Light, Hormones and Peptides - Its All About Timing

Every single living creature on earth evolved under light and dark cycles, humans are no exception. Light exposure differs depending on the time of day and humans evolved being exposed to different spectra of light at various points throughout the day. For instance, during the sun’s peak at noon the spectra is well rounded with a spike in the blue range between 400-500nm. As the sun begins to set the light is scattered which creates an appearance of orange or red across the 600-700nm range. Given that humans evolved under these different spectra of light at different times of the day it would be fair to comment that human physiology is affected by daily, seasonal changes and artificial light sources.


Appropriate light exposure at specific times of the day enhances human health whereas the opposite is true if we are exposed to the wrong spectra and the wrong time of day.


Let’s now look at how the sun at the correct time of day can regulate your hormones and create wellness, reduce disease risk factors and improve sleep.




Upon waking a rise in cortisol is observed in humans. Cortisol is a hormone that causes us to be alert. Cortisol increases are associated with bright light. Therefore, upon waking human eyes need to be in front of the sun. The eye is very important in stimulating the release of neurohormones, the eye is the gateway for light to enter the brain and stimulate the release or suppression of various hormones.


If bright light exposure stimulates cortisol release then why do we need to be outside to see the sun in the mornings and not just switch on a light?


The answer to that question is lux. Humans evolved under the sun, the brightest light. No artificial light source can match the lux of the sun. Therefore, to optimize cortisol production at the correct time of the day, we need to be out watching the sunrise!



Cortisol sometimes gets a bad wrap as being a stress hormone, this is true but stress is required first thing in the morning to start the endocrinological clock, without it we would not feel alert to face the day or feel relaxed later on in the day.


We know that cortisol rises in the presence of light and we need it highest during the start of the day and lowest before bed. Exposure to artificial lights after dark increases cortisol levels which leads to chronically elevated stress levels. Eventually these stress levels can escalate into anxiety or depression. The alert feeling that is generated when cortisol is secreted is obviously very negative to have pre-bed when you need to feel relaxed.


The below graph is how cortisol should look

Sunlight exposure in the morning and blocking blue and green light after dark will make sure you are in line with the “normal curve”


Serotonin and Melatonin


Serotonin is a neurotransmitter which regulates mood, appetite and sleep. Serotonin is manufactured in the gut via sunlight entering the eye and skin. We know that serotonin production is governed by the sun as if we look at human postmortems serotonin levels are higher in those who died in summer than in those who died in winter. Serotonin governs mood, this can be observed during winter months when sunlight exposure is drastically reduced. Days shorten and cloudy skies limit the amount of sunlight exposure humans can receive. This reduces serotonin production which lowers mood. Seasonal Affective Disorder (SAD) is a common disorder characterized by low mood brought about through low serotonin production from lack of morning sunlight.


Serotonin also plays a role in sleep. Melatonin is a  tryptophan metabolite synthesized from serotonin by N-acetyl transferase. What this means is that serotonin that is created in the body through exposure to sunlight is stored up and then used to help secrete melatonin after dark. This process can only be activated without the presence of both blue and green light. During a normal circadian rhythm this would be after the sun sets. However, due to the rise of artificial lighting, post sunset looks very different today than it did ancestrally.


Exposure to blue and green artificial light after dark stops serotonin from creating melatonin in the pineal gland. Therefore, blocking blue and green light after dark becomes essential for regulating proper sleep, so make sure you are wearing blue blockers that block both blue and some green light after dark. If you do not do this you will not produce as much melatonin and your sleep quality will be lower. Lowered sleep quality means less growth and repair. Less growth and repair means more dysfunctional mitochondria which makes us more susceptible to chronic diseases. Weight gain will also occur as dysfunctional mitochondria will be less efficient in creating ATP and energy will be lost to the system. When energy is lost to a system the system will increase in mass. See the below metaphorical image of a sun losing energy to its system and eventually growing is mass.



