Why is circadian biology the secret sauce that everyone needs to tap into? Well, let us tell you about the inner workings of our body that few too many are aware of. The SCN is the central system for our circadian timing system. These receptors are present in the eye as well as the skin. This system governs our cellular biology and is the reason why light exposure has such a profound impact on our health. Our skin and eyes both absorb light (whether natural or artificial). Both of these rhythms are meant to be in tune with one another so that they operate in harmony. Living organisms spend a 24-hour day getting energy, directing that energy to various bodily functions, protecting themselves, repairing and healing, and reproducing. Every single function that plays a role in these processes is governed by a circadian clock. The efficiency and effectiveness of these tasks are dependent on synchronicity within these systems. The human body is composed of millions of cells that work differently depending on their location. They all, however, have the same genome (genes from our DNA) that carry out biochemical processes including our circadian timing system. The expression of our genes directly impacts the health of our organs, disease susceptibility, and how we feel. The correlation between the functioning of these organs and bodily systems and the circadian clock is that these clock genes all give a circadian cycle that turns on and off at various times of the day and that is dependent on our light environment. This means that the light our eyes and skin are exposed to directly influences every single cell within our body. Not only that but these cells all communicate with one another and to work optimally should be synchronized and working together. They can only do this if nothing interferes with their on-and-off cycles. Modern-day exposure to artificial light and under-exposure to natural light has drastically influenced these cycles, and therefore functions of the bodily systems which has led to a rapid decline in health across the population. 

The most profound tool everyone has access to is the sun. Increasingly underutilized and even feared the sun is easily one of the most effective healing modalities we have access to. One that is responsible for many of our body’s functions. Our cells are designed to respond to various components of ultraviolet (UV) and infrared light. Our species has lived under and been consistently exposed to natural sunlight for the entirety of our existence. It is only in recent history that we have swayed from this and turned to, toxic sunscreen, avoidance, artificial lighting, and indoor living. It is no coincidence that our health has begun to deteriorate as a consequence. The day is triggered by light and signals the time for activity. Rest and regeneration are signaled by dark and is the time for sleeping. Light and dark control hormones via the pituitary and pineal glands. Both are vital to our well-being. Let’s break down the varying types of light the sun emits and what the purpose they serve within our biology.  


Different types of sunlight

Ultraviolet A (UVA) is a longer spectrum of light that is present year-round and plays a vital role in 

• Mood regulation
• Lowering blood pressure
• Hormonal balance— Including sex + stress hormones
• Natural sun protection 
• Immune system regulation
• Blood sugar
• Anti-inflammatory processes 
• Anti-microbial effects

UVA stimulates the release of nitric oxide which widens blood vessels increasing blood flow. Increased blood flow is critical to brain function (and therefore emotional regulation). Nitric oxide normalizes blood sugar, lowers inflammation, and is both anti-microbial and anti-tumor. Ultraviolet A is essential to long-lasting melanin. Melanin is the body’s natural way of protecting your skin from the negative effects of UV light. With 99.9% efficiency, melanin converts UV light into harmless heat in turn protecting your skin and DNA. 

Hormones produced by UVA

• Beta-endorphins— Responsible for pain management 
• Serotonin— Responsible for mood, sleep, digestion, libido, and healing processes.
• Dopamine— Responsible for a sense of well-being, movement, memory, the brain reward systems, and motivation

Ultraviolet B (UVB) has shorter wavelengths and the intensity varies by geographical location as well as time of year. Solar noon refers to the peak UV time each day it is when ultraviolets are at their highest intensity (the sun is highest in the sky). UVB is critical to 

• Bone health
• Endocrine function
• Immune system
• Natural sun protection 
• Metabolism regulation
• Gut health
• Brain function 

UVB triggers vitamin (hormone) D production. The hormone often referred to as vitamin D is responsible for regulating over 2000 genes in the body, maintaining bone health, immune +endocrine support, nervous system function, and the cardiovascular system. Deficiency may lead to a presentation of symptoms that include chronic fatigue, neurodegenerative diseases, depression, autoimmune disorders, cancer, and more. UVB boosts the neurotransmitter glutamate. Glutamate plays an essential role in our cognitive function, the production of endorphins (feel-good hormones & pain relief), regulating our metabolism, as well as rapidly influencing our gut microbiome. 

Blue light whether emitted from the sun or artificial light induces steroid hormones. 

