Sleep is surprisingly energy-intensive for the human brain(1). Whilst we may associate sleep with rest and rejuvenation, it has many important neural functions, including memory and knowledge consolidation. You may remember learning about the four stages of sleep in a biology lesson, but what about the broader processes that control sleep duration, timing and quality?
Firstly, the circadian rhythm; the internal clock that governs the body over each 24-hour period. Light and darkness have the biggest influence on circadian rhythm, but it is also influenced by factors such as food intake, exercise, schedule, stress and hormones(2). Each of these factors is changeable, and as such, circadian rhythm too can shift. For example, if we travel abroad, after a period of adjustment, the internal clock will shift to a totally different time zone.
Another component of sleep is chronotype – each person’s natural sleep-wake rhythm. Unlike circadian rhythm, chronotype has a strong genetic component and is fixed (although, spoiler alert: the one exception to this is during adolescence) (3). You may be familiar with the concept of ‘early birds’ and ‘night owls’. An early bird is naturally inclined towards an earlier sleep-wake cycle and is likely to be alert, productive and focused at 8 am when they arrive at work. In comparison, at 8 am, a night owl is experiencing ‘social jetlag’, a misalignment between chronotype and schedule. In the example of travel provided above, an early bird will always prefer to go to bed and wake up early, irrespective of the time zone and internal clock shift.
Sleep is a biological need, but it is not an automatic process. This means each person’s sleep routine and quality is different and can be impacted by factors such as age, gender, culture, race and socioeconomic status. The research reflects that older people, women and racial minorities are likely to get worse quality sleep, and less quantity(4). Certain intersections of these groups are at increased risk for insufficient sleep; for example, pregnant or menopausal women and minority groups from more deprived areas. In the long-term, a lack of sleep has been associated with serious negative physical and mental health consequences, as well as poorer cognitive functioning(5).
Adolescent sleep is particularly interesting because we see a change in circadian rhythm and chronotype during these developmental years(6). Teenagers become ‘night owls’, and their internal clock shifts due to less ‘sleep pressure’ (i.e. the drive for sleep, onset by factors such as hours awake and melatonin release). This means teens don’t feel sleepy until late into the night. The same pattern has been observed in animal studies using adolescent monkeys, lab rats and marmosets(7). In human adolescents, lack of sleepiness at night is compounded by psychosocial factors, such as having more ownership over bedtime, social media and screen use, alongside greater academic pressures.
Teenagers need around 9.25 hours of sleep each night to function optimally(8). Typically, they don’t fall asleep until late at night but have to be up again early in the morning for school. In short, teens are not getting enough sleep. Insufficient sleep is negative for all aspects of school life – from attendance and behaviour to mental health and attainment. Research studies have found that delaying school start times positively impacts many of these domains(9). Whilst there has been some limited successful advocacy regarding school start times in the US(10), in the UK, there have been significant challenges with implementing similar changes, even on a shorter-term basis for research purposes (11).
Whilst school start times are unlikely to change any time soon, there are other ways to support young people with their sleep. Promoting good ‘sleep hygiene’ can improve sleep quality and duration, benefitting school life (and mental health). You may already be familiar with some sleep hygiene practices, including having a consistent sleep-wake schedule, reducing temperature and light before bed and preventing blue-light exposure near bedtime. There are a lot of good quality, free online resources for teens, parents and teachers with further information, which you may consider exploring. The Sleep Charity has an educational workbook for adolescents, and further resources for younger children and adults also (12).
Patience and a sympathetic response might help, too, next time your teenager snoozes the alarm.
This blog post is part of a series exploring the domains of the Evolve Development Tracker (EDT), written by Bella Rubens. Bella is a PhD Candidate at University College London. She is co-funded by the Economic and Social Research Council and Evolve.
References
1. DiNuzzo M, Nedergaard M. 2017. Brain Energetics During the Sleep-Wake Cycle. https://doi.org/10.1016/j.conb.2017.09.010
2.Colten HR, Altevogt BM, Institute of Medicine (U.S.), editors. 2006. Sleep disorders and sleep deprivation: an unmet public health problem. Washington, D.C: Institute of Medicine.
3. Kalmbach DA, Schneider LD, Cheung J, Bertrand SJ, Kariharan T, Pack AI, et al. 2016. Genetic Basis of Chronotype in Humans: Insights From Three Landmark GWAS. https://doi.org/10.1093/sleep/zsw048
4. Grandner MA. 2022. Sleep, Health, and Society. Sleep Med Clin. https://doi.org/10.1016/j.jsmc.2022.03.001
5. Watson NF, Badr MS, Belenky G, Bliwise DL, Buxton OM, Buysse D, et al. 2015. Joint Consensus Statement of the American Academy of Sleep Medicine and Sleep Research Society on the Recommended Amount of Sleep for a Healthy Adult: Methodology and Discussion. https://doi.org/10.5664/jcsm.4950
6. Crowley SJ, Wolfson AR, Tarokh L, Carskadon MA. 2018. An update on adolescent sleep: New evidence informing the perfect storm model. https://doi.org/10.1016/j.adolescence.2018.06.001
7. Melo PR, Gonçalves BSB, Menezes AAL, Azevedo CVM. 2016. Circadian activity rhythm in pre-pubertal and pubertal marmosets (Callithrix jacchus) living in family groups. https://doi.org/10.1016/j.physbeh.2015.12.023
8. Short MA, Weber N, Reynolds C, Coussens S, Carskadon MA. 2018. Estimating adolescent sleep need using dose-response modeling. https://doi.org/10.1093/sleep/zsy011
9. Kelley P, Lockley SW, Kelley J, Evans MDR. 2017. Is 8:30 a.m. Still Too Early to Start School? A 10:00 a.m. School Start Time Improves Health and Performance of Students Aged 13–16. https://doi.org/10.3389/fnhum.2017.00588
10. Ziporyn T, Boeke E. American Academy of Sleep Medicine. 2023. Sleep advocacy in action: Shaping the future of school start times. https://aasm.org/sleep-advocacy-in-action-shaping-the-future-of-school-start-times/
11. Illingworth G, Sharman R, Jowett A, Harvey CJ, Foster RG, Espie CA. 2019. Challenges in implementing and assessing outcomes of school start time change in the UK: experience of the Oxford Teensleep study. https://doi.org/10.1016/j.sleep.2018.10.021 12. The Sleep Charity. Useful Resources. https://thesleepcharity.org.uk/information-support/useful-resources/
