The Power of Habit 5/5: The Circadian Rhythm

The final in my series on habits is probably the most important one yet, & which forms the foundation for all the others. When I learned about Circadian Rhythm (chronobiology) it changed my whole approach to life. I have spent the last 18 months studying it. In this concluding session I will attempt to provide a summary of the science, along with some tools to help you optimise your circadian rhythm. The universe is aligned in perfect symmetry, & humans flourish when they rediscover their alignment.

A Human Relationship With The Sun

Have you ever noticed that the sun rises & falls every single day? Have you ever wondered why we get tired when it gets dark & wake up when its light? Ever noticed how the morning song of a bird is aligned with the first glimpse of sunlight? I have a dog & she never needs an alarm clock. Like clockwork, I hear her paws trotting on my wooden floors at the same time every single day..

Nature has a way of alignment that is driven by the sun. There's is a reason cultures have worshipped the sun for millennia. The Roman's even had festivals that worshipped the god of sun, Sol Invictus (unconquered sun). Interestingly, the 25th December marked the winter solstice in the Roman calendar, with the evergreen Christmas tree later symbolising the lowest point of the sun. Anecdotally, there has been similarities between the 'Sun' & Jesus the 'Son' that have sparked debate around the festival of Christmas ever since the Roman times. The sun is evidently so important to our existence, & to the existence of every living thing on the planet! But our modern relationship with it is hindered due to how we spend our time.

Until recent history, like the birds & my dog, we too were aligned with the coming & going of the sun. However, today with most of our time spent indoors, or working anti-social shift patterns, we are lucky if we see the sun at all throughout the day. Moreover, almost all of our social time away from work is spent in front of the TV or scrolling on a phone. We have black out blinds on our windows to hide from the sun, so that we can stay longer in bed. Usually because we spent most of our evening watching Netflix late into the night!. Our lives are dominated by artificial light! With our sedentary routines & lifestyles do we even notice the sun coming or going? Ever noticed how in the summer when we spend more time outdoors that we feel better, happier, healthier?

Scientists who study chronobiology have discovered that our relationship to the sun is fundamental to living a long & healthy life. Like my dog, our bodies each have a 24 hour cycle that resets every single day. This our Circadian Rhythm. When we alter it there is evidence to suggest it can have detrimental effects on our health. There is significant evidence that our lack of alignment with the sun & our circadian rhythm correlates to obesity, depression, diabetes, cancers, heart disease & a range of other illnesses. So what is our circadian rhythm, & how can we better align ourselves with the sun?

Circadian Rhythm

Each living thing on this planet has a 24 hour cycle (or a body clock) which is called our circadian rhythm. It is a natural physical timetable that regulates our sleep-wake cycle (Satchin Panda, The Circadian Code). It can be triggered by endogenous processes (internal to the body), as well as respond to external environmental factors (Panda). Panda notes how every living cell & organ in our body have tasks that need to be completed according to a certain timetable. Much of our endogenous processes are activated by the sun. Moreover, our wakefulness & sleep cycles are the direct result of the regulation of light that either stimulates or makes us tired.

Andrew Huberman, professor of neuroscience at Stanford University, explains that our eyes are the external extension of our brain (see Huberman Lab podcast for more on this). Moreover, it is our eyes that communicate to our brains regarding our light exposure. As part of this communication, & to build on Panda's observations, hormones are released at crucial points throughout the day to regulate our mood. Cortisol, a stress or energy hormone is released in the morning to generate wakefullness & alertness. Melatonin, a hormone that is used to generate the sleep cycle & tiredness.

This is governed by a retina in the eyeball called Melanopsin, which is regulated by light exposure. As Melanopsin increases Cortisol is secreted, & Melatonin decreases. As Melanopsin decreases, Melatonin is secreted, & Cortisol decreases.

Cortisol

Cortisol not only activates alertness & wakefulness, but is directly related to our immune system & metabolism. Moreover, as part our of circadian cycle, cortisol activates our insulin secretion to help distribute carbohydrates & glucose to our muscles (or as melatonin decreases), so that during our peak period of mental/physical alertness (mid afternoon), our bodies can function efficiently. Cortisol gently increases during the morning, peaking around 10am, which is when your metabolism is most active.

