American Heart Association Says Antioxidant Supplementation May Not Lower Risk of Cardiovascular Disease

DALLAS--Consumption of a diet rich in food sources of antioxidants and other cardioprotective agents--not supplementation with antioxidantsis a more likely pathway to prevention of cardiovascular disease (CVD), according to a new Science Advisory released by the American Heart Association (AHA) in the August 3 issue of Circulation (110, 5: 637-641, 2004) (www.circulation.org).

While numerous meta-analyses and randomized clinical trials have been conducted on the relationship between various antioxidants and heart disease, they have typically failed to validate the hypothesis that antioxidant supplements have a beneficial effect on CVD morbidity and mortality. Further, the studies have differed with regard to subject populations studied, dose and type (e.g., synthetic or natural) of antioxidants or antioxidant cocktails, study length and study end points. In addition, the studies have historically been conducted on subjects who have had myocardial infarctions or subjects at high risk for CVD, rather than healthy subjects representative of the general population, and have been conducted over periods as varied as one year and 12 years.

To complicate matters, some studies have shown antioxidant supplements may have potentially adverse effects on CVD. For example, one study showed post-menopausal women with coronary disease receiving hormone replacement therapy given vitamin E plus vitamin C had an unexpected, significantly higher all-cause mortality rate and a trend for an increased cardiovascular mortality rate compared with vitamin placebo women (Waters DD et al. Effects of hormone replacement therapy and antioxidant vitamin supplements on coronary atherosclerosis in postmenopausal women: a randomized controlled trial. JAMA. 288, 19: 2432-2440, 2002.) (http://jama.ama-assn.org). Similarly, in another study, subjects with angiographically demonstrated coronary artery disease taking simvastatin/niacin and an antioxidant cocktail including vitamin E, beta-carotene, vitamin C and selenium had a 0.7 percent progression in stenosis (narrowing or constriction of the diameter of a bodily passage or orifice) after three years, compared with a 0.4 percent regression in the group on simvastatin/niacin only (Brown BG et al. Simvastatin and niacin, antioxidant vitamins, or the combination for the prevention of coronary disease. New England Journal of Medicine. 345, 22:1583-92, 2001.) (www.nejm.org).

In general, the studies showing either positive or negative effects of antioxidant supplementation on CVD end points are much smaller studies than the larger clinical trials that have consistently failed to show any beneficial effects of antioxidant supplements on several CVD end points.

Moreover, the advisory said, CVD risk reduction should be pursued not through antioxidant supplementation but though long-term consumption of a diet consistent with AHA Dietary Guidelines (Krauss RM et al. AHA Dietary Guidelines: revision 2000: a statement for healthcare professionals from the Nutrition Committee of the American Heart Association. Circulation. 102, 18:2284-99, 2000.) (www.circulation.org)--which include reduction of saturated and trans fats; increase in dietary fiber consumption; and increased consumption of fruits, vegetables, whole grains, low-fat or nonfat dairy products, fish, legumes, poultry and lean meats--the long-term maintenance of a healthy body weight by balancing energy intake with regular physical activity, and the attainment of desirable blood cholesterol and lipoprotein profiles and blood pressure levels; however, no consistent data suggest consuming micronutrients at levels exceeding those provided by a dietary pattern consistent with AHA Dietary Guidelines will confer additional benefit with regard to CVD risk reduction, the advisory said.

The advisory concluded that, although past clinical trials have not necessarily ruled out a role for oxidative mechanisms in the pathogenesis of human atherosclerosis, the existing scientific database of epidemiological evidence does not justify routine use of antioxidant supplements for prevention and treatment of CVD and called for further research to clarify the relationship between antioxidants and CVD.

The Council on Responsible Nutrition [CRN] agrees that further research is needed, said Annette Dickinson, Ph.D., President of CRN, in a statement released by CRN. In the meantime, people whose dietary patterns include the regular use of antioxidant supplements have no reason to change those habits. Antioxidants have been shown to enhance overall immune function, protect the eyes from cataracts and macular degeneration, slow the progression of Alzheimers disease and reduce the risk of some cancers. In addition, while many of the studies on vitamin E and heart disease have been disappointing, some have been positive. The AHA seems to be trying to prematurely close the door on supplement use, even while more studies continue.