By Karen Springen
Stay up and read this tonight (you’ll thank us in the morning!)
1. To function best, you need to get eight hours.
There's nothing magic about that number. Everyone has different sleep needs, and you'll know you're getting enough when you don't feel like nodding off in a boring situation in the afternoon, says New York University psychologist Joyce Walsleben, Ph.D., co-author of A Woman's Guide to Sleep .
2. If you can get it, more sleep is always healthier.
You wish. Some studies have found that people who slept more than eight hours a night died younger than people who got between six and eight hours. What scientists don't know yet: Whether sleeping longer causes poor health or is a symptom of it, says Najib Ayas, M.D., MPH, assistant professor of medicine at the University of British Columbia. Long sleepers may suffer from problems such as sleep apnea, depression, or uncontrolled diabetes that make them spend more time in bed.
3. Some people function perfectly on four hours of sleep.
Legendary short sleepers — including Bill Clinton, Madonna, and Margaret Thatcher — don't necessarily do better on fewer Zs. "They're just not aware of how sleepy they are," says Thomas Roth, Ph.D., sleep researcher at Henry Ford Hospital in Detroit. Too little sleep is bad for your health and your image: It can make you ineffective (it impairs performance, judgment, and the ability to pay attention), sick (it weakens your immune system), and overweight. In fact, women who slept five hours or less a night were a third more likely to gain 33 pounds or more over 16 years than women who slept seven hours, according to a Harvard Nurses' Health Study. Oddly, cutting too much sleep and getting less than six hours is associated with the same problems as sleeping too long: a higher risk of heart problems and death. And, of course, cheating on sleep hurts you behind the wheel: "Wakefulness for 18 hours makes you perform almost as though you're legally drunk," says Walsleben.