Why teen sleep is different: your shifting body clock

If you lie awake at 11pm and then struggle to get up at 6am, you are not lazy. Your body clock genuinely moves during the teenage years, and once you understand how it works you can work with it instead of fighting it.

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Two systems that decide when you sleep

• Your body clock (circadian rhythm) is an internal timer that makes you feel alert at some times of day and sleepy at others. Light, especially morning daylight, helps keep it set.
• Your sleep drive is the pressure to sleep that builds up the longer you are awake. IBE-UNESCO's Science of Learning Portal notes that in teenagers this 'sleep drive' builds up more slowly than in children.
• Put together, this means a teenager often does not feel properly sleepy until later in the evening, even when they are tired.
• Neither system responds to willpower alone. They respond to regular timings, light and habits, which is good news because those are things you can change.

What changes at puberty

• UCLA Health explains that before puberty, sleepiness usually begins around 8pm or 9pm.
• When puberty begins, the rhythm shifts a couple of hours later, so the body tends to signal sleep around 10pm or 11pm. UCLA calls this 'sleep phase delay'.
• IBE-UNESCO reports that in adolescents the release of melatonin, the hormone linked to night-time, is delayed until 10pm or later, so many teens may not be ready to sleep until at least 11pm.
• This is a normal stage of development, not a sleep disorder.

How much sleep you actually need

• The American Academy of Sleep Medicine (AASM) recommends that teenagers aged 13 to 18 sleep 8 to 10 hours per 24 hours (including naps) on a regular basis, and the CDC gives the same 8 to 10 hours for this age group. UCLA Health puts the average teen need at about nine hours.
• Once you are 18 or over, the NHS gives 7 to 9 hours as the adult range. If you are 18 or 19 and still feel tired on 7 hours, aim nearer the top of that range.
• Many teenagers fall short. IBE-UNESCO cites a CDC survey in which 78 percent of US high school students did not get 8 or more hours of sleep on an average school night.
• More is not always better either: the AASM notes that regularly sleeping more than the recommended hours may also be associated with health problems. Aim for regular and enough, not as much as possible.
• Worked example: if you must wake at 6:15am for school and you need about 9 hours, you want to be asleep by about 9:15pm, so lights out should be a little earlier than that.

The early-start problem

• A later body clock plus an early school, college or work start squeezes sleep from both ends.
• IBE-UNESCO notes that several US medical and nursing organisations have endorsed secondary schools starting no earlier than 8:30am, and that delaying start times by 30 minutes was associated with about 45 extra minutes of sleep on school nights.
• You probably cannot change your school's timetable, but knowing the cause helps you protect the part you control: your evenings and your weekends.
• Big weekend lie-ins can shift your clock even later, making Monday mornings harder. UCLA Health advises not sleeping in more than two hours past your usual weekday wake time.

Working with your clock

• Open the curtains or get outside soon after you wake. UCLA Health recommends opening curtains in the morning and keeping lights dim in the evening.
• Keep similar sleep and wake times every day, even at weekends, as Boston Children's Hospital advises for teens.
• Avoid caffeine after about 4pm (UCLA Health). The Caffeine lesson in this module explains why.
• If you nap, keep it short: UCLA Health suggests teens keep naps to under an hour so they do not push bedtime even later.
• Keep evenings calm and avoid very stimulating activities late at night (UCLA Health).