Circadian Rhythm Dyssomnias in Adolescence

Normally, our sleep-wake cycle approximates a 24-hour diurnal rhythm. We sleep during the dark part of the day and are awake during the light part. When studied in an artificial time-isolation environment, however, most humans demonstrate a free-running, endogenous rhythm of 25 hours. The 1-hour discrepancy each day requires that our biological clocks be reset by "zeitgebers," or stimuli that entrain our natural rhythm to a shorter period. The process is called phase delay and is accomplished by exposure to exogenous light, dark, and social interactions occurring at particular points in the 24-hour day (Wagner 1990). That is, both our sleeping and waking lives are regulated by a variety of time cues designed to enhance good sleep hygiene and the regular resetting of our biological clock. Within limits, schedule irregularities, such as staying up later or arising earlier by 1-2 hours, can be tolerated for short periods without upsetting the phase of the clock.

However, prolonged periods of sleep deprivation or persistent irregularity in sleep hygiene inevitably leads to circadian rhythm disorders. Jet lag syndromes resulting from rapid time zone changes and the dyssomnias of shift workers resulting from continuously changing schedules are typical examples.

Adolescence is also a time of disrupted schedules. Pressures at school and new social obligations cause adolescents to stay up late. Many adolescents have additional work demands, either athletic or occupational, that entail an extra commitment of hours (Carskadon 1990). Therefore, adolescence is a period when persons begin to stay up later and later. During the week, however, school schedules continue to require that adolescents rise early. Soon they become significantly sleep deprived. The problem is compounded when they "sleep in" on weekends, further disrupting their biological clock. Approximately 30% of adolescents report falling asleep in school. Many more complain of tiredness. Because adolescence is also the period for learning to drive motor vehicles and for experimenting with drugs and alcohol, the public health and personal safety issues involved in excessive sleepiness in adolescence are significant (Carskadon 1990).

The typical delayed sleep phase syndrome of adolescence is characterized by an inability to fall asleep at a usual bedtime and an inability to get up at a reasonable hour in the morning. The sleep log reveals bedtimes that do not result in rapid sleep onsets, sleep-onset times that are intractably later than the social norm (usually after 2:00 a.m.), little difficulty in maintaining sleep once asleep, and difficulty awakening at an appropriate hour in the morning. The total number of hours of sleep per night is reduced sharply, although on weekends, total sleep time is lengthened, with awakenings in the late morning or early afternoon. Once the biological clock is disrupted, the delayed sleep phase syndrome frequently persists during vacations, even when normal amounts of sleep are obtained and sleep debt is no longer significant. Similarly, when bedtime is regularly enforced, such as in a summer camp, the adolescent with delayed sleep phase syndrome typically cannot fall asleep until after midnight.