“Siri, what is Circadian?”

Put simply, circadian rhythms are the 24-hour clocks or “timing systems” built into our bodies over millions of years of evolution to keep us in sync with planet Earth’s natural cycles (such as the cycle between light and dark). They’re the quiet forces organizing how we feel and function throughout the day, such as when we feel awake or sleepy, hungry or satisfied, focused or foggy. These biological clocks are set by certain cues from our environment.

The most important of these environmental cues is light.

Circadian rhythms win the Nobel Prize in 2017

In 2017, the Nobel Prize in Medicine was awarded to three scientists who uncovered the inner workings of the body’s circadian rhythms. They revealed that our 24-hour biological clock is written into our DNA itself - controlled by “clock genes” that switch on and off in a precise daily cycle. Their discovery proved that nearly every cell in the body keeps time, and that our sleep, energy, hormones, metabolism, and mood all follow this built-in rhythm.

Why your circadian rhythm matters

Decades of research shows that circadian rhythm disruption is linked to almost every major chronic condition, but sleep quality, depth and timing is often the first area of our health to unravel.

When our internal clocks drift out of sync, we might struggle with insomnia, broken sleep, morning grogginess, mood and weight issues, skin problems, autoimmune symptoms, fertility challenges, focus issues and more (1–12).

In fact, Circadian Biology governs almost all processes within the body including:

Sleep quality and timing
Hunger and metabolism
Body temperature
Hormonal health
Immune function and inflammation
Heart and muscular function
Cognitive and emotional performance
Our response to stress
Cellular repair and aging

The good news is: when we realign our lives with nature’s time cues, especially light, our rhythms strengthen, sleep deepens and every biological system begins to function more effectively, meaning that both acute and chronic symptoms ease, and health improves.

How do circadian rhythms relate to sleep?

Circadian rhythms are one of the most critical factors influencing sleep. These rhythms govern our cycles of wakefulness and sleep by giving our bodies the relevant cues to wake up or wind down.

Natural daylight is bright and rich in blue light. Our bodies are designed to be stimulated and woken up by this kind of light, as each new dawn signalled to our ancestors that it was time to get moving. Conversely, our bodies are soothed and calmed by natural sunsets and firelight, which are dim and have very little blue light, but are rich in red and infrared light.

Modern life has disrupted our connection to our environment and these natural light signals. Now, instead of warm red firelight in the evenings, we are exposed to harmful artificial lighting, screens and devices, all of which are enriched with blue light and stripped of red and infrared tones.

One of the most important ways this impacts our sleep is by influencing the rhythm between melatonin, our master sleep and circadian hormone, and cortisol, our activity and “stress” hormone. Melatonin is the powerful sleep hormone that rises in the evening to help us transition into sleep. Cortisol begins to rise early in the morning to wake us up.

Crucially, melatonin and cortisol cannot both rise at the same time. So a rise in one, necessarily means a reduction in the other. This is critical because bright blue light suppresses the production of melatonin and increases cortisol. So, when we are exposed to artificial lighting and devices in the evening, our bodies are receiving the signal to wake up rather than wind down.

This is terrible news for our melatonin and our sleep. But the good news is, by adding healthy light to our environment and implementing some small changes to daily habits, we can easily realign our circadian rhythms for deeper sleep.

Our Published Research with Schools

In early 2024, Daniel White (our Co-Founder) delivered circadian-focused education and tools to over 500 secondary students across seven UK schools.

The results were clear: when students learned how to support their rhythm, especially their light exposure and sleep routines, they experienced meaningful improvements in sleep quality, morning alertness, focus, and emotional well-being.

Simple, low-cost circadian interventions helped these students sleep better, feel better, and function better during the day.

The answer to improving their mood, energy and performance was to bring them back into alignment with their natural rhythms.

Why is light so important?

Have you ever wondered how the body knows what time it is?

The body’s clock is set by light - most notably the natural light of the Sun. Natural light is a mixture of different wavelengths of light: ultraviolet (UV), visible and infrared. The composition of these wavelengths within sunlight changes throughout the day, from red and infrared-rich sunrises, to blue and UV-rich middays, then back again to red and infrared sunsets. This is why sunrises and sunsets are beautiful & relaxing to look at, but you cannot ever look directly at the Sun at other times. So when natural light enters your eye at any time of day, your body is able to register the “time” by analysing the different types of light being received.

Light is the most important “zeitgeber”, an environmental time cue responsible for healthy circadian rhythms. When light enters the human eye, it’s registered by receptors in the eye called melanopsin. These receptors then connect to a special “central clock” in the brain called the suprachiasmatic nucleus (SCN). The SCN then sets the clocks in every cell in your body. Light entering the eye is the most effective cue for setting our body clock, just like how we change our physical clocks and watches when we land in a new country in a different time zone.

The same is true for artificial light: it will influence your body clock when it enters your eye. This is why our circadian rhythms can be so sensitive to our indoor environments, especially in the evening before sleep.

Circadian disruption and young people

Circadian rhythms are especially fragile during childhood and adolescence, times when sleep is crucial for learning, emotional balance and healthy development.

Recent studies show that when young people’s rhythms are disrupted, sleep is one of the first areas to suffer. This can quickly spill over into problems with focus, mood, energy, anxiety and even risky behaviour seeking (14, 15).

Supporting healthy rhythms early in life means supporting healthier sleep, and therefore healthier minds and bodies for years to come.

Cultivating healthy rhythms

Strengthening your circadian rhythm is one of the most impactful steps you can take for your sleep and overall well-being.

Though often overlooked, your internal rhythm shapes how you feel, think, move, and most importantly, how deeply and restoratively you sleep each night.

At In Rhythm, we believe that addressing the root causes of circadian disruption is the next major shift in public health. When we fix the signals our biology depends on, especially light, sleep becomes deeper, energy steadier, mood calmer and long-term health becomes more resilient.

That’s why we’re committed to bringing you research-based products, education, and tools to help you live in rhythm with your biology, so you can flourish by sleeping well, feeling well and living well.