B vitamins are important for cell metabolism. Vitamins B6 (pyridoxine), B9 (folic acid), and B12 (cobalamin) can also reduce levels of the amino acid homocysteine. Homocysteine levels are commonly high in people over 65 and are linked to strokes, coronary artery disease, and dementia. In clinical trials, vitamin B supplements did not improve cognition but other trials suggest they may protect against cognitive decline in people with high homocysteine levels. At recomended doses, vitamin B supplements are generally safe.