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An increasing number of men think they've found the way to feel young again -supplements of the male hormone testosterone. Doctors worry that testosterone supplements might increase the risk of prostate cancer. A study in this week's Journal of the American Medical Association offers some reassurance, but doesn't completely absolve the hormone.

NPR's Patricia Neighmond reports on the safety and the temptations of testosterone.

PATRICIA NEIGHMOND: UCLA urologist Dr. Christopher Saigal calls it the dwindles, the way men describe their symptoms when they come to see him.

Dr. CHRISTOPHER SAIGAL (Urologist, UCLA): A lack of interest in sex, lack of desire for sex. They have fewer sexual thoughts and feelings. Less sexual activity. They feel tired more than they used to. They will complain of depression symptoms, you know, feeling sad.

NEIGHMOND: Add a little weight gain around the middle and a decrease in muscle mass and physical strength, plus Internet access and drug company marketing, and patients want to know could supplements of the male sex hormone testosterone help.

Sixty-five-year-old Jim Holland thought it was a good idea, and so a few years ago, he started taking testosterone in gel form, rubbing it on his shoulders. After about five weeks, he says, he saw results.

Mr. JIM HOLLAND: I definitely felt that I had more energy. I had more stamina. I could work through the day at a higher level of energy. I didn't find myself want to doze off after dinner. Mentally, I felt I could concentrate better, all of those things.

NEIGHMOND: As boys grow, testosterone helps develop their reproductive tract. It helps sprout facial hair, thicken vocal chords, increase strength, muscles and eventually libido. Men reach their testosterone peak at about age 30, and after that, levels in the blood decrease by about one percent a year. That means for a man like Jim Holland at 65, he has about one third less testosterone than he did when he was younger.

And although he's pretty sure that testosterone has helped him feel better, there have been no conclusive studies proving that. Most studies are small and short term. Some have even suggested risk, an increase in red blood cell production, which can thicken blood and make patients more vulnerable to heart attack and stroke. There are also concerns about prostate cancer. UCLA's Dr. Saigal.

Dr. SAIGAL: Because we know that when a person has prostate cancer that's spread, that if you remove testosterone from their body, medically castrate them basically, prostate cancer regresses. We're concerned that if we give them more testosterone and they have some hidden prostate cancer that hasn't surfaced yet, that will cause it to grow.

NEIGHMOND: But now, researchers at UCLA find that after six months of use, the hormone does not appear to affect prostate tissue. Urologist Dr. Leonard Marks headed the study.

Dr. LEONARD MARKS (Urologist): The placebo-treated men actually had a few more cancers, small cancers, than the testosterone-treated men. These cancers were all small, but some of them at least were clinically significantly. But there certainly was no carcinogenic effect of the testosterone replacement therapy that we could identify.

NEIGHMOND: Marks says this is good news for short term use of testosterone to help build muscle mass in burn patients, for example, or for HIV patients suffering from wasting syndrome. But Marks says the study was small, just 44 men, so the safety of long-term use, he says, is still a question.

And there are those who say there is little need in the first place. Dr. William Crowley directs the Harvard Reproductive Endocrine Sciences Center at Harvard Medical School. For most men, he says, decreased testosterone levels should not be considered a deficiency. Perceived symptoms, he says, can mostly be attributed to other issues.

Dr. WILLIAM CROWLEY (Harvard Medical School): They're developing more vascular disease as they get older. They often have more arthritis. They're less mobile. They're not as vigorous in their physical exercise. A variety of things that take their toll over life all roll up into the composite issue of not having enough energy and not feeling as well.

NEIGHMOND: One thing studies have proved, says Crowley, the placebo effect. In up to half of men who are not getting the real hormone, there are still reports of feeling better, stronger and more sexual. Long-term studies would be extremely helpful in answering once and for all questions about the actual effect and safety of supplemental testosterone.

Patricia Neighmond, NPR News.

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