@ Sydney Bright

Introduction

It is becoming increasingly evident that sunlight is an essential nutrient for the body. To be more precise, the various wavelengths coming from the sun provide different benefits to the body, and each play a vital role in human health. Even more so, they work in concert with one another, as one wavelength may help reduce the potentially harmful effects of another. Benefits are maximized and harm reduced when we are exposed to the full breadth of this rainbow. This article will attempt to shed light on these various benefits and synergies.

To put this discussion into context, it is important to consider the overall health benefits of sunlight exposure. In a Swedish study that followed 29,000 women over 20 years, it was found that the mortality rate was doubled in those who avoided sun exposure when compared to those that didn’t (Lindqvist et al. 2016). Women who avoided the sun were twice as likely to die, primarily from cardiovascular disease, and there was no difference between death from malignant melanoma between the two groups (Lindqvist et al. 2016).

To understand why sunlight is so beneficial to health, it is important to make clear the diverse range of wavelengths that come from the sun. We typically think of the sun as a provider of both visible light and warmth. However, the spectrum of light visible to the human eye is a narrow band of the wavelengths actually emitted by the sun.

As wavelengths become shorter, visible light becomes more blue. Beyond the visible spectrum on the blue end, we arrive at ultraviolet (UV) light. On the other end of the spectrum are the longer red wavelengths. Outside of the visible window on the red side is infrared (IR) light, which provides heat. For helpful context, consider how shorter wavelengths have a harder time penetrating our atmosphere. So, the skies of dawn and dusk are predominately filled with red and near-infrared (NIR) light, while the middle of the day contains more blue and UV light. The bulk of wavelengths from the sun throughout the day are on the NIR end. The entire spectrum of visible and non-visible light between UV and IR plays critical roles in human health, especially towards mitochondrial health and metabolism. To summarize these benefits and provide a general overview for the following article, the benefits are as follows:

• UV – aids in the production of vitamin D and melanin, but also causes DNA damage
  • Vitamin D improves immune system function and can repair DNA damage
  • Melanin stores electrons for use within mitochondria
• Blue – involved in our circadian rhythm as the absence of blue light triggers the production of melatonin, an important antioxidant.
• Near-infrared (NIR) – improves mitochondria function and energy production while also protecting us from the harms of blue and UV light.

Ultraviolet Light

Let’s begin with a discussion around the widely misunderstood light of UV. UV is often viewed as a dangerous form of light, given that it can cause DNA damage and lead to cancer. While true, this myopic point of view ignores the crucial benefits of UV light. UV light produces vitamin D, which counteracts the DNA damage caused by UV while providing many other benefits. Additionally, UV light triggers the production of melanin, which aids in mitochondrial function. Like all physiological processes in the body that are vital to survival, there is a release of POMC-derived endorphins when skin comes into contact with UV light (Fell et al. 2014). Any person likely reading this article can agree that sitting under the sun simply feels amazing. We are drawn to it in a deeply meaningful sense.

Vitamin D is one of the most important chemicals regarding health, and it is poorly named. The term ‘vitamin’ refers to a compound that is important for health but cannot be adequately made within the body and must be retrieved externally. Peoples of the Northern and Southern hemisphere who are exposed to less UV light during winter would, for example, historically retrieve their vitamin D from foods such as oily fish, seal blubber, whale blubber, and polar bear liver (Wacker and Holick 2013). In a similar way, vitamin D was given its name 100 years ago when it was found that cod-liver oil was capable of curing rickets, when it was found that the so-called vitamin could promote calcium deposition in bones (McCollum et al. 1922). It was only until much later, in 1981, when scientists discovered that human skin could also synthesize vitamin D (M. F. Holick 1981). A majority of human vitamin D is produced by the skin when exposed to UVB (280 – 315 nm), while a minor amount is gained through food (Prietl et al. 2013; Wacker and Holick 2013). Most cells and organs in the human body have vitamin D receptors and many organs also have the ability to produce it, this speaks to the incredibly important nature of this compound towards our health (Prietl et al. 2013; Wacker and Holick 2013). Vitamin D deficiency has been associated with various types of cancer, autoimmune disorders, type 1 diabetes mellitus, multiple sclerosis (MS), cardiovascular disease, and even schizophrenia (Michael F. Holick 2007; Wacker and Holick 2013). Multiple studies have also found that vitamin D deficiency increases all-cause mortality (Garland et al. 2014; Yang et al. 2011; Chowdhury et al. 2014).

