PERSONAL HEALTH : Biological Clock Ticking for Teens?

If your teen-ager loves late-night TV but can’t seem to get up for school, the late-bedtime preference might result from changes of puberty, says Mary Carskadon, a professor of psychiatry and human behavior at Brown University.

As children mature, biological changes might push them to stay up later, says Carskadon, based on her preliminary research. Her team surveyed about 500 students, ages 11 and 12 in different stages of puberty asking them what bedtimes and wake-up times they would choose. The more physically mature the students, the later the bedtime they picked on weekdays and weekends. The more physically mature students also slept in later on weekends, found Carskadon, whose study appears in the current issue of the journal Sleep.

The study contradicts the prevailing belief that teen-agers’ preferences for late bedtimes are based only on desires to buck parental control or to imitate adults, although she acknowledges these factors do play a role.

The physical changes at puberty jump-start the bedtime preference, while social factors reinforce it even more as a child enters adolescence.

If her ongoing research proves the biological clock hypothesis, it would have important educational implications, Carskadon says, suggesting that classes should start later for older children.

Meanwhile, she advises: “Teen-agers need to be given permission to sleep later when they can.”