NEW YORK - One quarter of adolescents go to bed after 11:30 on school nights, according to a new US study, which also finds those kids tend to perform worse in school and to have greater emotional distress than peers who go to bed earlier.
"If teens' sleep patterns are in conflict with their natural circadian rhythms, then that also has repercussions on cognitive function and emotional regulation as well as potential health consequences," said Dr. Judith Owens, director of Sleep Medicine at the Children's National Medical Center in Washington, DC, who was not involved in the study.
Based on surveys of adolescents across the US in the 1990s, and follow-up surveys as those kids grew into adulthood, researchers at the University of California, Berkeley, analyzed why teens were getting too little sleep and what the long-term effects might be.
It's estimated that between 45% and 85% of sixth-to-12th graders sleep less than the recommended nine hours on school nights, according to the report in the Journal of Adolescent Health. And nearly half of students - 44% - report difficulty staying awake during school, the authors write.
Lauren Asarnow and her colleagues used data from the National Longitudinal Study of Adolescent Health, a large ongoing study mandated by Congress. It began by interviewing adolescents in grades seven through 12 in the United States during the 1994-95 school year. The participants have been followed with four "waves" of further interviews so far.
The researchers used information from the first two Waves (1994-1995 and 1996) to study the bedtimes of 2,700 teens during the school year and during summer recess. They used information from the third Wave (2001-2002) to look for emotional distress.
At Wave I, 23% of the adolescents reported going to bed at 11:15 pm or later during the school year and 73% said they usually slept fewer than nine hours per night.
At Wave II, 22% of the adolescents reported going to bed at 1:30 am or later during the summer, and 23% said they went to bed after 11:15. Eighty percent said they usually slept less than 9 hours per night.
Adolescents who had late school year bedtimes in Wave I were more likely to have emotional distress in Wave III. Late school-year bedtimes in Wave II were not linked to emotional distress in Wave III, but late summertime bedtimes were.
Late school year bedtimes in both Waves I and II were also tied to lower grade point averages, though summer bedtimes had no association with lower grades.
While bedtime appears to be important to later distress, the researchers note, they were surprised to see that short total sleep times were not linked to distress or to lower school grades in Wave III.
The study also cannot prove that late bedtimes caused distress or problems at school, it only shows an association.
But, the authors write, "these findings underscore the… importance of intervention strategies that target bedtimes in an effort to reduce associated functional impairments, and improve academic and emotional outcomes."
The timing of bedtime is potentially just as important as the amount of time teens sleep because, like everyone else, they have a natural circadian rhythm.
"Adolescents really can't fall asleep much before eleven and are biologically programmed to wake up about eight," Owens told Reuters Health.
Owens, a professor of Pediatrics at George Washington University School of Medicine and Health Sciences, said adolescents typically need about nine hours of sleep in order to perform at optimal levels.
Owens said three areas of the brain develop throughout adolescence and these are also affected by sleep problems. The prefrontal cortex has control over the so-called executive functions, things like the ability to manage your time and predict the outcomes of your behavior; the amygdala is involved in emotional control and the striatum is involved in risk- and reward-type behaviors.
"People who are sleep deprived tend to perceive less in the way of negative consequences for taking risk and so they're more likely to take them," Owens said.
Owens is concerned that not much is known about the long-term effects of sleep issues, and worries they may be setting kids up for being overweight, or obese, or having type II diabetes and having cardiovascular consequences.
"Different physiological systems are developing in adolescence, the jury is still out about what kinds of long-term health effects this may be causing," Owens said.
Drowsy driving is another concern. Owens has found in her own studies that impairments associated with sleep loss are equivalent to, or worse than, impairments associated with moderate levels of intoxication.
Owens advises parents to set sleep rules so that teens get about nine hours of sleep every night, with bedtimes that are similar each night, including on the weekends. She said that naps aren't a substitute for a good night's sleep but a short afternoon nap can help recharge a teen's batteries.