The Teen Sleep Epidemic: Biology and School Start Times

“It’s too expensive to start the school day later.”

“Extracurriculars will suffer if we start school later.”

“We shouldn’t coddle teens by pushing school start times.”

These are just some of the arguments against later school start times for teens. Although the public has become increasingly aware of the sleep deprivation epidemic among teens in the US, the cost and logistic difficulties associated with addressing the problem have stymied attempts at reform. But what has been framed as a policy issue for education, is, at its deepest root, an issue of biology.

Teens need an average of 8 to 10 hours of sleep each night.[1] But only 20% of adolescents in the US report getting adequate sleep on school nights.[2] Insufficient sleep in teens has been linked to increased risk of unintentional injury and death, poor school performance, obesity, negative mood and increased irritability, and increased substance abuse.[1] Research also indicates that even short term sleep deprivation can alter neural plasticity,[3] the process by which the brain reorganizes in response to experience. Neural plasticity is important for learning and memory development during adolescence.[4]

So why don’t teenagers put down their X-box controllers, homework, or phones at 9 pm and get the rest they need? Perhaps it is just not that simple. Not only is the ability to make future-oriented decisions,[5] like going to bed earlier to avoid being sleepy the next day, still developing throughout adolescence, but biology is running the show when it comes to sleep.

The ability to fall asleep is influenced by two major biological processes: (1) the body’s circadian rhythm or internal clock, which drives the 24-hour sleep-wake cycle; and (2) homeostatic sleep drive, which is the body’s internal timer that generates a pressure for sleep when too much time has elapsed since the person last slept.

Both of these processes interact with the brain and are sensitive to hormonal changes that occur during puberty. Melatonin secretion, one of the major chemical agents that tells your brain when to get sleepy and go to bed, is low during periods of wakefulness, peaks at maximum sleepiness, stays relatively high during sleep, and declines again near one’s wake-time. Melatonin also acts on the flip side, promoting sleep onset by increasing homeostatic sleep drive.

So how does this relate to teenagers? Research shows that melatonin levels rise about two hours later in the day for adolescents than most children and adults, indicating a “sleep phase delay”. This physically makes it more difficult for teens to get to bed earlier.[6]

Because sleep phase delay pushes adolescent bed times later, and school start times force early wake times, most adolescents suffer from insufficient sleep during the week. On weekends, adolescents attempt to make up for this deficit by waking later.[2]  The chart below shows that between 9th and 12th grade, there is a 1.2 to 1.5 hour difference between the amount of time teens are sleeping during the week and the amount of sleep they get on the weekends.