When you lay in, or avoid light exposure your melanopsin receptors reduce the cycle of cortisol secretion, slowing down your metabolism, insulin secretion, & alertness. Which is why you often feel more groggy when you lay in. Likewise, if you eat your breakfast, or sugary high carb foods before the cortisol peak, your metabolism is slower to digest such foods.

Cortisol is directly connected to our exposure of light, which is why if you want to optimise the circadian cycle you should seek out sunlight as soon as you wake. Huberman notes how we should be exposing ourselves to natural light as a priority in the morning. When we don't avoid natural light in the morning we maximise our alertness. Research also suggests positive correlations with increased happiness & decreased depression when we optimise our cortisol secretion (Panda).

Melatonin

Cortisol decreases & melatonin increases with the reduction of daylight. This is where one of the greatest misalignments exists. As touched on above, melatonin increases when melanopsin decreases, which means when it gets dark we should get tired. However, because our evenings are spent indoors surrounded by bright lights, TV's & phones, we significantly inhibit the secretion of melatonin. Moreover, when we switch on our favorite series we often re-activate cortisol, imparting higher levels of cortisol than we need.

Too much cortisol can increase stress & anxiety. Additionally, because of the activated receptors of melanopsin from bright lights, melatonin is reduced & we struggle to get tired. Resulting in detrimental effects on our sleep. How often have you been tired after work & after eating your tea, to feel awake & alert again before you go to bed? (note: Caffeine is a stimulant & inhibits melatonin which is why drinking it after lunch is a bad idea!)

Important also to the melatonin cycle is eating at night. As cortisol decreases & melatonin increases, our immune system & metabolism again kicks in. When we eat late, i.e. past dark, our cortisol secretion is reduced, & we struggle to digest our food. The secretion of melatonin also inhibits insulin secretion which has negative affects on our digestion. When high carb or sugary foods are eaten late at night, our metabolism struggles to distribute the glucose to our muscles. The consensus in the scientific literature is that this correlates to obesity, diabetes, heart disease & many other illnesses.

The impact of breaking the circadian cycle leads to a perpetual negative cycle that has a detrimental impact on our health. That late night leads to a lay in, that leads to broken eating habits, & so it continues. Panda, among many others who have researched the circadian cycle, advocates a lifestyle shift that realigns with the sun. He has provided some tools to help us rediscover our natural rhythm.

Rhythms Realigned

The science, that I have attempted to outline as simply as possible, provides a glimpse into how best to develop new habits into your life. In reality however, the scientists often live in a non-realistic world, & lack a pragmatic view point. If you were to follow all of their advice you would probably end up saying goodbye to your social life completely. Likewise, with children, anti-social shift patterns, & limitations outside of our control, you could easily be left discouraged by the impossibility of realigning our circadian cycle.

I personally adopt a 'more often than not principle' that I have talked about previously (Ryan Holiday). & for those who cannot go for a run at 6:30am to see the sunrise, or who don't finish work until late evening, there are principles that can still be applied to optimise your cycle (Huberman). I therefore will deviate slightly from the literature so as to provide a pragmatic approach that can be transferred whatever your circumstance. Likewise, If going out on a Saturday is your thing until the early hours, do so knowing the implications it will have on your sleep-wake cycle for the coming week. Probably why the older we get, the longer it takes to recover from a hangover.

Time Restrictive Eating

Panda & Huberman both advocate for time restrictive eating to coincide with your cortisol/melatonin cycles. This will help your metabolism to efficiently digest & redistribute nutrients around the body. They recommend a 8-10 hour window eating cycle, so that your organs can have time to digest food before going to bed. It takes approx 5 hours to digest food, plus an additional 2 hours to distribute the nutrients around the body (Panda). When we eat late at night OR early in the morning, we are limiting our metabolism's ability to synthesise our food, resulting in increased risk of diabetes or obesity.

Applying the 'more often than not' principle I wait until around 10:30am before eating a good breakfast. Usually I run early mornings, so I complete all of my exercise fasted, unless its a long one, then Ill have electrolyte dense calories. I also aim to stop eating food around 8pm, apart from the odd guilty pleasure of crisps with some wine. If I could achieve this 80% of the time in a week I am happy. The circadian principle is to develop habits that ritualise eating routines with a value of longevity & health. Anyone struggling with weight management or low energy levels throughout the day, this principle will change the game! (I will be doing a series on weight loss in the new year. A topic I have also been studying).

