Sleep Resources

What Makes People Sleep?

Although people may put off going to sleep in order to squeeze more activities into the day, eventually the need for sleep becomes overwhelming and people must get some sleep. This daily drive for sleep appears to be due, in part, to a compound known as adenosine. This natural chemical builds up in the blood as time awake increases. While people sleep, the body breaks down the adenosine. Thus, this molecule may be what the body uses to keep track of lost sleep and to trigger sleep when needed. An accumulation of adenosine and other factors might explain why, after several nights of less than optimal amounts of sleep, people build up a sleep debt that people must make up for by sleeping longer than normal. Because of such built-in molecular feedback, people cannot adapt to getting less sleep than the body needs. Eventually, a lack of sleep catches up with everyone.
The internal "biological clock" and environmental cues govern time of day when people feel sleepy and go to sleep. The most important cues are light and darkness. The biological clock is actually a tiny bundle of cells in the brain that responds to light signals received through the eyes. When darkness falls, the biological clock triggers the production of the hormone melatonin. This hormone makes people feel drowsy as it continues to increase during the night. Because of the biological clock, people naturally feel the sleepiest between midnight and 7 AM. People may also feel a second and milder daily "low" in the mid-afternoon between 1 PM and 4 PM. At that time, melatonin production rises again and might make people feel sleepy.
The biological clock makes people the most alert during daylight hours and the drowsiest in the early morning hours. Consequently, most people do very good work during the day. In a 24/7 society, however, some people must work at night. Nearly one-quarter of all workers work shifts that are not during the daytime and more than two-thirds of these workers have problems with sleepiness and/or difficulty sleeping. Because some work schedules are at odds with powerful sleep-regulating cues like sunlight, night shift workers are often drowsy at work and have difficulty falling or staying asleep during the daylight hours.
The fatigue experienced by night shift workers can be dangerous. Major industrial accidents--such as the Three Mile Island and Chernobyl nuclear power plant accidents and the Exxon Valdez oil spill--are results of mistakes made by overly tired workers on the night shift or an extended shift.
Night shift workers also are at greater risk of being in car crashes when driving home from work. One study found that one-fifth of night shift workers had a car crash or a near miss in the preced­ing year because of sleepiness on the drive home from work. Night shift workers are also more likely to have physical problems, such as heart disease, digestive disturbances and infertility, as well as emo­tional problems. All of these problems can relate to the workers' chronic sleepiness. See "Working the Night Shift" for some helpful tips.
Other factors can also influence the need for sleep, including the production of cellular hormones called cytokines by the immune system. These compounds occur in large quantities in response to certain infectious diseases or chronic inflammation and may prompt a person to sleep more than usual. The extra sleep may help the person conserve the resources needed to fight the infection. Recent studies confirm that people who rest enough are improving the ability of the body to respond to infection.
People are creatures of habit and one of the hardest habits to break is the natural wake and sleep cycle. A number of physiological factors conspire to help people sleep and wake up at the same times each day. Consequently, people may have a hard time adjusting when traveling across time zones. The light cues outside and the clocks in a new location may suggest it is 8 AM and to should be active, but the body believes it is more like 4 AM and to should sleep. The result is jet lag--sleepiness during the day, difficulty falling or staying asleep at night, poor concentration, confusion, nausea and general malaise and irritability.