A number of studies have shown that raised homocysteine concentrations may contribute to cognitive impairment. It is also know that elevations in homocysteine, an amino acid, result from inadequate folate, vitamin B12, or vitamin B6 intake.
But it is not clear whether these associations between homocysteine and cognitive measures are causal or whether they are due to homocysteine, to independent actions of the B vitamins, or to both.
The new study, published in this month's issue of the American Journal of Clinical Nutrition (vol 82, no 3, pp627-635), found that folate was independently protective against a decline in spatial copying score after adjustment for other vitamins and for plasma homocysteine. It also protected against a decline in verbal fluency.
But a high homocysteine concentration was associated with a decline in recall memory.
The team from the Tufts University and the Boston University School of Public Health concluded that both low B vitamin and high homocysteine concentrations predict cognitive decline.
In another study out this month, the link with homocysteine concentration and decline in cognition was also demonstrated.
Writing in the 1 October issue of the American Journal of Epidemiology (vol 162, no 7, pp644-653), Dr Merrill Elias of Boston University and colleagues found that in people over age 60, increasing levels of total homocysteine in the blood were associated with decreasing levels of cognitive performance in several areas.
But they also found that high vitamin B12 levels correlated with better cognitive performance.