( Testosterone levels in American men hav...)Testosterone Levels in Men Decline Over Past Two Decades,Health

Testosterone levels in American men have been declining steadily over the past two decades, a new study in the Journal of Clinical Endocrinology and Metabolism concludes. //

The reasons for this decline are unclear; the study suggests that neither aging nor changes in certain health factors, such as obesity or smoking, can completely explain the phenomenon.

“Male serum testosterone levels appear to vary by generation, even after age is taken into account,” said Thomas G. Travison, Ph.D., of the New England Research Institutes (NERI) in Watertown, Mass., and lead author of the study. “In 1988, men who were 50 years old had higher serum testosterone concentrations than did comparable 50-year-old men in 1996. This suggests that some factor other than age may be contributing to the observed declines in testosterone over time.”

Testosterone is the primary male sex hormone. It is important for maintaining bone and muscle mass throughout life. Insufficient levels of testosterone have been linked to diabetes, low libido, and other medical conditions. Typically, testosterone levels in men peak around their late 20s, and then begin a gradual decline from age 30 onward. Testosterone also is present in women, but at significantly lower levels.

Travison and colleagues based their study on data from the Massachusetts Male Aging Study (MMAS). The MMAS comprised three separate data-collection periods over 17 years (1987-89, 1995-97, and 2002-04). The study involved collecting blood samples, as well as health and biographical data, from approximately 1,500 randomly selected men residing in the greater Boston area.

During each phase of the study, the researchers analyzed the subjects’ blood samples to measure total testosterone, from which they also calculated the amount of “bio-available” testosterone. Bio-available testosterone includes both free testosterone (unbound to proteins) and testosterone weakly bound to proteins
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