Men with many things to keep them up at night can add another suspect to the list: testosterone. Researchers at the University of Chicago Sleep, Metabolism and Health Center evaluated the sleep of 44 men, all of whom were overweight or obese, but otherwise healthy. A news release from the Endocrine Society reports that the researchers studied the brain’s slow-wave activity during non-rapid eye movement sleep, a reliable marker of sleep depth. Too little slow-wave activity can leave a person feeling unrested in the morning. To their surprise, the researchers found that a person’s BMI had no influence on slow-wave activity, but testosterone did. The big concern? As doctors increasingly prescribe testosterone to aging men, they may increasingly be interfering with a good night’s sleep.