Steroid hormones are

• Cortisol
• Estrogen 
• Testosterone 

These hormones are meant to maintain a delicate balance between the production and the destruction of them. While UVB produces them, UVA destroys them. This balance allows for homeostasis within the body and when overproduced without effectively ridding them steroid hormones can lead to stress, inflammation, and the symptoms associated with each. 

Red and infrared light represent the longest wavelength on the spectrum. They are critical to 

• Cellular repair and regeneration 
• Lowered inflammation
• The creation of new blood vessels
• Increased circulation
• Wound healing
• Activation of stem cells
• Stimulating energy production
• Enhancing cognitive function
• Reducing anxiety + depression

The creation of new blood vessels, increased circulation, and triggering energy production within mitochondria allows deeper oxygenation into cells and allows them to rapidly heal and repair. Chlorophyll compounds within cells capture sunlight and turn it into energy. This process activates the pathways responsible for healing and restoration across the body including the brain. 

The digestive system

The phases of digestion all have a circadian component relating to their efficiency in the day vs the night 

1. Saliva: Saliva production is up to 10 times more productive during the day. Saliva neutralizes any stomach acid that can come up the esophagus. Given that this is less active during the night, eating late at night can produce excess acid and lead to reflux symptoms. 
2. Gut Lining: The repair and regeneration of our mucosal lining in the gut is a circadian process. When sleeping our brain secretes the growth hormone that triggers the gut lining to repair damaged (leaky) cells. We need deep restorative sleep for these processes to play out effectively. 
3. Meal density & Timing: The secretion of stomach acid is high at night before we sleep. When we eat more production is stimulated. When you eat dense meals at night you are increasing this production significantly more than what would have happened earlier in the day. As the intestinal portion of digestion slows later in the day, the food consumed late at night sits for a longer period in the acidic environment of the stomach and can come back up again producing acid reflux symptoms causing damage to the esophagus and teeth. 
4. Gut motility: Gut motility refers to the movement of food and nutrients through the intestines. The muscles contract and expand pushing the food forward. This movement is notably more active during the day and is very slow at night. When we eat late at night our food cannot move through the intestinal tract at the speed that it should and this impacts our muscles in the stomach and GI tract. 
5. Gut microbiome: The GI tract is filled with microbes and bacteria. These all grow and thrive in various environments and respond and multiply at different times of day. The composition of the gut microbiome changes between day and night and the bacteria present is different at night, in the morning, and in the afternoon. These microbes have different roles in digestion and are a part of breaking down different nutrients. This is why the diversity of the microbiome is so important. When the circadian rhythm is disrupted the shifting of the gut environment is hindered which directly influences the health and presence of the varying microbes. Elements such as poor sleep, artificial light at night (phones, shift working, etc), and constant travel to different time zones all can impact our circadian rhythm and therefore gut health. 

Benefits of eating at consistent times with optimal space between bedtime:

• Diverse + healthy gut microbiome
• Regular + healthy bowel movements
• Improved liver function
• Reduced inflammation 
• Balanced cholesterol levels
• Normal blood sugar levels
• Reduced fat mass
• Improved sleep quality
• Kidney support
• Cardiovascular support
• Optimized brain function (including mood, emotional regulation, and concentration abilities)

The timing of our circadian clock within the digestive system is a core foundation to support the function of the rest of the systems within our body as well as our ability to get restorative sleep.

Sleep

From the moment we wake up SCN tracks our wake time and for every hour we’re awake our body needs 20-30 minutes of sleep. The organ’s genes and clocks synchronize with one another to create optimal conditions for rest and sleep. Melatonin production, lower heart rate, and lower body temperatures are all signaled so that when the time for sleep comes you are fully equipped and ready. Sleep debt refers to the amount of sleep you should get vs how much you are getting. Generally speaking, adults need 8 hours of rest and 7 of sleeping time. Children need 10 hours of rest and 9 hours of sleep. When you fall short of this (or have had disrupted sleep at night) then you are going into “debt” when you awake in the morning. Over time this debt builds and impacts the body’s ability to function. This sleep debt signals to the brain that it needs more sleep, however, your circadian system will still trigger you to wake. Naps do help make up for sleep debt and are a great way to add additional support and balance if you have disrupted sleeping routines. 