Though the historical benefits to vitamin D were attributed mainly to bone health, it is far more important. Vitamin D plays a critical role in protecting against invasive pathogens, reducing autoimmunity, and maintaining overall health (Wimalawansa 2023). Regarding immunity, one way it does this is by causing a shift away from proinflammatory responses to one more centered around T cell activation (Prietl et al. 2013). Vitamin D has therefore been shown to benefit other disorders that are related to immunity, such as a study that found vitamin D supplementation during pregnancy reduced asthmatic symptoms in children (Litonjua et al. 2016). That being said, it is important to highlight how there is no substitution for natural sunlight as a means of getting vitamin D. Naturally produced vitamin D from the skin lasts 2-3 times longer in the body (Wacker and Holick 2013). This is one of many likely reasons why the natural avenue should always be preferred over the supplemental. A similar line of reasoning follows in methods of getting UV light, as natural sun exposure leads to a decrease of all-cause mortality while the use of artificial tanning beds has been shown to increase all-cause and cancer mortality (Yang et al. 2011). More on why this likely occurs later.

Beyond vitamin D’s benefits to the immune system, it is important to focus on the compound’s role in mitochondrial health. In a previous article I wrote titled “Sunlight and Health”, I delve deeper into the importance of mitochondria and the science of how they work. In simplicity, imagine how all life on earth centers around energy. The sun provides energy to the earth, and the plethora of life on earth harness and facilitate the flow of that energy. Plants and animals share a symbiotic relationship within this system. Plants, through photosynthesis, take in sunlight, CO2, and water and create a glucose precursor and oxygen. This occurs within the chloroplast of plant cells. Within human cells, we have mitochondria. Our mitochondria, in turn, take in oxygen and glucose and produce CO2, water, and energy for our bodies in the form of ATP. What the plant breathes out, we breathe in, and vice versa. Mitochondria are central to all animal life on earth, and the ATP produced is central to all physiologic function. If your mitochondria are unhealthy, you are unhealthy and will experience disease.

Vitamin D plays a role in mitochondrial health at a DNA level. Our cells have DNA, which we inherited from our mother and father. On top of that, the mitochondria within our cells have their own set of DNA (mtDNA). Our mitochondria come from our mother’s egg, and therefore our mtDNA always is inherited from our mother. UV light can cause damage to both our DNA and mtDNA (Birch-Machin, Russell, and Latimer 2013). This is what gives UV light the ability to cause cancer. Additionally, damage to the mtDNA within our mitochondria can lead to mitochondrial dysfunction. The more poorly our mitochondria function, the less energy we produce for our cells, and the less healthy our cells become. There is research being developed that suggests the role of vitamin D is to counterbalance this danger by regulating gene transcription and reducing mtDNA damage. A mouse study conducted in 2011, for example, found that different shapes of vitamin D reduce the development of tumors in mice following UV exposure (Dixon et al. 2011). It is not unlike nature to create a system of checks and balances, to ensure that the damaging effects of UV light are counterbalanced by a compound produced by the body when exposure to that same light.

While vitamin D may be important for mitochondrial health by protecting against mtDNA damage, melanin potentially plays a much larger role. Melanin is the pigment in our skin that make us darker. Not only is the diversity in skin tones across humans due to variations in melanin content, but a tan is also the creation of more melanin. To be more specific, the skin’s exposure to UVA (315-400nm) leads to the creation of melanin (Wicks et al. 2011). The most obvious benefit to the production of melanin, which most people could appreciate, is that the darker or tanner our skin is, the less damage we will receive from UV light. In this way, melanin shares a similar responsibility to vitamin D, where both are protecting the body against the very thing that forms them. Even more crucially however, melanin acts as a battery for the mitochondria.

During cellular respiration, where mitochondria turn oxygen and glucose into energy, electrons are stripped from the glucose for use. In other words, what our mitochondria really need are oxygen and electrons, and the glucose is simply a means to an end. If the mitochondria are the engine, then the electrons are the fuel (assuming you are still breathing). Due to its chemical structure, melanin is a natural reversible oxidation-reduction system (Figge 1939). In other words, it can both store and release electrons. Melanin is therefore a kind of battery, retrieving electrons from various sources, and storing them for future use in our mitochondria as a substitute for food. When stated this way, and considering how food is important because both fats and carbohydrates fuel the body by providing electrons to our mitochondria, one can imagine how vitally important melanin is. Melanin is central towards the availability of electrons for use in our body to produce the energy to live. Without adequate melanin, your mitochondria will starve for fuel and not provide your body with the energy it needs to thrive.

