The study was conducted by Dennis T. Villareal, M.D., assistant professor of medicine and John O. Holloszy, M.D., professor of medicine in the division of geriatrics and nutritional sciences. Their results will be reported in the Nov. 10 issue of the Journal of the American Medical Association.
DHEA is produced by the adrenal glands. In humans, levels of DHEA peak at about age 20 and then gradually decline. By the time we are 70, we have only about 20 percent of the peak amount circulating in the body. The decline in DHEA has been associated with the deleterious effects of aging, according to the researchers.
Studies in rats conducted by Holloszy demonstrated that DHEA replacement has a protective effect against both the insulin resistance induced by a high-fat diet and the decrease in insulin responsiveness that occurs with advancing age.
"Earlier human studies indicated DHEA supplementation improved bone density and a sense of well-being," Villareal says. "In this study, we wanted to test whether our findings in the rat studies would hold true in people. We investigated whether DHEA could reverse some of the metabolic complications of aging if DHEA levels in elderly people were returned to the levels of their youth."
Volunteers ranged in age from 65 to 78, with an average age of 71, and the group was composed of 28 women and 28 men. Half of the patients were randomly assigned to receive a placebo while the other half received 50 milligrams of DHEA daily. The six-month study was double-blind: neither patients nor physicians knew who received DHEA or the placebo until the conclusion of the study.
Using highly sensitive MRI measurements of the amount of abdominal fat, the researchers found that compared with placebo, DHEA supplementation resulted in a decrease in visceral fat (within the abdomen) of 10.2 percent in the women and 7.4 percent in the men. DHEA therapy also resulted in a decrease in subcutaneous abdominal fat (below the skin surface) averaging 6 percent in both the women and the men. The researchers found no adverse effects from DHEA therapy.
At the end of the study, patients receiving DHEA had significantly lower insulin levels during oral glucose tolerance tests than at the start of the study. Their glucose levels remained unchanged, and these results indicate an improvement in insulin action. The degree of improvement in insulin action correlated closely to the amount of decrease in visceral fat.
"Among the different fat stores, visceral fat is specifically considered potent and metabolically active because its blood drains directly to the liver," Villareal says. "Fatty acids from visceral fat get deposited in the liver and other organs and then mediate the decrease in insulin action that leads to an increased risk for diabetes."
A larger study on the effects of one year of DHEA replacement is in progress, and Villareal and Holloszy are actively recruiting individuals in the 65 to 75 year age range to participate in this new study.
Villareal DT, Holloszy JO. Effect of DHEA on abdominal fat and insulin action in elderly women and men. JAMA. 2004 Nov. 10; 292(18):2243-2248.
Funding from the National Institutes of Health supported this research.
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