Over the last two decades, American men have made a number of major lifestyle changes—taking on a greater share of the housework, consuming an ever-widening array of skin-care products and even leaving jobs to stay home and raise the kids while their well-paid wives earn the dough. Now, a new study published online in the Journal of Clinical Endocrinology and Metabolism suggests that today's men are also changing on the inside: sporting significantly lower testosterone levels than their counterparts 10 or 20 years ago.
Using blood samples collected from more than 1,500 healthy men age 45 to 79 in the Boston area over a period of 17 years (originally gathered as part of the Massachusetts Male Aging Study), scientists at the New England Research Institutes (NERI) measured both total testosterone and “bio-available” testosterone, the portion of the hormone readily available to cells. Then they compared men of the same age in different decades. “We see about a 1 percent decrease per calendar year across men of the same age born at different times,” says NERI biostatistician Thomas G. Travison, lead author of the study. “In other words, a typical 50-year-old today would have about 20 percent lower [testosterone] than his father would have had 20 years ago. What was most surprising about the result was that we were able to explain so little of it.”
Scientists have known for years that testosterone rates in men begin declining naturally in the third decade of life, but this is the first study to document an overall generational decrease. “This is what would be termed provocative information,” says Dr. Marc Blackman, chief of the endocrine section in the National Center for Complementary and Alternative Medicine at the National Institutes of Health. “If this is true [in the wider population] and unchecked, men are getting a double hit—one due to natural aging, and now a cohort-related effect.”
Exactly what's behind that effect isn't known. The researchers looked at the rise in obesity (which decreases T levels), and the drop in smoking (which actually increases T levels) as possible culprits. Neither accounts for the change. Scientists say other health or environmental factors could be contributing to the problem. “One potential villain here would be chemicals in the environment used as pesticides, insecticides or fungicides that have estrogeniclike activity,” says Dr. S. Mitchell Harman, director and president of the Kronos Longevity Research Institute in Arizona. These compounds contain molecules that function like estrogen and signal the pituitary gland to inhibit testosterone secretion. “In low doses, we don’t see much of an effect in an individual. But looked at in the wider population, there could be a noticeable and important effect.”
Severe loss of testosterone can cause male hypogonadism, a condition in which male sex glands fail to secrete adequate levels of hormones, resulting in loss of skeletal muscle and bone mass and impairment of sexual activity. But even smaller deficiencies have been associated with increased rates of diabetes and cardiovascular disease. It's not known whether the level of change detected in the new study has any negative health effects.
The NERI study has also prompted scientists to take another look at controversial research, conducted around the world for decades, indicating that men have lower sperm counts now than similar-aged men had in the past. Skeptics, including Dr. Shalender Bhasin, chief of endocrinology at Boston Medical Center and a leading expert on testosterone, had long questioned the idea that the drop in semen quality was a generational phenomenon. With the new study documenting a similar change in T levels, however, Bhasin says he is reconsidering.
Additional research is needed to confirm the testosterone findings and tease out more information about which populations are affected. Until then, experts say there is just one message to take away: that men have more incentive than ever to maintain an active and healthy lifestyle, which can reduce the negative effects of naturally occurring hormone reductions. As for whether an entire generation of men with low testosterone will lead to more changes in society? Only time—and perhaps fewer dirty dishes—will tell.