Guys—rest up. Or your sex life will go downhill in a hurry. A University of Chicago study published in this month’s Journal of the American Medical Association says that a week of sleep loss lowered testosterone levels by up to 15 percent in otherwise healthy young men.

Prof. Eve Van Cauter, who led the study, has been studying the effects of sleep deprivation for more than 10 years. “(A level of ) 15 percent is not an insignificant amount, since it is about the amount that occurs with normal aging by 10 to 15 years,” she commented.

The sleep-deprivation part of the experiment included eight consecutive nights in a sleep laboratory in which study participants were allowed just five hours of sleep a night. Researchers say about 15 percent of adult workers in the United States get five hours or less of sleep per night.

So hit the snooze button, men. Your sexual health and well-being depend on it.