Benefits of Sunlight
Ultraviolet Radiation UVA/B
UVA comprises 95-97% of ultraviolet radiation (UVR). It penetrates deep and can generate hydroxyl and oxygen radicals that can then damage DNA.
UVB in excess can directly damage DNA , which causes skin cancers.
Both types of radiation can damage collagen fibers, destroy vitamin A in skin, accelerate aging of the skin, and increase the risk of skin cancers.
Benefits outweigh deficits
Only .1% of the total global burden of disease (in disability-adjusted life years [DALYs]) is related to too much UVR exposure.
A much larger annual disease burden results from very low levels of UVR exposure (WHO 2006).
Vitamin D Production
Sunlight exposure to the skin helps 7-dehydrocholesterol to produce vitamin D3 that is converted in the liver to 25[OH]D, 25-hydroxyvitamin D, which is a hormone that helps to regulate calcium and phosphorus absorption in the intestines and calcium flow into/out of the bones. In the kidneys, it is further converted to 1,25[OH]D, 1,25-dihydroxyvitamin D3 (the active form), which regulates at least 1,000 different genes, several involved in calcium metabolism, neuromuscular and immune system functioning.
How Much Exposure is Needed?
It depends upon your clothing, sunscreen, time of day, season, location on the planet, and skin tone.
White person ½ hour summer sun gives you 50,000 IU (1.25mg) Vitamin D, Tan person 20,000-30,000 IU, and dark-skinned 8,000-10,000.
5-30 minutes to face, arms, legs twice weekly is sufficient for Vitamin D synthesis (NIH).
What if I Don’t Get Enough?
- Rickets – growth retardation and skeletal abnormalities (bowed legs)
- Osteoporosis-low bone mass and loss of bone tissue that results in increased risk of fractures
- Osteomalacia-softening of the bone causing weakness, bone pain and increased risk of fractures
Sunlight and Serotonin/Melatonin
The melatonin precursor, serotonin, is affected by exposure to daylight. Serotonin is normally produced during the day, and is only converted to melatonin in darkness.
Melatonin is produced from serotonin in the dark, and its production stops when daylight enters your eyes.
Melatonin regulates circadian rhythms (daily occurrences like sleep), decreases infection, inflammation, cancer and autoimmunity, and suppresses UVR-induced skin damage.
Sunlight exposure in the morning leads to earlier melatonin release at night and better sleep, decreased symptoms of insomnia, PMS, and SAD.
Increased sunlight increases serotonin, which leads to positive mood, relaxation and focus.
Sunlight and Cancer
Over-exposure – Skin cancers are related to too much sunlight exposure. Melanoma is related to intermittent severe exposures (bad sunburns) whereas basal cell carcinoma and squamous cell carcinoma are related to prolonged low-level exposures.
Under-exposure – possibly related to Hodgkin lymphoma, breast, ovarian, colon, pancreatic, prostate, and other cancers.
One study showed that taking 2–4 times the daily dietary reference intake of 200–600 IU vitamin D3 and calcium resulted in a 50–77% reduction in expected incidence rates of all cancers combined over a four-year period in postmenopausal women living in Nebraska.
Although excessive sun exposure is an established risk factor for cutaneous malignant melanoma, continued high sun exposure was linked with increased survival rates in patients with early-stage melanoma.
Vitamin D and other diseases
There is some evidence that elevated levels of Vitamin D decrease the chance of developing multiple sclerosis.
As with MS, Diabetes Type 1 is more prevalent in higher latitudes, and decreases with Vitamin D supplementation.
Metabolic Syndrome is possibly associated with low Vitamin D levels.
Hypertension has interactions with sunshine and Vitamin D (UVB, not UVA).
It may have relations to rheumatoid arthritis, asthma, and immune system function.
Other diseases potentially affected by vitamin D include collagen-induced arthritis, Lyme’s disease, autoimmune encephalomyelitis, thyroiditis, inflammatory bowel disease, & systemic lupus erythematosis.
Other Sun Dependent Pathways
- Direct immune suppression — Exposure to both UVA and UVB can have direct immunosuppressive effects through up-regulation of cytokines (TNF-α and IL-10) and increased activity of T regulatory cells that remove self-reactive T cells. These mechanisms may help prevent autoimmune diseases.
- Alpha melanocyte-stimulating hormone release — has been implicated in immunologic tolerance, suppression of contact sensitivity, and limiting oxidative DNA damage, thus reducing melanoma risk.
- Calcitonin gene-related peptide — Released by UVA/UVB, is linked with immunologic tolerance, and may relate to psoriasis’ treatment with sunlight exposure.
- Neuropeptide substance P — increases lymphocyte proliferation and chemotaxis but local immune suppression.
- Endorphins – UVR increases blood levels of natural opiates called endorphins.
Adapted from Benefits of Sunlight: A Bright Spot for Human Health
(National Institute of Environmental Health Sciences)