The Circadian Rhythm is essential for health
Introduction
Billions of years ago the Earth was formed from dust that was spinning. Physics postulates that the earth continues to spin because ‘mass maintains a state of motion unless acted upon by another force, this is known as inertia’. This inertia is what causes the Earth to spin on its axis, resulting in the cycles of day and night as the Earth faces the sun at different points during this rotation. The evolution of life over the past 4.5 billion years has therefore adapted to this station of the planet which causes the predictable daily changes in the light and dark cycle over a 24 hour period.
So how does this relate to the Circadian Rhythm?
Circadian Rhythm is translated from the Latin ‘Circa Diem’ which literally means ‘around a day’. Within the 37 trillion cells found within the Human organism each cell possess a biological clock which dictates the timing of cell functioning over a 24 hour period which repeats daily, hence the term ‘Rhythm’. So the body carries out functions based on a timing system which are necessary for survival, this includes; hormone secretion, appetite control, changing body temperature and much more. So the body's Circadian Rhythm is important because we need these functions to occur at the right times in the day. For example, if the body was to secrete the sleep inducing hormone ‘Melatonin’ in the morning it would not be advantageous because it is during this time in the 24 hour cycle that we want to be productive and alert in terms of working or from an evolutionary standpoint gathering food and resources.
Is the Circadian Rhythm really that important?
The Circadian Rhythm is essential for the health and well-being of humans but don’t just take my word for it. In 2017, 3 scientist won the Nobel prize in ‘Physiology or Medicine’ for their discoveries of “The molecular mechanisms controlling the Circadian Rhythm”. Bare in mind that this prize is awarded for achievements that have provided the greatest benefits to humankind.
The Molecular mechanism of the Circadian Rhythm is an ‘auto regulated self sustaining inhibitory feedback loop’. Put simply, the cells in our bodies can switch on and off functions based on the needs of the body at different times. Thus adapting our physiology to the time of the day. These mechanisms are based on the predictable changes in day and night. However, external environmental factors such as artificial lighting in our homes and prolonged screen times on phones, TV’s and laptops has disrupted these once stable fluctuations in the light and dark cycles found in a ‘natural environment’. Subsequently, the rhythmic cellular functions in our bodies can be disrupted. A mismatch between the external environment and our inner biological clocks can have detrimental effects on our well-being. The Circadian Rhythm is “the largest known regulatory network in normal Physiology, responsible for daily fluctuations in gene expression” which directly affects our physical, mental and behavioral capacities”.
So how does light affect the circadian Rhythm ?
In the Human retina we have melanopsin containing retinal ganglion cells. The Melanopsin found within these ganglion cells is a collection of blue-light sensing Neurons (5000 of them). These Melanopsin Neurons are non-image sensing, meaning that they will not allow you to distinguish the material world. Rather, their function is to detect differing wavelengths of blue-light.
Light is a form of electromagnetic energy which travels in waves. We measure wavelengths in Nanometers (1 Nanometer = 1 billionth of a meter) (10-9). The visible light spectrum consists of wavelength measurements ranging from 380 to 700 nm. As we measure the distance between successive peaks in a wavelength, the closer the peaks are to one another, the more energy is being transmitted. As such, lower numerical measurements emmitt more energy.
Over the course of a day, the natural light spectrum fluctuates which the Melanopsin Neurons in our eyes directly respond to. From sunrise we see a warmer/softer light spectrum as wavelengths measure around 580 nm. By the time we reach midday the wavelengths become shorter, around 460nm, transmitting the strongest intensity of blue light. By sunset we see a return to a softer and less intense wavelength of light until the darkness of night.
