Sleep and the Teenage Brain

The emerging consensus among top doctors? Early school start times hurt kids

BY ALICE PARK

ANYONE WITH A TEENAGER IN THE house is well aware of the daily struggle: It’s “I don’t want to go to bed yet; I’m not tired” in the evening followed by “I’m not ready to get up yet; I’m exhausted” in the morning. Something about the decade between 12 and 22 seems to put adolescents in a parallel world in which they’re wide-eyed and alert when the sun goes down and drowsy when it rises. Should we just call it a case of teens being teens?

Not really, say researchers. While contrarianism is baked into adolescence for many young people, their oddly calibrated body clocks have less to do with rebellion than with the needs of the brain and the body at that stage of development. And experts are now saying that rather than fighting it—forcing teens to sleep early and rise even earlier—it’s time to accept and even embrace it. Because the consequences of not tending to the unique sleep needs of the teenage brain could come with untold consequences.

The American Academy of Pediatrics (AAP) is getting behind this idea, coming out in favor of later school start times for middle and high schoolers in 2014, based on growing scientific evidence that when it comes to sleep, teens really are different from the rest of us. That evidence is based on some sound biology, which says that giving adolescents more time to slumber in the morning is better for their mental and physical health.

“The evidence is clearly mounting both in terms of understanding the repercussions that chronic sleep loss has on the health, safety and performance of adolescents,” says Judith Owens, director of the Center for Pediatric Sleep Disorders at Boston Children’s Hospital. “And there is also really compelling data supporting the fact that delaying school start times is a very important intervention that can mitigate some of the impact of sleep loss.”

Some of the consequences of that sleep loss showed up in a 2006 poll conducted by the National Sleep Foundation (NSF). Among 1,602 teens who answered questions about their sleep habits, 87% of high school students said they didn’t get 9 to 10 hours of sleep, which researchers say they need to function at their best and promote healthy mental and physical development; most average seven hours of sleep on weeknights. Technology is making the problem worse; teens in 2015 were 17% more likely than teens in 2009 to report sleeping less than seven hours a night, according to a 2017 study, which concluded that screen time was likely to blame. And the effects of sleep deprivation may show up in their grades; about 30% of students in the survey reported falling asleep in class at least once a week, and studies consistently connect less sleep with lower grades in school and on standardized tests.

That’s why the idea of letting teens start school later is starting to garner wider national support—but it hasn’t happened overnight. Before endorsing the idea, the AAP’s Adolescent Sleep Working Group took four years to review studies on how inadequate sleep among teens—especially likely on school nights—can contribute to health issues such as obesity, diabetes, mood changes and behavior problems.

The AAP even analyzed studies linking poor sleep to increased reliance on substances like caffeine, tobacco and alcohol and sleep deprivation’s effect on academic performance. The evidence, it concluded, supports giving teens more time in bed by delaying school start times until at least 8:30 a.m. Even a half-hour delay, some studies showed, can have dramatic effects on kids’ health and academic performance.

“We know that implementation of our recommendations will be challenging,” says Cora Breuner, a professor of pediatrics at the University of Washington School of Medicine and a member of the AAP working group. “But we stand behind these recommendations and strongly ask that they be considered for the health of our children.”

LETTING THE BIOLOGY DO THE SLEEPING

Not everyone is convinced, though, that later start times are the answer, partly because it’s so hard to draw a cause-and-effect line between poor sleep and some of the particularly unhealthy trends that emerge during adolescence, such as substance use, unprotected sex and other risky behaviors. Does poor sleep affect teen health, or is it a result of the whirlwind of physical and emotional changes that occur during adolescence?

“There’s a lot of research supporting the notion that adolescents are more and more sleep deprived,” says David Curtis, director of psychology training at the Texas Child Study Center. “However, the research isn’t great about clearly identifying why that is. So it’s a bit of a chicken-and-egg argument.”

What the data do show is that our need for sleep changes over time. As we get older, we need less sleep. Infants spend most of the day and night slumbering as their bodies and brains continue to develop, but between ages 6 and 13, that changes to a recommended 9 to 11 hours a night. Teens and adults need slightly less, 8 to 10, but polls show that up to one third of U.S. teens don’t get this many hours on a regular basis.

Part of the reason has to do with teens’ still-developing bodies, as data strongly suggest that puberty may biologically wire teens to stay up late and wake up late, which means that forcing them to bed earlier won’t do much good. Something in the hormonal changes occurring during that period of development shifts their body clocks—which regulate the balance between sleeping and being awake—to later, like daylight savings in reverse. “The sleep pressure signal builds up as you stay awake during the day and is relieved at night. But that process gets a little slower during adolescence,” says Mary Carskadon, a professor of psychiatry and human behavior at Brown University Medical School and the director of the Sleep and Chronobiology Research Lab at Bradley Hospital. “That makes it easier for teens to stay awake a little longer.”

It’s not that they need less sleep—they still need about eight to nine hours a night—but their sense of tiredness may come later at night, so they can’t fall asleep earlier even if they want to.

