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Homocysteine, folic acid, and B vitamins
Homocysteine is an amino acid that plays a role in coronary artery disease. It is metabolized (chemically transformed) into methionine and cysteine with the help of the B vitamins; folic acid (B9), B12, and B6 (pyridoxine). Therefore, insufficient amounts of these B vitamins in the body can theoretically hamper the metabolic breakdown of homocysteine, and hence increase its blood levels. High levels of homocysteine in the blood (hyperhomocysteinemia) can damage the inner surface of blood vessels, promote blood clotting, and accelerate atherosclerosis.
The current state of knowledge regarding folic acid, homocysteine, and heart attacks is as follows:
- The level of blood folate is an important determinant of the blood homocysteine level. Low blood folate levels are associated with high blood levels of homocysteine.
- Low blood folate is common among individuals who do not take multivitamins, but unusual among those who do.
- The consumption of folic acid supplements or folic acid fortified cereals can increase blood folate levels and decrease blood homocysteine levels.
- In a large population study involving women, those who had the highest consumption of folic acid (usually in the form of multivitamins) had fewer heart attacks than those who consumed the least amount of folic acid.
Even though current scientific evidence suggests that taking folic acid and vitamin B supplements to lower homocysteine levels should help prevent atherosclerosis and heart attacks, conclusive proof is still lacking because:
- There are no conclusive controlled studies demonstrating that increasing folic acid intake actually prevents atherosclerosis and heart attacks.
- There is no clinical study demonstrating that lowering blood levels of homocysteine actually prevents atherosclerosis and heart attacks.
There is also no official recommendation as to who should be tested for hyperhomocysteinemia. The optimal doses of the B vitamins, folic acid, B12, and B6, required to prevent and treat hyperhomocysteinemia are also uncertain. For folic acid, a daily dose of 0.8-1.0 mg is probably adequate.