The light sensors in the eye are directly connected to 20,000 Neurons located in the Hypothalamus of the brain called the Suprachiasmatic Nucleus (SCN). The SCN acts as the central pacemaker of the Circadian Rhythm in our bodies. It receives light cues from the environment, in which, differing wavelengths of light detected by the eyes cues different signaling processes by the SCN. An example would be approaching night time there is little to no blue light wavelengths detected by the eyes, this signals to the SCN that it is night time. From this environmental cue the SCN coordinates the necessary functions to induce sleep by communicating with the pineal gland by the SCN to secrete the sleep inducing hormone Melatonin. As the sun rises our eyes will detect more blue light. This light causes the SCN to coordinate the processes of awakening by signaling to the adrenal gland to secrete a surge of the hormone cortisol to transition us from sleep to wakefulness.
To paraphrase Dr. Satchin Panda ‘the light sensors in our eyes connect the SCN to the outside world, from which functions of the body are matched to the environment’. So the SCN regulates the timing and subsequent functions of organs and cells in the body, each of which has optimum times to function and rest. If we can get these Physiological processes in sync with our environment we can experience vitality in terms of health because, as previously mentioned, the rhythm of bodily functions directly affects our physical, mental and behavioral functioning and as such our direct experience of reality.
How does Food and digestion affect the Circadian Rhythm?
So, as well as light, the ingestion of food also affects our Circadian Rhythms. As I’ve mentioned, our organs carry out different functions over a 24 hour period and have optimum times for doing so. The Liver is a good example of this. At night time around 11pm till 3am (depending on your own rhythms) the processes of detoxification are prioritised by the body, it is essential for the removal of accumulated toxins from many sources including food and the polluted atmosphere. However, if we eat late at night, the Circadian Rhythm can be disrupted as the energy that would be directed to the processes of digestion and the other organs involved in these processes hinder this key function of the liver associated with this time in the 24 hour cycle. If this is a chronic behavior (done repeatedly over a long time) It can lead to serious health complications. It is known that modern cultures are associated with a magnitude of health complications from diabetes, obesity and gut disorders.
Human Evolution and their interaction with light
Many humans in the modern world now have virtually unlimited access to food at any time of the day. This is often seen as a state of thriving but this may in fact be to our detriment. More and more research is strongly highlighting the importance of when we are eating, the timing of food ingestion, rather than solely focusing on what we are eating. The accessibility of food is easier than ever with packed fridges, food deliveries to door steps and a huge array of fast food businesses. Consequently, our likelihood of continually disrupting our Circadian Rhythm each night is high.
Many people are eating food late at night in brightly lit homes, engaging with blue light emitting screens. The Problem here is that our eyes have not evolved to distinguish the sources of blue light. We have only been using artificial lighting in the last 130 years and electronic screens in even less time, but we have been on Earth as evolved Homo sapiens for around 200,000 years. During our evolution, our sources of light came from the moon, fires and candle light, neither of which emit blue light and therefore do not stimulate the Melanopsin in our eyes. However, the prolonged blue light from screens in modern living does stimulate the Melanopsin in our eyes. This hinders the optimum functioning of the Circadian Rhythms, causing alertness at night and drowsiness in the day.
Is Artificial lighting ethical?
The interaction between light and our physiology may also prevent deeper philosophical questions to consider. One of which being “is artificial lighting ethical?”. As I have discussed, our exposure to blue light directly affects our physiological functions including melatonin suppression, thermoregulation, heart rate, alertness and much more. So consider hospital patients, nurses, school children and office workers. These cohorts of people are all indoors under artificial lighting for prolonged periods of time and as such their health and wellbeing is in part influenced by the modulation of blue light that they are exposed too.. This may sound overly deep to consider but the research clearly presents how sensitive human beings are to lighting and the subsequent impacts on our health (school children, Hospital patients/staff, Office workers). However, we can use this knowledge to our advantage, which is the case. Research on tunable lighting presents the use of measurable light spectrums which are being implemented into dynamic lighting systems (lighting which emits light spectrums over a 24 hour period to mimic that of the natural environment, to better synchronise our Circadian rhythms). So far this approach of dynamic lighting has been considered a success in terms of participant response physiologically and psychologically. Impacts on patient welfare, cognitive functioning of students and well-being of office workers and nurses are all wider but important considerations when it comes to light exposure. Consider your own exposure to light now. Is it artificial lighting indoors? Where is it predominantly coming from? How long do you spend in true darkness?
