“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.
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 analysed the subjects’ blood samples to measure total testosterone, from which they also calculated the amount of “bio-available” testosterone.
The NERI team carefully analysed the data to compare men of similar ages during each phase of the study. After accounting for age and additional factors such as obesity, smoking, and medications, the researchers found that, each year, the subjects’ total and bio-available testosterone decreased an average of 1.2 and 1.3 percent, respectively.
For men 65-69 years of age in this study, average total testosterone levels fell from 503 ng/dL (nanograms/deciliter) in 1988 to 423 ng/dL in 2003. A normal, healthy adult male usually has blood total testosterone concentrations that range anywhere from 300-1000 ng/dL.
The researchers caution that, given the surprising results, independent studies are necessary to replicate and confirm their findings.
MEDICA.de; Source: Endocrine Society