Evening activities teens choose to do may have more long-term impact than they imagine on both physical and mental health.

The issue is sleep, according to research from Brigham Young University that was just published in the Journal of Research on Adolescence. The study found that activities can lead to earlier bedtimes and greater ease falling asleep or they can hinder and shorten sleep.

“In addition to its role in physical health, sleep plays a vital role in mental health, memory and cognitive development during adolescence,” wrote Blake L. Jones, an associate professor of developmental psychology, and Jocelyn S. Wikle, assistant professor in the School of Family Life.

Sleep is also one of the first things to be sacrificed when people are busy or stressed, according to Jones.

“Sleep is one of the three pillars of health that affects everything in our body, along with diet and exercise. And a lot of times, people put so much focus on diet and exercise that they forget about sleep,” Jones told the Deseret News.

Both sleep duration and quality matter, the researchers said, but the study looked only at duration. The researchers also note differences between bedtime — when one goes to bed — and sleep onset time, which is when one actually sleeps. The period in between can last mere minutes or long hours.

The activities that invite going to sleep earlier and getting on average 90 minutes more sleep include doing homework, talking to parents and playing sports in the early evening —  those that use some brain power or physical exertion a while before going to bed.

They’re not causing early sleep, Jones said. “But there’s an association with going to bed earlier.”

Hanging out with friends, viewing social media, visiting public places, snacking and watching TV all cut into sleep time when they occur late at night. They prolong the evening.

Kids are spending about the same amount of time on passive leisure activities, like watching TV during the six hours before going to sleep, Jones noted. But the kids who go to bed later are pushing that passive leisure time back and doing it after they do those other things, like hanging out with friends.

The researchers note that “youth who use the end of messaging activities or the end of a television show to cue bedtimes have later bedtimes relative to youth who use feelings of tiredness to cue bedtime.”

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Teens and sleep

The survey used nationally representative data from the American Time Use Survey on 10,341 adolescents ages 15-18. The focus was on sleep onset time.

The researchers heralded sleep onset time and duration as one of the potentially modifiable risk factors that have big effects over time for teens during a developmental period they described in the study as “an important time in physical, emotional, cognitive and social development.”

Sleep matters for everyone — but getting sleep right is crucial for adolescents. Their brains are still developing and their hormones are changing, too. Jones said sleep regulates many hormones, which in turn regulate a lot of what the body does. He gives the example of cortisol, the primary stress hormone. Inadequate sleep can ramp up cortisol, which can elevate blood sugar levels and increase the risk of diabetes. “Then we’re more likely to be obese and have hypertension and all kinds of other things because we’re not getting enough sleep,” he said.

Additionally, the parasympathetic nervous system — the so-called “rest and digest” nervous system — is “really engaged” during sleep, he said. That’s when it does a lot of its repair work, mending damaged tissue and healing injuries. It’s also when a great deal of digestion and metabolism regulation take place. And sleep is vital for brain development, he notes.

The study says lack of sleep may influence teens’ executive functioning, how well they manage emotions, impulse control and plan for the future. “All of which support teens navigating increased autonomy and responsibility through adolescence and into early adulthood,” the study noted.

So teens who don’t get enough sleep are more likely to have less impulse control, poor attention span and make bad decisions. Self-control and ethics may lag, too. Besides that, teens who get short sleep as adolescents tend to become short sleepers as adults, which brings problems for them, too.

The study cites past research that found out of 22 well-documented obesity risks, how long one sleeps was the biggest predictor of obesity. Sleep duration is linked to depression, emotional stress, anxiety, learning problems and in some cases psychiatric and developmental disorders. Inadequate sleep also raises the risk for substance use and suicidality.

Just as adults may arise on schedule to get to work, teens arise to go to school or other activities. The time one gets up is less flexible than when folks go to sleep.

Wikle said that activities that shift bedtimes to later lead to less sleep and more harm for teens.

That’s why decisions around bedtime and prioritizing sleep can change trajectories.

Playing catch up and circadian rhythms

Every person of every age has an individual, natural circadian rhythm. There are general, age-specific trends, though. Younger children need lots and lots of sleep and their bodies release hormones that help make them sleepy about 8 or 9 p.m., when it starts getting dark.

After puberty, the body switches it up. The National Sleep Foundation says teen bodies also need more sleep than they will require when they are adults. The recommendation is eight to 10 hours, but their bodies typically don’t tell them to get sleepy until about 10 or 11 p.m. However, most can’t sleep in without missing school or work. “So their body is fighting. It tells them to stay awake at the very time they actually need to be getting more sleep,” said Jones.

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When they become adults, their bodies will want to go to bed earlier again. And their sleep needs will decline. The foundation says adults who get at least seven hours of sleep a night are in good shape.

“So we fight that a lot with teens because we tell them to go to bed and their body is telling them to stay up late. It can be kind of challenging for parents,” Jones added.

There’s a summer/weekend pattern for many teens when it comes to sleep: Stay up late every night, but sleep in on weekends and in the summer when school’s out to try to “catch up” on sleep.

Can you?

Not as much as people think.

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“If you were a couple of hours short of sleep for the week, you can make up a little bit of that within a few days,” Jones said. “But after a few days, that window of making it up is gone.” So if you’re missing an hour or two of sleep all week long, even if you sleep in on the weekend, most studies have shown it’s really not going to make a difference.

“It’s not a good strategy,” he said.

“If I had to guess, why (some) are going to bed early and spending more time with parents, it’s probably kids whose parents monitor things a little bit more closely and maybe have a bit more structure and rules in their homes,” Jones added.

Wikle said adapting eventing routines can help teens get adequate sleep. She and Jones are among experts who say not to wait for the new school year to try to get a handle on late-night sleep patterns. Instead, start moving them up 15 minutes every few days well in advance.

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