17 mins read

The Circadian Rhythm

Optimizing your biological rhythms enhances physical and mental performance.

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Our inner clocks are out of sync, and our health is suffering. The misalignment of our illuminated lifestyle with plus hectic work and social schedules is contributing to chronic disease. Our temporal deregulation has become so severe that Circadian Rhythm Disruption resembles a Traumatic Brain Injury. [source]

“Professional football players playing close to the circadian peak in performance demonstrate a significant athletic advantage”

Creating circadian rhythms synchronicity provides a significant performance advantage and improves virtually every aspect of your physiology.

What are Circadian Rhythms?

Life on Earth evolved by adapting to daily fluctuations in light - day and night. Bacteria protected their DNA from UV-induced mutations by replicating genes at night. Organisms evolved to thrive in their niche environment, using resources physically and temporally like adopting the best times to perform specific actions, like hunting.

Environmentally triggered temporal adaptations (biochemical, physiological, and behavioral) must align with the environment. In mammals, including humans, this internal time-management system is called the Circadian Rhythm. Like any good timepiece, it needs to be robust, self-sustaining, and relevant. What use is a clock if it tells the wrong time?

Unfortunately, our modern environment lacks temporal coherence. We have variable meal times, light at night, and flexible sleep patterns. Biological clocks require near-constant conditions to effectively track and predict time and energy requirements. But that is not what we give them!

Circadian Rhythm in Humans

The selective advantage of time-sensitive biology has propagated through our genetic lineage several times.[source] The ability to anticipate biological fluctuations by entraining internal processes to external conditions has provided an ‘edge’ for over 2.5 billion years.[source]

Internal and external coherence is maintained by biological clocks that respond to the environment. zeitgebers (German for ‘time givers) are external cues (environmental and social) that influence internal biology. Light is the primary zeitgeber, but other influences (such as temperature, routine, food, and stress) also impact our ability to be ‘on time.

In just a few decades, humans have taken complete control of our environment; heat, light, and food supply. This has undermined predictable natural rhythms. Global business, international travel, and shift work have pushed people out of their ‘natural’ time-zone.

Reduction in natural light exposure, excessive use of caffeine, sedentary lifestyles, variable food times, and late-night binges have pushed us out of sync with our natural biology. Eroding our natural rhythms and zeitgebers creates a host of metabolic problems, immune dysfunction, neurobehavioral abnormalities, and cancers.[source, source, source]

Aging is accelerated when Circadian Rhythms are misaligned. Alzheimer’s, schizophrenia, and bipolar depression are associated with circadian disruption.[source]

Is our circadian rhythm in our brain or in our cells?

Within the hypothalamus (the brain region controlling homeostasis) lives the suprachiasmatic nucleus (SCN); it contains 20,000 neurons that create a ‘master’ clock. [source] The SCN receives information about external light conditions directly from the retina (back of the eye) and is exceptionally sensitive.

Exposure to light either advances or delays the signal sent out by the SCN. This, in turn, synchronizes genetic, biochemical, and behavioral rhythms with the natural dark-light cycle. The neurons ‘tick’ at a regular pace, and resonate with neighboring neurons, to create a robust self-sustaining rhythm for both gene expression and brain activity. [source]

Neurons from the SCN project into hypothalamic nuclei that regulate sleep, wakefulness, temperature, and appetite.[source] The SCN, in turn, imposes a regular schedule of activity and drives a rhythmic release of neurotransmitters, hormones, and glucocorticoids (like cortisol).

Circadian Rhythm Disorder

The impact of disruption is multifaceted. Symptoms appear in various systems which, typically escalate until resolved or disease manifests:

  • Reproductive issues
  • Endocrine (hormonal) issues
  • Immune compromise and increased cancer risk
  • Metabolic and energy management issues
  • Adrenal and neuropsychiatric issues 

Circadian-controlled biological systems are critical; minor disturbances (reducing temporal logistical efficiency – like a postal strike) create major problems.

How do you know if you have Circadian Rhythm Disorder?

Do you have any of these early signs of Circadian Rhythm Disruption?

