Circadian Rhythms and Sleep
Why do so many teenagers struggle with falling asleep early or waking up in the morning?
Circadian rhythms are internal rhythms helping to maintain a state of balance within the human body. Responding to external cues, for example, cycles of light and dark over a 24-hour period, many aspects of human biology have a circadian rhythm, for example, sleep core body temperature, appetite and immune function.
Sleep and wake cycles are the human body’s strongest circadian rhythm. During the teenage years, the circadian clock shifts to a slightly later rhythm, therefore delaying the timing of when sleep can be initiated and prolonging wakefulness into the later evening. This is known as having an ‘eveningness’ tendency and is why teenagers are more likely to be awake later in the day and sleep longer into the next morning. Additionally, our sleep drive (pressure to sleep) alters throughout the adolescent phase in that the sleep pressure build up is slower in the teenage years and the transition from wake to sleep takes longer to achieve, meaning a later time to sleep. This can make ‘choosing’ to go to sleep difficult for teenagers as the brain is still in a state where it is promoting wakefulness rather than sleep (Kelley et al., 2015).
Can staying up late on weekends seriously affect a teen’s body clock or mental health?
The human body likes to stay in balance and therefore routine is key. With our sleep if we disrupt the body’s natural rhythm of sleep and wake states (asleep at night, awake in the day), the body reacts negatively to this disruption through physical and mental factors. Having irregular sleep schedules from socially imposed sleep schedules results in a state of ‘social jetlag’ where there is a mismatch between the body’s internal clock (circadian rhythm)
and your differing sleep patterns on weekdays versus weekends. It’s effectively like experiencing jet lag without traveling.
Staying up late on the odd occasion won’t have too much of an effect providing a good sleep schedule is returned to the following night, but regular late schedules play havoc with the body’s sleep routine and negative outcomes, such as mental health difficulties, can arise. So, if you have a late night on a weekend try to get back onto a regular sleep routine as soon as possible after the late night.
Is there an ideal sleep schedule for teenagers to support their natural circadian rhythm?
Everyone’s sleep is different but overall, a teenager will typically require 8-10 hours of sleep, however in some cases 7 or 11 may be appropriate for some individuals who find they need slightly less or more than the average recommendations (Rausch-Phung & Singh, 2023). Knowing your sleep need shows good self-awareness and can be assessed simply, based on how you feel when waking up: consider are you refreshed, alert and fully productive during
the day? If not, then more sleep may be required. Scheduling your sleep around school or college times can be tricky as often these are at odds with the later sleep times teenagers experience. Having a regular routine with sleep will help during this phase and using naps where appropriate can be beneficial.
Teenagers are biologically programmed to be alert later within the normal 24-hour period and this is shift in circadian rhythm is common to both genders. As teenagers you will be familiar with the ‘before school argument’, where early school times are the predominant logistical problem when feeling sleepy.
However, it is not just a case of ‘lazy’ teenager. Biology does at least provide some explanation as to why young people turn into night owls during their
adolescent years (Winnebeck, 2024).
Puberty and Hormonal Changes.
Throughout childhood sleep quantity remains relatively stable. Only once puberty begins do we see a separation of sleep disturbances related to gender, with female sleep being inextricably linked with the monthly menstrual cycle and its associated hormones. Some of these hormones play a part in regulating sleep e.g. Oestrogen and Progesterone and whilst the research needs more detail behind it, there is certainly an association between these two hormones and sleep. For example, Oestrogen is associated with better sleep quality and reduced sleep latency (the time it takes to fall asleep). It also helps to regulate body temperature, which is important for initiating and maintaining sleep. Progesterone has a natural calming effect on the brain, aiding deeper sleep and supports respiratory (breathing) stability during sleep, which may help reduce the risk of sleep-disordered breathing, such as sleep apnoea, which is a leading sleep disorder.
Puberty is a major developmental change for teenagers with lots of biological milestones met. With the shift in their circadian rhythm causing later sleep schedules, teenagers can often feel tired and groggy, particularly in the mornings. Having a regular sleep schedule and using naps where you can if you like them (don’t force it if not) can help with the daytime fatigue. The best time to nap is for around 20-30 minutes between 2 and 4 pm.