Blue Light

To contextualize the role blue light plays in human health, it is important to revisit an important byproduct of cellular respiration within mitochondria. When mitochondria turn electrons and oxygen into energy, there is a byproduct formed known as reactive oxygen species (ROS). ROS play important roles in the body, but in excess they can cause DNA damage and disrupt various cellular processes. For example, UV light causes cancer due to the ROS generated, and studies have found that blue light does the same in both the skin and eyes (Nakashima, Ohta, and Wolf 2017; Abdouh et al. 2024). This research suggests that excess blue light or blue light in isolation can damage the eyes and cause harm like UV light.

Blue and UV light are predominant during the middle of the day. Though both may cause oxidative stress on the body, the body simultaneously counteracts this damage through melatonin. Think of melatonin as the junk remover for mitochondria. Throughout the day mitochondria produce energy, and ROS is formed. During our nighttime sleep, melatonin plays an important role as an antioxidant and removes the excess ROS (Leon et al. 2004).

The relationship between blue light and melatonin is important. During the day, when blue light is present, our body suppresses the production of melatonin (West et al. 2011). When the sun sets and there is no longer a heavy presence of blue light, our body begins to produce melatonin for sleep. This is a central function for how our body gets tired at night and gets ready for sleep. This is also why artificial light at night, from our modern technology, is harmful to human health because it tricks the body into the continual suppression of melatonin production. Without proper melatonin production, our cells buildup too much ROS and this can cause mitochondrial dysfunction and other sleep related issues.

Beyond the importance of getting good sleep and producing melatonin to remove excess ROS from our cells, the existence of artificial light and excess blue light is problematic during the day as well. As stated previously, blue light causes ROS buildup in both the skin and eyes (Nakashima, Ohta, and Wolf 2017; Abdouh et al. 2024). As with most harms from sunlight, our body has adapted with a backup plan. During the day, when blue and UV light is present, there is simultaneous exposure to NIR light (650-1200nm). Recent research suggests that NIR also counterbalances the harm of blue light by increasing melatonin synthesis in the mitochondria (Tan et al. 2023). This highlights the importance of receiving the full spectrum of light from the sun, as one wavelength counterbalances the damages of the other.

Near-Infrared Light

While indoor living has been commonplace for humans across generations, and modern technology has over saturated our bodies with blue light, some recent changes to our technology have made things worse. Incandescent light bulbs emit NIR light, this is why they got warm. However, LED lights do not emit NIR light. Therefore, where people of past generations were potentially exposed to a lot of artificial light at night, this was counterbalanced by the NIR emitted by those same lightbulbs. Now, modern humans use LEDs and spend 93% of our time indoors with zero exposure to NIR, which is 90% of the light emitted by the sun (Tan et al. 2023).

Not only does NIR light protect our bodies from the damaging consequences of blue light, but it similarly protects us against UV light. As stated previously, NIR may result in the production of melatonin within mitochondria during the day, helping protect against the ROS buildup and mtDNA damage. Additionally, research has also found that NIR light protects from UV light in other ways. For example, a study in 2008 found that pretreating skin with NIR light (660nm) prevented sunburns (Barolet and Boucher 2008). Another study found that red and NIR light (620-690nm) altered gene expression and upregulated DNA repair (Kim et al. 2019). Again, this highlights the theme that the body has produced the means to protect itself from the harms of the sun via other rays emitted. However, the protection from harmful rays is best achieved when exposed to the full spectrum of light wavelengths as they change throughout the day. The light of dawn and dusk is predominately red and NIR. Therefore, this research suggests that being exposed to morning light will protect the body from the potentially cancer-causing effects of the UV light later in the day. A human being who lived outside would naturally be exposed to this spectrum of light every day. However, modern humans may be inside in the morning, go to the beach during the middle of the day, and get sunburned because they do not properly receive the full spectrum of light as nature intended every day.

Lastly, it is important to explore the ways NIR improves mitochondrial function. If electrons are the fuel source for this engine, and melatonin is the junk removal, then NIR is the lubricant. NIR improves the energy output of mitochondria, and there are various hypotheses for how this occurs. One hypothesis is that NIR boosts the functionality of cytochrome c oxidase, one of the chromophores used in the electron transport chain (ETC) of cellular respiration within mitochondria (De Freitas and Hamblin 2016). Another involves NIR light’s ability to modify the viscosity of water which increases the efficiency of the final step in the ETC, the ATP synthase (Sommer, Haddad, and Fecht 2015). ATP synthase can be thought of as a kind of pump that produces ATP, in this way NIR can be thought of almost literally as a lubricant for this pump.

