For decades, I assumed I needed to sleep just five to six hours a night. I nearly always awoke before the alarm in the morning. But I also nearly always fell asleep at concerts and plays, on the subway or while reading or riding in a car.
Last summer, when I was able to operate completely on my body's own time clock, I discovered that it preferred seven to seven and a half hours of sleep. I also discovered that when I slept at night for however long my body wanted to, my daytime dozes all but disappeared.
Surveys have shown that few of us past infancy and toddlerhood are receiving the amount of sleep our bodies and brains need to restore them to full function for the day ahead. And many of us - children, teenagers and adults of all ages - may pay a hefty price.
Crucial brain functions occur in sleep that cannot be reproduced when we are awake. But more than intellectual prowess can suffer; though definitive data are still lacking, a chronic shortage of sleep has been linked to serious physical ills, including heart disease, diabetes and obesity.
From infancy to adulthood, there are marked changes in how much sleep people need each day, the amount of time spent in each stage of sleep and how easily they fall asleep and stay asleep, a factor scientists call sleep efficiency.
Newborns sleep 16 to 18 hours a day, though rarely more than 4 hours at a time. By about three months, the time pediatrician Richard Ferber, Director of the Center for Pediatric Sleep Disorders at Children's Hospital Boston, suggests parents should try to enforce a more reasonable sleep schedule, babies' sleep patterns begin to respond to circadian rhythms of day and night. Year-old infants typically sleep 10 to 12 hours a night and nap 3 to 5 hours during the day.
The amount of sleep children need decreases gradually with age; preschoolers need 10 to 12 hours. By age 6, a tendency to be a lark or a night owl emerges, the latter often leading to havoc on school days, when children have to be awakened earlier than their body clocks dictate.
Sleep deprivation seems to start early. A 2004 survey by the National Sleep Foundation found that on average, children in every age group from infancy through fifth grade failed to get even the low end of the recommended range of sleep.
The real agony emerges in adolescence. As children go through puberty, two things happen to make getting enough sleep problematic: They need more sleep than prepubescent children, not less - 9 to 10 hours a night - and their body clocks shift to a later time to fall asleep and, consequently, a later awakening.
Amy Wolfson, a psychologist at the College of the Holy Cross in Worcester, Massachusetts, and Mary Carskadon, a sleep researcher at the Brown University School of Medicine in Providence, Rhode Island, have found that few adolescents sleep the amount they need. The average eighth-grader sleeps less than eight hours, and more than a quarter of high school and college students are chronically sleep deprived, they reported.
In a report last February in the journal Pediatrics, researchers from the Columbia University School of Nursing estimated that "15 million American children are affected by inadequate sleep." They based this on the findings of a national health survey in 2003 of 68,418 children ages 6 to 17. In the study, the percentage of children who failed to sleep enough rose with age and increased markedly among children 12 and older.
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