Teens who want to stay up late and sleep in or who feel drowsy during the day may have a harder time with behavior and reasoning than their peers who simply fail to get enough rest at night, a U.S. study suggests.
Even though the study found more than one in five adolescents get less than seven hours of sleep on school nights, the amount of sleep kids got didn't influence what's known as self-regulation, or the ability to manage things like memory, behavior, emotions and impulses, the study found.
Adolescents who were night owls, though, were significantly worse at self-regulation than their peers that tended to turn in and wake up early. And teens who were the most tired during the day struggled much more with self-regulation than youth who suffered the least from daytime drowsiness.
"In other words, it's not how long you sleep that has the biggest impact on self-regulation, but when you sleep in relation to the body's natural circadian rhythms and how impaired you are by sleepiness," said lead study author Dr. Judith Owens, director of sleep medicine at Boston Children's Hospital.
For many teens who need to be at school early, these results suggest they're being set up to struggle with academics and their health.
The American Academy of Pediatrics (AAP) recommends that teens get 8 to 10 hours of sleep. Due to changes in circadian rhythms - the body's internal "clock" - coinciding with puberty, most teens cannot fall asleep much before 11 p.m.
"Their morning wake time should be around 8 a.m. to allow them to get both an optimal amount and timing of sleep," Owens said by email. "Both insufficient and misaligned sleep has consequences for physical and mental health (increased obesity risk, depression) safety (car accidents, sports injuries) and academics (absenteeism, lower grades)."
That's why the AAP also advises schools not to start before 8:30 a.m.
"The results of this study suggest that the kind of circadian misalignment and daytime sleepiness associated with early school start times are associated with impaired self-regulation, which in turn may contribute to risk taking behaviors, poor control of emotions and impaired thinking skills," Owens added.
To assess how sleep relates to self-regulation, researchers analyzed data from an online survey of 2,017 students in 7th through 12th grades at 19 public schools in Fairfax County, Virginia.
Participants were 15 years old on average, and 54 percent were in high school.
On average, the students reported getting about 7.7 hours of sleep on school nights, researchers report in Pediatrics.
Daytime sleepiness was associated with lower self-regulation regardless of whether teens were night owls or early risers, the study found.
Having a night owl or "eveningness" circadian rhythm was also, independently, tied to poor self regulation.
The study doesn't prove that daytime sleepiness or a natural tendency to hit the sack at a certain time can directly cause poor self-regulation, the authors note. It's also impossible to rule out the possibility that poor self-regulation actually makes it harder for teens to sleep, the researchers also point out.
Even so, the findings suggest it's important for schools to offer delayed start times that try to accommodate teens' natural inclination to stay up late and sleep in, said Dr. Sujay Kansagra, author of My Child Won't Sleep and a pediatric neurology researcher at Duke University in Durham, North Carolina.
"Unfortunately, their brains have a natural tendency to shift bedtime to later at night," Kansagra, who wrote a commentary accompanying the study, said by email. "Couple this with early school start time and you run the risk of chronic sleep deprivation that leads to poor school performance and an increase in unsafe behaviors."
Absent later school start times, parents can still take steps to help teens develop better sleep habits, Kansagra said.
"Limit bright lights from TV, smartphones, and tablets for one hour prior to the desired bedtime," Kansagra said. "Artificial lights suppress melatonin and make it harder to fall asleep."