Benefits of Sunlight for Health: How Light Impacts Your Body, Brain, and Sleep

Benefits of Sunlight for Health: How Light Impacts Your Body, Brain, and Sleep

Light—the very word often evokes images of warm sunrays streaming through a bedroom window in the early morning, a bright summer day at the beach, or the simple act of flipping on a light switch at night. While these associations are familiar and comforting, light is far more than a convenience or a pleasant experience. It is one of the most powerful and fundamental forces influencing human health.

At LIVENBREATHE, the “L” stands for Light—with a primary focus on the importance of sunlight, while also recognizing the therapeutic value of artificial light sources, such as blue, white, red, and infrared light therapies. From cellular energy production to mood regulation, sleep quality, immune function, and chronic disease prevention, light plays a role that cannot be overstated.

Overview

This article explores why light is so essential to life and health, how sunlight affects vitamin D production, mood, sleep, and circadian rhythms, and why emerging research into infrared and photobiomodulation therapies is reshaping modern wellness.

All guidance is based on peer-reviewed research and clinical recommendations.

Important note: This content is for educational purposes only and is not a substitute for medical advice. Individual needs vary based on health status, medications, and environment.

Sunlight: The Foundation of Life on Earth

Sunlight is not just beneficial—it is equivalent to life itself. The sun is the primary sustaining energy source for nearly all living organisms on Earth. This is why natural light exposure is so important. Plants convert sunlight into chemical energy through photosynthesis, forming the foundation of the global food chain. Humans and animals depend on plants either directly or indirectly for nutrition.

Sunlight also powers evaporation, which drives the water cycle and regulates global weather patterns. This matters greatly for humans, as the human body is composed of approximately 60–70% water¹, and hydration is critical for every physiological process, from temperature regulation to cellular transport and detoxification.

When viewed through this lens, it becomes clear why sunlight is inseparable from human survival and health.

The Spectrum of Sunlight and Its Biological Effects

Natural sunlight contains a broad spectrum of electromagnetic wavelengths, ranging from far infrared (greater than 2000 nm) to ultraviolet radiation (280–400 nm)². Each portion of this spectrum interacts with the human body in unique ways.

• Ultraviolet (UV) light influences vitamin D synthesis and immune regulation

• Visible light affects mood, alertness, and circadian rhythms

• Infrared (IR) light penetrates deeply into tissues, influencing cellular energy production and inflammation

Unlike artificial indoor lighting, sunlight provides this complete and balanced spectrum, which is why outdoor light exposure has such profound biological effects.

Vitamin D and Sunlight: Why Deficiency Is a Modern Epidemic

Among sunlight’s many health effects, its role in vitamin D production is one of the most critical and well-researched.

Despite its importance, modern lifestyles have drastically reduced sun exposure. Studies show that the average person spends 93% of their time indoors³. While 96% of adults go outside daily, more than half (58.8%) spend one hour or less per day outdoors⁴. Even children now spend just four hours per week playing outside⁵.

As a result, an estimated 42% of Americans are vitamin D deficient⁶, a statistic with serious implications for public health.

How UVB Light Triggers Vitamin D Production

Vitamin D synthesis is a remarkable biological process triggered specifically by UVB radiation from the sun.

• The sun emits approximately 500 times more UVA than UVB rays⁷

• UVA rays penetrate deeply and contribute to skin aging and certain cancers

• UVB rays, though less abundant, are responsible for sunburn—and critically—vitamin D production

When UVB rays strike the skin, they convert a cholesterol derivative called 7-dehydrocholesterol into previtamin D₃. This compound then undergoes thermal changes to become vitamin D₃ (cholecalciferol).

Vitamin D₃ is further processed:

• In the liver, it becomes calcidiol (25-hydroxyvitamin D)—the form measured in blood tests

• In the kidneys, it is converted into calcitriol, the biologically active form that regulates calcium, immune function, and gene expression

While this process may sound complex, it underscores a critical truth: sunlight initiates a cascade essential to human health.

Health Benefits of Optimal Vitamin D Levels

Vitamin D is fundamental for:⁸

• Calcium absorption in the intestines

• Bone density and skeletal strength

• Muscle contraction, including heart muscle

• Neuronal signaling in the brain and spinal cord

Low vitamin D levels are associated with:

• Vascular dysfunction

• Arterial stiffening

• Left ventricular hypertrophy

• Elevated cholesterol and lipid disorders

Observational studies consistently show that higher serum vitamin D levels are linked to reduced cardiovascular disease risk and mortality⁹.

Additionally, vitamin D plays a role in:

• Reducing inflammation

• Regulating immune responses

• Supporting glucose metabolism

• Modulating cell growth

Populations living in regions with fewer daylight hours show higher rates of colon, pancreatic, prostate, and ovarian cancers, suggesting a protective role of sunlight and vitamin D exposure¹⁰.

Sunlight and Mental Health: Depression, Mood, and Serotonin

Light doesn’t only affect physical health—it profoundly influences mental and emotional well-being.

Sunlight and Depression

Light therapy has long been used as an effective treatment for depression, particularly seasonal affective disorder (SAD). One key reason is its impact on serotonin, a neurotransmitter associated with calmness, happiness, and emotional stability.^11.

