Normal Age-related Changes in Sleep and Wakefulness

Normal Age-related Changes in Sleep and Wakefulness

The newborn spends nearly 50% of total sleep time in REM sleep. Because infants may sleep up to 16 hours a day, the infant may spend 8 hours in REM sleep per day. Often to the conster-nation of the parents, the newborn has a polyphasic sleep–wake pattern, with short bouts of sleep and wakefulness throughout the 24-hour day, until several months of age when the child eventually sleeps through the night. Daytime napping, how-ever, often persists until the age of 4 to 6 years. Stages 3 and 4 sleep increase in the early years. Maximal “depth” of sleep may occur during the prepubertal period, when children are often difficult to awake at night. Adolescents often still need at least 10 hours of sleep. Yet, during adolescence, stages 3 and 4 sleep decline and daytime sleepiness increases, partially in association with the normal Tanner stages of pubertal develop-ment. Teenagers are also phase delayed which means that they may not get sleepy until the early morning hours (e.g., 2–3 AM) and do not naturally wake up until the later morning hours. Early school start times and social pressures may produce mild sleep deprivation during weekdays, with some catch-up on weekends.

As adults enter middle age and old age, sleep often be-comes more shallow, fragmented, and variable in duration and circadian timing compared with that of young adults. Stages 1 and 2 and wake time after sleep onset tend to increase; REM latency and stages 3 and 4 decline, probably at an earlier age in men than in women and possibly related to changes in brain structure and metabolism. Daytime sleepiness and napping usu-ally increase with age, often as a function of disturbed noctur-nal sleep. The elderly frequently choose an “early-to-bed, early-to-rise” pattern reflecting, in part, an apparent phase advance of the circadian clock. Even when they retire at the same time that they did when they were young, they still tend to wake up early, thus sleep-depriving themselves. This can lead to daytime sleepiness and napping. Although average total sleep time ac-tually increases slightly after age 65 years, greater numbers of persons fall into either long-sleeping (.8 hours) or short-sleep-ing (,7 hours) subgroups. Psychiatrists should always consider the role of chronobiological factors when evaluating patients with sleep disorders, especially the elderly, who have more sleep–wake complaints than younger persons. The sleep–wake patterns of the early bedtimes of the elderly, short REM latency, sleep fragmentation at night and napping during the day may reflect a phase-advance and reduced amplitude of the circadian oscillator.

Factors that could contribute to these age-related patterns include loss of influence from Zeitgebers (light, work schedules, social demands, physical exercise) and a weaker signal from the circadian oscillator to effector systems. Indoor living conditions or loss of hearing and sight may deprive individuals of cues that synchronize the circadian system. In a significant number of totally blind persons, for example, the circadian oscillator free-runs in the normal environment, with resulting regular periods of insomnia and hypersomnia every 3 weeks as the circadian oscil-lator delays by about 45 minutes each 24 hours while the subject tries to maintain a normal sleep period (11PM–7AM). In a study of normally sighted elderly individuals in San Diego, California, exposure to self-selected bright light averaged 45 minutes and 90 minutes per day for healthy women and men, respectively; 30 minutes per day for patients with Alzheimer’s disease living at home; and 2 minutes for chronically ill, institutionalized pa-tients (Jacobs et al., 1989). Perhaps not surprisingly, the elderly in one nursing home study never spent more than an hour in either consolidated sleep or wakefulness throughout a 24-hour period (Jacobs et al., 1989).