The Benefits and Harms of UV Exposure for Vitamin D Formation
UV exposure is important for Vitamin D formation, but excessive periods of exposure can be detrimental to health. Explain the pros and cons of UV radiation on epidermal skin cells, and how can a person effectively prevent being exposed to excess levels of radiation.
Ultraviolet (UV) light helps nourish life on earth. Even though UV exposure is essential as in vitamin d formation, healthy skin and protection against various diseases however excess exposure can have sinister effects on our health such as the development of skin cancer, aging. Therefore, preventative measures need to be taken to limit our exposure to UV radiation. Hence this assignment discusses the importance of appropriate levels of UV radiation and the harmful effects induced by overexposure. The assignment also discusses various methods for protection against excess UV exposure.
Benefits of Ultraviolet radiation
The primary benefit of UV radiation is that it is used to synthesize vitamin D in the body. Vitamin D is made from 7-dehydrocholesterol (7-DHC) by cells located in the skin upon exposure to UVB radiation in a non-enzymatic process. Firstly, the B ring of 7-DHC is broken by UVB from the sun resulting in the formation of pre-D3. Pre D3 then isomerizes into vitamin D3 under heat. Vitamin D can also be obtained from the diet in the form of D2. The production of vitamin D3 directly correlates to the intensity of UVB and the pigmentation of the skin. D3 is then converted into 1,25-dihydroxy vitamin D in the liver by CYP21R enzymes. The kidney and various other tissues metabolize 25-hydroxyvitamin D (25OHD) into 1,25 (OH)2D3, which binds to the vitamin D receptor thus inducing activation of transcription factors, which result in uptake of intestinal calcium absorption. Healthy calcium absorption is necessary for bone growth and development as vitamin D is also necessary for the prevention of various bone-related disorders such as rickets and osteoporosis. Adequate exposure of UV is also necessary to prevent vitamin D deficiency, which is caused by low UV exposure that also results in an increased risk of PTG hyperplasia due to reduced levels of 25OHD.
The UV light has also been identified to have cardiovascular benefits such as reducing high blood pressure. UVA exposure results in the conversion of nitrate obtained from the diet and nitrate found in stores on the dermis and epidermis into nitrite via nitrate reductase enzymes and UVA. This is followed by the conversion of nitrite into Nitric oxide by Xanthine Oxidoreductase. Nitric oxide causes arterial vasodilation by activation of cyclic GMP in vascular smooth muscle cells, which decreases mean arterial pressure thus decreasing blood pressure and decreasing the risk of cardiovascular disease incidence.
UV also plays a key role in immune system modulation particularly in the development of various autoimmune disorders such as asthma, multiple sclerosis, rheumatoid arthritis and inflammatory bowel disease, which are associated with vitamin D deficiency and low UV exposure. It is known that UVA and UVB have immunosuppressive effects via the up-regulation of TNF-A, T regulatory lymphocytes, and IL-10, which are known to cause autoimmune diseases.
UV radiation can also be used for the treatment of skin disorders such as psoriasis. Psoriasis is a chronic inflammatory disease affecting the skin. Therefore, phototherapy using UV radiation was developed with the first type of phototherapy being the broadband ultraviolet B light. However, newer methods such as PUVA and UVB have been developed, which specifically target diseased skin and can be used depending on the lesion size without affecting nearby healthy skin.
The UV radiation can also affect the presence of microbiome on the skin through the production of pyrimidine dimers and microbial photoproducts leading to microbial killing. The UV radiation can also result in the activation of pathogen-associated molecular pattern response, which results in the release of various microbial signals such as oleic acid, porphyrins that result in inflammation. UV can also induce a negative effect on microorganisms resulting in the formation and release of antimicrobial peptides by keratinocytes, which can directly affect the numbers of mutualistic and harmful bacteria.
Harmful effects of Ultra-Violet Radiation
The UV radiation is a known carcinogen. UVB is known to result in the creation of pyrimidine dimers. Similarly, UVA also induces the formation of the same however to a lesser extent. Ultraviolet light consists of 3 types called UVA, UVB, and UVC. UVA spanning a wavelength of 200 to 400 nm is known from the creation of cyclobutane pyrimidine dimers. UVA results in the formation of reactive oxygen species through the formation of singlet oxygen and type-1 photosensitization reactions as UVA can cause oxidative base modifications at guanine bases. The main mutations induced by UVA radiation are guanine to thymine and guanine to adenine transversions. UVB exposure also results in the formation of cyclobutene pyrimidine dimers and pyrimidine 6-4 pyrimidone photoproducts. This followed by the activation of DNA repair enzymes. Incorrect repair of these damaged DNA lesions results in the formation of mutations in epidermal cells. UVB results in the cytosine to thymine transition and cytosine and thymine double transition mutations. UVB also induces mutations in the BRAF gene through base transversions and substitutions. UV radiation also results in mutation of the p53 gene, which is a key tumor suppressor gene that controls key signaling pathways in response to DNA damage, oxidative stress and other forms of cell stress. These mutations and changes are seen in melanoma however these are also seen in basal cell carcinoma and squamous cell carcinoma.
Excess exposure to UV radiation is also known to induce premature aging. UV radiation activates reactive oxygen species, which activate receptor tyrosine kinases resulting in the activation of a cascade of downstream effectors, which result in the modification of extracellular matrix through the activation of the MAPK cascade by phosphorylation and activation of activator-protein 1. Activator-protein 1 suppresses collagen formation simultaneously increasing matrix metalloproteinase. Hence, therefore, UV induces a collagen deficit which leads to skin wrinkling, thinning and sagging that are visible signs of aging.
Prevention against excess UV radiation
The main method of protection against UV induced damage is via the use of sunscreens. Sunscreens have been studied for protection against various forms of skin cancers such as melanoma and keratinocyte derived cancers such as basal cell and squamous cell carcinoma. Regular use of sunscreens also prevents the development of actinic keratoses into cancer. It is also established that sunscreen helps prevent photoaging and also inhibits the acute and chronic effects induced by UV radiation on the skin.
There are two types of sunscreens suitable for human use. These consist of physical blockers, which block ultraviolet radiation from being absorbed by the skin. Examples include zinc oxide and titanium dioxide. The other type of sunscreen consists of chemical sunscreen which absorbs UV radiation e.g. oxybenzone and avobenzone. The effectiveness of a sunscreen is proportional to its sun protection factor, which measures sunscreen protection from UVB radiation.
Other additional forms of protection from harmful UV radiation could be through the use of clothing by covering the vulnerable parts of the skin hence blocking the exposure to UV radiation. Another method to inhibit the harmful effects of UV radiation is by the use of red-orange oral supplemental antioxidants which strengthen the antioxidant defense systems of the body and also protect against photoaging.
The use of an umbrella is also another effective method to reduce exposure to UV radiation. Additionally, staying indoors and limiting time spent outdoors are also effective methods for protection against the harmful effects of UV radiation. It is also known that UV rays are strongest from 10 am to 4 pm, hence spending time in the sun outside these times are an effective method of protection. Lastly, the correct use of sunscreen based on the manufacturer’s instructions is also ideal in the prevention of skin cancer and UV induced aging.
Hence this assignment outlines the importance of UV radiation on our lives as it plays a vital role in the production of vitamin D, its role in the prevention of cardiovascular disease, autoimmune disorders, for the treatment of skin conditions such as psoriasis and its role in microbiome regulation on our skin. Despite this, it is very harmful particularly as high exposure leads to the development of skin cancers and induces premature aging. Hence, we need to spend time in the sun as it benefits and improves our health however we should also take suitable preventative measures to protect us from its harmful effects.
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