While approximately 90% of serotonin is produced in the gut, serotonin is also produced¹²:

• In the retina of the eyes by amacrine neuron cells

• In the raphe nuclei of the brainstem

When bright light enters the eyes, specialized retinal cells send signals to serotonin-producing neurons through what is known as the retino-raphe tract. Although brain-produced serotonin accounts for a smaller percentage overall, it has a disproportionately powerful effect on mood because it doesn’t have to pass through the blood brain barrier.¹³

Research shows that serotonin production increases with both sunlight intensity and duration, and drops significantly during winter months—helping explain the prevalence of seasonal affective depression.

Here’s an interesting fact, Vitamin D also directly supports serotonin synthesis by activating the genes responsible for its production in the brain, offering another explanation for why sunlight exposure improves mood and emotional resilience.¹⁴

Sunlight and Sleep: How Light Affects Circadian Rhythm

Healthy sleep would not be possible without regular exposure to natural light.

Sunlight helps regulate the circadian rhythm, the internal biological clock that controls sleep-wake cycles, hormone release, metabolism, and organ function.

Scientific evidence mounting over the last decades has unveiled the location of the mammalian “master biologic clock” in the paired suprachiasmatic nuclei (SCN) of the anterior hypothalamus.¹⁵

Here’s how it works:

• In response to sunlight, the photopigment melanopsin in the retina signals to the SCN environmental brightness, which then directs the Pineal gland to convert dietary tryptophan into serotonin which gets stored in the gland

• As darkness falls, the SCN again directs the Pineal gland to convert serotonin into melatonin by the enzyme AANAT¹⁶, and is released into the bloodstream to facilitate sleep onset

• Cortisol is activated by morning light and also rises during the day, promoting alertness and energy

• As darkness falls, cortisol levels drop making way for melatonin to facilitate sleep onset

Melatonin release follows a smooth, bell-shaped curve at night. Likewise, cortisol follows a similar curve but peaks during the day. The quality of these curves directly correlates with:

• Overall health of the circadian rhythm

• Sleep depth

• Sleep duration

Disrupted light exposure—especially insufficient daylight and excessive artificial light at night—leads to poor sleep, metabolic dysfunction, and impaired mental health.¹⁷

This entire process orchestrated by the SCN in response to sunlight is complex but essential for life. Dr. Jacob Liberman OD, Ph.D explains that light acts as a biological guide, transmitting time-of-day information to trillions of cells.¹⁸

Infrared Light Therapy and Photobiomodulation Benefits

Beyond visible and UV light, infrared (IR) wavelengths play a crucial but often overlooked role in human health.

Near-infrared light (750–1100 nm) makes up approximately 54% of the solar radiation¹⁹ that reaches Earth. Research suggests it plays an essential role in sustaining life by supporting mitochondrial function and cellular energy production.

Photobiomodulation (PBM) therapy—using red and near-infrared light—has been studied since the 1960s and has demonstrated benefits for:

• Wound healing

• Pain reduction

• Inflammation control

• Hair growth

• Depression

Optimal therapeutic wavelengths range from 630 to 850 nm, with carefully controlled energy doses.

Infrared light has been shown to:^20-21

• Boost metabolism

• Increase ATP production in mitochondria

• Stimulates melatonin production in mitochondria which is acts as a potent antioxidant, thus reducing oxidative stress

• Improve blood flow via nitric oxide release

• Enhance cognitive performance

• Reduce PTSD symptoms

• Traumatic brain injury recovery

These findings highlight that sunlight’s benefits extend far beyond what we can see with the naked eye.

Why Light is a Cornerstone of Total Wellness

From vitamin D synthesis and cardiovascular protection to mood regulation, sleep quality, and cellular energy production, light is one of the most powerful determinants of human health.

Modern lifestyles—characterized by indoor living, artificial lighting, and limited sun exposure—have distanced us from a health necessity fundamental to the proper functioning of our light-driven biological clocks. 

For this reason, no discussion of health and wellness is complete without acknowledging the essential role of light.

In the next installment, we’ll explore how much sunlight you actually need to receive these benefits safely and effectively—so stay tuned.

Key Takeaways

• Light—especially natural sunlight—is essential for human life, health, and energy.

• Sunlight drives vitamin D production, which supports bone, cardiovascular, immune, and mental health.

• Modern indoor lifestyles significantly reduce light exposure, contributing to widespread vitamin D deficiency.

• Sunlight helps regulate mood by increasing serotonin and plays a key role in preventing depression and seasonal affective disorder.

• Light exposure during the day is critical for maintaining a healthy circadian rhythm and deep, restorative sleep at night.

• Infrared and red light support cellular energy, reduce inflammation, enhance healing, and improve mitochondrial function.

• Light acts as a biological signal, guiding cellular activity through photobiomodulation.

