Sleep and Children's Physical Health
Biological Factors That Affect Sleep, Societal Factors, Effects of Insufficient Sleep
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.
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.
While societal and familial factors influence these trends, at least one biological process may also be involved. As children move through puberty they often begin to prefer activities occurring later in the day. This shift toward evening preference may be expressed biologically as a shift in the timing of the body's readiness for sleep and wake, also referred to as circadian timing of sleep phase. A shift toward evening preference accompanied by a biological tendency to delay sleep phase may make it easier for adolescents to stay up later. Sleeping later in the morning would offset this tendency and allow students to be more consistent in the sleep they obtain on school nights, but this conflicts with trends for the average school day, which usually starts and ends earlier as children move from primary to middle to secondary school.
The direct consequence of these social, behavioral, and biological trends is that older children and adolescents often do not obtain enough sleep on school nights to optimize daytime alertness and, they therefore carry a burgeoning sleep debt into the weekend. The typical solution is to wake up later on weekends. In adolescence, weekend sleep amounts average approximately nine hours per night, which might allow students to "pay back" the sleep debt accumulated across the week–if that debt was not so large. Given the amount of sleep determined to optimize alertness (approximately nine hours) and the fact that school-night sleep amounts average below 7.5 hours for adolescents, the average adolescent accumulates seven or more hours of sleep debt per school week. In addition to failing to pay back the sleep debt, going to bed later and sleeping substantially later in the morning on weekends can possibly exacerbate evening preference and delay the circadian timing of sleep phase, thus making sleep less likely to occur at a student's normal bedtime on Sunday.
Effects of Insufficient Sleep
The consequences of insufficient sleep and chronic daytime sleepiness in the lives of school-age children and adolescents are difficult to characterize at this time due to the limited number of scientific studies with this age range. Available data suggests that behavior, health, learning, and mood are likely to be impaired by excessive sleepiness among pediatric groups, but causal connections have not been proven and any relation between amount of sleep loss and amount of subsequent impairment (a dose-response relationship), has yet to be described.
Behavior. Children who show increased sleepiness or who have a disorder that compromises the quality and/or quantity of sleep appear to be at greater risk for daytime behavioral problems. Decreased behavioral difficulties have been associated with successful treatment of sleep disorders.
Health. Correlations have been shown between poor quantity and/or quality of sleep and the following: increased days sick from school, increased physical complaints, risk for accidents or injuries, and adoption of health-risk behaviors such as increased consumption of alcohol, nicotine, and caffeine. Of particular note for older adolescents, drivers age twenty-five or younger were shown to be responsible for a majority of fall-asleep automobile crashes in one region of the country.
Performance and learning. Tests of cognitive performance administered to students with sleep disorders or to healthy students experimentally sleep-restricted have generally failed to produce consistent results, but data suggest that students process information and react more slowly following inadequate sleep, and may be more prone to errors with socalled higher cognitive functions that involve abstract problem solving, creativity, or rule-governed behavior. Survey studies consistently demonstrate that students with later school-night bedtimes, more irregular bedtimes, less sleep on school nights, sleep problems, and increased complaints of daytime sleepiness have lower academic achievement than children with earlier, more regular bedtimes, more sleep, no sleep problems, and fewer complaints of sleepiness. Improved performance and academic achievement have been reported following treatment for sleep disorders.
Mood. Preliminary results from experimental and correlational studies provide consistent support for an association between inadequate quantity and quality of sleep among children and diminished happiness and/or increased depressed mood.
In conclusion, there is a need to learn more about the life-enhancing benefits of increasing sleep and the high cost of failing to protect it among children and adolescents. Determining the optimal quantity and timing of nocturnal sleep is likely to vary among individuals but existing trends suggest that many students should consider expanding school-night sleep opportunities, especially in the second decade. Students need to be more consistent with bedtimes and risetimes on school and non-school nights to avoid confusing the biological clock. Students also need to avoid caffeinated beverages and nicotine, as these substances can mask sleepiness and lead to difficulty falling asleep if taken later in the day. A brief afternoon nap is a much healthier alternative. Parents need to work with their children to create sleep-friendly family routines that make it easier for children (and adults) to protect sleep. Finally, more work is needed in communities to create sleep-friendly school schedules and work guidelines for minors, and to raise awareness about the risks associated with drowsy driving.
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CARSKADON, MARY A. 1999. "When Worlds Collide: Adolescent Need for Sleep Versus Societal Demands." Phi Delta Kappan 80:348–353.
CARSKADON, MARY A., ed. 2002. Adolescent Sleep Patterns: Biological, Sociological, and Psychological Influences. Cambridge, Eng.: Cambridge University Press.
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GRAHAM, MARY G., ed. 2000. Sleep Needs, Patterns, and Difficulties of Adolescents: Summary of a Workshop. Forum on Adolescence, Board on Children, Youth, and Families, National Re-search Council, Institute of Medicine. Washington, DC: National Academy Press.
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SADEH, AVI; RAVIV, AMIRAM; and GRUBER, REUT. 2000. "Sleep Patterns and Sleep Disruptions in School-Age Children." Developmental Psychology 36:291–301.
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