Homocysteine as a risk factor for atherosclerosis.

OBJECTIVE: To review the role of homocysteine as a risk factor in the pathogenesis of atherosclerosis and to provide recommendations for the treatment of hyperhomocysteinemia. DATA SOURCES: A MEDLINE search using key terms such as homocysteine, atherosclerosis, folic acid, vitamin B6, and vitamin B12 was conducted for the time period 1966 through January 1999. STUDY SELECTION: An article was selected for inclusion in this review if it assessed the relationship and proposed mechanisms of hyperhomocysteinemia on the vasculature, physiologic changes due to hyperhomocysteinemia, and outcomes due to hyperhomocysteinemia, such as morbidity and mortality. In addition, studies that assessed the treatment outcomes of hyperhomocysteinemia were evaluated. DATA SYNTHESIS: Studies of patients with cerebral vascular disease reveal elevated homocysteine concentrations in 30-40% of patients compared with controls. Many studies demonstrate a correlation between elevated homocysteine concentrations, risk of myocardial infarction, and mortality. In addition, hyperhomocysteinemia and decreased folic acid concentrations have been identified in end-stage renal disease (ESRD) and type 2 diabetic patients, while both concentrations remained normal in healthy controls. Studies using folic acid 650 microg/d reduced homocysteine concentrations to within normal therapeutic range after two weeks of treatment. Studies with vitamins B6 and B12 have demonstrated that the use of either alone is ineffective, but when combined or administered with folic acid, homocysteine concentrations return to normal. All therapies must be given for the lifetime of the patient. In addition, patients must use discretion in their diet, as common beverages, such as coffee, have a strong correlation with hyperhomocysteinemia, while foods high in folic acid, vitamin B6 and vitamin B12 may reduce homocysteine concentrations. Additional prospective studies are needed to determine effects of treatment of hyperhomocysteinemia and various diets on atherosclerotic morbidity and mortality.
CONCLUSIONS: Studies demonstrate a positive correlation between hyperhomocysteinemia and atherosclerosis. The treatment of choice for hyperhomocysteinemia is folic acid. Although the optimal dose is not known, 650 microg/d is the minimum effective dose. To date, no studies have assessed the effects on morbidity and mortality when treating high homocysteine concentrations in atherosclerotic patients.