotranscobalamin levels and higher methylmalonic acid levels -- both of which are markers for low levels of vitamin B12 -- were each independently linked to faster mental decline. Higher folate levels along with low B12 levels did not accelerate mental decline.

The findings suggest that doubling a person's vitamin B12 levels by taking oral supplements could slow cognitive decline by one third, according to Clarke and his team.

Based on the findings, low levels of vitamin B12 appear to precede mental decline, the researchers conclude. "Correction of vitamin B12 deficiency may be appropriate among those with relevant symptoms," they write.

Current trials comparing vitamin B12 to placebo for heart disease prevention may provide a definitive answer to whether the vitamin can indeed preserve mental function in aging people, they add.

SOURCE: American Journal of Clinical Nutrition, November 2007.