Teens stay up late at night and sleep late into the morning, a result of a natural shift in their circadian rhythms. That biological schedule puts them at odds with the adult world, as well as early start times for high school. But does the mismatch cut down on how much they actually sleep, and does that affect how stressed they feel? Data from Sleep Cycle reveals some intriguing insights: Teens who live in states that have early school start times get less shut-eye than those who live in states with later start times, and the short snoozers report greater levels of stress than those who sleep even just a little longer. Overall, by the way, American teens sleep less than those in Europe, but more than those in South Korea and Japan.

Sleep Cycle is a company that makes a smart-phone app by the same name. When a phone is placed on a bed, the app records a person’s movements during the night, using the phone’s accelerometer. The movements are a proxy for when the individual is in light sleep, deep sleep or REM sleep (the dream state). The app tracks the sleep cycles and adjusts an alarm to wake the person in the morning when he or she is in the lightest sleep, which some scientists think helps people feel more rested, compared with being woken up during deep sleep.

Of course, the app records when people go to bed and rise, and users can enter comments, such as how stressful their day was. When Sleep Cycle asked teens ages 14 to 19 if they would voluntarily share data about their sleep patterns, 63,234 said yes.

The results back up sleep researchers, biologists and social scientists who say high school should start later in the morning, allowing teens to get more sleep. Here are some data, sent to me by Amanda Parmer at Sleep Cycle:

  • Across all 50 states, the average bedtime for teenagers is 11:38 p.m.; the earliest average is 11:15 p.m. in Wyoming. Teens in Washington, D.C., have the latest bedtime at 12:08 a.m.
  • In U.S. states where districts start high school earlier than 8:00 a.m., teenagers are sleeping less. For instance, teenagers in New Jersey, Georgia, Tennessee, Arizona and Louisiana get between 6 hours, 52 minutes and 6 hours, 56 minutes of sleep a night, 12 to 16 minutes less than the national average of 7 hours, 8 minutes.
  • In states with later school start times (after 8:30 a.m.), teenagers are getting more sleep than the national average. For instance, teenagers in Minnesota, New Mexico and Iowa get between 7 hours, 11 minutes and 7 hours, 18 minutes.
  • West Virginia teens spend the least time in bed; at 6 hours, 47 minutes, they sleep 21 minutes less than the national average. They are also the most stressed out of teens in all states.
  • Louisiana teens sleep 12 minutes less than the national average and hold the number two spot for the most stressed.
  • Vermont teens hold the number 2 spot for most time in bed, at 7 hours, 23 minutes—15 minutes more than the national average. They have the third latest wake-up time, at 7:10 a.m., and they are the least stressed nationwide.
  • American teenagers, at an average of 7 hours, 8 minutes, get less sleep than their counterparts in Europe (an average of 7 hours, 38 minutes in the U.K., for example), where secondary schools start much later. But teenagers in South Korea and Japan get an hour and 20 minutes less sleep than American teens, with an average of 5 hours, 47 minutes.

I wonder how stressed those teens are.

It’s worth noting that other apps and gadgets such as Fitbit also track certain aspects of sleep. And if you like gadgets, check out our holiday gadget guide.

Image courtesy of LadyofHats on Wikimedia Commons