Lower levels of serotonin = lower levels of melatonin (under the right light/dark conditions). Therefore, serotonin levels through appropriate sunlight exposure is essential to sleep.


What we do in the first part of our day impacts the hormones for sleep later in the day.


It is also worth pointing out that full visible spectrum sunlight is the only way to increase serotonin levels (diet can also play a role by consuming foods high in tryptophan but light is the best way). Exposure to artificial light does not raise serotonin levels.


The above chart shows the ideal circadian cycles of both serotonin and melatonin. The lines with less of rise are in elderly people as their eyes deteriorate, most likely through overexposure to artificial light which has caused damage to the receptors responsible for processing blue and green light.


Gaba and Dopamine


Gaba is also produced when we are exposed to sunlight. Gaba creates a sense of calm in the body. Dopamine is also stimulated and produced when exposed to sun light. Dopamine makes us feel alert and gives us a sense of well being. Both these neurohormones are vital for a well-balanced sense of wellness and worth.


Neuropeptide Y and Gastrin Releasing Peptide


These two peptides are controlled by light. Stimulus of the retina by light stimulates the release of neuropeptide Y and gastrin releasing peptide. Both these hormones have an influence in making us feel hungry. This is evidence that humans should be eating during the day when these peptides are stimulated by the sun. It is also evidence that given sunlight stimulates the release of these peptides that we should ideally be eating our meals outside under the sun.


The issue with today’s society is we often eat our largest meal of the day in the evenings under artificial light. Artificial light after dark is stimulating these hunger hormones. The problem with this is artificial lighting is causing us to feel hungry in the dark hours, when we are not supposed to. This can lead to over consumption of calories which then leads to weight gain. Ideally, we would eat in response to these peptides, ancestrally. By this I mean eating your food during day light hours, outside, and not eating after dark. This is made so much easier when we do not stimulate the release of neuropeptide Y and gastrin releasing peptide after dark through exposure to artificial lighting. Its very difficult to fight our hormones so managing them is paramount.


Growth Hormone


During the dark hours growth hormone peaks. Sleep is vital for growth and repair as we have already mentioned. Therefore, we need darkness for growth hormone to perform optimally. Good sleep is brought about through serotonin stimulating the release of melatonin. This can only occur without the presence of blue and green light. Therefore, blocking both blue and green light after dark is essential to good sleep and optimal growth hormone production.



Growth hormone governs metabolism. Therefore, a disrupted circadian cycles through exposure to artificial light at inappropriate times of the day will damage metabolism which has been shown in numerous studies.



Final Thoughts


Hormones and peptides are stimulated or suppressed by light and dark cycles. The whole animal and plant kingdom evolved under circadian light and dark cycles. In the modern world humans are not getting the correct spectra of light at the right times of day. Our modern world is characterized by lack of sunlight and overexposure to artificial light.


If we want to live a life free of mismatch diseases we need to make sure our hormonal profiles are synced correctly. The only way for us to do this is to align our circadian rhythms through correct light and dark cycles. We need to be up with the sunrise, stimulating the release of hormones and peptides, some of which will create a circadian cascade influencing release of other hormones later in the day that give us optimal sleep and health.


We need to be blocking artificial light after dark, especially blue and green light. Artificial light after dark is not allowing serotonin to work in the pineal gland to stimulate the release of melatonin. This is disrupting our sleep and leading to poor, disease laden aging. The other hormones mentioned are also affected by artificial light so its not just the common misconception that artificial light just blocks melatonin after dark. 


Light exposure/non-exposure has to be in line with natural light/dark cycles with as little exposure to artificial lighting as possible, it’s really that simple yet billions of us do not live like this and we wonder why we have a planet riddled with diseases that did not exist 200 years ago.


Optimal health and sleep is all about the timing of Light > Hormones and Peptides

















Related Articles

Leave a Reply

Your email address will not be published. Required fields are marked *