Helping patients lower their risk of coronary artery disease remains an important task for family physicians. Typically, the focus has been on the reduction of risk factors by controlling plasma lipid levels, blood pressure and weight. However, recent advances in the understanding of atherosclerosis have suggested that dietary antioxidants may play a role in preventing primary or secondary coronary artery disease. Specifically, antioxidants may inhibit proatherogenic and prothrombotic events in the coronary arterial wall. Writing for the Nutrition Committee of the American Heart Association, Tribble reviewed the literature to define the potential role of antioxidants in the prevention of coronary artery disease.
Antioxidants derived from dietary sources, including vitamins C and E, and beta-carotene, have received the greatest attention with regard to prevention of coronary artery disease. Many food sources contain antioxidants (see the accompanying table). Foods that contain α-tocopherol (vitamin E) and beta-carotene are of particular interest, as both of these substances are carried within low-density lipoproteins. Also of interest is the role of selenium, copper, zinc and manganese, as these trace elements are believed to act as antioxidants as well.
The American Heart Association evaluated the results of large cohort studies and primary and secondary prevention trials. Large observational studies have shown that consumption of antioxidant-rich foods or supplements reduces the risk of coronary artery disease. The largest of these cohort studies is the Nurses' Health Study, in which 85,000 participants were followed for approximately eight years. The risk of coronary disease was lowest among women with the highest intake of vitamin E. None of the studies reviewed found a link between disease risk and consumption of vitamin C. Even though observational studies support a relationship between disease risk and consumption of dietary antioxidants, evidence from randomized trials on primary prevention is lacking. However, results from secondary prevention trials have been more supportive. For example, the Cambridge Heart Antioxidant Study showed that the risk of myocardial infarction was reduced up to 77 percent in patients who took high dosages of vitamin E.
The author concludes that, given the current evidence, patients should be advised to follow a balanced diet consistent with the dietary guidelines of the American Heart Association, with emphasis on antioxidant-rich fruits, vegetables and whole grains. Diet alone may not provide the levels of vitamin E associated with a lower risk of coronary disease, but the absence of data from randomized trials precludes establishing a general recommendation for vitamin E supplementation.