Taking a supplement that boosts the hormone DHEA significantly reduced abdominal fat and improved insulin action in a small group of elderly patients, according to a new study.

Accumulation of abdominal fat -- the so-called "spare tire" -- is one of the more common effects of aging. The research adds this phenomenon to bone-density loss and perhaps other aging problems brought about at least in part by a plunge in levels of the hormone.

Produced by the adrenal glands, DHEA levels peak in humans at about age 20, and then gradually decline. By age 70, we have only about 20 percent of that young-adult peak amount left circulating.

Researchers at Washington University in St. Louis had already found in rat studies that giving a DHEA supplement helped protect against both insulin resistance brought on by a high-fat diet and a decrease in insulin responsiveness that occurs as we age.

"We wanted to test whether our findings in the rat studies would hold true in people, 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," said Dr. Dennis Villareal, an assistant professor of medicine. He is co-author of the study, published Wednesday in The Journal of the American Medical Association.

The test was carried out on 28 women and 28 men, ages 65 to 78. Half of the patients were randomly assigned to receive a placebo, while the others got 50 milligrams of DHEA daily. Neither the doctors nor the patients knew who got which pill until the six- month study was over.

The researchers used magnetic resonance imaging to measure the amount of abdominal fat and oral glucose-tolerance tests to gauge improvement in insulin action. The images showed significant decreases in both visceral (within the abdomen) and subcutaneous (just below the skin surface of the middle) fat in both men and women.

The improvement in insulin action closely followed the decreases in abdominal fat.

"Among the different fat stores, visceral fat is specifically considered potent and metabolically active, because blood drains directly to the liver," Villareal said. "Fatty acids from visceral fat get deposited in the liver and other organs and then bring about the decrease in insulin action that leads to an increased risk for diabetes."

The researchers found no adverse effects from taking the DHEA supplement, which is already widely available as a dietary supplement without prescription.

Villareal and co-author Dr. John Holloszy are now working to set up a larger study of seniors ages 65-75 to track the effect of the supplement for a full year.

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By the numbers

Abdominal fat fell by an average of 10.2 percent in the women and 7.4 percent in the men on DHEA therapy, and about a 6 percent decrease in fat below the skin surface in both sexes.