Large doses of B vitamins can halve the rate of brain shrinkage in elderly people with memory problems. It may slow their progression toward dementia.
A two-year clinical trial was the largest to date into the effect of B vitamins on "mild cognitive impairment," a condition which is a major risk factor for Alzheimer's disease and other forms of dementia.
"[Researchers] conducted a two-year trial with 168 volunteers with MCI who were given either a vitamin pill containing very high doses of folic acid, vitamin B6 and vitamin B12, or a placebo dummy pill ...
[O]n average the brains of those taking the vitamin treatment shrank at a rate of 0.76 percent a year, while those taking the dummy pill had an average brain shrinkage of 1.08 percent."