Increased intakes of B vitamins may slow cognitive decline in people with mild cognitive impairment, suggests a new UK study.
The randomized controlled trial investigated potential links between vitamin B supplementation, homocysteine levels and cognitive function. In the study, 266 people over the age of 70 with diagnosed mild cognitive impairment were assigned to receive a B vitamin supplement providing 0.8 mg of folic acid, 0.5 mg of vitamin B12 and 20 mg of vitamin B6 or a placebo every day for two years (1). The study results showed that homocysteine levels in the B vitamin group decreased by an average of 30% in comparison to the placebo group and executive mental function was stabilized. In addition, there was a significantly slower decline of global cognition and episodic and semantic memory in the B vitamin group.
One interpretation of the data is that lowering homocysteine concentrations by administering B vitamins slows brain atrophy, which in turn slows both cognitive and clinical decline. This would be consistent with several studies showing that the whole-brain atrophy rate is strongly correlated with decline in various cognitive measures. The fact that some studies reported no benefits of B vitamin supplementation on cognitive function may be due to too short trial durations or the inclusion of participants who were either healthy or already had dementia too advanced for an improvement to be detected.
Wasting in the brain (atrophy) is a common symptom of mild cognitive impairment and can be an early warning sign of dementia. Raised concentrations of the amino acid homocysteine seem to be one important factor determining the rate of atrophy. A study reported that people with serum homocysteine levels above 14 mmol/L had twice the risk of dementia (2). Tissue and plasma concentrations of homocysteine are known to be determined by the status of B vitamins, which are cofactors for enzymes involved in homocysteine metabolism.