Most people focus on how much they sleep—but when you sleep is just as important. Dr. Saurabh Sethi, a California-based gastroenterologist, says, “Good health depends not only on how much sleep you get, but also on when you get it.” Staying up too late disrupts the body’s internal clock, or circadian rhythm, leading to long-term health effects.

“If you regularly stay up past midnight, you might experience several health issues,” Dr. Sethi warns. Deep and REM sleep happen earlier in the night and are essential for recovery. Delaying sleep cuts into those vital stages, even if you clock eight hours. “The later you fall asleep, the more damage you might be doing to your system.”

Poor sleep timing is also linked to weight gain. Hormones like ghrelin and leptin shift when you sleep late—ghrelin increases hunger, while leptin, which helps you feel full, drops. This leads to more cravings and late-night snacking. “People who sleep earlier tend to have lower body fat,” says Dr. Sethi.