Sleep is not a passive extravagance that people allow themselves to indulge in. On the contrary, sleep is a highly regulated, active state of being that engages many aspects of one’s physiology in a complex manner. It is essential to life. While the purpose of sleep remains a complicated mystery, depriving one’s self of sleep has serious consequences for one’s health and waking functions. Nevertheless, sleep continues to be encroached upon by daily activities. Of particular concern are accounts of inadequate sleep and daytime sleepiness among school-age children and adolescents, and the potential impact these conditions may have on development and learning.

Biological Factors That Affect Sleep

Sleepiness refers to the tendency for a waking person to fall asleep. This tendency may be strong or weak, and is determined by both homeostatic and circadian influences. Homeostatic determinants include the amount of time since a child last slept and the amount of sleep debt (i.e., previously poor or inadequate sleep over one or more nights) that the child is carrying. Sleep debts can only be paid back with sleep, and increasing homeostatic pressure to sleep cannot, ultimately, be denied.

The circadian system influences daytime sleepiness through clock-dependent alerting. Clock-dependent altering refers to the function of people’s circadian system to promote wakefulness at certain times of their biological clock–namely, at the beginning and just before the end of their biological “day”–thereby helping them wake from sleep in the morning and stay awake in the latter part of the day when homeostatic pressure increases. Clock-dependent alerting is lowest in the early afternoon, which helps to explain why an adolescent or young adult may find it easier to fall asleep in the early afternoon than in the early evening.

While sleepiness is primarily determined by homeostatic and circadian influences, environmental and time-of-day factors influence the immediate effects of sleepiness on daytime functioning. Arousing elements of one’s external environment and/or internal state can temporarily mask sleep tendency. Someone out late at a nightclub after working all day has an increased tendency to fall asleep, but this can be masked temporarily by arousing environmental elements (e.g., music), the physical exercise of dancing, and possibly by consuming psychostimulants, such as caffeinated beverages, nicotine, or certain illicit drugs. But sleepiness that is masked is not diminished and could quickly be unmasked after leaving the nightclub.

Depending on the time of night and the amount of homeostatic pressure, the person could experience microsleeps during the drive home. Microsleeps are brief, involuntary sleep attacks of a second or more that can occur outside of awareness. They are more likely to occur when excessive sleepiness is unmasked at a time of low clock-dependent alerting, such as during one’s biological “night.”

Daytime sleep tendency also appears to be affected by age or, more specifically, pubertal development. Mary Carskadon and colleagues examined sleep and sleepiness in children studied annually from age ten to age sixteen or seventeen. Study participants were allowed a sleep opportunity (i.e., bedtime to risetime) of ten hours per night at each assessment, and daytime sleep tendency was measured the following day using the Multiple Sleep Latency Test (MSLT), a series of objective tests measuring the time it takes to fall asleep under optimal “nap” conditions.

Results across years showed virtually no change in the average amount of sleep (9.2 hours) recorded from bedtime to risetime. Thus, the need for sleep at night did not appear to decrease across puberty. However, when children reached midpuberty their midday sleep tendency on the MSLT appeared to increase relative to their prepubertal levels, even though participants were sleeping the same amount at night. These results demonstrate that pubertal development is associated with an increase in daytime sleepiness, suggesting that postpubertal adolescents may actually need more sleep to maximize daytime alertness.

Societal Factors

For the average middle and high school student, getting 9.2 hours of sleep or more on school nights may seem impossible and not worth the sacrifices required to maintain such a schedule. This is not surprising. The twenty-four-hour society of the United States makes ever-increasing demands on the time available for studying, working, and exercising, and offers ever-increasing opportunities for socializing and recreating. As a result, students are easily drawn into a pattern of pursuing daily activities at the expense of a good night’s sleep.

In addition, role models for marginalizing the importance of sleep are plentiful. Physicians, lawyers, stockbrokers, and even political operatives are portrayed on television as heroically pushing their physical limits and rising above their lack of sleep. Closer to home, parents often fail to convince children to “do as I say not as I do” with regard to obtaining a good night’s sleep, as they often allow their own commitments to encroach on sleep. Thus, from the beginning of primary school to the end of secondary school the average amount of time students spend sleeping on school nights gradually diminishes at the rate of one hour every three years, mostly through postponing bedtime. By the end of high school students average just over seven hours of sleep each school night, close to the adult work-night average of just under seven hours. These trends in school-night sleep time have been described in industrialized countries around the world.

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