  • Consistent difficulty falling asleep, staying asleep, or both.
  • Nonrestorative sleep (feeling tired even after getting enough sleep).
  • Daytime sleepiness or sleepiness during shift work.
  • Fatigue, exhaustion, and lethargy.
  • Impaired productivity and performance.
  • Decreased alertness and difficulty concentrating.
  • Reduced psychomotor coordination.
  • Impaired judgment and trouble controlling mood or emotions.
  • Irregular aches and pains, including headaches.
  • Stomach problems or digestive issues

Note: The above could also be present even without Circadian Rhythm disorder or be signs of an entirely different underlying condition.

Your Circadian Rhythm may even regulate gene expression.

A complex system of genes and proteins interact in a time-sensitive manner through interlocked transcriptional-translational feedback loops (TTFLs). The SCN, together with the peripheral clock genes, creates temporal harmony; coordinating biology and behavior with the external environment. Micro-DNA analysis revealed global disruption of genetic pathways in the liver (controlling glucose and lipid metabolism). Circadian disruption can manifest at a molecular-genetic level in a relatively short time.

Studies that mutate or delete clock-components “unanimously support a view that normal clock function is important to well‐being”

Cells and tissues have their own time-keeping ability. Until recently, it was thought that the SCN provided timing information to the body. Now we know the relationship is bi-directional. The SCN works with the peripheral clocks to harmonize the whole operation.

The SCN controls the master clock (that ‘tiks’ even without a dark-light cycle) and is synchronized with peripheral clocks - creating a Federation of timekeepers that collectively agree on the ‘right’ time (to perform a function). [source] The Federated model suggests the SCN exerts its ‘standard’ rhythm only when zeitgebers are missing or conflicting. [source] This means you can provide specific zeitgebers to resynchronize and retrain the entire system!

Local tissue clocks control the expression of specific genes. Regulatory pathways crucial to survival (like glucose management) are under tight time control to ensure coordination with other organs (liver, muscle, and adipose tissue) [sourcesourcesource]

The basic SCN rhythm is reinforced with hormonal patterns (notably melatonin and cortisol) that contribute, compliment and consolidate the cycles. The secreted factors act to propagate, entrain and enhance the amplitude of the SCN signal. This means if either your cortisol or melatonin levels are disrupted (stress and insomnia anyone?) any irregularities in the cycle are exaggerated, and the problem gets worse. Until you interrupt the cycle.

Wakefulness & Daily Cycles

Daylight drives alertness, with cortisol and other hormones that keep us awake. As light levels drop, the reduction in SCN stimulation initiates melatonin production to make us sleep. This aligns sleep and wakefulness to day and night, creating restorative rest and optimizing daylight hours for activity.

Wakefulness is the main cycle controlled by the SCN, but many other circadian oscillations are coming to light. Blood glucose management, metabolism, inflammation, the immune system, mood, memory, DNA repair, and neuroregeneration are all subject to daily rhythms. [sourcesource]

'Internal Clock' Controlled Processes

The criticality of clock-controlled processes reveals how and why becoming ‘out of phase’ can be so detrimental to health. These are the key biological processes under rhythmic control:

  • Expression of detoxification enzymes (to mop up free radicals).
  • Oxidative defenses in Red Blood Cells
  • Lipolysis and Free Fatty Acid release from White Adipose Tissue (fat)
  • Endocrine clock genes that control lipolysis, adipogenesis, and energy conversion.
  • Genes controlling immune response and metabolic processes.
  • Brown Adipose Tissue thermoregulated lipolysis to generate heat
  • Glucose levels, FFAs uptake, and clearance of serum lipids
  • Insulin and glucagon levels are circadian influenced, independent of feeding.
  • The pancreas has a functional circadian clock that controls insulin secretion.
  • Some fecal bacteria show rhythms of abundance and decline in the gut.
  • Oscillation of gastrointestinal activity and nutrient absorption.
  • Renewal of skin and gut epithelial cells.
  • Vitamin-D control of serum calcium levels and bone formation.
  • Rhythmic activity of liver enzymes (10% of liver genes are rhythmical).
  • Genes associated with the metabolism of carbohydrates, lipids, amino acids, and bile.
  • Daily oscillations in NAD+ (used by SIRT1 to deacetylate clock-related proteins).

Can You Choose Your Chronotype?

There is a ‘chicken and egg’ conflict regarding chronotypes. Are we genetically pre-destined to be early or late risers? Do our actions influence epigenetic adaptations, steering our time preferences? Or, are some people better able to pick up the subtle environmental cues or more able to stay in tune without predictable signals?

