Homocysteine is an amino acid, found in proteins. High levels of homocysteine in the blood has been associated with hardening or blocking of arteries (atherosclerosis) and are a risk factor for the progression of peripheral arterial disease. Blood levels of homocysteine can be normalised by taking vitamin B (folic acid, vitamins B12 and B6 or pyridoxine) supplements and betaine.
People with peripheral arterial disease have poor blood flow in their legs caused by atherosclerosis. Symptoms include a limited ability to exercise or walk without developing cramping pains in the legs. There is growing evidence that even people without symptoms have a two to three times greater cardiovascular risk than the general population. Although people can be treated surgically (such as a bypass graft) or radiologically (angioplasty) to remove blood clots and improve arterial circulation there is an appreciable risk of failure within 12 months, mainly because the arteries narrow and close up again (restenosis). High levels of homocysteine (hyperhomocysteinaemia) may contribute to restenosis. The review authors made a thorough search of the medical literatures looking for randomised controlled trials using any therapy for the set purpose of lowering plasma homocysteine levels compared with no active treatment. They did not find any completed trials. There is currently a trial underway in the USA, called the Homocysteine and Progression of Atherosclerosis Study (HPAS), where patients are randomised to treatment with 4 mg/day folic acid versus non-active placebo, with a follow up period of five years.