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TAIPEI, TAIWAN. High blood levels of the amino acid homocysteine have been
associated with an increased risk of atherosclerosis. Homocysteine is formed in the body
from methionine (an amino acid found in proteins) in a process that can be blocked by
folic acid and vitamins B6 and B12. High homocysteine levels can induce endothelial
dysfunction (a narrowing of the arteries) which in turn is believed to be a precursor of
atherosclerosis. Researchers at the National Taiwan University Hospital now report that
homocysteine-induced endothelial dysfunction can be avoided or very significantly
ameliorated by supplementing with folic acid and vitamin B6 and vitamin B12. The study involved two men and fourteen women between the ages of 41 and 55 years. At the start of the study all participants had their blood levels of homocysteine and their blood flow through the brachial artery measured after a 10-14 hour overnight fast. They were then given an oral methionine loading test to simulate the intake of a high protein meal. Four hours later their average homocysteine level had increased from 7 micromol/L to 22.7 micromol/L and the blood flow (flow-mediated vasodilation) had decreased by 40 per cent. The experiment was repeated, but this time 5 mg of folic acid was given together with the methionine; the results were similar to those obtained in the first experiment indicating that folic acid does not act immediately as an "antidote" to a high intake of methionine.
The participants were then given 5 mg of folic acid, 100 mg of vitamin B6, and 0.5 mg of
vitamin B12 daily for five weeks. At the end of the five weeks their average homocysteine
level had decreased to 5.2 micromol/L. The methionine loading test was repeated. Four
hours later the average homocysteine level among the participants had increased to 17
micromol/L, but there was no statistically significant difference in blood flow before and
after the methionine loading test. The researchers conclude that short-term (five weeks)
administration of folic acid and vitamins B6 and B12 will reduce post-methionine load
homocysteine levels and eliminate or ameliorate endothelial dysfunction (an early
manifestation of atherosclerosis).
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