Simple, yet supportive

1. Sunrise— Exposing your eyes, and as much skin as possible, to early sunrise is priming your body for your day. Sunrise light only consists of infrared and red light, there is no UV. This means that you are reaping all of the benefits of infrared light without any UV. Infrared light stimulates energy production and prepares your body for UV light. This is the prime time to prep your skin for UV light, especially as you begin increasing sun exposure. The blue light present in the light initiates hormone production (waking you up). The blue light photoreceptors in the eyes pass information to the suprachiasmatic nucleus (SCN). In addition to the many healing properties of infrared light, the early morning sun also supports both your mood and brain function as well as sleep. 

2. Sunset— As the light spectrum changes your eyes respond to this and entrain your circadian rhythm by triggering the biological wind-down routines within the body. These wind-down routines include melatonin release as the blue light begins to vanish. This signals the body to stop producing stress hormones. The key here is to avoid blue light entirely after sunset so your body can activate its rest and repair systems. Artificial light signals that more stress hormones need to be released and disrupt the natural state of being. Additionally, sunset is void of all UV light and full of red and infrared light. This is important at the end of the day because it allows your cells to repair any “damage” from UV exposure throughout the day. Light is all about balance. The quality of our sleep relies on the absence of artificial light after sunrise. To read more about the importance of sleep and its impact on your health read here.

After the sunsets, some tools can be utilized to limit/remove blue light exposure. 

• Red light bulbs (with 0% blue light) can be used in place of other lighting
• Candles contain zero artificial light and are an excellent circadian-friendly option
• Blue light-blocking glasses as well as covering your body with hoodies/pants/etc (remember your skin as light receptors) is another way to support your circadian rhythm at night.  

3. Solar noon- UV light peaks at solar noon. This timing is dependent on geographical location. This is the time of day when UVB is most potent and therefore expedites the amount of vitamin D, as well as other hormones, that your body can create. While regular exposure at varying times of the day is critical to supporting and strengthening your circadian system, solar noon is a great opportunity to maximize benefits. Be sure that you have spent sufficient time building your internal sun protectant before jumping outside at this time. If you have tendencies to burn or have not spent time outside then you would only want to be out at this time for a very short amount of time while you work on building your sun callus. 

4. Exercise— Exercising, in all of its forms, at the same time every day is essential to your circadian rhythm. It allows your body to know exactly when to expect a hormonal shift as your body exerts itself. A huge bonus to exercise outside. 

Your body can tell time through movement. Exercising in the early morning is an excellent cue to the start of your day. This resets your peripheral clocks including skeletal muscles, the cardiovascular system, and the digestive tract.

Some of the benefits of early morning exercise

• Increased alertness and focus
• Improved sleep
• Better energy throughout the day
• Hormonal regulation
• Blood pressure
• Blood sugar 

In the late afternoon body temperature peaks. This improves nerve conduction speed, joint mobility, blood flow, and glucose metabolism. Exercise before dinner, followed by a nutrient-dense meal, can aid in recovery, muscle growth, and muscle repair. It is important to live adequate time between exercise and bedtime so that your body can fully enter its healing and restorative state before sleeping. Aim for at least a 2-hour gap between workouts and bedtime. 

There are varying benefits to exercise times— Remember exercise doesn’t only include the gym. Even walking at these times offers immense support. Consistent timing of movement is the most crucial component of circadian support. 

5. Eating! Meal times kickstart the metabolic system, digestive clock genes, and hormones. Consistent meal times entrain your body to be ready to metabolize your food. When food is eaten regularly at the same time of day the clock genes work together and drastically improve digestion, gut microbiome, and bowel movements. In-between meal times is when your digestive organs are repairing. This resting time allows optimal function in your organs. They need breaks to perform at their best. 

In the morning we metabolize food the most effectively and is a great time to eat a dense meal. As we approach sunset our digestive system begins to slow down. Your last meal should be eaten 3-4 hours before bed to support cellular repair, sleep energy, gut health, and overall well-being.

Eating outside under the sun is an incredibly healing habit for your gut health. The genes and cells in your digestive tract respond to the light frequency and are better supported for optimal function. The UV light is incredible for your gut microbiome. 

The two most important takeaways are time outside and consistency in routine are the best things you can do for your circadian system! There are many tiny habits and shifts you can begin to make to support these foundations and over time they will integrate into your physical and mental routine. The benefits of syncing your circadian clock to your light environment are monumental for your health and well-being.