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.
Here are some of the benefits and dangers of sunshine.
Benefits of Sunshine and Ultraviolet Light
Ultraviolet light leads to 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. 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. People that frequently tan have been studied for the presence of addiction and appear to meet accepted criteria for substance-related disorder. 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. 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. 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. 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. 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. 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.
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. 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. 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.
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.
* This Website is for general skin beauty, wellness, and health information only. This Website is not to be used as a substitute for medical advice, diagnosis or treatment of any health condition or problem. The information provided on this Website should never be used to disregard, delay, or refuse treatment or advice from a physician or a qualified health provider.
Skobowiat C, Dowdy JC, Sayre RM, et al. Cutaneous hypothalamic-pituitary-adrenal axis homolog: regulation by ultraviolet radiation. Am J Physiol Endocrinol Metab.2011;301(3):E484-493; PMID: 21673307 Link to research.
Barfield ET, Barry SM, Hodgin HB, et al. Beta-endorphin mediates behavioral despair and the effect of ethanol on the tail suspension test in mice. Alcohol Clin Exp Res.2010;34(6):1066-1072; PMID: 20384608 Link to research.
Grisel JE, Bartels JL, Allen SA, et al. Influence of beta-Endorphin on anxious behavior in mice: interaction with EtOH. Psychopharmacology (Berl).2008;200(1):105-115; PMID: 18604523 Link to research.
Burnett FE, Scott LV, Weaver MG, et al. The effect of naloxone on adrenocorticotropin and cortisol release: evidence for a reduced response in depression. J Affect Disord.1999;53(3):263-268; PMID: 10404712 Link to research.
Fell GL, Robinson KC, Mao J, et al. Skin beta-endorphin mediates addiction to UV light. Cell.2014;157(7):1527-1534; PMID: 24949966 Link to research.
Kourosh AS, Harrington CR, Adinoff B. Tanning as a behavioral addiction. Am J Drug Alcohol Abuse.2010;36(5):284-290; PMID: 20545604 Link to research.
Meesters Y, Gordijn MC. Seasonal affective disorder, winter type: current insights and treatment options. Psychol Res Behav Manag.2016;9:317-327; PMID: 27942239 Link to research.
Terman JS, Terman M, Lo ES, et al. Circadian time of morning light administration and therapeutic response in winter depression. Arch Gen Psychiatry.2001;58(1):69-75; PMID: 11146760 Link to research.
Wehr TA, Skwerer RG, Jacobsen FM, et al. Eye versus skin phototherapy of seasonal affective disorder. Am J Psychiatry.1987;144(6):753-757; PMID: 3591996 Link to research.
Maestroni GJ. The immunoneuroendocrine role of melatonin. J Pineal Res.1993;14(1):1-10; PMID: 8483103 Link to research.
Calvo JR, Rafii-el-Idrissi M, Pozo D, et al. Immunomodulatory role of melatonin: specific binding sites in human and rodent lymphoid cells. J Pineal Res.1995;18(3):119-126; PMID: 7562368 Link to research.
Garcia-Maurino S, Pozo D, Carrillo-Vico A, et al. Melatonin activates Th1 lymphocytes by increasing IL-12 production. Life Sci.1999;65(20):2143-2150; PMID: 10579467 Link to research.
Giron-Caro F, Munoz-Hoyos A, Ruiz-Cosano C, et al. Melatonin and beta-endorphin changes in children sensitized to olive and grass pollen after treatment with specific immunotherapy. Int Arch Allergy Immunol.2001;126(1):91-96; PMID: 11641610 Link to research.
Gonzalez-Haba MG, Garcia-Maurino S, Calvo JR, et al. High-affinity binding of melatonin by human circulating T lymphocytes (CD4+). FASEB J.1995;9(13):1331-1335; PMID: 7557023 Link to research.
Maestroni GJ, Conti A. The pineal neurohormone melatonin stimulates activated CD4+, Thy-1+ cells to release opioid agonist(s) with immunoenhancing and anti-stress properties. J Neuroimmunol.1990;28(2):167-176; PMID: 1972943 Link to research.
Moore CB, Siopes TD. Melatonin enhances cellular and humoral immune responses in the Japanese quail (Coturnix coturnix japonica) via an opiatergic mechanism. Gen Comp Endocrinol.2003;131(3):258-263; PMID: 12714007 Link to research.
Dong T, Zhi L, Bhayana B, et al. Cortisol-induced immune suppression by a blockade of lymphocyte egress in traumatic brain injury. J Neuroinflammation.2016;13(1):197; PMID: 27561600 Link to research.
Aubin F. Mechanisms involved in ultraviolet light-induced immunosuppression. Eur J Dermatol.2003;13(6):515-523; PMID: 14721768 Link to research.
Norval M. The mechanisms and consequences of ultraviolet-induced immunosuppression in the skin and eye. Eye Contact Lens.2011;37(4):176-184; PMID: 21709488 Link to research.
Ullrich SE. Mechanisms underlying UV-induced immune suppression. Mutat Res.2005;571(1-2):185-205; PMID: 15748647 Link to research.
Hewison M. Vitamin D and immune function: an overview. Proc Nutr Soc.2012;71(1):50-61; PMID: 21849106 Link to research.
Vanherwegen AS, Gysemans C, Mathieu C. Vitamin D endocrinology on the cross-road between immunity and metabolism. Mol Cell Endocrinol.2017;10.1016/j.mce.2017.04.018PMID: 28461074 Link to research.
DeLuca GC, Kimball SM, Kolasinski J, et al. Review: the role of vitamin D in nervous system health and disease. Neuropathol Appl Neurobiol.2013;39(5):458-484; PMID: 23336971 Link to research.
D'Orazio J, Jarrett S, Amaro-Ortiz A, et al. UV radiation and the skin. Int J Mol Sci.2013;14(6):12222-12248; PMID: 23749111 Link to research.
Polefka TG, Meyer TA, Agin PP, et al. Effects of solar radiation on the skin. J Cosmet Dermatol.2012;11(2):134-143; PMID: 22672278 Link to research.
Wirz-Justice A, Terman M. Chronotherapeutics (light and wake therapy) as a class of interventions for affective disorders. Handb Clin Neurol.2012;106:697-713; PMID: 22608653 Link to research.