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What Modern Science Says About Teen Sleep

Teenage sleep is a unique time in the sleep lifecycle.

 Deposit Photos
Source: Deposit Photos

I’m a parent of two teenagers, a boy, 16 and now driving, and a girl, 14. They’re full of energy (just not so much first thing in morning) and they’re busy all day long. School, sports, music, friends— their jam-packed schedules and wide-ranging interests make for lots of long days and nights.

I’m The Sleep Doctor—and getting my teens to sleep as much as their growing bodies and minds need is a challenge. If you’re a parent of a teenager, I’m right there with you in the trenches.

We’ve been learning a lot of important information about teens’ sleep in recent weeks. I thought I’d bring that information together in one place, to take a closer look at some new details that are useful for every parent to know.

A quick primer on teens’ sleep

Before we dive into the latest science on sleep in teens, it’s important to remember that teen sleep works differently than adult sleep. It’s also different from the sleep patterns that teenagers had as younger children. Teenage sleep is a unique time in the sleep lifecycle.

When boys and girls hit puberty, the timing of their biological clocks begins a dramatic shift toward a preference for evenings, a shift that lasts throughout adolescence. Teens’ bio clocks are delayed by much as two hours or more. They are true Wolves, based on the archetypes from my book, The Power of When. Their bodies start producing the sleep hormone melatonin later in the evenings—usually around 11 p.m. And melatonin levels stay elevated later in the mornings, which is why they are so hard to wake up!

Biologically, teens are programmed to be up and alert later at night and less awake in the morning. That puts their natural, biological sleep at odds with social time—particularly on school days. A teen who has to get up at 6:30 a.m. for school is like an adult who needs to get up for work at 4:30 a.m.

This biological-social clash for teens puts them especially at risk for sleep deprivation. During the school week, teens may lose as much as 2-3 hours of sleep a night. Biological clocks typically begin a shift back to earlier timing around the age of 20. But the years of adolescence can bring prolonged sleep deprivation during a critical time of physical, social, emotional, and intellectual development. During teenage years, the brain continues to undergo significant development—and sleep is essential fuel for that developmental growth.

Teenagers a sleeping less than a generation ago

The hours teens sleep have been on the decline for decades. A first-of-its-kind, nationally representative study of teen sleep in the US found that teenagers’ sleep dropped significantly over a 21-year period from 1991-2012, with only about half of teenagers reporting sleeping 7 hours a night or more. The study also found that older teens reported sleeping less than younger teens, and that girls were more likely to report sleeping less than 7 hours a night than boys.

There is no single magic number of hours for all teenagers. As with sleep throughout our lives, individual sleep needs vary. It’s important to be alert to the signs of sleep deprivation rather than to focus too narrowly on a nightly number. That said, the National Sleep Foundation recommends that teenagers 14-17 need somewhere in the range of 8-10 hours of sleep a night. (Young adults ages 18-25 need 7-9 hours.)

With so many teens not even reaching 7 hours of nightly rest, it’s clear there’s widespread sleep deprivation among our teenagers today. And as some of the latest research demonstrates, that can have serious health consequences for teens.

Poor sleep in teens boosts heart and diabetes risks

A brand-new study on teens’ sleep shows that both the quality and the quantity of their nightly rest may have a significant impact on their heart and metabolic health. The study, published in the journal Pediatrics, looked at sleep hours and sleep quality in more than 800 teenagers and analyzed how sleep habits affected important markers of cardiovascular and metabolic health.

They found nearly a third of teens in the study slept less than 7 hours a night. And many of the teenagers had low sleep efficiency scores, a key indicator of poor sleep quality. Sleep efficiency is a measurement of time spent fully asleep compared to total time spent in bed. If your teen spent 10 hours in bed and 9 of those hours fully asleep, her sleep efficiency score would be 90 percent. A threshold sleep efficiency score is 85 percent. At that number or higher, sleep quality is considered fair—or better, as the number goes higher. In this new study, researchers the median sleep efficiency score was 84 percent—meaning half of all teens were no higher than 84, and not quite reaching the low end of a healthy sleep efficiency range.

Scientists then looked at how sleep quantity and sleep quality affected what is known as a metabolic risk score. That’s a score tabulated from measurements of:

  • Blood pressure
  • Cholesterol and triglyceride levels
  • Waist circumference
  • Insulin resistance

As its name suggests, a higher metabolic risk score indicates greater risk for metabolic and cardiovascular diseases, including heart disease and diabetes. The scientists found teens who slept longer and experienced higher sleep quality (sleep efficiency) had lower metabolic risk scores. On the other hand, teens who slept less and had lower sleep efficiency scored higher for metabolic risk. These teenagers were more likely to have larger waist circumferences, higher blood pressure, higher cholesterol, and higher fat mass.

