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What is homocysteine?

Homocysteine is an amino acid. Amino acids are the building blocks of proteins. It is not possible to get homocysteine from the diet. It must be made from methionine, another amino acid that is found in meat, fish, and dairy products. Vitamins B6 (pyridoxine), B12 and folic acid are needed to make this reaction occur.

Foods containing methionine are transformed into homocysteine in the bloodstream. Homocysteine is converted in the body to cysteine, with vitamin B6 facilitating this reaction. Homocysteine can also be recycled back into methionine using vitamin B12-related enzymes.

Cysteine is an important protein in the body that has many roles. It is involved in the way proteins within cells are folded, maintain their shape, and link to each other. Cysteine is a source of sulfide and is part of the metabolism of different metals in the body including iron, zinc and copper. Cysteine also acts as an anti-oxidant.

If homocysteine cannot be converted into cysteine or returned to the methionine form, levels of homocysteine in the body increase. Elevated homocysteine levels have been associated with heart attack, stroke, blood clot formation, and perhaps the development of Alzheimer's disease.

Medically Reviewed by a Doctor on 6/24/2015

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Homocysteine Definition

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.

SOURCE: Homocysteine.

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