Recommendations
Finally, based on the information I have presented and the recommendations by Dr. Satchin Panda, I would like to offer you some practical recommendations to enhance the functioning of your Circadian rhythms and as such your health and wellbeing.
Firstly, going outside outside as soon as you wake up. Make it a habit to get up and go straight outside to expose yourself to the natural morning light. Even on cloudy days in England you will be exposed to measurements of light ranging from 5000 to 10,000 lux (Lux is a standardised unit of measurement of light level intensity) bare in mind that you only need around 1000 lux to activate the Melanopsin in the eyes which signals to the SCN that it is morning time and as such the Circadian rhythm is regulated accordingly. In addition to this, you should aim to accumulate 60 minutes of exposure to natural light throughout a day. If you have a busy schedule this may sound a lot but we can break this down into manageable parts. You may do 10 minutes in the morning, 15 on a break, 25 at lunch and 10 minutes in the afternoon or after work. Doing this throughout the day provides the necessary light cues for the SCN to maintain synchronicity between the time of day and our Circadian rhythms.
Secondly, the next recommendations are to prevent the disruption of the Circadian rhythms. We should reduce light to less than 20 lux at least 1 hour before sleeping. To do this, not using electronic screens at night. I have personally set a rule of no screens after 9pm. Set your own time, something that you will stick to, maybe when the sun sets. I have found that in this time period after 9pm, where I would have previously been distracted, I am now becoming better attuned with my own mind as I am not constantly distracted or stimulated by screen time.
As well as reducing screen time, you want to do the same with artificial lighting in your home. Consider using dim lighting in the evening or candles/red lighting or even better turning everything off. Another good habit is getting out in the evening, taking this time to gaze at the stars. Doing both of these, I have found that I fall asleep much earlier and easier, promoting a much better quality of sleep. Sleep hygiene is a whole other topic for itself but in short the positive effects on health are well documented in the literature (The Extraordinary Importance of Sleep).
Finally, the last recommendation is to eat in a time restricted manner. A good example being an eating window of 8 hours (e.g. 10am till 6pm) followed by a fasting window of 16 hours (e.g. 6pm till 10am) in which no food is ingested. As I have discussed, our metabolism is intertwined with the day and night cycle. During daylight our bodies gut microbiome, hormone secretion and many other metabolic functions are heightened which most efficiently process the foods we eat. Conversely at night time different physiological functions are heightened and prioritised by the body. I discussed the Liver’s heightened time of detoxification but this is just one of many processes. Other processes such as; muscular, cellular and neurological repair and regeneration take place; signaling pathways such as cell death to remove infected and damaged cells from the body alongside many other crucial processes at night for the body to maintain a healthy state. However, eating late a night disrupts this long list of functions at night by the body and misleading cause of health issues like diabetes, obesity, gut disorders, hypertension and more. By eating in a time restricted manner which is in sync with the day and night cycle, you optimise your body's physiological functioning regarding metabolism and recovery. I find that an 8 hour eating window followed by 16 hours fasting works well for me. But eating windows up to 10 hours are shown in current research to reduce the risk of numerous chronic diseases (Ten-hour time-restricted eating). 10 hours should be realistic for most people. Set a defined eating window and reap the rewards. Additional benefits will be experienced regarding your relationship with food, discipline and financial savings.
Conclusion
The key take home is that we are truly intertwined with our environments. We are nature. We can often see/feel ourselves as separate from our environment in our modern lives which isolate us from the elements. But as discussed, the very physiological functioning of our bodies is interlaced with the rotation of the planet, the cycles of day and night, heat and cold. As such, failure to attune to these natural cycles can hinder our optimal functioning as human beings and lead to health complications. So Expose yourself to light in the day time and minimise your exposure to light and night time. Eat during day light and don’t eat at night time. Simple foundational principles to stick too.