Here’s a key detail: The scientists took into account other factors in teens’ lives that might increase their metabolic risk, apart from sleep. In their analysis, they factored for diet, television watching, and levels of physical activity. Independent of these factors, sleep hours and sleep quality affected teens’ metabolic risk.

We’ve seen substantial evidence showing the connection between poor sleep and obesity in teens. This new research goes further, giving us more detailed information about the risks to heart health and metabolic health that teens face if they don’t get enough high-quality sleep.

Teen girls more negatively affected by sleep loss than boys?

Sleep deprivation and poor-quality sleep are harmful for all teens. But new research suggests that adolescent girls may be more affected by lack of sleep than boys. Canadian scientists looked at possible gender differences in sleep’s impact on teenagers’ daily functioning. They found teenager girls were more likely than boys to:

  • Have a harder time staying awake in class, in the morning and afternoon
  • Have more trouble staying awake to do homework
  • Feel less motivated about school
  • Miss school as a result of feeling tired
  • Feel too tired to spend time with friends
  • Take naps on the weekends

The results of this study are preliminary, and I’ll be interested to see what the full results show. I’ve long been interested in the gender differences related to sleep. This remains an under-studied aspect of sleep science that could have tremendous impact on how we understand and treat sleep. We need more research exploring the differences in the way gender influences how children, teens and adults experience sleep.

We know from other research that teenage girls appear to be at greater risk for sleep deficiency than teenage boys. We need to pay attention to all our teens’ sleep—while also recognizing that boys and girls may face different needs and challenges when it comes to staying rested and able to function at their best.

Is sleep loss behind screen-time-related depression in teens?

I talked recently about a new study that points to sleep problems as the key link between teens’ screen time and an increased risk for depressive symptoms. Researchers at several universities collaborated on a study which found that poor sleep helped to explain the association between greater amounts of screen time and higher rates of depressive symptoms in teenagers. Essentially, the scientists found that teens who spent more time looking at screens got less sleep, and that lack of sleep led to greater risk for depressive symptoms.

The study looked at four different types of screen time: social media messaging, web surfing, watching TV and movies, and gaming. Different types of screen time had different relationships to depressive symptoms: social messaging was less strongly connected to depressive symptoms than gaming. And sleep only partially accounted for depressive symptoms in gaming, according to the study’s analysis. But greater amounts of all four types of screen time were linked to higher rates of depressive symptoms in teens, with sleep appearing to play a significant or determinative role.

As I said a few weeks ago, I think depressive symptoms are likely to be a result of several factors—sleep deprivation via screen time being one significant one. We’ve seen rapidly accumulating evidence of just how much screen time cuts into sleep for teens. There’s really no question that the light and stimulation from screens can interfere with teens’ (and adults’) ability to get enough high-quality, restful sleep. But we’re still working to unravel the very complex relationship between depression, technology, and sleep.

How to help teens sleep better

I’ll start with the screen time issue. Setting enforceable limits around technology and sleep with teenagers is important. Charging phones overnight outside the bedroom is a good way to do that. That keeps teens from middle-of-the-night texting that can truly sink their sleep. Even with that limit in place, they are likely to have their heads in screens, watching YouTube or Snapchatting, long after we’d ideally have them stash their phones for the night. I recommend having your teens wear Swanwick Glasses for evening, pre-bed screen time. These are terrific, comfortable, blue-light-blocking glasses. I use them when I need to look at screens at night (which I typically avoid). They’re a great way to make a reasonable compromise with your teens you both can live (and sleep) with.

Here is a recent guide to my strategies for parents (and grandparents) to use to help teens get more sleep. I will say I think it is important to engage teens in the process of making a sleep plan. Nothing stirs rebellion like a rule handed down without discussion or explanation. You can’t force a teenager to sleep. And it doesn’t make sense to tell a teen to “go to bed” at 9:30 p.m. when in most cases, their bodies just won’t let them fall asleep. Talk with your teens about the bigger picture—how the things they want to achieve in life are fueled by sleep. Even better, get a trusted adult who isn’t the parent—like a doctor or school counselor—to have that conversation.

And keep advocating for later school start times in your community! Even a modest shift to later morning start times is consistently shown to make a real difference for teens, both in their sleep and their classroom performance. Just this spring, new research was released showing that middle school students who started school at 8 a.m. rather than 7:20 a.m. got more sleep on school nights and felt less tired and more alert in class.

We’ve got to do all we can to help teenagers get the sleep they need today and help them establish strong sleep habits they can take with them throughout their lives.

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