Circadian Rhythm 101

Oh, what an interesting topic this is! 

The circadian rhythm is essentially our body’s biological clock that keeps our cells and body systems in sync. While our circadian rhythm is innate and not something we have to intentionally program our body to do, it can be disrupted by our lifestyle and environment (hint: there is a culprit we are all guilty of!), which is why more and more people are paying attention to their circadian rhythms. In this post, you will learn about the circadian rhythm pertaining to what it does, how it impacts our gut, hormones, sleep, and appetite, the signs and symptoms of a disrupted circadian rhythm, what can disturb it, and our top tips to avoid disruption to our circadian rhythm. 

Circadian Rhythm and the Sleep-Wake Cycle

The circadian rhythm is our body’s biological clock that acts on a 24-hour cycle (24.2 to be exact) that keeps our cells and body systems in sync, making it essential to our wellbeing – we all have a circadian rhythm! 

Our circadian rhythm is dependent on light to help our bodies stay regulated, with the presence or absence of sunlight helping to “reset” our clocks daily. We are all aware of this sensation in that we naturally wake up with the sunrise and fall asleep with the sunset. 

Our circadian rhythm and our hormones go hand in hand where there are two major hormones at play: cortisol and melatonin

Cortisol, while often put in a negative light given its association with stress and weight gain, actually plays an imperative role in the body – it tells our body to wake up! In a healthy individual, cortisol will peak within the first hour of waking and tapers off throughout the day with its lowest levels in the beginning phases of sleep. If you think about it, this pattern makes complete sense, given it is highest in the morning hours to promote wakefulness and alertness, preparing the body for physical activity and feeding, and then slowly decreases throughout the day (part of the reason for the afternoon slump) preparing for rest. 

Most of us have heard of melatonin in relation to sleep and have possibly even tried taking melatonin before bed to promote tiredness and restful sleep. What many of us may not realize is that melatonin is actually a major regulatory hormone in the body, given its role in the sleep-wake cycle. Melatonin naturally begins to increase around sunset (yup, your body is smart and recognizes this decrease in natural light), peaks in the middle of the night, and slowly begins to taper off from there to decrease sleepiness and increase wakefulness. 

As you can see, cortisol and melatonin are regulatory hormones in the body that have a symbiotic relationship – one promoting wakefulness and the other promoting sleep.

How your circadian rhythm impacts your hormones, sleep, and digestion

The impact of our circadian rhythm throughout our body is systemic, regulating our endocrine system (hello hormones), metabolism, digestion, sleep, cardiovascular system, mood, and more! A key way it does this is by helping our body identify day and night, each of which the body has distinctly different processes. 

The body favors wakefulness during our biological day in preparation for physical activity and feeding. As a result, our metabolism increases to support these activities. This involves an increase in key hormones like cortisol and insulin (key in blood sugar regulation and utilization) and a decrease in leptin (satiety hormone) and melatonin. 

In contrast, our body favors sleep, rest, and repair during our biological night. As a result, our metabolism slows to conserve energy. This involves decreasing key hormones like cortisol and insulin (for steady blood glucose levels when sleeping) and increasing leptin (satiety hormone) and melatonin.  


The regulation of our circadian rhythm is largely dependent on light, with the production of melatonin being stimulated by darkness and inhibited by light. However, with the rise in technology (and our dependence on it!), our eyes and bodies (yes, our skin absorbs light too) are exposed to more consistent light than ever before, disrupting our natural circadian rhythms. 

The light admitted from our screens is called blue light and is problematic. This is because it inhibits melatonin production and may even stimulate cortisol throwing our body’s biological clock out of whack. Additionally, screens are not the only ones to blame, with our body being so sensitive that even brightly lit rooms, particularly at night, are disruptive to our circadian rhythm. 

So how does this impact you? Perhaps you have noticed that you have more trouble falling or staying asleep when you are on your phone before bed. This phenomenon is no coincidence, given the relationship between blue light and melatonin production. 

Aside from sleep, disruptions to our circadian rhythm from artificial light impact our hormones, metabolism, digestive system, and mood. 

Signs and Symptoms your circadian rhythm is off: 

  • Low-quality sleep (waking up later in the morning and not being able to fall asleep at night, waking up throughout the night)
  • Lack of energy 
  • Hormonal imbalances
  • Changes in appetite 
  • Dysregulated blood sugar 
  • Poor digestion
  • Mood changes
  • Weight gain 
  • Trouble concentrating
  • Poor exercise tolerance & recovery 

Those who are most at risk for an irregular circadian rhythm are night-shift workers, those who suffer from chronic anxiety and stress, those who exercise late at night, those who have poor sleep habits (wake up and go to bed at different times), and those who travel often (especially across different time zones). 

Tips to avoid disruption to your circadian rhythm and “reset” it

In our opinion, the best things you can do for your circadian rhythm are to reduce light exposure before bed ( at least 2 hours before bedtime), have a consistent routine (waking, sleeping, eating, exercising, etc.), and watch the sunrise and set as much as possible! 

Tips to help your circadian rhythm: 

  • Stay away from screens at night (at least 2 hours before bedtime) – while this may seem impossible, setting some ground rules for yourself and getting into a routine may be helpful (ex. watch TV for an hour after dinner (7-8), then take a bath with a candlelit while listening to calming music (8-9), do a skin-care routine (9-9:30), get into bed). 
  • Dim the lights, light a candle, or buy a redlight for your bedroom – red light does not affect circadian rhythm, so buying can be helpful and create a fun vibe!
  • Set recurring alarms and reminders to go to bed – not only does this create a routine that your body will get used to, but then you do not have an excuse to use your screen at night. 
  • Wear blue light blocking glasses – my fav is izipizi
  • Put Bluelight protectors on your devices – a good company is ocushield
  • Turn on night shift on your devices 
  • Eat at similar times daily 
  • Exercise at similar times daily (not late at night!)
  • Stay off your phone upon waking – I know it seems impossible but hear me out! Try using an old-fashioned alarm clock or get an alarm like hatch that slowly wakes you up with light 
  • Go on a 10-20 minute walk outside every morning to get the bright sunlight – This is very helpful in resetting your circadian rhythm and keeping it in sync. Also, do not wear sunglasses! 
  • Avoid caffeine within the first hour of waking and after 1 pm
  • Limit alcohol intake – the best time to drink is during happy hour to minimize disruptions to your sleep.
  • Stick to a 25-30 power nap (when needed) – any more than this will be disruptive to your body and leave you feeling groggy rather than energized!
  • Use a sunlamp upon waking to help increase natural cortisol production if you’re waking up when it is dark outside or you are not getting natural light exposure

The Bottom Line

Our circadian rhythm is your body’s master clock that helps to regulate all of your cells and body systems, affecting sleep-wake cycles, hormone activity, hunger and fullness, metabolism, and more! Unfortunately, the circadian rhythm can be easily disrupted by exposure to artificial light and inconsistent routines, so adopting daily practices to protect and support our circadian rhythm is key for our overall health and wellbeing.

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