The health benefits associated with chronotype suggest we should be trying to steer our temporal destiny and seek zeitgebers that realign us with ‘natural’ time. The mental and physical performance gains from an efficient, entrained, and naturally resonant rhythm can provide an energetic edge for everyone from athletes to entrepreneurs.

Circadian Chronotypes

Differences in day and night activity and alertness allow us to label chronotypes.

  • Early (E-types) wake up and fall asleep earlier than Late (L-types).
  • E-types and L-types have very different social timetables.
  • Extreme E-types can be waking up when extreme L-types are going to sleep.
  •  L-types have more problems with Social Jet Lag.

It’s possible to assess chronotype using self-reporting questionnaires (including the floating Circadian Rhythm Test button on this page). But, accuracy depends on recall and estimating how you would respond to different mental and physical tasks.

Alternatively, studies using Ambulatory Circadian Monitoring (ACM) sensors gather moment-to-moment data (environmental light and temperature exposure, wrist temperature, body position, and activity) under free-living conditions. This vast dataset can help classify individuals. Typically some 60% sit in the middle with no preference, approximately 20% are early-types & 20% are late-types.

Benefits of Chronotype Alignment

Circadian-controlled genes are involved in all of your critical biological functions. This means even minor gains in efficiency have an impact. When the whole system resonates in harmony with your schedule, you can expect the following:

  1. Consistent restorative and refreshing sleep.
  2. Optimal production of digestive enzymes and bile.
  3. Rhythmic and regulated hormones (including ovulation).
  4. Energy production.
  5. Enhanced detoxification and improved liver function.
  6. Efficient digestion and nutrient absorption.
  7. Reduced oxidative stress and increased blood oxygenation.
  8. Improved immune function and cellular rejuvenation.
  9. Improved mental clarity and memory consolidation.
  10. Enhanced cellular cycling (e.g. growth, repair, or apoptosis).
  11. Better heart function and reduced risk of heart disease.
  12. Reduced levels of stress and a more balanced mood.
  13. Improved glucose control and balanced appetite.
  14. Reduced risk of DNA damage and cancer.
  15. Use of hormones at peak release times (e.g. getting up)
  16. Efficient thermoregulation of body temperature.

Improving your Circadian Rhythm makes your body much more efficient. An efficient body has ‘spare’ energy to think, repair the body, remove toxins and operate at peak performance.

Establishing optimized circadian rhythms, entrained to your routine, allows you to schedule critical tasks for peak performance points in your day.

What regulates your circadian rhythm

It is possible to re-establish an efficient and healthy circadian resonance with the natural environment (or optimize your lifestyle e.g. shift-work). By modifying personal zeitgebers you can entrain a more efficient oscillation of gene expression.

Through careful analysis of shifts in your energy, glucose, sleep, and subjective well-being, it's possible to identify and optimize your genetic expression.

Zeitgebers put you back in control of your genes - you get to shift their operation to suit your lifestyle! All you need is the right data to determine what optimizes YOUR rhythm.

1. Light
  • Natural light is the most powerful and predominant zeitgeber.
  • Exposure your eyes to natural sunlight as early in the day as possible.
  • Just a few minutes of natural light is needed to mark your ‘subjective dawn’.
  • Limit light before bed and create a ‘subjective dusk’ (limit light exposure after dusk)
  • Prevent exposure to short (stimulating) wavelengths of light at night (blue light filters).

Increasing Light after Dawn
  • Mimic sunlight if there isn’t enough/any present for your preferred ‘dawn’.
  • Try a dawn simulator, lightbox, blue-bulb, or natural-spectrum light to illuminate your morning.

Limiting Light after Dusk
  • Dim room lights and use red-orange-yellow light bulbs (not blue).
  • Use blue-light filtering software on devices and consider blue-light filtering glasses.
  • Exposure to bright light at night can ruin your rhythm and should be avoided.

Natural Light Exposure
  • Sunlight offers many health benefits, including the activation of light-dependent Vitamin D.
  • Sun seeking behavior is associated with lower mortality – get some gentle sun on your skin.
  • Go camping for a rapid system reset; connect with dawn and dusk; limit light and technology.

