Brain atrophy (shrinkage) is common in older people, but especially pronounced for individuals who develop Alzheimer's disease. It has also been noticed, that low levels of omega-3 fatty acids and elevated homocysteine (usually due to deficiency of folate, vitamins B12 and B6 and choline) are associated with brain atrophy.

In a clinical study of 168 people (over 70y) with mild cognitive impairment, a daily dose of folic acid (0.8mg), B12 (0.5mg) and B6 (20mg) vs placebo was administered for 2 years. At the end of the study (called VITACOG), MRIs were performed to see if the B vitamin cocktail had any effect on the progression of brain atrophy.

It did, and the results weren't subtle. Compared to the placebo group (n=83), the brain atrophy rate in the B vitamin treatment group (n=85) was slowed by 40%. This is a dramatic result, but there is a catch. This only occurred in the group in which the omega-3 levels at baseline were high (>590umol/L). B vitamins had no significant impact when the omega-3 fatty acid levels were low (<390umol/L).