Just as the symptoms of menopause in women are attributed to a sharp drop in estrogen production, the signs of aging often seen in men—changes in body composition, energy, strength, and sexual function—are usually attributed to a less drastic decrease in testosterone production that typically occurs in the middle years.
HMS researchers at Massachusetts General Hospital have found that insufficient estrogen could be at least partially responsible for some of these changes in men. The study appeared in the September 12 issue of the New England Journal of Medicine.
Traditionally, a diagnosis of male hypogonadism—a drop in reproductive hormone levels great enough to cause physical symptoms—has been based solely on a measure of blood testosterone levels. But there has been little understanding of how much testosterone is needed to support certain physical functions.
A small portion of the testosterone that men make is normally converted into estrogen by an enzyme called aromatase. The higher the testosterone level in a healthy man, the more is converted into estrogen. Since any drop in testosterone means that there is less to be converted into estrogen, men with low testosterone also have low estrogen levels, making it unclear which hormone supports which functions. The Mass General team set out to determine the levels of hormone deficiency at which symptoms begin to occur in men and whether those changes are attributable to decreased levels of testosterone, estrogen, or both.
The study enrolled two groups of men, ages 20 to 50, with normal reproductive function. All participants were treated with a drug that suppresses normal production of all reproductive hormones.
Men in one group were randomly assigned to receive daily doses of testosterone gel at one of four dosage levels or a placebo gel for 16 weeks, while men in a second group received the same testosterone doses plus an aromatase inhibitor that suppressed the conversion of testosterone into estrogen.
Overall, the results imply that testosterone levels regulate lean body mass and muscle size and strength, while estrogen levels regulate fat accumulation. Sexual function—both desire and erectile function—is regulated by both hormones.