2. Sleep

Altered sleep-wake patterns displace sleep, and sleep is the next most important zeitgeber. Sleep is fundamental to your rhythm and a biological necessity that we often skimp. Regular sleep patterns (with less than one-hour variation) entrain quicker payoff. The sleep-inducing hormone melatonin is made exclusively in the dark!

Winding Down and Falling Asleep
  • Start to reduce light after natural dusk (limit blue light) to start melatonin production.
  • Avoid eating and vigorous exercise for 2 hours before you want to get to sleep.
  • Slow down the central nervous system (CNS) with relaxing activities 30 to 45 minutes before bed.
  • Consider a ‘winding down’ ritual to enhance entrainment (turn off devices, meditate, journal, read, listen to relaxing music, brush teeth, etc.).
  • Keep the bedroom for sleep and sex; orgasm is calming, stimulating the endocannabinoid system.
  • Ensure your bedroom is cool enough and has sufficient airflow – sleep is temperature-dependent - your brain needs to cool slightly to change phases during sleep.
  • Reduce sources of electromagnetic radiation (mobile phones, wifi, smart devices) as for some people they can interfere with sleep microstructure and reduce the duration of REM sleep.

Listen to Your Body

Instead of overriding tiredness with coffee (which messes with alertness), consider a nap instead. Napping (ideally early afternoon) improves memory, learning, creativity, alertness, mood and reduces stress:

  • Brief naps (5-15 min) offer immediate benefits lasting a few hours.
  • Longer naps (> 30 min) initially impair alertness (sleep inertia after waking) but produce sustained cognitive improvements.
  • The longer you have been awake, the longer your nap needs to be for complete restoration.
  • Regular nappers get better, so like any skill you need to practice.
  • The first 7-10 min of sleep can result in a substantial increase of alertness due to rapid dissipation of substances inhibiting wakefulness.

Athletes napping for 20 to 90 minutes between 1pm and 4pm improved: performance, perception, and psychological state without compromising night-time sleep quality.[source]

3. Stimulants, Supplements and Smells

Avoid caffeine-containing substances and stimulants after midday (coffee, green tea, chocolate and even chili). Consider supplementation with nutritional metals:

  • Magnesium  – helps muscles relax and get to sleep quicker/stay asleep.
  • Zinc - calming and helps you get to sleep quicker.
  • Melatonin supplementation enhances natural levels, making it easier to get to sleep. Melatonin ‘hangovers’ cause lethargy the next day and long-term use can interfere with natural production – use with caution, melatonin marketing is proving to be more effective than its results. Melatonin has not been shown to help shift circadian rhythms, but it will knock you out if you are struggling.
  • Herbs and essential oils (notably lavender) can help you get to sleep, they can also enhance entrainment by creating a smell-based neurological anchor to make your bedtime into a sweet smelling ritual.

4. Temperature

The SCN sits in the home of homeostasis, the hypothalamus. Homeostatic thermoregulation (body temperature) varies throughout the day. Piggy-backing this temporal-temperature signature can reset and retrain your rhythms. Anticipatory regulation expects a rhythm oscillation between 36.5 and 38.5 °C. Cells with peripheral clocks respond to temperature change, helping synchronize with the SCN. Thermo-detecting proteins seem to be able to reset molecular-peripheral clocks.

  • Warming the skin (hot shower) drops core body temperature (due to peripheral vasodilation) and reduces sleep latency (time to get to sleep) by 10 minutes. [source]
  • Whole body cold water immersion also improves sleep quality and circadian synchronization, but it’s a little less practical! [source]

5. Diet

The next critical factor is food intake (type, time, and portion size) with glucose and insulin-regulating peripheral clocks (e.g. liver and kidneys). Peripheral circadian clocks entrain to food and de-couple from light and the SCN. For most of the body, this means the signals from food are more important than the SCN. Using the Federated model, it becomes obvious that the body needs to try and predict significant energy drains (such as digestion). If you often eat at 3 am, this is the key signal you will entrain and resonate with. Food availability drives both behavior and metabolic functions (e.g. seeking food, insulin secretion)

So, avoid late-night snacking unless you want to entrain your stomach to a different time zone!

  • Digest food when the digestive capacity is maximized (typically midday, but varies by person) and keep evening food ‘lighter’ so it digests before you go to bed (avoid lots of fat and protein).
  • Circadian Rhythm Fasting (e.g. Fasting from 4 pm to 8 am for just one day) quickly synchronizes peripheral clocks but not the SCN.
  • The autophagy-inducing mTOR pathway has also been implicated as a vital synchronization pathway used by peripheral clocks.

