Over the past several years, the media has bombarded us with various treatments for low serum testosterone in men to prevent andropause, the male equivalent of menopause in women.

But in a recent study published in the New England Journal of Medicine, Dr. Joel Finkelstein of Massachusetts General Hospital pointed out that “a lot of things we think are due to testosterone deficiency are actually related to the estrogen deficiency that accompanies it.”

Surprisingly, the new research shows that it may not be a testosterone deficiency that plays a role in a reduced sex drive and more fat as men age but rather a deficiency in estrogen—the female hormone. The study points out that estrogen is needed by men as well as women and offers the first clear evidence that too little estrogen can cause certain “male menopause” symptoms. Testosterone is the main male sex hormone, and in men, some of the testosterone is converted into estrogen. As men age, the levels of both testosterone and estrogen diminish.

When men report to their doctors with the symptoms of andropause—diminished libido, strength, and energy—most physicians prescribe a testosterone patch, cream, or injection. (Testosterone cannot be given by mouth because it is very toxic to the liver when taken orally.) Physicians do not usually prescribe estrogen for men, and the study indicated that the way to remedy low estrogen is to give men testosterone and allow the body to convert it.

The study, which involved 400 healthy male volunteers, aged 20 to 50, separated the effects of testosterone and estrogen by first giving the men a monthly injection that temporarily reduced testosterone production to prepuberty levels. The volunteers were then given various doses of testosterone gel or a dummy gel, and half were also given a drug that prevents the conversion of testosterone into estrogen.

The design of the study allowed researchers to compare the effects of different levels of both estrogen and testosterone on strength, libido, and body composition.

The researchers concluded that muscle size and strength depended on testosterone, body-fat mass depended on estrogen, and both hormones were needed to maintain normal sex drive and performance.

Animal research supports this observation. In one experiment, mice that were altered so they did not produce any estrogen grew fat and had no sex drive. And on the human level, male-to-female transsexuals were noted to have an increased libido when given estrogen.

This new study seems to support the need for testosterone replacement as men manifest signs of andropause. Unlike estrogen, however, testosterone does not fall off as sharply with age as estrogen does in women after menopause.

At the end of the day, if a man’s serum testosterone is below the normal level and he experiences the symptoms of andropause, it seems medically safe, prudent, and efficacious to prescribe testosterone replacement therapy in a monitored environment. As the population ages and the life expectancy increases, the case for prescribing testosterone—to prevent frailty, increase muscle and bone strength, enhance mobility, and improve impaired thinking skills—becomes more justifiable, and its use can be expected to increase dramatically in the years to come.

Dudley S. Danoff, MD, FACS is the attending urologic surgeon and founder/president of the Cedars-Sinai Medical Center Tower Urology Group in Los Angeles, California. He is the author of Penis Power: The Ultimate Guide To Male Sexual Health (Del Monaco Press, 2011) and Superpotency (Warner Books).

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