Whether or not your homocysteine levels are elevated depends upon the total methionine content of dietary protein and the amount of vitamin B6, B12 and folic acid in your diet.

The conversion of homocysteine to methionine is controlled by vitamin B12 and folic acid, which remethylate homocysteine to methionine. The build up of homocysteine causes the formation of homocysteine thiolactone made from methionine in the liver by an enzyme that participates in protein formation and other processes. This build up of homocysteine thiolactone causes low density lipoprotein to become aggregated, or sticky. When LDL homocysteine thiolactone aggregates are released from the blood into the liver, they are taken up by the macrophages of the artery walls to form the foam cells that are seen in early arteriosclerotic plaques.These foam cells then degrade these aggregates and release fat and cholesterol into the developing plaques. The foam cells also release homocysteine thiolactone into surrounding cells of the artery walls, which affect the way that cells handle oxygen. As a result, highly reactive free radicals accumulate within cells, damaging the lining cells of arteries, causing blood clots to be formed and stimulating the growth of arterial muscle cells which form fibrous and degenerative elastic tissue.