Summary

In summary, the research involving how sunlight affects mitochondrial health highlights the importance of the full spectrum of wavelengths, each of which plays a vital role in human health throughout the day. Having exposure to one, without the other, can lead to imbalances and mitochondrial disease. The red and NIR light in the morning helps our mitochondria produce more energy throughout the day, while also preparing our bodies for the beneficial yet dangerous wavelengths to come. In the middle of the day, we receive much more UV and blue light, which help us produce vitamin D and melanin, both central to health and wellness. Once the sun sets, and blue light is absent, we produce melatonin for sleep. During our sleep, the melatonin removes the dangerous byproducts of our energy-producing day, protecting us from disease and preparing us for the following day. Mitochondria are central to human health and life on earth, and the rays from the sun are central to mitochondrial health.

Respecting nature and its cycles is vital for us humans who are increasingly immersing ourselves in a world dominated by technology. Our ancestors did not have to reconcile with these ideas, because life forced these exposures upon them. If we wish to maintain health in our modern world, we must be able to find balance. Even though some might think they can escape into the virtual world, our bodies will always and forever be connected and reliant upon the natural one.

References

Abdouh, Mohamed, Yunxi Chen, Alicia Goyeneche, and Miguel N. Burnier. 2024. “Blue Light-Induced Mitochondrial Oxidative Damage Underlay Retinal Pigment Epithelial Cell Apoptosis.” International Journal of Molecular Sciences 25 (23): 12619.

Barolet, Daniel, and Annie Boucher. 2008. “LED Photoprevention: Reduced MED Response Following Multiple LED Exposures.” Lasers in Surgery and Medicine 40 (2): 106–12.

Birch-Machin, M. A., E. V. Russell, and J. A. Latimer. 2013. “Mitochondrial DNA Damage as a Biomarker for Ultraviolet Radiation Exposure and Oxidative Stress.” The British Journal of Dermatology 169 (s2): 9–14.

Chowdhury, Rajiv, Setor Kunutsor, Anna Vitezova, Clare Oliver-Williams, Susmita Chowdhury, Jessica C. Kiefte-de-Jong, Hassan Khan, et al. 2014. “Vitamin D and Risk of Cause Specific Death: Systematic Review and Meta-Analysis of Observational Cohort and Randomised Intervention Studies.” BMJ (Clinical Research Ed.) 348 (apr01 2): g1903.

De Freitas, Lucas Freitas, and Michael R. Hamblin. 2016. “Proposed Mechanisms of Photobiomodulation or Low-Level Light Therapy.” IEEE Journal of Selected Topics in Quantum Electronics: A Publication of the IEEE Lasers and Electro-Optics Society 22 (3): 348–64.

Dixon, Katie M., Anthony W. Norman, Vanessa B. Sequeira, Ritu Mohan, Mark S. Rybchyn, Vivienne E. Reeve, Gary M. Halliday, and Rebecca S. Mason. 2011. “1α,25(OH)₂-Vitamin D and a Nongenomic Vitamin D Analogue Inhibit Ultraviolet Radiation-Induced Skin Carcinogenesis.” Cancer Prevention Research (Philadelphia, Pa.) 4 (9): 1485–94.

Fell, Gillian L., Kathleen C. Robinson, Jianren Mao, Clifford J. Woolf, and David E. Fisher. 2014. “Skin β-Endorphin Mediates Addiction to UV Light.” Cell 157 (7): 1527–34.

Figge, Frank H. J. 1939. “Melanin: A Natural Reversible Oxidation-Reduction System and Indicator.” Experimental Biology and Medicine (Maywood, N.J.) 41 (1): 127.

Garland, Cedric F., June Jiwon Kim, Sharif Burgette Mohr, Edward Doerr Gorham, William B. Grant, Edward L. Giovannucci, Leo Baggerly, et al. 2014. “Meta-Analysis of All-Cause Mortality According to Serum 25-Hydroxyvitamin D.” American Journal of Public Health 104 (8): e43-50.

Holick, M. F. 1981. “The Cutaneous Photosynthesis of Previtamin D3: A Unique Photoendocrine System.” The Journal of Investigative Dermatology 77 (1): 51–58.

