Surprising new research from the University of Chicago suggests reduced sleep can lower testosterone levels in healthy young men.

While the study involved a very small sample, findings are consistent with emerging research that suggests low sleep duration and poor sleep quality can disrupt the endocrine, or hormonal, system, which is involved in metabolism, growth, tissue function and mood.

The study is found in the June 1 issue of the Journal of the American Medical Association (JAMA).

Investigators found that men who slept less than five hours a night for one week in a laboratory had significantly lower levels of testosterone than when they had a full night’s sleep.

Low testosterone has a host of negative consequences for young men, and not just in sexual behavior and reproduction. It is critical in building strength and muscle mass, and bone density.

“Low testosterone levels are associated with reduced well-being and vigor, which may also occur as a consequence of sleep loss” said researcher Eve Van Cauter, Ph.D.

According to experts, at least 15 percent of the adult working population in the U.S. gets less than 5 hours of sleep a night.

The 10 young men in the study were recruited from around the University of Chicago campus. They passed a rigorous battery of tests to screen for endocrine or psychiatric disorders and sleep problems. They were an average of 24 years old, lean and in good health.

For the study, they spent three nights in the laboratory sleeping for up to 10 hours, and then eight nights sleeping less than five hours. Their blood was sampled every 15 to 30 minutes for 24 hours during the last day of the 10-hour sleep phase and the last day of the five-hour sleep phase.

The effects of sleep loss on testosterone levels were apparent after just one week of short sleep.

Five hours of sleep decreased their testosterone levels by 10 percent to 15 percent (the same amount of reduction that is expected by aging 10 – 15 years). The young men had the lowest testosterone levels in the afternoons on their sleep-restricted days, between 2 p.m. and 10 p.m.

The young men also self-reported their mood and vigor levels throughout the study. They reported a decline in their sense of well-being as their blood testosterone levels declined. Their mood and vigor fell more every day as the sleep restriction part of the study progressed.

In general, testosterone levels in men decline by 1 percent to 2 percent a year as they age. Testosterone deficiency is associated with low energy, reduced libido, poor concentration, and fatigue.

Source: University of Chicago Medical Center