WATERDOWN, MA — The good news is that a male contraceptive may be only years away. The bad news is that at the rate American men are going, they may not need one.According to a new study, the last two decades have seen a steady decrease in the level of the sex hormone testosterone in American men. Between 1988 and 2003, levels in men aged 65 to 69 dropped from 503 nanograms/decileter to 423 nanograms/decileter.

Nobody knows exactly what’s going on, although factors such as weight, smoking, and age do not appear to be the cause. Nonetheless, “Male serum testosterone levels appear to vary by generation, even after age is taken into account,” according to Thomas G. Travison, the lead author of the New England Research Institutes in Waterdown, MA’s study.

Lower sex drive and diabetes are only two health issues related to decreased levels of testosterone. Bones and muscles also depend upon the sex hormone for their continued health and well-being.

It’s not just men in their 60s who are experiencing testosterone drops, however. Even young men are experiencing levels lower than any seen during the past 20 years. “This suggests that some factor other than age may be contributing to the observed decline in testosterone over time,” Travison observes.

About 1,500 men in the greater Boston area participated in the study, which included analyzing blood samples and studying the individuals’ health and lifestyle information. Data was collected between 1987 and 1989, again from 1995 to 1997, and most recently from 2002 to 2004 as part of the Massachusetts Male Aging Study.

More information about the study can be found in the Journal of Clinical Endrocrinology and Metabolism.