Holick, Michael F. 2007. “Vitamin D Deficiency.” The New England Journal of Medicine 357 (3): 266–81.

Kim, Hyun Soo, Yeo Jin Kim, Su Ji Kim, Doo Seok Kang, Tae Ryong Lee, Dong Wook Shin, Hyoung-June Kim, and Young Rok Seo. 2019. “Transcriptomic Analysis of Human Dermal Fibroblast Cells Reveals Potential Mechanisms Underlying the Protective Effects of Visible Red Light against Damage from Ultraviolet B Light.” Journal of Dermatological Science 94 (2): 276–83.

Leon, Josefa, Dario Acuña-Castroviejo, Rosa M. Sainz, Juan C. Mayo, Dun Xian Tan, and Russel J. Reiter. 2004. “Melatonin and Mitochondrial Function.” Life Sciences. Elsevier Inc. https://doi.org/10.1016/j.lfs.2004.03.003.

Lindqvist, P. G., E. Epstein, K. Nielsen, M. Landin-Olsson, C. Ingvar, and H. Olsson. 2016. “Avoidance of Sun Exposure as a Risk Factor for Major Causes of Death: A Competing Risk Analysis of the Melanoma in Southern Sweden Cohort.” Journal of Internal Medicine 280 (4): 375–87.

Litonjua, Augusto A., Vincent J. Carey, Nancy Laranjo, Benjamin J. Harshfield, Thomas F. McElrath, George T. O’Connor, Megan Sandel, et al. 2016. “Effect of Prenatal Supplementation with Vitamin D on Asthma or Recurrent Wheezing in Offspring by Age 3 Years: The VDAART Randomized Clinical Trial.” JAMA: The Journal of the American Medical Association 315 (4): 362–70.

McCollum, E. V., Nina Simmonds, J. Ernestine Becker, and P. G. Shipley. 1922. “Studies on Experimental Rickets.” The Journal of Biological Chemistry 53 (2): 293–312.

Nakashima, Yuya, Shigeo Ohta, and Alexander M. Wolf. 2017. “Blue Light-Induced Oxidative Stress in Live Skin.” Free Radical Biology & Medicine 108 (July): 300–310.

Prietl, Barbara, Gerlies Treiber, Thomas R. Pieber, and Karin Amrein. 2013. “Vitamin D and Immune Function.” Nutrients 5 (7): 2502–21.

Sommer, Andrei P., Mike Kh Haddad, and Hans Jörg Fecht. 2015. “Light Effect on Water Viscosity: Implication for ATP Biosynthesis.” Scientific Reports 5 (July). https://doi.org/10.1038/srep12029.

Tan, Dun-Xian, Russel J. Reiter, Scott Zimmerman, and Ruediger Hardeland. 2023. “Melatonin: Both a Messenger of Darkness and a Participant in the Cellular Actions of Non-Visible Solar Radiation of near Infrared Light.” Biology 12 (1): 89.

Wacker, Matthias, and Michael F. Holick. 2013. “Sunlight and Vitamin D: A Global Perspective for Health: A Global Perspective for Health.” Dermato-Endocrinology 5 (1): 51–108.

West, Kathleen E., Michael R. Jablonski, Benjamin Warfield, Kate S. Cecil, Mary James, Melissa A. Ayers, James Maida, et al. 2011. “Blue Light from Light-Emitting Diodes Elicits a Dose-Dependent Suppression of Melatonin in Humans.” Journal of Applied Physiology (Bethesda, Md.: 1985) 110 (3): 619–26.

Wicks, Nadine L., Jason W. Chan, Julia A. Najera, Jonathan M. Ciriello, and Elena Oancea. 2011. “UVA Phototransduction Drives Early Melanin Synthesis in Human Melanocytes.” Current Biology: CB 21 (22): 1906.

Wimalawansa, Sunil J. 2023. “Infections and Autoimmunity-the Immune System and Vitamin D: A Systematic Review.” Nutrients 15 (17): 3842.

Yang, Ling, Marie Lof, Marit Bragelien Veierød, Sven Sandin, Hans-Olov Adami, and Elisabete Weiderpass. 2011. “Ultraviolet Exposure and Mortality among Women in Sweden.” Cancer Epidemiology, Biomarkers & Prevention: A Publication of the American Association for Cancer Research, Cosponsored by the American Society of Preventive Oncology 20 (4): 683–90.