Copper May Be Behind Legumes' Heart-Healthy Properties

GRAND FORKS, N.D.--Increased dietary copper through legume consumption may protect against heart disease, according to an editorial published in the Aug. 12 issue of the Archives of Internal Medicine (162, 15:1780-1, 2002) (archinte.ama-assn.org). In her editorial, Leslie M. Klevay, M.D., S.D.(Hyg), a researcher at the U.S. Department of Agriculture's Human Nutrition Research Center, discussed the First National Health and Nutrition Examination Survey Epidemiologic Follow-Up Study (Arch Int Med, 161, 21:2573-8, 2001), in which researchers from Tulane University School of Public Health and Tropical Medicine in New Orleans identified a reduced risk of coronary heart disease with increased legume consumption. The Tulane researchers concluded legumes protected against heart disease because of the possible protective properties of calcium, fiber, folate, magnesium, potassium or vegetable protein, but Klevay believes copper is the heart-healthy nutrient.

In reviewing research on copper and heart disease, Klevay noted copper deficiency affected numerous characteristics: 1) it elevated cholesterol, blood pressure and uric acid; 2) it adversely affected electrocardiograms; 3) it impaired glucose tolerance; and 4) it promoted thrombosis and oxidative damage. Of the nutrients the Tulane researchers cited as possibly protective, fiber and magnesium have single effects on cholesterol levels or electrocardiograms, but they do not have effects on several characteristics simultaneously, according to Klevay.

Klevay cited research on the copper content of legumes, of which soy and lima beans ranked in the upper tertile of 235 foods for copper content. Diets low in copper may explain much of the epidemiology and pathophysiology of ischemic heart disease, according to Klevay.

The Tulane study demonstrated those with more frequent legume intake demonstrated lower systolic blood pressure, less hypertension, lower levels of total cholesterol and hypercholesterolemia, and less diabetes, in spite of having eaten more fat. Klevay attributed this effect to increased copper consumption, as previous animal research demonstrated a high-fat diet produced cardiovascular lesions in mice only when copper intake was insufficient.

In her conclusion, Klevay stated copper supplements have improved oxidative defenses in middle-aged people, and although increased copper intake from legumes was considerably less than what is found in supplements, the lower dose may have been effective because of the longer duration of supplementation of a much larger population.

"While many constituents of legumes may play a role in decreasing the risk of cardiovascular disease, evidence from prospective studies support the roles of fiber, folate, potassium, calcium and magnesium in decreasing risk of cardiovascular disease," wrote Linda Bazzano, Ph.D., the lead researcher on the Tulane study, in reply to Klevay's conclusions. "Moreover, randomized controlled trials show that soybean protein reduces serum total and low-density lipoprotein cholesterol levels, and that potassium supplementation lowers blood pressure. Such evidence is not available for dietary copper."