The science driving the CDC’s new report on school start times

Last week the Centers for Disease Control and Prevention (CDC) issued a report outlining the chronic loss of sleep experienced by 2 out of 3 (!) American teenagers due in large part to early school start times. Many people wonder why teens can’t simply adjust their bedtime in order to clock the 9 hours of sleep they need. The answer: establishing an earlier sleep schedule for a teenager involves fighting their biological circadian rhythm.

The brain structure at the core of your circadian rhythm

Circadian rhythm is the internal body clock that regulates biological processes in a 24 hour cycle. The circadian biological clock is controlled by a part of the brain called the Suprachiasmatic Nucleus (SCN), a group of cells in the hypothalamus that respond to light and dark signals.

The SCN ensures certain body functions work in harmony with our sleep-wake cycle. Prior to awakening in the morning, the SCN sends signals to raise body temperature and produce hormones like cortisol, helping the body wake up. In the evening prior to bed, the SCN sends signals to lower body temperature produce hormones such as melatonin, helping the body to go to sleep.

The circadian system generates a “clock dependent alerting process during waking hours,” which basically means that your body produces hormones like cortisol that cause you to feel alert during certain times of the day, as set by your internal biological clock. Trying to sleep during these times leads to worse sleep quality, because you are essentially fighting your biological clock.

Teenager sleeping in class
A later start time should help teenagers have more productive mornings at school

The difficulty of fighting teens’ sleep cycles

Even if a teenager is successful in getting into bed by 9:30 pm (approximately the time a high schooler would need to be asleep to get a full recommended night’s sleep for a 7:30 am school start time), if her biological circadian rhythm has her bedtime pegged at 1 am, then the result will be poor sleep quality. Tacking on a couple of hours of sleep for the night likely won’t lead to much benefit.

While the biological underpinnings of this hormonally late-shifted circadian rhythm are not fully understood, studies indicate that, relative to adults, teenagers are more sensitive to light in the evening/night hours and less sensitive to light in the morning hours. This makes it even harder for them to push their circadian rhythm back to better match their daily schedules.

The effects of sleep deprivation on grades, car accident risk, and mood are indisputable.  Hopefully the CDC report will encourage school districts across the country to adopt schedules that are more compatible with teen’s natural sleep schedules, but here are some other tips for improving sleep in teenagers:

  • Stay away from caffeine and nicotine which are both stimulants after noon. Also avoid alcohol which can disrupt sleep.
  • Avoid heavy studying or computer games right before bed, they can be stimulating and make falling asleep more difficult.
  • Avoid bright light in the evening (this includes the light from electronic devices like computers, cell phones, and tablets), but open blinds or turn on lights as soon as the morning alarm goes off to aid awakening.
  • If necessary, sleep in on the weekend, but no more than 2 or 3 hours later than usual awakening time or it will disrupt the body clock.

 

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