My 16-year-old daughter is finally entering the homestretch of sophomore year, and she has been chronically sleep deprived since September. The reasons are multiple but when you add together 45 minutes of homework per class per night, plus a few extra-curricular activities, plus the downtime spent everyday watching a John Green video on YouTube or chatting with friends, and a normal amount of procrastination, it adds up to between 5 and 7 hours of sleep on an average school night. Throw in a term paper or heavy exam week and the average can easily drop to 3 or 4.

My daughter is hardly atypical. In fact, multiple studies have shown that the vast majority of teens today are living with borderline to severe sleep deprivation. According to sleep expert Dr. Mary Carskadon, a professor of psychiatry at Brown University and director of chronobiology and sleep research at Bradley Hospital in Providence, Rhode Island, teenagers actually need more sleep than younger kids, not less. Nine and a quarter hours of sleep is what they need to be optimally alert. According to a 2010 large-scale study published in The Journal of Adolescent Health, a scant 8% of US high school students get the recommended amount of sleep. Some 23% get six hours of sleep on an average school night and 10% get only 5 hours.

In studies conducted by Carskadon, half the teens she evaluated were so tired in the morning that they showed the same symptoms as patients with narcolepsy, a major sleep disorder in which the patient nods off and falls directly into REM sleep.

Related: What Happens When Teenagers Don’t Get Enough Sleep

When you consider the fact that many of these kids are getting behind the wheel in the early morning and driving themselves to school, the issue of sleep becomes literally a matter of life and death.

What’s going on here?

So what exactly is keeping teenagers up so late? Unfortunately biology, technology, and societal expectations together create a perfect storm for the chronic sleep deprivation. The major contributors to adolescent sleep debt come down to these:

Biology

Along with the more obvious hormonal changes that transform your child into a teen, are shifts in the production of melatonin, the sleep hormone. That is why your teenager actually seems more awake at midnight than at dinner and left alone would probably sleep until ten or eleven. It may drive you crazy but, says Dr. Max Van Gilder, a pediatrician in Manhattan, “that is the normal circadian rhythm for 15- to 22-year-olds.” Effectively, they are in a different time zone than the rest of us.

“It’s a major contributing factor to sleep deprivation which is unique to adolescence,” says Dr. Allison Baker, a child and adolescent psychiatrist. “The typical high school student’s natural time to fall asleep is 11pm or later. We really need to adjust the environment instead of asking teenagers to adjust their physiology.”

The problem is compounded when many adolescents, like my daughter, try to make up for lost sleep on the weekends, sometimes sleeping upwards of 12 hours on Friday and Saturday nights, which only further disrupts their sleep cycle. But who has the heart to wake them?

Technology

It’s not just that Facebook, Twitter, Instagram, Tumblr and YouTube are distractions that keep kids up later, it’s the actual light coming off all the electronic devices they’re exposed to, especially late at night. Electronics emit a glow called blue light that has a particular frequency. When it hits receptors in the eye, says Dr. Van Gilder, “those receptors send a signal to the brain which suppresses the production of melatonin and keeps kids from feeling tired. And adolescents are low on melatonin and start producing it later to begin with.” Dr. Van Gilder says he’s seen adolescent bedtimes pushed back an hour to an hour and a half over the years since teens started doing their homework on computers. “On average, my teenage patients are going to bed at around 12:30 now.”

Teens who are up late writing papers on computers or chatting with their friends are effectively creating an even more stimulating environment that will only keep them from being able to fall asleep when they want to.

Homework

Andrea Pincus and Andrew Multer consider it a good night when their 16 year-old son, Jake Multer, a sophomore at The Dalton School in Manhattan, gets to bed by 12:30. And there’s lots of fighting that goes on around the issue of homework and bedtime. “He tells us we micromanage him,” Pincus says. “He tells us we’re helicopter parents, but does he mention he stays up until 5 or 6am writing a paper?” Pincus and her husband are torn between making Jake go to bed and encouraging him to finish his work regardless of how long it takes. “There’s the anxiety of a kid like Jake who cares about the work. He works with a very nice group of kids on certain assignments and it’s great that they have each other but they also on some level add to the anxiety because you always have one kid who’s staying up later or pulling an all-nighter, putting in more work on a paper or studying for a test and it creates this extra anxiety and competition.”

Related: How to Help Teenagers Get More Sleep

His brother Sam, 13 and an eighth grader at Hunter College High School in Manhattan, is more or less resigned to being sleep deprived. He figures his current bedtime—anywhere between 11pm and 12:30am—which is so late “for the most part due to homework,” will only get later as he gets older. He says his parents want him to go to bed earlier but “they recognize that if I did that I wouldn’t get my work done and it’s important to me and it’s important to them.” Sam however also admits to having a procrastination and time management problem, some of which he believes comes from being so tired in the afternoon.

Overscheduling

We live in a culture that values activity over sleep and there is no part of that culture that reinforces that idea more than the college admissions process. Teens are constantly being told that they have to be “well-rounded” which, in an age when colleges are becoming ever more selective means that the more they do, the better their applications will look. And for some kids, being involved in a lot of extracurricular activities may truly be a matter of pursuing a diversity of passions. Either way, the result is an ever-narrowing window for sleep.

Katrina Karl, 16, is finishing up her junior year at Joel Barlow High School in Redding, Connecticut. She takes 5 academic classes, participates in the three theatrical productions her school puts on every year and volunteers at the middle school in her town. On top of that she works 13 hours a week at a local grocery store to help pay for summer theater camp and to save money for college. This past year, she says, was brutal. “I was lucky if I got 4 to 5 hours of sleep a night,” she says. On the nights she worked, Karl wouldn’t get home until 9 or 10 o’clock. Then she would start doing several hours of homework. Katrina’s bus picks her up at 6:15am and the first period bell rings at 7:20am.

Karl says she’s been living this way since about halfway through freshman year. “Everyone at my school is exhausted,” she says.

Earlier School Start Times

Very early high school start times, like Karl’s, are not uncommon, despite the fact that they run completely counter to the biological needs of adolescents. “Multiple studies have shown that high school students aren’t functional before 9 am,” says Dr. Van Gilder.

Cathi Hanauer, an author and the editor of the anthology The Bitch In The House, has been at the center of a 7-year battle to change the 7:20 start time of her North Hampton, Massachusetts, high school. “It started before my daughter got to high school. She’s now one year out of college. My son is a sophomore. The resistance has been huge,” she says, “despite the fact that 60% of the students are falling asleep in school.”

According to Hanauer, it all comes down to bussing and sports. The school buses used for the high school are used for the middle and elementary schools that have later start times. Pushing back the start time for the high school would mean either making the younger kids get up earlier or adding more buses which is not in the school budget. Then there are concerns that later start times will compromise the practices of sports teams.

Hanauer and some of the other parents got a consultant in who designed an affordable busing plan and in 2013 the school board finally passed a resolution to move the high school’s start time to between 8:00 and 8:30. They have since overturned the decision. “I’m done,” Hanauer says. “It’s been the most frustrating thing I’ve ever been involved with.”

With more than half of American teenagers living with chronic sleep deprivation, parents and teachers tend to overlook the profound effects it has on kids’ physical, mental and behavioral health. The sleep deficit is not in fact, a normal part of being a teenager. It’s part of an invisible epidemic that we need to start addressing.

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