Adding to this biological pressure to be night owls are other forces that reinforce teens’ tendency to sleep at night and wake in the morning. Cellphones, computers and 24-7 social media connections mean that the conversation among teens never sleeps—and therefore they don’t either. (Add to that the growing research that all that screen time affects our circadian rhythms, throwing off the natural cues that would otherwise tell us when we’re sleepy or when it’s time to be alert.)

THE DOMINO EFFECT

In the NSF survey, more than half of the teens reported feeling unhappy, depressed or hopeless about the future and feeling worried or anxious most of the time. Those with the highest incidences of these symptoms also reported the most troubled sleep—not getting enough hours at night and feeling sleepy during the day or taking longer to fall asleep at night.

Understanding how this connection between mood and sleep works is especially critical since there’s also evidence that some people march down the path toward depressive symptoms when they don’t get enough sleep. Genes may be responsible for that. A study of college students found that some people inherit a specific form of a gene involved in regulating the brain’s mood chemical serotonin. That gene makes them more vulnerable to depressive symptoms when they don’t sleep well. If they do get enough sleep, they aren’t as prone to feeling the blues.

“That makes us think about sleep as an environmental exposure,” says Carskadon, who conducted the study. “That means your sleep environment could be an exposure that makes you more vulnerable to certain problems.” The students she studied showed higher risk for depression. It’s possible that poor sleep influences other genes too, making people more vulnerable to conditions like heart disease and cognitive problems.

In fact, other studies have linked poor sleep and the incidence of ADHD among children, although whether the attentional problems trigger sleep disturbance or whether sleep deficits can make ADHD worse is still being studied.

And it’s not just the brain but the body that feels the effects of insufficient sleep. A study of 270,000 8th-, 10th- and 12th-grade students at 130 public and private schools across the country revealed that over the 20-year study period, adolescents, not surprisingly, got less and less sleep. And by asking teens two questions about their sleep habits—how often they slept for at least seven hours a night and how often they slept less than they should—researchers got a better idea about why. They uncovered a possible period effect—something that affects all the students at every age—that contributed to their sleeping fewer hours.

The researchers found that the largest drop in the average number of adolescents reporting at least seven hours of sleep nightly occurred during two consecutive periods: 1991–1995 and 1996–2000. That time corresponds almost exactly with the increase in childhood obesity. Obesity has been tied to health disturbances such as sleep apnea, and the simultaneous decrease in the amount of sleep teens get and the increase in their average body-mass index suggests a strong connection. It’s unclear what is cause and what is effect, however, since sleeping less also disturbs the normal metabolic functions that help minimize fat deposition.

LET THEM SLEEP IN

One way to break that cycle, say a growing number of sleep experts, may be to let teens start school later in the day. That way, they won’t be fighting their bodies’ natural desire to stay up longer yet won’t be depriving themselves of the eight to nine hours of shut-eye they need. And so far, the studies are encouraging.

In fact, in a 2014 survey of 70 school districts and more than 1,000 schools that had adopted later start times for high school students, researchers found that teachers, parents and the students themselves were seeing substantial benefits. In one district that pushed back start times by one hour, half of the students reported getting eight or more hours of sleep, compared with 37% who had prior to the shift.

Owens and her colleagues also conducted a study among students at an independent school that delayed start times by 30 minutes. That was enough to move bedtimes ahead by an average of 18 minutes, something that surprised her and her team. They also found that the delay increased the percentage of students getting eight or more hours of sleep a night. “Anecdotally, a lot of the students said they felt better with the extra half hour of sleep they got in the morning, and that motivated them to go to bed earlier as well,” she says. “They said they could focus better and concentrate better and that it took them less time to get their homework finished so they could go to bed earlier.”

Of course, having high school students start later may have a domino effect on everything from their extracurricular activities, including after-school sports, to childcare for parents who rely on older children to take care of their younger siblings after school. That’s what makes it a challenge for many communities that aren’t ready to make such drastic changes.

But it is possible. Some schools, for example, have created after-school programs in which younger children can remain at school in a supervised setting until their older siblings or parents can take them home. And in communities where elementary school students are starting school earlier to accommodate later bus service for older students, volunteers have manned the stops to ensure that younger children are safe while they wait to be picked up during early morning hours.

“Communities and school districts really need to go all in and make a commitment [to it],” says Carskadon. “Where it doesn’t work is where schools just dabble and say they will try it for six months to see how it works.”

With the AAP firmly behind the idea of starting teens’ school day later, she and other experts hope that school policies will soon take their cue from teen biology. “The hope is that this statement will galvanize communities,” says Carskadon. “Now they have another tool in their tool kit and another set of evidence and advice to take to school committees and school boards to get communities moving on addressing adolescent sleep.”

Given the state of the data on how poor sleep affects adolescent development, adds Owens, “to do nothing is really to do harm. The status quo of starting schools at 7:15 or 7:20 is not in the best interest of the students.”

STAY UP LATE Teens have a body clock that keeps them up at all hours, often reading or on their computers.

SAVED BY A (LATER) BELL? There is a national movement to push back school start times to accommodate the sleep needs of young people’s developing bodies and brains.