A new study of high-dose B vitamins suggest the rate of brain shrinkage may be slowed by treatment in elderly people with mild cognitive impairment (MCI). Overall, B vitamins given at a dose high enough to reduce homocysteine (an amino acid) by 31.7% in this trial had a "pretty dramatic effect" on the rate of brain atrophy also of about 30% compared with placebo.

The effect was greater among those subjects with the highest homocysteine levels. "The treatment actually reduced the rate of shrinkage by 53%, which is a huge effect," said Dr. Smith, the study leader. "We were absolutely delighted with this strong result."

Neuroimaging studies have established that even in the healthy elderly, the brain shrinks at a rate of about 0.5% per year. In those with Alzheimer's disease, the rate is accelerated to about 2.5% per year, and those with MCI fall somewhere in between, with an intermediate rate of about 1%.
Homocysteine has been confirmed a risk factor for brain atrophy, as well as cognitive impairment and dementia. "Since homocysteine levels can be regulated by B vitamins, because they are the main cofactors in the enzymes involved in metabolizing homocysteine, the question is, 'If you lower homocysteine by giving B vitamins, will you reduce the rate of shrinkage of the brain?'"

Of course, the big question is whether this reduction in the rate of brain atrophy translates into maintaining cognition. The trial was not big enough to answer that question statistiaclly. However, another study, NORVIT also looked at cognitive outcomes, and showed no effect of B vitamins in improving cognitive performance over 2 years in otherwise healthy elderly subjects (N Engl J Med. 2006;354:2764-2772, 2817-2819).

For now, I’m going to continue taking vitamins.