If hitting the sheets extra late every night is the norm for you, it might be in your best interest to change your routine. A new study finds that skipping sleep can drastically lower testosterone levels in healthy guys in as little as one week. A recent study funded by the National Heart, Lung, and Blood Institute found testosterone levels dropped significantly in men who don’t get enough sleep—equivalent to aging 10-15 years. These lower levels affect more than just the libido as testosterone deficiency is also linked to lower energy, poor concentration, fatigue and decreased strength. "Low testosterone levels are associated with reduced well being and vigor, which may also occur as a consequence of sleep loss," said Eve Van Cauter, PhD, director of the study, which appeared in the Journal of the American Medical Association. The team of researchers at the University of Chicago Medical Center found that men who slept less than five hours a night for one week had lower levels of testosterone than when they’re fully rested. The study analyzed 10 healthy, lean guys, averaging around 24 years old. When deprived of sleep, their testosterone levels dropped by a whopping 10-15%— with the lowest levels reported between 2-10 p.m. The study notes that testosterone is essential for building strength, muscle mass and bone density, not to mention revving up the sexual drive. For a better night’s sleep try these habits of highly effective snoozers.