Getting up early is bad for teens’ health

The American Pediatric Society recommends that classes do not start before 8 AM for 12-15 year olds and before 8:30 AM  for 15-18 year olds. We often hear that teens need to get up later for physiological reasons. Is this a myth or reality? “Indeed, when they get up too early, young people risk sleep deprivation, which leads to fatigue and poor concentration, says Virginie Bayon, Associate physician at the CHUV’s Center for Investigation and Research in Sleep (CIRS).” At issue is a shift in the biological clock, a transformation directly related to hormonal changes. 

“This phenomenon occurs in all cultures. It is also observed in other mammals. Moreover, when the gonads (reproductive organs) are removed from an animal, the period of sleep is not delayed at puberty.” Generally, this gap appears around 13 years old, a little earlier for some girls, and reaches a peak between ages 15 and 18 before abating and then disappearing. Plans to adapt school schedules are underway in Lausanne and elsewhere in Switzerland. “Studies show that with the change of schedule, young people do not go to bed later, and they sleep more overall.” 

Physiological changes

What exactly is going on? Melatonin, which helps us fall asleep, is secreted by the body later than before. Usually, this hormone is released in response to darkness. Its concentration in the blood increases at the end of the day and reaches its peak in the middle of the night. Since melatonin has vasodilating properties, it contributes to the decrease of body temperature, which makes you want to sleep. If this phenomenon occurs later, as is the case in adolescence, sleep will be delayed, and the entire circadian cycle will be disrupted.   

A second explanation is that the teenager must be awake for a longer period before (s)he feels an irresistible urge to crawl into bed. The sleep pressure, that is to say, the time it takes to wake up before you can fall asleep, builds up more slowly in adolescence. This slowdown disrupts the homeostatic process, which allows for a balance between waking and sleeping. Nevertheless, the recommended sleep duration is between eight and ten hours per night for 14-17 year olds. Finally, the sleep structure is also remodeled. Early in the night, sleep becomes less deep. “From age 13, the proportion of slow-wave sleep drops by 30%.”

The impact of screens and stimulants

These major physiological changes are compounded by external factors that delay falling asleep, such as energy drinks and evening activities (homework, sports, etc.). Also, the use of the smartphone or computer in the evening has a particularly harmful effect on sleep: on the one hand, the light source near the face slows down the rise of melatonin (especially in teenagers); on the other hand, these devices require digital interactions, which keeps us cognitively awake. These screens should be turned off at least one hour before bedtime.