Evidence

Research on the use of vitamin B-12 for specific activities and conditions shows:

• Heart and blood vessel disease. Researchers had previously believed that vitamin B-12, when combined with folic acid (vitamin B-9) and vitamin B-6, might prevent diseases of the heart and blood vessels by reducing the levels of an amino acid in the blood (homocysteine). However, studies show that the combination of these vitamins doesn't seem to reduce the risk or severity of cardiovascular disease and stroke.
• Dementia. Vitamin B-12 deficiency is associated with dementia and low cognitive function, but it's not clear whether vitamin B-12 supplements might help prevent or treat dementia.
• Athletic performance. Unless you have a vitamin B-12 deficiency, there's no evidence that vitamin B-12 supplements will boost your energy or make you a better athlete.