Illuminating the Health Benefits of Sunlight
Around 4.6 billion years ago, the sun was born from a solar nebula. About one million Earths could fit inside the sun, and it contains 99.8% of the mass of our solar system. One hundred million tons of dynamite would need to be exploded every second to match the amount of energy produced by the sun.1 Earth is the only planet whose perfect distance from the sun permits life to thrive as we know it. Is your mind blown yet?
The phenomenon that is our sun is the life-sustaining heartbeat of our entire existence, and we owe a great deal of appreciation for it.
National Daylight Appreciation Day
Appropriately celebrated on June 21, the summer solstice, National Daylight Appreciation Day is essentially a day to honor the sun on the day with the most daylight hours.2 Before humans understood the scientific reasons behind the shortening and lengthening of days throughout the year, the summer solstice was recognized by some cultures as the day the sun god left the world of the living for the world of the dead, ultimately to be reborn again in the deepest part of winter when the days begin to lengthen once again. We know now that the longest day of the year is the result of the natural rotation of the Earth around the sun on its angled axial tilt. But this doesn’t mean there aren’t reasons to celebrate anymore!
To truly appreciate and celebrate the sun, it is helpful to understand exactly how it is essential for our health and well-being.
Our Relationship with the Sun
Like nearly all other life on our planet, we need sunlight, directly and indirectly, to survive. However, our relationship with the sun has always been complicated. In our human history, we’ve gone from being equatorial sun worshippers to a sun adverse society, back to sunseekers to cure trending maladies, to currently being sun phobic for fear of skin cancer and aging.3 By the 1600s, social norms kept most of us completely clothed from head to toe, even during the summer. By the late 1800s, 90% of children in industrialized cities had some manifestation of rickets due to lack of sun exposure. In the 1900s, doctors started prescribing sunbathing for tuberculous, rickets, and mental health conditions. Then beginning in the 1930s, the U.S. Public Health Service began issuing warnings about sun-related health risks. Today, the average American spends about 90% of their time indoors and this has an effect on our health.4
How Does Sunlight Affect Our Health?
There are two types of ultraviolet radiation (UVR) from the sun that affects us. UVA radiation can penetrate the skin deeply and contribute to skin cancer by generating DNA-damaging molecules. UVB radiation is responsible for sunburns and can directly damage DNA. Both types of radiation can harm collagen fibers, destroy vitamin A in the skin, accelerate skin aging, and increase the risk of skin cancers.
However, too much ultraviolet radiation exposure only accounts for 0.1% of the total global burden of disease in disability-adjusted life years (DALY). In contrast, the annual disease burden of 3.3 billion DALYs worldwide is thought to be the result of not enough UVR exposure.5 So, as you can see, there are two sides to the coin here. Too much sun or too little sun can both be deleterious to our health.
On a positive note, the correlation between sun exposure and gut microbiome diversity—a very recent topic of research—might be closely linked. Early studies suggest that the diversity of microbes in our gut are positively influenced by UVB light. Two studies of gut microbiome health and diversity in relation to UVB exposure—one examining a woman in Vancouver, Canada regularly exposed to artificial UVB light, and another a group of hunter-gathers in the Amazon naturally exposed to UVB light from the sun—observed a higher diversity and abundance of microbes in relation to UVB light exposure in both test subjects.6
Sunlight is not just ultraviolet light, though, it is full-spectrum light (contains all the colors of the rainbow), as well as dynamic light (changes throughout the day and year). Exposure to natural full-spectrum light can improve mental clarity, alertness, concentration, productivity, and mood. Plus, spending time outdoors, especially in nature, comes with a whole host of its own wellness benefits, but that’s for another time.
The correlation between sun exposure and gut microbiome diversity has recently come into question. Early studies suggest that the diversity of microbes in our gut are positively influenced by UVB light.6
What Are the Health Benefits of Sunlight?
