British Summer Time ended on Sunday, marking the start of the evenings drawing in a little earlier and shorter days.
This time of the year always makes me more conscious of our circadian rhythms. The contrast between dark and light, night and day becomes more dominant. It’s common to hear people talking about leaving home in the mornings in the dark and returning back in the dark. Light seems to become more precious.
In this post, I wanted to explore what circadian rhythms are and the science behind them. As natural cycles, they govern so much of how we feel.
At this time of year, I’ve noticed for myself and others how simple habits and rituals can help make the darker months easier. These can have a positive impact on our circadian rhythms which are so important for our mental health and physiological health.
What are circadian rhythms?
You will often hear our circadian rhythm referred to as our body’s internal clock. Circadian comes from the Latin words circa and diem which mean “approximately a day,”. These rhythms are roughly 24-hour cycles that regulate many processes in the body. There are over 100 circadian rhythms which influence functions including whether we are sleepy or alert, hormone levels, digestion and body temperature.
The master rhythm, often called the “circadian pacemaker,” is controlled by a part of the brain called the suprachiasmatic nucleus (SCN), which sits in the hypothalamus. The SCN takes its cues from light: when light enters the eyes, it signals to the brain that it’s daytime, suppressing melatonin (the sleep hormone) and helping us feel awake. As light fades, melatonin levels rise, preparing us for rest.
How modern life overrides natural rhythms
For most of human history, our circadian rhythms were in step with the rising and setting of the sun and the changing seasons. Our hunter gatherer ancestors spent much of their days outdoors.
The increased use of technology in recent decades has meant our boundaries of day and night are now blurred. Artificial lighting, screens and constant connectivity mean we stay up later, rise earlier and spend huge amounts of time indoors in spaces lit artificially rather than by natural light. These changes have meant that our circadian rhythms can often become imbalanced.
At this time of year, these issues come into focus as we spend more time indoors and turn the lights on earlier in the day. Reduced exposure to natural light as well as patterns such as shift work and digital culture mean the boundaries our ancestors had between rest and activity have broken down. Over time, this can confuse our internal clock leading to fatigue, low mood, difficulty sleeping and reduced concentration.
In my counselling practice, I often meet clients who stay up late at night watching YouTube, scrolling social media or playing video games. Invariably they are having issues with anxiety, low mood, tiredness and maintaining focus. Research has shown that exposure to screens at night can impact our sleep, mood and attention1,2. I have found that when I support clients to make changes to their evening screen time, improvements can quickly follow.
The science of circadian health
At its simplest, the circadian rhythm is our internal timing system – a quiet metronome running in the background of every cell. It regulates the ebb and flow of our energy, sleep, hunger, and mood throughout the 24-hour day. The SCN, often described as the master clock, takes its cues from light and helps synchronise smaller clocks throughout the body in the liver, gut, heart, and muscles, so that digestion, hormone release, and alertness happen in tune.
When these rhythms are aligned, we tend to feel alert during the day, sleepy at night, and emotionally balanced. But when they fall out of sync, even slightly, we may notice changes in mood, concentration, and resilience.
Hormones play a key part in this rhythm. Cortisol, often thought of as the stress hormone, naturally peaks in the morning, helping us wake and focus. Melatonin, the sleep hormone, rises in the evening as darkness falls, guiding the body into rest. Core body temperature, heart rate, and metabolism also follow daily cycles, finely tuned patterns of light and darkness.
When our internal clock falls out of sync
When this delicate timing system is disrupted – by late-night screen use, irregular sleep, or reduced daylight in winter – the effects can be wide-ranging. Research shows that circadian misalignment can alter the release of serotonin and dopamine, two neurotransmitters central to mood regulation3. It can also affect the quality of sleep, concentration, and emotional stability. This helps explain why many people notice a dip in energy or mood as the days shorten. In some, the effect is strong enough to cause seasonal affective disorder (SAD), a form of depression linked to reduced daylight and changes in melatonin balance4.
Understanding this doesn’t mean we can control every fluctuation, but it can provide understanding. What we sometimes interpret as tiredness, irritability, or lack of motivation may simply be the body responding to a seasonal rhythm – a biological invitation to slow down. It reminds us we are still part of nature, governed by the same cycles of light and dark that shape the rest of the living world.
Scientists are now exploring how aligning daily routines with our natural clock – a field known as chronobiology – might improve physical and mental health. Some studies suggest that the timing of meals, exercise, or medication can influence how well the body functions. This growing understanding of circadian health is a reminder that balance isn’t just psychological; it’s physiological too.
Supporting our natural rhythms
The good news is that there are simple, practical ways to support your circadian rhythms:
– Seek morning light – Spend time outside in the first few hours of daylight. Natural light helps reset your internal clock and boosts alertness.
– Dim lights in the evening – Reduce bright or blue light exposure before bed to allow melatonin to rise naturally.
– Keep a steady sleep routine – Going to bed and waking up at similar times helps stabilise your rhythm.
– Limit screen time before sleep – Even small changes, like dimming your phone or using night mode, can make a difference.
– Move your body – Gentle exercise, especially outdoors, supports energy regulation and sleep quality.
– Create wind-down rituals – Reading, journaling, or quiet reflection can signal to your body that it’s time to rest.
As the nights draw in, it can be comforting to remember seasonal slowing is natural and our bodies seek balance. Sometimes, honouring our rhythms means allowing ourselves to rest a little more, to move more gently, and to find small ways to reconnect with light in the darker months.
1 Green, A., Cohen-Zion, M., Haim, A., & Dagan, Y. (2017). Evening light exposure to computer screens disrupts human sleep, biological rhythms, and attention abilities. Chronobiology International, 34(7), 855–865. https://doi.org/10.1080/07420528.2017.1324878
2 Harvard Health Publishing. (2024). Blue Light Has a Dark Side. Harvard Health Publishing; Harvard Medical School. https://www.health.harvard.edu/staying-healthy/blue-light-has-a-dark-side [Accessed 28/10/2025]
3 Walker, W. H., Walton, J. C., DeVries, A. C., & Nelson, R. J. (2020). Circadian rhythm disruption and mental health. Translational Psychiatry, 10(1). https://doi.org/10.1038/s41398-020-0694-0
4 Rosenthal, N. E. (1984). Seasonal Affective Disorder. Archives of General Psychiatry, 41(1), 72. https://doi.org/10.1001/archpsyc.1984.01790120076010
