Homocysteine, an amino acid that is linked to inflammation, heart disease, osteoporosis and other health problems, is also linked to dementia. Researchers at the University of Oxford found that high homocysteine levels doubled the risk of cognitive impairment and dementia. Vitamins B12, B6 and folic acid are nutrients that are necessary for the body to convert homocysteine into a less noxious substance.

A recent study, appearing in the American Journal of Clinical Nutrition (Nov. 2007, Vol 86, Number 5, pp. 1384-1391) followed over 1600 subjects for 10 years and found that high levels of Vitamin B12 (measured as holotranscobalamin) reduced. The researchers measured Vitamin B12 levels (by testing methylmalonic acid and holotranscobalamin—both are indicators of Vitamin B12 status). They measured cognitive function three times over the ten year course of the study. Doubling the holotranscobalamin levels resulted in a reduction in the rate of cognitive decline of 30%. Folic acid levels did not seem to affect cognitive decline.