Sacred Sleep Cycles

Matthew Walker, professor of neuroscience & psychology at California University, has changed the game when it comes to the importance of sleep. There is not a scientist out there who doesn't now recognise the importance of sleep from Walker's work (Walker, Why We Sleep). Walker explains from our circadian rhythm why getting a minimum of 7 hours sleep per night is critical for our neuro synthesisation to take place. There is a reason why our smart watches now monitor our sleep cycles.

The principle is to be obsessive about developing a sleep-wake cycle. Going to bed & waking up at the same time every day has become sacred. Again, 'more often than not' I will ensure I follow this principle. In the summer it is much easier, & to be honest I find it harder during the winter months, because of limited sunlight. If you are lucky enough not to work shifts, this is much easier to apply. I am disciplined most of the time about limiting my Netlix binging, so I have time to read before going to sleep by 10:30 latest.

Light Exposure

With melanopsin being the driving factor for cortisol & melatonin, light exposure is critical to our circadian cycle. Developing habits that evolve around realigning ourselves with the sun has been the single most important change I have made. Again, in the summer it is much easier than the winter, because I have pretty much waved goodbye to my window blinds. The goal is to encourage as much natural light in the morning as possible to kick start that cortisol cycle. This ensures our metabolism, immune system, & alertness is optimised throughout the day. Likewise, by waking up with the sun you naturally regulate the tiredness cycle, creating a positive knock on routine for going to bed.

In the same way the melatonin cycle cannot kick in with bright, blue lights in the evening. Most devises have night mode now built in to them because of this knowledge to reduce the level of light. Many people are surprised when they can't sleep, but have every light in the house on, a blaring TV, & are glued to a phone before bed. Too much light stimulus activates cortisol & reduce melatonin that helps you to sleep.

My household has developed a routine of switching off our lights in the evening to make it as dark as possible. In our bedroom we have a dimmed lamp that is bright enough just to see my book. Likewise, 'more often than not' I will limit my phone use right before bed. I have replaced this with a book, which actually increases my tiredness before I go to sleep. Again, when you sleep well you wake up easier, & you are aligned with your circadian cycle.

Exercise

Finally, the best way to metabolise your food, maximise your cortisol cycle, & regulate your sleep-wake cycle is to regularly exercise. Many people struggle with sleep for the sole reason of living a sedentary lifestyle, sitting down all day at a desk - thus not burning enough energy. Exercise enables the cortisol to maintain healthy levels, reducing stress & depression, while burning the calories of your food. Basic biology!

I am fortunate to get my early morning sun light exposure with my running, providing a balance of energy expenditure that ensures I am tired in the evening. Research suggest however, that exercise mid-to late afternoon is probably healthier, because your cortisol cycle is peaked for maximum alertness (Huberman). Likewise, caffeine before a workout in the afternoon optimises the fat oxidation process, making it more efficient to burn the calories.

Summary

There is a consensus among the science of longevity & health that realigning our Circadian Rhythm is the single best thing we can do to live a long & healthy life (see Peter Attia). Anyone who is struggling with weight management, or depression, lack of focus, insomnia, or fatigue throughout the day, making these subtle changes to our habits & routines will be better than any medication or fad diet on the market. Changing how & when we eat, limiting our light exposure, being rigorous about our sleep, & getting regular exercise will literally change your life experience. Health & longevity is my ultimate value. I want to be highly functional well in to my old age. I do not want diabetes or cancers. I know so many people who have had these diseases, & the evidence is clear that they can be avoided.

Our Circadian Rhythm is what aligns us with the universe. We are biologically & neurologically designed to revolve around the sun. It doesn't take a lot to break our bad habits with a bit of intentionality. Many of these habits have become sacred & ritualised in my life, to the point where I no longer think about them. Remember, a habit is an unconscious pattern! If you value longevity why not aim to incorporate some of these in to your daily routine? It doesn't mean the odd late night, lay in, or evening snack can no longer happen. As long as you apply the 'most often than not' principle, you too can realign your circadian rhythm. Its just how nature intended.

Much love,

Ross