The most widely known health benefit of sunlight is its ability to boost the body’s vitamin D levels. Vitamin D is produced in the skin through a photosynthetic reaction activated by exposure to UVB radiation. It is now believed that at least 1,000 different genes governing almost every tissue in the body are regulated by 1,25-dihydroxy vitamin D3, the active form of vitamin D, as well as immune and neuromuscular functioning and calcium metabolism.7
Vitamin D from sunlight benefits our health by:
Strengthening our bones and muscles
Supporting immunity
Reducing the risk of developing lung, colon, and breast cancers
Improving heart function
Reducing inflammation
Alleviating some symptoms of depression
Now, that is something worth celebrating!
Vitamin D Deficiency
Recent studies have exposed the possible link between vitamin D deficiency and cancer, cardiovascular disease, diabetes, autoimmune disorders, and depression. Vitamin D deficiency is a global health problem affecting about one billion people. An estimated 50% of the global population has insufficient vitamin D levels, with that number being highest among the elderly and obese. Factors such as lifestyle, geographic location, air pollution, and skin pigment melanin (darker skin receives a smaller effective dose than lighter skin in the same conditions and exposure time) can also influence your vitamin D levels. 8
Chronic or severe vitamin D deficiency can cause a decline in intestinal calcium and phosphorus absorption, which can then cause hypocalcemia (too little calcium in your blood) and hyperparathyroidism (too much parathyroid hormone in your bloodstream). Hyperparathyroidism can then lead to phosphaturia (impaired capacity to reabsorb phosphate) and accelerated bone demineralization, which further results in osteomalacia (softening of your bones) and osteoporosis (weakening of your bones).
As far as the right calcium level, the recommendations and literature vary, but most experts define vitamin D deficiency as a serum 25(OH)D level less than 20ng/mL. On the other side of the spectrum, too much vitamin D can be toxic, but this would only occur if too much vitamin D was taken in supplement form, elevating levels to more than 88 ng/mL, not via excessive sunlight exposure. 9
How to Get Vitamin D and Stay Safe in the Sun
The general recommendation for sun exposure for vitamin D is 10 to 15 minutes of unprotected sun exposure between 10 a.m. and 3 p.m. If you are worried about the damaging side of sunshine, you can limit the unprotected exposure zone to just your arms, legs, stomach, or back; your whole body doesn’t need to be unprotected to get the recommended dose of vitamin sunshine. After your short window of unprotected sun exposure has been met, make sure you apply sunscreen with sun-filtering ingredients such as zinc oxide and/or titanium dioxide and wear a hat and protective sun clothing if you are planning on continuing to spend time outdoors.
Sunshine and Serotonin
As diurnal (active during the day) beings, our natural rhythms are synced to the sunlight and darkness. Our modern lifestyle (i.e., shift work, too much screen time) sometimes interferes with these natural cycles that regulate the release of melatonin (at night) and serotonin (during the day). Without enough sun exposure, serotonin levels can decrease, leading to a dip in energy and mood. Low serotonin levels related to lack of sunlight during the winter or rainy season are responsible for major depression with seasonal patterns. Artificial lightboxes, which mimic bright natural light, are sometimes used to treat symptoms of seasonal depression caused by a lack of sunlight.
Celebrate the Sun
While the sun certainly has a sinister side, we would not be here without it. We evolved as a species to depend on the sun for vitamin D, the release of hormones, and so many different biological functions. Our health and happiness are inextricably linked to that fiery star 93 million miles away, and what better way to celebrate the sun than by spending a little time each day soaking it up in gratitude!
Resources:
Choi, CQ. (June 9, 2021). Earth's sun: Facts about the sun's age, size and history. Space.com.
National Daylight Appreciation Day. (June 22, 2021). National Today. nationaltoday.com.
Mead, MN. Benefits of sunlight: A bright spot for human health. (April 2008). Environmental health perspectives. PubMed Central. ncbi.nlm.nih.gov.
Report on Indoor Air Quality, EPA. (n.d.). epa.gov. Accessed May 21, 2022.
Mead, MN. Benefits of sunlight: A bright spot for human health. (April 2008). Environmental health perspectives. PubMed Central. ncbi.nlm.nih.gov.
Conteville, L. C., & Vicente, A. C. P. (2020, September 2). "Skin exposure to sunlight: A factor modulating the human gut microbiome composition". Gut microbes. PubMed Central. ncbi.nlm.nih.gov.
