Sleep

What the Research Says About Sleep Duration

The first thing experts will tell you about sleep is that there is no "magic number." Not only do different age groups need different amounts of sleep, but sleep needs are also individual. Just like any other characteristics you are born with, the amount of sleep you need to function best may be different for you than for someone who is of the same age and gender. While you may be at your absolute best sleeping seven hours a night, someone else may clearly need nine hours to have a happy, productive life. In fact, a 2005 study confirmed the fact that sleep needs vary across populations, and the study calls for further research to identify traits within genes that may provide a "map" to explain how sleep needs differ among individuals.

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Though scientists are still learning about the concept of basal sleep need, one thing sleep research certainly has shown is that sleeping too little can not only inhibit your productivity and ability to remember and consolidate information, but lack of sleep can also lead to serious health consequences and jeopardize your safety and the safety of individuals around you.

For example, short sleep duration is linked with:

• Increased risk of motor vehicle accidents
• Increase in body mass index – a greater likelihood of obesity due to an increased appetite caused by sleep deprivation
• Increased risk of diabetes and heart problems
• Increased risk for psychiatric conditions including depression and substance abuse
• Decreased ability to pay attention, react to signals or remember new information

According to researchers Michael H. Bonnet and Donna L. Arand, "There is strong evidence that sufficient shortening or disturbance of the sleep process compromises mood, performance and alertness and can result in injury or death. In this light, the most common-sense 'do no injury' medical advice would be to avoid sleep deprivation."

On the other hand, some research has found that long sleep durations (nine hours or more) are also associated with increased morbidity (illness, accidents) and mortality (death). Researchers describe this relationship as a "U-shaped" curve (see illustration) where both sleeping too little and sleeping too much may put you at risk. This research found that variables such as low socioeconomic status and depression were significantly associated with long sleep. Some researchers argue that these other variables might be the cause of the longer sleep: the fact that individuals with low socioeconomic status are more likely to have undiagnosed illnesses because of poor medical care explains the relationship between low socioeconomic status, long sleep and morbidity/mortality. Researchers caution that there is not a definitive conclusion that getting more than nine hours of sleep per night is consistently linked with health problems and/or mortality in adults, while short sleep has been linked to both these consequences in numerous studies.

"Currently, there is no strong evidence that sleeping too much has detrimental health consequences, or even evidence that our bodies will allow us to sleep much beyond what is required," says Kristen L. Knutson, PhD, Department of Health Studies, University of Chicago. "There is laboratory evidence that short sleep durations of 4-5 hours have negative physiological and neurobehavioral consequences. We need similar laboratory and intervention studies to determine whether long sleep durations (if they can be obtained) result in physiological changes that could lead to disease before we make any recommendations against sleep extension."

But a key question is how much is too much or too little. Researchers Shawn Youngstedt and Daniel Kripke reviewed two surveys of more than 1 million adults conducted by the American Cancer Society and found that the group of people who slept seven hours had less mortality after six years than those sleeping both more and less. The group of people who slept shorter amounts and those who slept longer than eight hours had an average mortality risk that was greater, but the risk was higher for longer sleepers. Youngstedt and Kripke argue that for those who would normally sleep longer than eight hours, restricting their sleep may actually be healthier for them, just as eating less than one’s appetite may be healthier in a more sendentary society.

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Though research cannot pinpoint an exact amount of sleep need by people at different ages, the following table identifies the "rule-of-thumb" amounts most experts have agreed upon. Nevertheless, it's important to pay attention to your own individual needs by assessing how you feel on different amounts of sleep. Are you productive, healthy and happy on seven hours of sleep? Or does it take you nine hours of quality ZZZs to get you into high gear? Do you have health issues such as being overweight? Are you at risk for any disease? Are you experiencing sleep problems? Do you depend on caffeine to get you through the day? Do you feel sleepy when driving? These are questions that must be asked before you can find the number that works for you.

What You Can Do

To begin a new path towards healthier sleep and a healthier lifestyle, begin by assessing your own individual needs and habits. See how you respond to different amounts of sleep. Pay careful attention to your mood, energy and health after a poor night's sleep versus a good one. Ask yourself, "How often do I get a good night's sleep?" If the answer is "not often", then you may need to consider changing your sleep habits or consulting a physician or sleep specialist. When Ellen's family members began this process, they realized that often they weren't getting what they would call a "good night's sleep." This led each of them to reevaluate how much sleep they needed and whether their sleep habits were healthy ones.

To pave the way for better sleep, experts recommend that you and your family members follow these sleep tips:

• Establish consistent sleep and wake schedules, even on weekends
• Create a regular, relaxing bedtime routine such as soaking in a hot bath or listening to soothing music – begin an hour or more before the time you expect to fall asleep
• Create a sleep-conducive environment that is dark, quiet, comfortable and cool
• Sleep on a comfortable mattress and pillows
• Use your bedroom only for sleep and sex (keep "sleep stealers" out of the bedroom – avoid watching TV, using a computer or reading in bed)
• Finish eating at least 2-3 hours before your regular bedtime
• Exercise regularly during the day or at least a few hours before bedtime
• Avoid caffeine and alcohol products close to bedtime and give up smoking

If you or a family member are experiencing symptoms such as sleepiness during the day or when you expect to be awake and alert, snoring, leg cramps or tingling, gasping or difficulty breathing during sleep, prolonged insomnia or another symptom that is preventing you from sleeping well, you should consult your primary care physician or sleep specialist to determine the underlying cause. You may also try keeping a sleep diary to track your sleep habits over a one- or two-week period and bring the results to your physician.

Most importantly, make sleep a priority. You must schedule sleep like any other daily activity, so put it on your "to-do list" and cross it off every night. But don’t make it the thing you do only after everything else is done – stop doing other things so you get the sleep you need.

Nap/Napping

More than 85% of mammalian species are polyphasic sleepers, meaning that they sleep for short periods throughout the day. Humans are part of the minority of monophasic sleepers, meaning that our days are divided into two distinct periods, one for sleep and one for wakefulness. It is not clear that this is the natural sleep pattern of humans. Young children and elderly persons nap, for example, and napping is a very important aspect of many cultures. View the Knol entry on nap/napping.