Navigating bedtime with a teenager is, in many homes, a nightly battle with a constant refrain: Get off your phone! Go to bed!

Research shows that today's teenagers are more sleep-deprived than ever before. Adolescents need between eight and 10 hours of sleep, according to the Centers for Disease Control and Prevention. But nearly 80% of American teenagers aren't getting that, and experts say it's affecting important areas like mental health and school attendance.

Bedtime routines aren't just for toddlers. Teenagers need them too, says Denise Pope, an expert on child development and a senior lecturer at Stanford University's Graduate School of Education.

Experts in adolescent sleep say a few small changes to how parents and teens approach sleep can make a dramatic difference.

The first step to setting up a better bedtime routine is dealing with technology.

-- Separate children from their devices at night. Phones, tablets, streaming services and video games aren't the only things keeping kids up at night, but experts agree they are a major factor in delaying sleep.

"Get the temptation out of the bedroom," Pope says. If the phone is within arm's reach, it's hard to ignore when notifications buzz. Many teens say they fall asleep while scrolling, or reach for their phone if they have trouble sleeping, and end up scrolling for hours.

-- Be prepared for excuses. "My phone is my alarm clock" is something a lot of parents hear. The solution: Buy an alarm clock.

-- Put screens away an hour before bedtime. Exposure to light prevents the release of melatonin, the hormone released by the brain that makes us feel drowsy.

Then, replace screens with a new wind-down routine.

-- Try to get to bed around the same time each night and start winding down at least 30 minutes before. During that time, silence notifications, take a warm shower, read a book. To get an idea of what your teen's bedtime should be, try an online " bedtime calculator," such as the one from the American Academy of Sleep Medicine.

-- Avoid caffeine and energy drinks in the afternoon and evening.

-- The best sleep environment is a cool, dark, quiet room. In noisy households, earplugs and a sleep mask can help. If a bedroom is too warm, it can affect getting to sleep and staying asleep, says adolescent sleep expert Kyla Wahlstrom.

Some of the telltale evidence of sleep deprivation: being irritable, grumpy, short-tempered, emotionally fragile, unmotivated, impulsive and more likely to see the world and oneself through a negative lens. A sleep-deprived teen also may fall asleep during the daytime, in the car or in class.

"We often blame adolescents for being lazy or unruly or having bad behavior, much of which could be attributed to the fact that they are chronically sleep-deprived," says Wendy Troxel, a clinical psychologist who has conducted numerous studies on adolescent sleep.

How do you tell the difference between a sleepy teen and a cranky-but-well-rested one?

-- One key sign is what sleep expert Joanna Fong-Isariyawongse calls "zombie mornings."

"If your teen hits snooze five times, takes forever to get out of bed, asks you for a big cup of coffee first thing in the morning, most likely they are running on empty," says Fong-Isariyawongse, a neurologist at the University of Pittsburgh.

-- Extreme mood swings are another sign. Sleep is critical for emotional processing, which is why sleep-deprived teens are more likely to be irritable, anxious or depressed.

-- A sleep-deprived teen may fall behind in school, because sleep is essential for learning and memory consolidation.

-- Teens who sleep less are more likely to make bad choices when it comes to drug or alcohol use, drowsy or reckless driving and risky sexual behavior.

-- Does your teen sleep until lunchtime on weekends? "Most likely they are not getting enough sleep during the week," says Fong-Isariyawongse. It's fine to sleep in a bit, but try to limit it to a couple hours. Otherwise, it throws off the body clock and makes it harder to wake up when the new school week begins.

Explain to your teens why sleep matters, and that it's not just nagging parents who say so. The data on mental health and sleep is vast.

-- Many studies show that depression, anxiety and the risk of suicidal thinking go up as sleep goes down.

-- Beyond mood, sleep deprivation affects physical and athletic ability. That's why several NFL and NBA teams have hired sleep coaches. Teens who are sleep-deprived sustain more physical injuries, because they take more risks, their judgment is impaired, and reflexes and reaction times are not as fast. Teens who get more sleep perform better in sports, and when they do get injuries, they have a quicker recovery time.

-- More teenage car accidents come from drowsy driving than driving under the influence of alcohol, studies show. Teens who say they get less than eight hours of sleep a night are more likely to text while driving, not wear a seat belt, drink and drive -- or get in a car with a driver who has been drinking.

As any parent knows, telling their teenager to go to sleep does not always work. You need to get their buy-in.

"Kids need to be educated about sleep, and their brain health and emotional health, and how it all ties together," says Wahlstrom. "Tell your kids, 'You'll do better in school, better in sports, you'll look better after a good night's sleep.' Because until they want to help themselves, they won't do it."

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