Put simply, circadian rhythms are the internal 24 hour timing systems built into the human body over millions of years of evolution. They exist to keep us aligned with the natural rhythms of planet Earth, most notably the daily cycle of light and dark.
These rhythms quietly organize how we feel and function across the day. They influence when we feel awake or sleepy, hungry or satisfied, focused or foggy. They shape our energy, mood, hormones, metabolism, immune function, and ability to repair and regenerate.
Circadian rhythms are set by cues from our environment, known as zeitgebers or “time givers.”
The most powerful of these cues is light.
Circadian Rhythms Won the Nobel Prize
In 2017, the Nobel Prize in Physiology or Medicine was awarded to Jeffrey C. Hall, Michael Rosbash, and Michael W. Young for uncovering the molecular mechanisms that drive circadian rhythms.
Their work revealed that the body’s 24 hour clock is written directly into our DNA. Specialized “clock genes” switch on and off in a precise daily cycle. This discovery showed that nearly every cell in the body keeps time, and that sleep, energy, hormone release, metabolism, mood, and cellular repair all follow this internal rhythm.
Circadian biology is not a side system. It is foundational.
Why Your Circadian Rhythm Matters
Decades of research now show that circadian disruption is linked to almost every major chronic condition. Often, sleep quality, depth, and timing are the first areas to unravel.
When our internal clocks drift out of sync, people may experience:
Difficulty falling or staying asleep
Morning grogginess and low energy
Mood instability and anxiety
Weight and metabolic issues
Skin and inflammatory conditions
Hormonal and fertility challenges
Brain fog and reduced focus
Autoimmune and immune dysregulation
Circadian biology governs nearly every process in the body, including:
Sleep timing and quality
Hunger and metabolism
Core body temperature
Hormonal balance
Immune function and inflammation
Cardiovascular and muscular performance
Cognitive and emotional regulation
Stress responsiveness
Cellular repair and aging
The encouraging news is that when we realign our lives with natural time cues, especially light, these rhythms strengthen. Sleep deepens. Energy steadies. Biological systems regain coherence. Both acute and chronic symptoms often ease as the body returns to rhythm.
How Circadian Rhythms Shape Sleep
Circadian rhythms are one of the most important drivers of healthy sleep. They govern the daily cycle of wakefulness and rest by telling the body when to be alert and when to wind down.
Natural daylight is bright and rich in blue wavelengths. Human biology evolved to be stimulated by this light, as sunrise historically signaled the start of activity. In contrast, natural evenings were shaped by sunsets and firelight, which are dim and low in blue light, but rich in red and infrared wavelengths.
Modern life has disrupted this ancient signaling system.
Instead of warm, low intensity light at night, we are now exposed to artificial indoor lighting, screens, and devices that are heavily enriched in blue light and stripped of red and infrared tones.
This directly affects the balance between two key hormones:
Melatonin, the master sleep and circadian hormone that rises in the evening
Cortisol, the hormone that promotes alertness and activity, rising toward morning
Melatonin and cortisol cannot rise at the same time. When one increases, the other must fall.
Blue light exposure in the evening suppresses melatonin and elevates cortisol. In effect, our bodies receive a “wake up” signal precisely when they should be preparing for sleep. This disrupts sleep depth, delays sleep onset, and fragments the night.
The good news is that by restoring healthier light environments and making small, consistent changes to daily habits, circadian rhythms can be realigned and sleep can improve dramatically.
Why Light Is So Powerful
How does the body know what time it is?
The body’s master clock is set by light, particularly sunlight. Natural light contains a dynamic mixture of ultraviolet, visible, and infrared wavelengths. The balance of these wavelengths changes predictably throughout the day, from red and infrared rich sunrises, to blue and ultraviolet dominant midday light, then back again at sunset.
When light enters the eye, specialized receptors called melanopsin containing retinal ganglion cells detect it. These cells communicate directly with a central clock in the brain called the suprachiasmatic nucleus. The suprachiasmatic nucleus then synchronizes clocks throughout every tissue and organ in the body.
Light entering the eye is the most powerful signal for setting our internal clock, much like adjusting a watch when crossing time zones.
Artificial light carries the same influence. This is why indoor lighting environments, especially in the evening, can strongly shift circadian timing, for better or worse.
Circadian Disruption in Young People
Circadian rhythms are especially sensitive during childhood and adolescence. These are periods when sleep is essential for learning, emotional regulation, and healthy brain development.
Research shows that when circadian rhythms are disrupted in young people, sleep is often the first casualty. This can quickly cascade into issues with attention, mood, anxiety, emotional regulation, and increased risk taking behaviors.
Supporting healthy rhythms early in life supports healthier sleep, more stable nervous systems, and better long term outcomes across mental and physical health.
Introducing the Better Sleep Bulb - Published Research With Schools
In early 2024, Daniel White, Co Founder of In Rhythm, delivered circadian focused education and practical tools to over 500 secondary school students across seven schools in the United Kingdom.
The results were clear. When students learned how to support their circadian rhythm, particularly through healthier light exposure and sleep routines, they experienced measurable improvements in sleep quality, morning alertness, focus, and emotional wellbeing.
Simple, low cost circadian interventions helped students sleep better, feel better, and function better during the day. Bringing biology back into alignment with natural rhythms proved to be a powerful lever for mental health, learning, and performance.
Cultivating Healthy Rhythms
Strengthening your circadian rhythm is one of the most impactful steps you can take for your sleep and overall wellbeing.
Though often overlooked, your internal clock shapes how you think, feel, move, and recover. When circadian signals are clear and consistent, sleep becomes deeper and more restorative. Energy stabilizes. Mood calms. Long term health becomes more resilient.
At In Rhythm, we believe that addressing the root causes of circadian disruption represents the next major shift in public health. When we fix the signals biology depends on, especially light, the body remembers how to regulate itself.
That is why we are committed to delivering research based education, tools, and products that help people live in rhythm with their biology so they can sleep well, feel well, and live well.
The Missing Link: Circadian Rhythm and the Autonomic Nervous System
What is often overlooked is that circadian rhythms are not just about sleep timing. They are one of the primary regulators of the autonomic nervous system (ANS).
The ANS governs the balance between sympathetic activity (alertness, stress, mobilization) and parasympathetic activity (calm, digestion, repair). Circadian signals, especially light, are what tell the nervous system when to activate and when to recover.
When circadian rhythms are strong and well aligned, the ANS naturally shifts throughout the day:
Daytime light supports healthy sympathetic activation for focus, movement, and performance
Evening darkness and low light support parasympathetic dominance, allowing the body to rest, repair, and regenerate
When circadian rhythms are disrupted, this balance breaks down. The nervous system can become locked in a state of chronic activation, unable to fully downshift at night. Over time, this leads to autonomic dysregulation, where the body struggles to move smoothly between stress and recovery.
In many cases, these symptoms are not isolated problems. They are downstream effects of a nervous system that has lost its rhythmic cues, blood pressure and sugar issues.
By restoring circadian alignment, especially through appropriate light exposure and timing, we are not just improving sleep. We are re teaching the autonomic nervous system how to regulate itself again.
This is why circadian biology is increasingly being recognized as a root cause lever in nervous system health. When the timing signals are corrected, the ANS often recalibrates naturally, reducing the need to chase symptoms individually.