Several groups of investigators have reported the impact of supplementation with vitamins B6, B12, and folic acid, administered alone or jointly, in patients with homocystinuria, resulting from an excess of homocysteine. Folic acid appears to be useful in most subjects; very high doses of B6 (100 mg or more daily) also seem to have broad utility, whereas lower doses may benefit only those whose baseline B6 status is poor. The efficacy of supplemental B12 may likewise hinge on baseline B12 status. Not surprisingly, serum homocysteine levels tend to correlate inversely with serum levels or dietary intakes of these vitamins in the general population, indicating that vitamin nutriture is an important determinant of serum homocysteine in people who don't take B vitamin supplements. This may explain why low serum levels of folic acid or vitamin B6 have been shown to be cardiovascular disease risk factors. Among regular users of supplemental vitamins, average serum homocysteine is reported to be about 1.5 micromolar lower than in those who do not supplement, which should correspond to a 15% reduction in cardiovascular disease risk. Lower homocysteine levels in people who eat breakfast cerals may reflect the fact that such cereals are frequently enriched with B vitamins.
https://lpi.oregonstate.edu/f-w99/vascular.html
