Homocyst(e)ine and cardiovascular disease: A critical review of the epidemiologic evidence

Purpose: To review epidemiologic studies on the association between homocys t(e)ine level and risk for cardiovascular disease and the potential benefit s of homocysteine-decreasing therapies. Data Sources: Computerized and manual searches of the literature on total h omocysteine levels and cardiovascular disease. Study Selection: Prospective studies and major retrospective epidemiologic studies evaluating the association between homocyst(e)ine levels and cardio vascular disease and the association between blood levels or dietary intake of folate, vitamin B-6, and vitamin B-12 and cardiovascular disease. Data Extraction: Relevant data on patient population, plasma homocyst(e)ine levels, duration of follow-up, and main results were extracted from studie s that met the inclusion criteria. Data Synthesis: The designs and results of studies included in this review are summarized. A formal metaanalysis was not performed because the studies were heterogeneous in method and design. Conclusions: Results of epidemiologic studies suggest that moderately eleva ted plasma or serum homocyst(e)ine levels are prevalent in the general popu lation and are associated with an increased risk for cardiovascular disease , independent of classic cardiovascular risk factors. Simple, inexpensive, nontoxic therapy with folic acid, vitamin B-6, and vitamin B-12 reduces pla sma homocyst(e)ine levels. Although the association between homocyst(e)ine levels and cardiovascular disease is generally strong and biologically plau sible, the data from the prospective studies are less consistent. In additi on, epidemiologic observations of an association between hyperhomocyst(e)in emia and cardiovascular risk do not prove the existence of a causal relatio n. Therefore, the effectiveness of folate, vitamin B-6, and vitamin B-12 in reducing cardiovascular morbidity and mortality requires rigorous testing in randomized clinical trials. Several such trials are under way; their res ults may greatly affect cardiovascular morbidity and mortality, given the s implicity and low cost of vitamin therapy.