DON'T LOSE THAT SNOOZE DON'T LOSE THAT SNOOZE The American Academy of Sleep Medicine, the National Sleep Foundation and other sleep experts offer these tips on getting a good night's sleep: -Do not stay up late to talk on the phone or surf the Internet. -Keep computers and TVs out of the bedroom. -Stick with a regular bedtime. -Avoid food or drinks with caffeine, especially at night. Such stimulants can keep you awake. -Don't stay up all night to cram for a big work project or to finish homework if you're in school. -Avoid vigorous exercise within a few hours of bedtime. ADULTS NEED LESS SLEEP -- UP TO A POINT ADULTS NEED LESS SLEEP -- UP TO A POINT Sleep needs vary, depending on age and other factors. On average, here's how many hours of sleep a night the experts recommend: -Preschoolers, 11 to 13 -School-age kids, 10 to 11 -Teens, 8 to 9 -Adults, 7 to 8 Source: The National Sleep Foundation "The ability to compensate for lost sleep is itself lost, which is damaging mentally and physically." -Fred Turek, sleep researcher, Northwestern University You've got a long list of e-mails to return, bills to pay and, oh, yeah, you don't want to miss the latest episode of The Office. By the time you crawl into bed, it's nearly midnight. The alarm goes off at 6 the next morning, and bingo! You've just joined the legions of Americans who are bleary-eyed and flat-out tired most days of the week. For years, sleep researchers have been preaching the dangers of lost sleep: People who are fatigued can't pay attention to routine tasks, have trouble learning and are prone to a laundry list of health problems, from depression to high blood pressure. New research suggests an added risk to losing sleep day after day: Humans and animals that have chronic sleep deprivation might reach a point at which the very ability to catch up on lost sleep is damaged, says Fred Turek, a sleep researcher at Northwestern University in Evanston, Ill. His research on sleep patterns in rats appeared this summer in the Proceedings of the National Academy of Sciences. That, together with findings from a human study, suggests people who lose sleep night after night might not recover the alertness they need to perform well during the day. So far the studies don't tell researchers whether the damage is permanent. But they do suggest that people who go to work fatigued day after day might perform consistently at a subpar level. "They may say, 'Hey, I'm doing fine. I don't need more sleep,' even as their performance on memory and attention tests goes down," Turek says. People who lose sleep because of a single all-nighter typically make up for it by boosting the amount of deep sleep they get the next night, says study co-author Aaron Laposky, also from Northwestern. Deep sleep is thought to restore alertness and helps keep memory and other brain functions in top form. People also make up for the occasional bout of insomnia by sleeping in on weekends, Laposky says. But is that capacity lost when sleep deprivation becomes a fact of life? At Northwestern, researchers kept lab rats awake for 20 hours and then let them sleep for four hours. After the first night, the rats recovered; when they were allowed to sleep, the rats fell into a deep sleep more frequently than they did when well-rested. But after three nights of sleep deprivation, the rats failed to show an increase in deep sleep. And at the end of the five-day study, the animals were given a chance to sleep in, but the rats recovered almost none of the lost sleep. "The ability to compensate for lost sleep is itself lost, which is damaging mentally and physically," Turek says. Sleep expert David Dinges says people seem to respond to a chronic lack of sleep the same way. Dinges, a researcher at the University of Pennsylvania School of Medicine in Philadelphia, and his colleagues studied 48 healthy people. Some got eight hours of sleep a night while others stayed up, losing from two to four hours of sleep a night. By the end of two weeks, the people who had lost sleep at night said they no longer felt tired during the day. But test scores revealed a different story, according to the 2003 study published in the journal Sleep. The sleep-deprived group had trouble paying attention, had slower reaction times and developed impairments in memory, Dinges says. The ability to fend off sleep might have evolved to help animals and humans survive a natural disaster. People forced to evacuate during a fire or hurricane often lose sleep for a short period, but they're more likely to make it through a crisis alive, Turek says. The trouble is humans have built a society that runs round the clock, Turek says. Cellphones, laptops and other electronic devices make it easy to stay connected at all hours. All-night TV and an extended workday also can rob sleep, says James Walsh, executive director of sleep medicine at St. Luke's Hospital in St. Louis. Surveys now show that most people in the USA get less than seven hours of sleep a night, about an hour less than the average sleep time 40 years ago. No one really knows the full effect of the steady erosion of sleep time. Only a study that keeps track of lots of sleepy humans for a long time would answer that question, Turek says. But even if the damage can be reversed, there's plenty of scientific evidence suggesting that sleep loss is bad for your health. For example, fatigue might play a role in obesity. And there's no question that sleep loss plays a role in fatalities on the highway. The National Sleep Foundation says drowsy driving is the likely cause of more than 100,000 car crashes each year in the USA. For that reason alone, Dinges and other experts recommend getting seven to eight hours of sleep on most nights. Losing just an hour night after night can lead to foggy thinking and slow reaction times. "The deficits can become severe," Dinges says. People who put off bedtime to get more done might find it's wiser to make their sleep a priority. "You need to make sure sleep time is protected," he says. Conversation guidelines: USA TODAY welcomes your thoughts, stories and information related to this article. Please stay on topic and be respectful of others. Keep the conversation appropriate for interested readers across the map.