The Centers for Disease Control and Prevention has declared it a "public health epidemic." It's been linked to obesity, cardiovascular disease, diabetes, depression, even premature death. Yet many of us continue to put ourselves at risk. "Sleep deprivation is taken much less seriously than it should be," says Wilfred Pigeon, Ph.D., director of the sleep lab at the University of Rochester Medical Center and author of Sleep Manual: Training Your Mind and Body to Achieve the Perfect Night's Sleep. "It's true that one night of sleeping an hour less than you need is no big deal. We all do it once in a while. But if you're constantly getting an hour or two less than you need, the cumulative effect can be profound." Many of us fall into that category. Adults typically need seven to nine hours of sleep a night. Yet 15 percent of U.S. adults ages 19 to 64 say they sleep less than six hours on weeknights, according to a 2011 poll by the National Sleep Foundation. For some of us, sleep is squeezed out by an overstuffed schedule. For others, it's cut short by a sleep disorder, such as: Restless legs syndrome—Trouble sleeping caused by a strong urge to move the legs, often coupled with strange and unpleasant sensations in your legs Insomnia—Difficulty falling or staying asleep that affects you the next day Sleep apnea—Interrupted sleep caused by repeated, brief pauses in breathing Bulging Waistbands The effects of too-little sleep go beyond simply feeling tired. For instance, have you been hitting the gym and watching what you eat, but you just can't seem to lose weight? One reason might be lack of sleep. A 2010 study in Annals of Internal Medicine included 10 overweight adults who ate a reduced-calorie diet. When they slept only 5.5 hours a night, they lost less body fat and more lean body mass than when they slept 8.5 hours. The shorter sleep time was also associated with feeling hungrier during the day. "If you really want to lose weight, you need to pay as much attention to sleep as you do to diet and exercise," says Tracey Marks, M.D., an Atlanta psychiatrist and author of Master Your Sleep: Proven Methods Simplified. Broken Hearts You might also see the effect of sleep deprivation in your cardiovascular health. "Short sleep duration is associated with heart disease and hypertension," says Dr. Pigeon. In addition, sleep apnea has been linked to atherosclerosis (hardening of the arteries), stroke, and irregular heart rhythms. Being sleep deprived also increases your risk of developing type 2 diabetes. If you have diabetes, lack of sleep and poor sleep quality make it harder to keep your blood sugar under control. Sleep loss isn't only a symptom of depression, but also a potential cause. "And people with insomnia or nightmares have a much higher rate of suicidal thoughts and suicide," says Dr. Pigeon. On the plus side, when sleep disorders are treated, depressive symptoms often diminish. Drowsy Drivers According to a National Sleep Foundation poll, 60 percent of U.S. adult drivers say they've driven while drowsy within the past year, and more than one-third admit to actually nodding off behind the wheel. Research shows that drivers who have been awake for 24 hours are impaired to a degree that's comparable to being legally drunk. Drowsiness at work has been linked to industrial disasters, medical errors, and air traffic controllers dozing off at their posts. If people keep getting too little sleep for several nights in a row, "reaction time gets slower and slower. And performance on cognitive tasks gets worse and worse," says Dr. Pigeon. If you aren't careful, you might find yourself caught in a vicious cycle. "You're sleep deprived, so you work slower and less efficiently, and the job takes longer," says Dr. Marks. "You need to bring more work home with you, and you stay up later to do it. The next day, you're even sleepier than before." To break free of this cycle, make sleep a priority in your daily schedule. And if sleep problems persist, talk with your doctor. Sleep deprivation is a serious health hazard. Consider this your wake-up call.