Sunshine and Health
On a gloomy day like today it’s easy to miss the sun, but even on sunny day’s we often take sunshine for granted and don’t enjoy it’s benefits as much as we should. Most public health messages of the past century have focused on the hazards of too much sun exposure. UVA radiation (95–97% of the UVR that reaches Earth’s surface) penetrates deeply into the skin, where it can contribute to skin cancer indirectly via generation of DNA-damaging molecules such as hydroxyl and oxygen radicals. Sunburn is caused by too much UVB radiation; this form also leads to direct DNA damage and promotes various skin cancers. Both forms can damage collagen fibers, destroy vitamin A in skin, accelerate aging of the skin, and increase the risk of skin cancers. Excessive sun exposure can also cause cataracts and diseases aggravated by UVR-induced immunosuppression such as reactivation of some latent viruses.
However, excessive UVR exposure accounts for only 0.1% of the total global burden of disease in disability-adjusted life years. In contrast, a WHO report noted that a markedly larger annual disease burden worldwide might result from very low levels of UVR exposure. This burden subsumes major disorders of the musculoskeletal system and possibly an increased risk of various autoimmune diseases and life-threatening cancers.
Benfits of Sunlight on Health
Vitamin D Production
The best-known benefit of sunlight is its ability to boost the body’s vitamin D supply- most cases of vitamin D deficiency are due to lack of outdoor sun exposure. At least 1,000 different genes governing virtually every tissue in the body are now thought to be regulated vitamin D, including several involved in calcium metabolism and neuromuscular and immune system functioning.
Unlike other essential vitamins, which must be obtained from food, vitamin D can be synthesized in the skin through a photosynthetic reaction triggered by exposure to UVB radiation. The efficiency of production depends on the number of UVB photons that penetrate the skin, a process that can be curtailed by clothing, excess body fat, sunscreen, and the skin pigment melanin.
Without sufficient vitamin D, bones will not form properly. In children, this causes rickets, a disease characterized by growth retardation and various skeletal deformities, including the hallmark bowed legs. More recently, there has been a growing appreciation for vitamin D’s impact on bone health in adults.
Hormone Production
Humans are programmed to be outdoors while the sun is shining and home in bed at night. This is why melatonin is produced during the dark hours and stops upon optic exposure to daylight. This hormone is a key component for many of the body’s circadian rhythms. It also plays an important role in countering infection, inflammation, cancer, and auto-immunity.
When people are exposed to sunlight or very bright artificial light in the morning, their nocturnal melatonin production occurs sooner, and they enter into sleep more easily at night.
Melatonin production also shows a seasonal variation relative to the availability of light, with the hormone produced for a longer period in the winter than in the summer. The melatonin rhythm phase advancement caused by exposure to bright morning light has been effective against insomnia, premenstrual syndrome, and seasonal affective disorder (SAD).
Additional Sun-Dependent Health Benefits
The sun may be best known for boosting production of vitamin D, but sun exposure has many other effects:
Direct immune suppression: Exposure to both UVA and UVB radiation can have direct immunosuppressive effects-these mechanisms may help prevent autoimmune diseases.
Alpha melanocyte-stimulating hormone: Upon exposure to sunshine, the skin releases chemicals that actually help limit oxidative DNA damage resulting from UVR and increases gene repair, thus reducing melanoma risk.
Calcitonin gene-related peptide (CGRP): Released in response to both UVA and UVB exposure, this potent neuropeptide could help explain sunlight’s efficacy in treating skin disorders such as psoriasis and eczema.
Endorphins UVR increases blood levels of natural opiates called endorphins, which are hormones that reduce pain. Their other benefits of endorphins include:
promoting a sensation of well-being and improving mood
boosting the immune system
relieving pain
promoting relaxation
helping wounds heal
helping people feel more alert
increased productivity
reducing depression
Lack of Sunlight
Days without sunshine can be tough for many people, but some individuals find a lack of sunlight more challenging than others. The National Institute of Health says that the following characteristics put people at higher risk of developing depression and SAD:
having a family member who has experienced SAD
a history of depression, attention deficit hyperactivity disorder (ADHD), anxiety, or other mental disorders
Living far away from the equator
It is also of note that 4/5 people with SAD are female.
The Takeaway
Sunlight is essential for human health and well-being. The health benefits of sunlight include, but are limited to, generating the production of vitamin D, supporting bone health, lowering blood pressure, preventing disease, and promoting good mental health. After years of fearing the sun, many experts are now recommending a middle-ground approach that focuses on modest sun exposures while wearing sunscreen and / or protective clothing. It’s recommended to get sun exposure as soon as possible upon waking- even on a cloudy day your skin can still absorb beneficial UVB rays.