Periods, Hormones & Mental Health
How hormonal changes during the menstrual cycle affect sleep, mood, and anxiety levels
Can poor sleep make period symptoms like cramps, fatigue, and moodiness worse?
The menstrual cycle can affect sleep in many ways, whether it be through period pain, heavy bleeding or the symptoms of pre-menstrual syndrome. As a result, teenage girls may feel more tired at certain stages of the month as they navigate their sleep through the monthly changes of the menstrual cycle.
Sleep is individualised and not all teenage girls sleep may be affected over the course of their menstrual cycle, but it is important to note that for some the menstrual cycle can be quite debilitating and sleep may be significantly impacted. Premenstrual syndrome can occur in the late luteal phase of the menstrual cycle, right before a woman has her period. This has a whole host of symptoms, many of which can be linked to poor sleep. In particular, a decrease in mood, increased fatigue and possibly, some anxiety or depression which, in extreme cases, can be quite debilitating.
The link between mental health and sleep is reciprocal and can be quite complicated given the myriad of mental health disorders. Teenage girls may experience premenstrual symptoms related to mental health, such as anxiety or depression. When we have had a phase of restricted sleep, we may also be more sensitive to pain. This can be particularly problematic for teenage girls who live with period pain. Being tired may make the pain worse. Certainly, being tired will exacerbate symptoms of pre-menstrual syndrome whether it be mental health symptoms or more physical.
Is there a link between period-related hormone fluctuations and disrupted sleep or nightmares?
Nightmares can occur randomly or in response to a life event. More likely in adults, and more prevalent in women than men, they typically occur in the REM phase of sleep (Sleep Stage four). A nightmare is defined as an extended, extremely unhappy dream that usually involves efforts to avoid threats to survival, security, or physical integrity (Cappadona et al., 2021). Symptoms of nightmares vary, but usually involve some sort of physical symptom, such as
sweating and shortness of breath. They are highly emotional with fear, anger, shame and sadness also being reported. They can occur nightly in extreme cases (nightmare disorder) or as little as less than once a month.
How can teenagers tell the difference between hormonal moodiness and a deeper anxiety issue?
Distinguishing between normal hormonal ups and downs and a deeper issue can be tricky particularly in the teenage years. If your symptoms are affecting quality of life, then do seek advice from a GP. It may also be useful to keep a sleep dairy note down feelings alongside this, and for women, recording menstrual cycle symptoms too.
What role does sleep play in managing anxiety and emotional ups and downs during puberty?
Sleep plays a huge role in managing some of the emotional ups and downs of puberty. Given sleeps reciprocal relationship with mental health it is important to focus on getting good sleep during the teenage years. As above it may also be useful to keep a sleep dairy and note down feelings alongside this, and for women, recording menstrual cycle symptoms too.
Are there practical sleep habits or breathing techniques you recommend to reduce anxiety related symptoms?
Practical tips for reducing anxiety might be getting some fresh air, preferably in the first third of the day, doing some form of physical activity e.g. Yoga, a run or a walk. Mindfulness or breathing exercises may also be beneficial. If you are experiencing symptoms of puberty that are affecting your daily life, then seek advice from a health care professional.
What science-backed strategies can help teens improve their sleep despite hormonal challenges?
Good tips for improving sleep are ensuring a regular routine around bedtime and get up time. This is often hard for teens with early starts for school that are not in line with their biology telling them to go to bed later and sleep for longer. Regular physical activity along with some fresh air can also aid sleep. In addition, relaxation techniques such as reading, listening to music or mindfulness may also be beneficial. Having a well-balanced diet and eating at
appropriate mealtimes as well as turning off screens when its time to go to sleep will also help with good sleep health.
How important is light exposure (like sunlight or screens) in regulating a teen’s circadian rhythm?
Natural light is very important for regulating sleep. The body relies on cues from bright light or dim light to know if it is time to signal sleep or waking. If you can get some natural daylight every day, preferably in the first third of the day, then this is known to aid sleep. Screens are slightly different in that they don’t provide bright light to aid waking like natural light does. It used to be thought that screens hampered sleep because of the blue light they emit interfering with sleep signalling processes. However, this is now thought to not be as big an issue as first thought. The problem with screens is having the self-discipline to turn them off when it is time for sleep. Going beyond your sleep time is hazardous to your sleep health, particularly if you do it on a regular basis.
