Circadian Rhythm – What it is and why it matters for sleep
It’s no accident we’re designed to feel tired at night and more energised, alert and ready to take on the world in the morning.
It’s all down to our internal body clock, ticking away over a 24-hour period to help regulate sleep, alertness, hormone production and many other biological processes – and it regulates what’s called the circadian rhythm cycle.
Circadian rhythms are most associated with the sleep-wake cycle but they can also affect mental wellbeing and energy levels. And, we’re not the only living things on this planet to have them, animals and plants do too!
What is a circadian rhythm?
Understanding what is a circadian rhythm can help explain why you naturally feel sleepy at night, more alert during the day and why disrupted sleep patterns can leave you feeling tired and unfocused. Looking after your body’s internal clock can support good sleep quality, improve daytime energy and encourage a healthier sleep-wake cycle.
A circadian rhythm is your body’s natural 24-hour internal timing system.
It’s a fascinating process which is mainly influenced by light and dark but other factors such as what we eat, stress, physical activity and temperature can all affect it.
Located within a group of nerve cells in the brain, our internal body clock influences the rhythms to help regulate many biological functions, including the sleep-wake cycle, body temperature, hormone release and metabolism.
One of the most important jobs of the circadian rhythm is regulating when you feel awake and when you feel sleepy, responding to environmental signals, particularly light and darkness.
During daylight hours, exposure to natural light helps keep your body clock aligned with the outside world and promotes alertness. As daylight fades, it tells your brain to begin producing more melatonin, a hormone that helps prepare your body for sleep.
How circadian rhythm affects sleep
Increasing melatonin production signals that it is time to prepare for sleep, reducing body temperature and making you feel less on it in the alertness stakes.
In the morning the opposite happens – exposure to light reduces melatonin production, body temperature rises and you feel more alert.
Hormones which regulate energy levels and appetite – initiating time to eat and time to stop – also follow circadian rhythms.
Circadian rhythms are key to vital bodily functions helping to conserve energy, eat when we need to and digestion while giving us downtime to grow and heal.
When they’re out of sync it can lead to feelings of low energy and a lack of alertness during the day.
When your body clock stays aligned with your daily routine, it can support good sleep quality, making it easier to fall asleep, stay asleep and wake feeling refreshed. However, if your internal clock becomes disrupted, you may find it harder to fall asleep at your desired bedtime or feel sleepy during the day.
Signs your circadian rhythm is out of sync
A disrupted body clock can affect both your sleep and how you feel during the day. Some common signs include:
- Difficulty falling asleep at your usual bedtime
- Waking during the night or earlier than intended
- Waking up feeling unrefreshed
- Daytime fatigue
- Poor concentration
- Changes in mood or irritability
- Health problems such as obesity and high blood pressure
These symptoms can have many different causes, but a disrupted sleep-wake cycle may be one contributing factor.
Common causes of circadian rhythm disruption
Several everyday factors can affect your body’s internal clock. Some of the most common are:
Irregular sleep schedules – Going to bed and waking up at different times each day can make it harder for your body to maintain a consistent sleep-wake cycle.
Excessive screen time at bedtime – Phones, tablets and other electronic devices emit blue light, which can delay melatonin production if used close to bedtime.
Shift work – Working nights or rotating shifts often requires sleeping at times that conflict with the natural light-dark exposure affecting the body’s natural circadian rhythm, making it more difficult to achieve sufficient sleep.
Jet lag – Travelling across multiple time zones can temporarily disrupt your body clock while it adjusts to the
Bad habits and stress – Stress or alcohol and caffeine before bed can make it more difficult to relax before bed, affecting both sleep onset and overall sleep quality.
How to reset your circadian rhythm
If you’re wondering how to reset your circadian rhythm, small lifestyle changes may help support a more consistent sleep-wake cycle.
Keep regular sleep and wake times – Going to bed and waking up at similar times every day, including weekends where possible, helps reinforce your body’s internal clock. Try not to nap late in the afternoon.
Get plenty of natural daylight – Morning exposure to daylight provides an important signal that helps regulate the circadian rhythm and promote daytime alertness.
Reduce evening screen time – Limiting exposure to bright screens before bed may help minimise disruption to your natural melatonin production.
Create a relaxing bedtime routine – Developing a consistent better sleep routine, such as reading, listening to calming music or taking a warm bath, can help your body recognise when it is time to wind down. These healthy sleep habits may help support a regular sleep schedule over time.
Limit caffeine and alcohol before bedtime – Caffeine can make it harder to fall asleep. While alcohol can initially make some people feel sleepy, it may disrupt sleep later in the night.
If you’re looking for how to fix your sleep schedule, small adjustments are usually more effective than making large changes all at once. Gradually adjusting your bedtime by up to an hour or two to make the transition easier.
Circadian rhythm changes throughout life
The body’s internal clock naturally changes as we age.
Teenagers often experience a shift towards later bedtimes and wake-up times due to changes in circadian rhythms during puberty. This is known as ‘sleep phase delay’.
During adulthood, sleep patterns tend to stablise around night and day however some people are naturally morning larks or night owls! Work, family commitments, stress and lifestyle factors can affect sleep schedules leading to lack of sleep and day time fatigue.
As people get older, they may naturally become sleepier earlier in the evening and wake earlier in the morning. Older adults may also experience lighter or more fragmented sleep.
When to seek professional advice
Occasional sleep difficulties are common.
Regular problems sleeping is known as insomnia and healthy sleep habits can help you to get back into your natural sleep pattern.
Consider speaking with your pharmacist or GP if:
- A better sleep routine and other lifestyle changes have not helped
- Your sleep problem has gone on for months
- It’s affecting your day-to-day life and you find it difficult to concentrate due to fatigue.
You can also find more information about sleep and common sleep difficulties in the About Sleep section of the Sominex website.
Final thoughts
Your circadian rhythm helps regulate when you feel awake and when you feel sleepy, making it an important part of maintaining good health and wellbeing.
Although everyday factors such as shift work, travel and screen use can sometimes disrupt your body clock, maintaining healthy sleep habits such as keeping regular sleep times, getting enough daylight and following a relaxing bedtime routine can help support good sleep quality and a healthier sleep-wake cycle.
Sominex (Promethazine). Night time sleep aid. Contains promethazine hydrochloride. Always read the label.