A clock you never wind
Long before alarm clocks, the body had its own. Scientists call it the circadian rhythm: in the words of the US National Institute of General Medical Sciences, “the physical, mental, and behavioral changes an organism experiences over a 24-hour cycle.”1
It is not a modern idea, or even a human one. Almost all organisms have circadian rhythms, from bacteria to plants and animals.6
In people, a large group of nerve cells in the brain called the suprachiasmatic nucleus, or SCN, acts as the master clock. It coordinates the smaller clocks found throughout the body, so that, ideally, everything runs on the same schedule.1
The discovery that won a Nobel Prize
In 2017, the Nobel Prize in Physiology or Medicine went to Jeffrey C. Hall, Michael Rosbash and Michael W. Young for showing how this clock works inside cells.2
Working with fruit flies, they studied a gene called period. They found that its protein, PER, builds up during the night and breaks down during the day. Together with other proteins they identified, called TIM and DBT, it forms a self-regulating loop that keeps time.3
The same principles apply across multicellular life, including us. As the Nobel announcement put it, the clock “regulates critical functions such as behavior, hormone levels, sleep, body temperature and metabolism.”3
Every one of us carries a clock that was keeping time long before we learned to read one.
A conductor and an orchestra
It helps to picture the master clock as a conductor. Organs and tissues keep their own time, like sections of an orchestra, and the SCN keeps them playing together.1
Each of those clocks is built the same basic way. NIGMS describes a biological clock as “composed of proteins encoded by thousands of genes that switch on and off in a specific order.”1
That is why rhythm is not only about sleep. The same daily timing reaches hormones, body temperature and metabolism, as the Nobel researchers showed.3
Light is the loudest signal
An inner clock is only useful if it stays in step with the world outside. Its strongest cue is light.
The master clock “controls production of the hormone melatonin based on the amount of light the eyes receive,” NIGMS explains. In the evening, it tells the brain to make more melatonin, and sleepiness follows.1
Timing matters as much as brightness. Training material from the CDC’s National Institute for Occupational Safety and Health describes it this way: bright morning light shifts the clock earlier, so you get sleepy earlier in the evening and wake earlier; bright evening light shifts it later.4
The effect is not small. According to the same source, light in the hours around your usual bedtime can shift the system about two hours later per day, while light around your usual wake time can shift it about one hour earlier.4
One detail surprises most people: light can reach the clock even through closed eyelids.4 A truly dark bedroom is not a luxury; it is part of the signal.
Light is not the only clock-setter
The clock listens to more than the sun. NIGMS lists food intake, stress, physical activity, social environment and temperature as other factors that affect circadian rhythms.1
Put simply, the shape of your day talks to your clock: when you eat, when you move, when you wind down and when you see people.
The cues your clock listens to, across one day. Light matters most; meals, movement and wind-down routines help.
When those signals disagree, we notice. The Nobel Committee described how “our wellbeing is affected when there is a temporary mismatch between our external environment and this internal biological clock,” as when we cross time zones and feel jet lag.3
Many people live a mild version of that every week, with late nights at the weekend and an early alarm on Monday.
Larks, owls and everyone in between
Not everyone’s clock sits at the same time of day. Some people are wide awake at 6 am; others do their best thinking near midnight.
Part of that difference appears to be written in our genes. A 2019 study of 697,828 people, drawn from the UK Biobank and 23andMe, linked the time people prefer to go to bed with hundreds of genetic variations.7
So being a night owl is not a failure of discipline. The useful question is not “how do I become a morning person?” but “which cues can I keep steady, given the clock I have?”
Sleep, the part of the rhythm you can protect
Sleep is where the daily rhythm is easiest to see, and where most of us have some room to act.
For adults aged 18 to 60, the American Academy of Sleep Medicine and the Sleep Research Society recommend at least seven hours of sleep per night on a regular basis.5
Duration is only half of it. A steady schedule gives the clock the same cues every day, which is the whole point of a clock.
Six small ways to work with your clock
Try this week
- Get outside early. A short walk in morning daylight is a strong, free cue for your clock.
- Dim the evening. Lower, warmer light in the last hours before bed sends the opposite signal.
- Make the bedroom dark. Blackout curtains or a simple eye mask keep stray light from reaching the clock.
- Keep your wake time steady, weekends included. It is the anchor the rest of the day hangs on.
- Give meals a rhythm. Regular mealtimes are one of the cues your body’s clocks listen to.
- Build a wind-down. A calm, repeatable routine (reading, stretching, a quiet hour) tells the day it is ending.
These are general wellness ideas, not medical advice. If you have ongoing trouble sleeping, talk to a healthcare professional.
Why we think about rhythm at THERA
Wellbeing rarely comes from one big change. It is built from small cues repeated every day: light, food, movement, rest.
That is how we think about the time people spend with us, too. A THERA session is gentle and unhurried, one calm hour in a full week. If you are curious, you can read how a THERA session works, step by step.
Sources
- National Institute of General Medical Sciences (NIH). Circadian Rhythms fact sheet. Last updated May 20, 2025. www.nigms.nih.gov
- The Nobel Assembly at Karolinska Institutet. The 2017 Nobel Prize in Physiology or Medicine, press release, October 2, 2017. www.nobelprize.org
- ScienceDaily. 2017 Nobel Prize in Physiology or Medicine: Molecular mechanisms controlling the circadian rhythm. October 2, 2017. www.sciencedaily.com
- Centers for Disease Control and Prevention, NIOSH. Effects of Light on Circadian Rhythms. Work Hour Training for Nurses, Module 2. www.cdc.gov
- Watson NF, et al. Recommended Amount of Sleep for a Healthy Adult: A Joint Consensus Statement of the American Academy of Sleep Medicine and Sleep Research Society. Journal of Clinical Sleep Medicine. 2015;11(6):591–592. aasm.org
- Smith K. Why Am I So Tired? Biomedical Beat, National Institute of General Medical Sciences (NIH). July 26, 2023. nigms.nih.gov
- National Library of Medicine (NIH). News: The Human Genetics of Night Owls and Early Birds, Behind the Headlines, January 31, 2019, on Jones SE, et al. Genome-wide association analyses of chronotype in 697,828 individuals. Nature Communications. 2019. www.ncbi.nlm.nih.gov
This article is for general information and wellbeing. It is not medical advice and is not a substitute for care from a qualified healthcare professional. THERA WELLNESS® products are general wellness products and are not intended to diagnose, treat, cure or prevent any disease.