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Sleep: Understanding the Basics (cont.)

Sleep at Different Stages of Life

Infancy

Infants have an overall greater total sleep time than any other age group. Their sleep time can be divided into multiple periods. In newborns, the total sleep duration in a day can be 14-16 hours. Over the first several months of life, sleep time decreases; by age 5-6 months, sleep consolidates into an overnight period with at least 1 nap during the day.

REM sleep in infants represents a larger percentage of the total sleep at the expense of stages III and IV. Until age 3-4 months, newborns transition from wakefulness into REM sleep. Thereafter, wakefulness begins to transition directly into NREM sleep.

Adulthood

In adults, sleep of 8-8.4 hours is considered fully restorative. In some cultures, total sleep is often divided into an overnight sleep period of 6-7 hours and a nap of 1-2 hours.

Some people may need as little as 5 hours or as much as 10 hours of sleep every day. The period of time a person sleeps depends also on the fact whether he or she has been deprived of sleep in previous days. Sleeping too little creates a "sleep debt." This debt needs to be adjusted by sleeping for longer periods over the next few days. People who sleep less have an impairment of judgment and reaction time.

Old age

People tend to sleep more lightly and for shorter periods as they get older. In elderly persons, the time spent in stages III and IV decreases by 10-15%, and the time in stage II increases by 5% compared to young adults, representing an overall decrease in total sleep duration.

Time taken to fall asleep and the number and duration of overnight arousal periods increase. Thus, to have a fully restorative sleep, the total time in bed must increase. If the elderly person does not increase the total time in bed, complaints of insomnia and chronic sleepiness may occur.

Sleep fragmentation results from the increase in overnight arousals and may be exacerbated by the increasing number of medical conditions related to old age, including sleep apnea (interrupted breathing during sleep), musculoskeletal disorders, and cardiopulmonary disease.