References

1. The Water in You: Water and the Human Body. USGS. (n.d.). https://www.usgs.gov/special-topics/water-science-school/science/water-you-water-and-human-body

2. Kift, R. C., & Webb, A. R. (2024a). Globally estimated UVB exposure times required to maintain sufficiency in vitamin D Levels. Nutrients, 16(10), 1489. https://doi.org/10.3390/nu16101489

3.  Klepeis, N. E., Nelson, W. C., Ott, W. R., Robinson, J. P., Tsang, A. M., Switzer, P., Behar, J. V., & Hern, S. C. (2001). The National Human Activity Pattern Survey (NHAPS): A resource for assessing exposure to environmental pollutants. Journal of Exposure Science & Environmental Epidemiology, 11(3), 231–252. https://doi.org/10.1038/sj.jea.7500165

4. Downs, S. (2022, June 29). A survey of modern life: Outdoor time. Medium. Building H. https://medium.com/building-h/a-survey-of-modern-life-outdoor-time-3a99d9fa3acb

5.  White, M. P., Alcock, I., Grellier, J., Wheeler, B. W., Hartig, T., Warber, S. L., Bone, A., & Depledge, M. H. (2019). Spending at least 120 minutes a week in nature is associated with good health and wellbeing. Scientific Reports, 9, Article 7730. https://doi.org/10.1038/s41598-019-44097-3

6. Garnham, C. (2022, November 30). 42% of Americans are deficient in vitamin D. Are you at risk? If so, what can you do about it? HealthMatch. https://healthmatch.io/blog/42-of-americans-are-deficient-in-vitamin-d-are-you-at-risk-if-so-what-can7. What is the difference between UVA and UVB rays?. University of Iowa Health Care. (n.d.). https://uihc.org/health-topics/what-difference-between-uva-and-uvb-rays 

8. Heiskanen, V., Pfiffner, M., & Partonen, T. (2020). Sunlight and health: Shifting the focus from vitamin D3 to photobiomodulation by red and near-infrared light. Ageing Research Reviews, 61, 101089. https://doi.org/10.1016/j.arr.2020.101089

9. U.S. Department of Health and Human Services. (n.d.). Office of dietary supplements - vitamin D. NIH Office of Dietary Supplements. https://ods.od.nih.gov/factsheets/VitaminD-HealthProfessional/

10. Holick, M. F. (2008). Vitamin D and sunlight. Clinical Journal of the American Society of Nephrology, 3(5), 1548–1554. https://doi.org/10.2215/cjn.01350308

11. Lambert, G., Reid, C., Kaye, D., Jennings, G., & Esler, M. (2002). Effect of sunlight and season on serotonin turnover in the brain. The Lancet, 360(9348), 1840–1842. https://doi.org/10.1016/s0140-6736(02)11737-5

12. Warren, S. (2020, June 3). Boost your serotonin and melatonin naturally. Somatic Movement Center. https://somaticmovementcenter.com/serotonin-melatonin/

13. Zhong, W. et all, Shahbaz, O., Teskey, G., Beever, A., Kachour, N., Venketaraman, V., & Darmani, N. A. (2021). Mechanisms of nausea and vomiting: Current knowledge and recent advances in intracellular emetic signaling systems. International Journal of Molecular Sciences, 22(11), 5797. https://doi.org/10.3390/ijms22115797

14. Sansone, R. A., & Sansone, L. A. (2013, July). Sunshine, serotonin, and Skin: A partial explanation for seasonal patterns in psychopathology?. Innovations in clinical neuroscience. https://pmc.ncbi.nlm.nih.gov/articles/PMC3779905/

15. Ralph, M. R., Foster, R. G., Davis, F. C., & Menaker, M. (1990). Transplanted suprachiasmatic nucleus determines circadian period. Science, 247(4945), 975–978. https://doi.org/10.1126/science.2305266

16. Masters, A., Pandi-Perumal, S. R., Seixas, A., Girardin, J.-L., & McFarlane, S. I. (2014). Melatonin, the hormone of darkness: From sleep promotion to Ebola treatment. Brain Disorders & Therapy, 4(1), 1000151. https://doi.org/10.4172/2168-975X.1000151

17. Shirani, A., & St. Louis, E. K. (2009). Illuminating rationale and uses for light therapy. Journal of Clinical Sleep Medicine, 05(02), 155–163. https://doi.org/10.5664/jcsm.27445

18. Yurich, G. (2020, November 28). Exposure to morning sunlight profoundly affects mood, health, and nighttime sleep. 1000 Hours Outside. https://www.1000hoursoutside.com/blog/exposure-to-morning-sunlight

19. Giménez, M. et all (2022). Effects of near-infrared light on well-being and health in human subjects with mild sleep-related complaints: A double-blind, randomized, placebo-controlled study. Biology, 12(1), 60. https://doi.org/10.3390/biology12010060

20. Clark, A. (2024, February 6). Why our mitochondria need sunlight. Allison Clark Intuitive. https://www.allisonclarkintuitive.com/blog/why-our-mitochondria-need-sunlight

21. Salehpour, F., Mahmoudi, J., Kamari, F., Sadigh‑Eteghad, S., Rasta, S. H., & Hamblin, M. R. (2018). Brain photobiomodulation therapy: A narrative review. Molecular Neurobiology, 55(8), 6601–6636. https://doi.org/10.1007/s12035-017-0852-4