What are common myths you hear about teen sleep and hormones that you’d love to correct?
People will comment that teenagers are lazy because they don’t get up in the mornings and go to sleep late. Really what is happening is a biological shift in a teens brain causing a change in sleep patterns during the teenage years. The phase delay in teenage sleep is a natural occurrence which in most cases reverts to normal sleep times once a teen reaches adulthood.
So, teenagers aren’t’ lazy they are predisposed to sleep later thanks to a biological shift during their teenage years. What doesn’t help with the lazy teenager label is teens staying on screens beyond their sleep time and not getting sufficient sleep and therefore sleeping even later into
the morning than is necessary.
If you could give just one piece of advice to teens struggling with sleep, mood swings, or period-related anxiety, what would it be?
Trust sleep is a natural process and that good sleep will come. Get regular fresh air and movement which will help with sleep. Where you are struggling with sleep, be it for example, due to period pain or anxieties about exams, seek support from your GP and network of family, friends and organisations, some of which are listed, here:
• Anxiety UK National charity helping people with Anxiety – Anxiety UK
• Calm. An app for guided meditation and sleep stories www.calm.com
• Ending endometriosis starts by saying it | Endometriosis UK (endometriosis-UK.org)
• Mental Health First Aid England Mental Health First Aid starts with you · MHFA England
• Mind.org.uk
• PCOS UK help for sufferers of Polycystic Ovary Syndrome (pcos-UK.org.UK)
• Teen Sleep Hub Useful Resources – The Sleep Charity
• Sleep Diary – The Sleep Charity
References:
• Kelley, P., Lockley, S. W., Foster, R. G. & Kelley, J. (2015). Synchronizing education to adolescent biology: ‘Let
teens sleep, start school later’. Learning, Media and Technology, 40(2), 210–226.
• Rausch-Phung, E. & Singh, A. (2023). Is 7 Hours of Sleep Enough? Sleep Foundation. www.
sleepfoundation.org/sleep-faqs/is-7-hours-of-sleep-enough
• Cappadona R, De Giorgi A, Di Simone E, Zucchi B, Rodriguez-Borrego MA, Lopez-Soto PJ, Fabbian F,
Manfredini R. (2021). Sleep, dreams, nightmares, and sex-related differences: a narrative review. European
Review for Medical and Pharmacological Sciences, 25(7), 3054-3065.
Dr Sarah Gilchrist has spent over 20 years working in the high performance sport industry, latterly as a Technical Lead for the UK Sports Institute and Senior Physiologist with British Rowing. Her doctorate specialised in sleep and athletic performance and she now provides consultancy on a range of performance areas, particularly relating to sleep. She is a previous Chair of The Chartered Association of Sport and Exercises Sciences Accreditation committee and is a High Performance Sport Accredited practitioner. Her book, ‘The Essential Guide to Women’s Sleep: Supporting Healthy Sleep Practices for Wellbeing and Performance’ is out in October 2025.
We’ve been given a special 15% off discount for Dr Sarah Gilchrist’s book: ‘The Essential Guide to Women’s Sleep: Supporting Healthy Sleep Practices for Wellbeing and Performance’. Use code: TSPSG15 at the checkout here: https://uk.jkp.com/products/the-essential-guide-to-womens-sleep. This code is valid until 20/10/25 11.59pm. A donation from the sales will be given to The Sleep Charity.
Book overview: Maintaining good sleep is a crucial yet often underrated pillar of a person’s wellbeing and general health. Despite this, there is limited guidance on how and why the various phases women experience in their lifetime may impact their quality of sleep, and what can be done to improve it.
This practical and accessible guide for health professionals introduces the concept of female sleep health across the lifetime, including key stages such as menstruation, fertility, working life, birth, perimenopause, and menopause. It also addresses sleep disorders, pain, and the impact poor sleep may have on mental health.
Readers will benefit from practical and detailed strategies on improving sleep, guidance on sleep aides and technology, and signposts to when clinical intervention is needed. Published: Oct 21 2025
