The Broad Effects of Sunlight and Sun Exposure: Benefits and Dangers

All life on this earth requires energy from the sun. Sunlight enters our world and not only provides us with energy from calorie-rich foods, but its rays also make direct contact with our skin, enter our eyes, and have profound physiological effects. Researchers have only scratched the surface of understanding, but what we have learned about the effects of sunlight is immensely complex and fascinating. One of the most interesting effects of sunlight includes changes to the human body’s circulating hormones. These molecules have systemic effects, widespread to change not only our mood but also immune function and more.

Living in an area of constant cloud cover, such as the Pacific North West, means long winters without much sunshine that gives way to celebrated skies of blue in the spring. Many are immediately uplifted by the long-anticipated shift in weather, providing an incredible incentive for outdoor enthusiasts to make their way into the warmth of our sun’s rays. It is difficult to determine what is so very attractive about UV light, but research has demonstrated some physiological effects of light radiation that might help to explain. One of the effects is the creation of “feel-good” chemicals known as endorphins, a result of producing pigmentation stimulating molecules after ultraviolet exposure.^[1]

Here are some of the benefits and dangers of sunshine.

Benefits of Sunshine and Ultraviolet Light

Ultraviolet light leads to the production of “Feel-Good” endorphins

Endorphins play an important role in how we feel. Certain opiates, such as beta-endorphin, have been found to be significantly lower in concentration in the serum of mice suffering from deficits in coping and increased anxious behavior.^[2,3] Reductions in internally generated opioids have also been linked with the development of depression.^[4] Additional effects of sunlight on mice were studied, demonstrating that UV exposure resulted in a rise in blood opiate concentration, imparting an opioid-like physical dependence that guided behavior choices.^[5] People that frequently tan have been studied for the presence of addiction and appear to meet accepted criteria for substance-related disorder.^[6] This effect of endorphin production from UV light might explain the attraction many of us experience to the sun.

Ultraviolet light and the production of melatonin

Individuals with Seasonal Affective Disorder, a condition characterized by a recurrent depression that comes on with the onset of winter, have shown to benefit from light therapy. This therapy involves exposure to ultraviolet light, where the person is exposed to controlled amounts of ultraviolet light in an ultraviolet light booth. Light therapy has been studied for its effects on melatonin, a hormone released in rhythm with the light cycle. Research shows that those with Seasonal Affective Disorder differ in their phase of melatonin onset by up to six hours.^[7] Researchers examined a group of 42 patients with Seasonal Affective Disorder regarding their melatonin release over time with the introduction of light at different times of the day. This study demonstrated that light therapy resulted in a shift in this cycle, known as the circadian rhythm, and the researchers concluded that positive results of light therapy were secondary to a correction of this rhythm.^[8] Further research conducted on light therapy showed that the effects of light therapy were linked to light exposure to the retina, rather than the skin.^[9] The retina, when exposed to light that enters the eye, disinhibits the pineal gland and contributes directly to the gland’s release of the hormone melatonin. This further argues that the stimulation of melatonin release from the pineal gland is likely responsible for the beneficial effects of light therapy. 

Ultraviolet light and the immune system

Increasing scientific theories are being produced linking light to the immune system. Interestingly, researchers are finding evidence for an axis that exists between melatonin and endogenous opiates like β-endorphins affecting the immune system.^[10] Melatonin has shown to stimulate white blood cells to release opiates that may act as signaling molecules.^[11-16] Cortisol, a hormone stimulated by light and thought of as the opposing force to melatonin in our circadian rhythm, has immunosuppressive effects.^[17] Multiple other mechanisms of ultraviolet light have also been tied to immunosuppression.^[18-20]

Another hormone produced by light, a product of direct contact with the skin, is Vitamin D. This hormone has additionally shown to have broad effects on the immune system.^[21,22] These studied effects of light could additionally explain the general affinity to sun exposure. Evidence like that of low Vitamin D status having ties to psychiatric disorders is a further suggestion of this.^[23]

Dangers of Sunshine and Ultraviolet Light

It is very important to consider the dangerous effects of ultraviolet light. UV radiation has damaging effects on DNA and can result in severe life-threatening conditions.^[24] Remaining protected from the sun is very important, especially for those with lighter skin types that are prone to burning with modest exposure. Avoid use of artificial tanning beds and minimize sunlight exposure during peak hours, seeking shade when possible. Consider the presence of reflective surfaces around that allow sunlight to reach you while under covers. Sunlight exposure can not only lead to superficial sunburns but also deadly cancers such as melanoma. Examine your skin frequently for newly formed or changing moles, and be sure to be thorough, using a mirror or involving a partner. Seek medical professional attention if you observe changes in moles or sores that do not heal because skin cancers are much more easily treated when caught early.^[25] Consult your doctor before considering any form of therapy that includes ultraviolet light exposure. Contraindications to light therapy include pre-existing retinal diseases, the use of photosensitizing drugs, and recent eye surgery.^[26]

Hormesis, a term to describe favorable responses to low exposure to otherwise harmful agents such as stress, is an appropriate consideration in determining the therapeutic benefit of sunlight. More research is indicated in the use of ultraviolet radiation in the treatment of hormonally and even immunologically derived medical conditions. When thinking about how the skin is affected by UV light, it is important to consider both the benefits and dangers of sunlight. Sun protective habits such as avoidance of intense sunlight and the use of sun protective clothing to avoid sun overexposure are very important to avoid sun overexposure.