Homocysteine: An amino acid produced by the body, usually as a byproduct of consuming meat. Homocysteine is made from another amino acid, methionine, and then in turn is converted into other amino acids.
Elevated levels of homocysteine in the blood appear to make for an elevated risk of cardiovascular (heart and vessel) disease. Levels of homocysteine as low as 12 micromoles per liter of blood plasma have been found associated with an increased risk of heart attack, stroke, peripheral vascular disease and venous thromboembolism (blood clots in the veins). A homocysteine level of 15 micromoles or above has a heart attack rate three times as high as normal. Even a level of 12 micromoles can double the coronary risk.
Homocysteine can damage blood vessels in several ways. It injures the cells that line arteries and stimulates the growth of smooth muscle cells. Homocysteine can also disrupt normal blood clotting mechanisms, increasing the risk of clots that can bring on a heart attack or stroke.