6. Stress

Secretion of the wakefulness hormone cortisol is what gets us going in the morning. So, it should be no surprise that stress (cortisol excess) interferes with circadian regulation. Several clock genes have promoter or enhancer regions that respond to stress hormones. Clock gene activation provides the molecular basis for how stress impacts circadian rhythms. Stress reduces night-time pineal melatonin production and increases daytime production. Inflammation also signals physiological stress which impacts the production of other hormones.

  • Reduce stress with exercise, sex, and relaxing activities (reading, walking, journaling, meditating).
  • Limit stressful stimuli especially near bedtime (news, difficult people, and horror films!).

7. Activity

The ‘active’ phase of the day should contain exercise, social interaction, and feeding. When these activities are missing, the day is not ‘complete’. Daily exercise reduces stress, tires you out, and uses up stimulating hormones. Night-time exercise can dramatically shift the phase timing of melatonin production – it confuses the body so much that the next day's circadian dusk is delayed by up to 12 hours. Activity creates internal coherence between peripheral clocks and the SCN. During the day it is ‘movement’ that directs different physical demands; wake up, get up, go hunt, rest, socialize, fight, mate, sleep, etc. Chrono-biologically there are benefits to exercising at different times of day:

  • Greater strength in the evening (exacerbated by evening training)
  • Resistance training in the morning has bigger strength gains.
  • Regular training (at set times) could reduce long-term gains (surprise your body!).

8. Routine

Whatever your rhythm, it will be enhanced by routine (gaining more efficiency). Try and create consistency (in timing) across your work and personal life. Plan to compensate sleep for timezone ‘changes’ (international travel or personal behaviors). Awareness of your rhythm plus performance data will help you optimize your temporal alignment. Personal experimentation will highlight the best times of day for you, depending on your needs.

Circadian Synchronicity

Just 10-days of circadian synchronicity increases insulin sensitivity and decreases blood glucose, cortisol & blood pressure!

If you had a watch that consistently runs late would you call it an L-type watch? What if the watch started getting dim, had poor battery life, and was getting slower by the day; would you describe this as a ‘feature’ or ‘type’ of watch? No. You would say the watch had a problem!

Science has a tendency to label and study states of maladaptation, not optimized adaptation! Insulin resistance is maladaptation to the food being eaten and toxins inflaming the pancreas. Burnout is maladaptation to levels of stress and the inability to reduce cortisol levels. Late-type chronotypes are maladapted to living a healthy life in our modern environment. But, by resetting the timing, using the language of zeitgebers we can rewrite the schedule!

The critical component of circadian rhythms is the ‘match’ or resonance with the environment, not simply adhering to a specific 24-hour schedule. The ‘free-running period ‘ is what happens to the clocks when they are not working together.

A limited number of animal studies have tracked the benefits of establishing resonant alignment with physiological and behavioral clocks. Human studies are starting now. With me and you.

The performance potential from adding just a little more energy and efficiency is immense. The personal gains in mood and stress reduction make it an experiment worth putting effort into.

Micro-DNA analysis and qualitative assays have pinpointed an ‘ideal time, for an average human, in ideal conditions. This doesn’t often exist, but it is a starting point when considering a schedule. Are you optimizing your day in alignment with your body?


circadian rhythm chart

How to determine your circadian rhythm

1. Circadian Rhythm Test

We can’t easily change many things in our modern lives, let alone the time of sunrise and sunset. But, we can pay attention to the signals we give the body and, in turn, get better at meeting our own needs. Your SCN works in unison with organs, cells, and DNA to create a schedule that works. By increasing body awareness, you can train that schedule to align with your life and make it more efficient.

Try this free Circadian Rhythm Assessment  

2. Basis Circadian Rhythm Automatic Tracking

For a more accurate, daily system to track your circadian rhythms, you can use Basis. Basis uses sleep and activity data from your wearables to continuously interpret your circadian rhythm and guide you on how to improve your lifestyle habits to get you more in sync with your circadian rhythm and enhance your health.


17 mins read
The Circadian Rhythm

Optimizing your biological rhythms enhances physical and mental performance.