Sex Hormone Drop Traced to Exercise

Men who exercise intensely appear to experience a drop in the production of hormones involved in potency, fertility and sex drive, University of Michigan Medical Center researchers say.

They studied six marathon runners and found, for the first time, that heavy exercise has an effect on the production of certain hormones. “We don’t know whether running 10 miles per week or 20 miles per week would do the same thing,” said Dr. Ariel Barkan, who reported the findings in the current issue of the New England Journal of Medicine. “I suspect if we look very carefully we may find similar abnormalities.”

It has long been known that female runners, ballet dancers and other women who exercise heavily experience a drop in the female hormone estrogen, sometimes enough to cause a cessation of menstruation and bone deterioration.

But until now no studies have found a similar effect in men--probably because the earlier studies were flawed by having relied only on single blood samples, the Michigan researchers surmised.

Their study compared the runners, who were doing 80 to 120 miles a week, with 13 non-marathoners by taking a series of blood samples while they rested and while they exercised.

Although the study found there was a change in hormone output, none of the men in the study reported any sexual problems. The researchers called for more detailed studies.