VITACOG Trial

If you are older, have memory problems and a documented high homocysteine, B-vitamin treatment is worth discussing with your doctor. With a normal homocysteine, this trial gives you little reason to take them.

Why homocysteine

Homocysteine is an amino acid, a by-product of the body's handling of methionine, that is toxic to neurons and blood vessels at high levels. It is an independent risk factor for brain shrinkage and cognitive decline. Vitamins B6, B9 (folate) and B12 are the cofactors that clear it from the blood, so lowering it with B vitamins is a plausible way to protect the brain. See Homocysteine.

What the trial found

In adults with mild cognitive impairment, high-dose B6, folate and B12 slowed the rate of whole-brain shrinkage by 29.6%: 0.76% a year on the vitamins against 1.08% a year on placebo. In the quarter of participants with the highest homocysteine (above 13 µmol/L), the slowing was 53.3%.^[1]

Later metabolomic work on the same trial, which profiles the small molecules in the body, showed the vitamins were reshaping homocysteine and neurotransmitter-related chemistry, not acting through a single mechanism.^[2]

The omega-3 twist

A re-analysis found the benefit appeared only in people who already had high blood levels of omega-3 fats. In those with good omega-3 status, the vitamins slowed brain shrinkage by about 40%, and by up to about 46% in the group with the most EPA (eicosapentaenoic acid, one of the fish-oil fats) in their blood. In those with low omega-3, they did essentially nothing.^[3] A companion analysis found the same omega-3 dependence for cognitive decline.^[4]

Other trials have not confirmed this cleanly. Post-hoc checks of two trials in middle-aged and older adults with raised homocysteine pointed different ways: in one, which used folic acid alone, people with low omega-3 benefited more; in the other, only one omega-3 fat, DHA (docosahexaenoic acid), showed any link.^[5][6] It remains an unconfirmed subgroup finding. Pairing B vitamins with adequate omega-3 is reasonable, not required.

Why to hold it loosely

• It measured scans, not thinking. The trial was designed to detect a difference in brain shrinkage, not in cognition.
• The subgroup numbers are fragile. The subgroup results were not adjusted for testing many comparisons, so the exact percentages could easily be off, even if the direction is right.
• The wider effect on thinking is very small. The largest recent meta-analysis, 17 trials in about 5,300 adults aged 60 or older, found a very small benefit of B6, folate or B12 on overall thinking ability once outlier and single-blind trials were set aside, probably too small to notice in daily life, and similar whether people had normal cognition, mild impairment or dementia. It did not test whether people with high homocysteine gain more.^[7]

What to do

1. Consider it mainly with a documented high homocysteine, and discuss it with your doctor.
2. Don't expect to feel sharper. The trial showed slower brain shrinkage, and the effect of B vitamins on thinking in trials is very small.
3. Mind the B6 dose. The trial gave 20 mg of B6 a day, above the European upper limit of 12 mg, and high-dose B6 can damage nerves; see Vitamin B6.

For the wider picture on protecting the brain, see Dementia prevention.

Further reading

• Smith AD et al. Homocysteine-lowering by B vitamins slows the rate of accelerated brain atrophy in mild cognitive impairment: a randomized controlled trial. PLoS ONE 2010.^[8]
• Jernerén F et al. Brain atrophy in cognitively impaired elderly: the importance of long-chain ω-3 fatty acids and B vitamin status in a randomized controlled trial. Am J Clin Nutr 2015.^[9]
• van Soest APM et al. Positive effects of folic acid supplementation on cognitive aging are dependent on ω-3 fatty acid status: a post hoc analysis of the FACIT trial. Am J Clin Nutr 2021.^[10]
• Berg J et al. Efficacy of B Vitamin Supplementation on Global Cognitive Function in Older Adults: A Systematic Review and Meta-analysis. Nutr Rev 2025.^[11]