How to Avoid Sleep Debt

Getting too little sleep produces a sleep debt. When you build up a big sleep debt, you may run out of steam before you are done for the day.

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How Much Sleep Do You Need?

Most adults need about 7 to 8 hours' sleep per day for optimal alertness, ideally at night. Just as people differ in height and weight, however, people vary in how much sleep they need to feel their best. Perhaps 5 of every 100 adults function well when they average less than 7 hours sleep per day. Another 5 in 100 adults need 9 or even 10 hours sleep per day to feel well-rested.

How many hours do you think you need to feel fully alert? Track your sleep for 2 weeks with a sleep-wake diary. Do you average less than 7 to 8 hours' sleep per day? How does the amount of sleep you get affect how sharp or fatigued you feel in waking hours? Do you feel well-rested most of the time?

If not, you may need more or better quality sleep. Keying into how you feel in your waking hours is the first step to figuring how much sleep you need.

If you take a two week vacation—and are willing to devote some of it to working on improving your sleep—this would be a great time to assess your personal sleep need. Ideally, you'd stay in the same place, and sleep at the same time each day, preferably at night.

For the first few days, you may need to make up lost sleep. After that, go to bed at the same time each night, and sleep until you wake up the next morning without using an alarm. The amount you average over a week likely represents your unique built-in sleep need.

People with predictable work schedules often go to bed around the same time, and use an alarm clock to awaken at the same time on work days. Some change their sleep and wake times on days off.

Railroaders and others with either unpredictable work schedules or predictable schedules that vary over the week often go to bed and get up at different times. Consequently, they also often get varying amounts of sleep.

Railroaders' schedules are far more demanding than those of people who work only in the daytime. They also are more challenging than those of workers who rotate from days to evenings to nights, and follow the same schedule for days or weeks in a row.

Further, because humans are programmed to stay active in the daytime, and sleep at night, railroaders—like others who work at night—typically feel less alert when working at night than when working in the day.

Railroaders commonly focus more than workers in most other occupations on organizing their hours off to assure that they get sufficient sleep. They need to tune into their daily rhythms of alertness and sleepiness, and try sleep at a time of day when it is easy to sleep.

Recharging the Batteries and Measuring Sleep (01:23)
Daniel Cohen, MD, MMSc, of Harvard, explains how we can recharge our internal battery to avoid sleep debt. He also explains how scientists measure sleep needs.

Do You Get Enough Sleep?

When you get all the sleep you need, you charge the battery in your brain. In well-rested adults, the battery charge lasts about 15 hours.

If you need 8 hours' sleep, but get only 6 hours, you charge your battery only part of the way. As a result, it drains faster than a battery that is charged fully. You will feel sleepier sooner, and your performance will deteriorate faster than it would if you had obtained sufficient sleep.

When you get less sleep than you need, you start to build up a sleep debt. An 8-hour sleeper who sleeps only 6 hours is 2 hours in debt.

Missing sleep night after night produces a larger and larger sleep debt. Each successive night with too little sleep magnifies the adverse consequences. It makes you feel as if you are carrying a heavy backpack; you slow down and grow weary quickly.

Use your sleep-wake diary to calculate your sleep debt for the past week: 7 days times 8 hours of sleep per day equals 56 hours. Did you get that much sleep last week? Subtract your total from 56: that's your sleep debt for just one week.

While you don't have to make up one hour for every hour you miss, you need to sleep longer consistently to boost your average. If you're carrying a sleep debt, aim to get your average as close as possible to the amount of sleep you need to feel your best. Then, try to keep it there.

Sleep Myths Debunked

People who frequently short-change themselves on sleep forget how great it feels to be well-rested. They get used to feeling tired all the time. They try to convince themselves that they can manage just fine. They often cling to myths about sleep.

  • Myth: I can catch up on my days off.

    Facts: A couple of days of good sleep will help pay down a modest sleep debt. If the debt has been building for many days or weeks, it will take more than 2 days of good sleep to wipe it out. If you sleep longer than usual on days off, you may throw off your body clock. To make up for missed sleep on days off, use recovery naps rather than extending your main sleep bout. See Sleep Drive, Naps, & Caffeine.
  • Myth: I regularly get 6 hours of sleep or less, and I feel fine.

    Facts: Perhaps only one person in 25 functions at their best while averaging 6 hours of sleep per day. In one study, a group of healthy young men were allowed to sleep an average of 6 to 7 hours for 5 days—about one hour less than they needed. After missing this small amount, they performed as badly on a series of tests as they did after staying awake an entire night.
  • Myth: I can tell when I'm wearing down.

    Facts: People who are nodding off, with eyelids drooping and head bobbing, still may claim, "I'm not sleepy at all."

    People who have had too much to drink typically deny they are drunk. Sleepy people similarly lose the ability to appreciate how sleepy they are. They seldom realize how poorly they perform compared to when they are well-rested.

    There's no warning signal that flashes when you're about to fall asleep. You may experience brief lapses called microsleeps. You think you're awake, and then—oops—you're not.
  • Myth: Missing an hour or two of sleep is no big deal.

    Facts: A sleep debt keeps you from thinking clearly and reacting quickly. It slows eye-hand coordination and decision-making, and increases the likelihood of making mistakes.

    A chronic sleep debt harms bodily processes, such as blood sugar regulation. It increases the risk of becoming obese, and developing diabetes, heart disease, and other illnesses. The Harvard Nurses' Health Study found women who averaged 5 hours or less sleep per day gained far more weight over the 16 years of the study than women who averaged 7 hours' sleep per day.

How to Prevent Sleep Debt


  • Make sleep a priority. When you have to choose between getting enough sleep and work, family, or social obligations, consider your current level of sleep debt. Don't put your safety and health on the line.
  • Nap when possible. If you don't get all the sleep you need one day, try to make it up as soon as possible. Learn more about the best time and length of naps at Sleep Drive, Naps, & Caffeine.
  • Get social support. Talk with your family about your sleep needs. Ask their help in scheduling family activities to let you to get sufficient, high quality sleep. Don't expect them to tiptoe around the house while you sleep. Soundproof your bedroom, or sleep in a room removed from household activity.
  • Make time for "dates" with your spouse or partner that will not steal time from sleep. Try to keep up social relationships with friends, even if you end up meeting them for pancakes instead of for pizza, or catch a movie together in the afternoon instead of the evening.

Getting Family Support (01:17)
Michael Coplen, Federal Railroad Administration human factors researcher and former locomotive engineer, tells how important family is to railroaders getting good sleep.

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This content was last reviewed on June 5, 2012