We spend a lot of time on fresh air under the sun in summer: beaches, rivers, parks, etc. It is a great opportunity to get a free sun tan, become more attractive and… healthier. It is well known that moderate amounts of sunlight stimulate vitamin D production that regulates calcium metabolism. But, at the same time scientific researches have shown that sun rays have a great negative effect. What is beneficial and what is dangerous about the sun tanning? How can we minimize negative effects of it?
Sun tanning is a complicated biochemical and physiological process. The reason why skin becomes darker is an intensive formation of pigment melanin from amino acid tyrosine under the influence of solar UV radiation. It is synthesized in special skin cells called melanocytes. Then melanin is transported to the upper layer of skin cells (keratinocytes) that store oxidized melanin performing its function.
There are two types of ultraviolet (UV) light reaching the Earth’s surface: UVA (long wavelength, 320-400nm) and UVB (medium wavelength, 280-320nm). UVA causes the oxidation of the existing melanin, making it darker. It creates the actual tan color of the skin through its protection is very week. Although UVB is almost all blocked with the ozone layer, penetrated light stimulates synthesis of a great amount of melanin in melanocytes. The main purpose of melanin is to protect lower skin layers from the damage by absorbing harmful UV light. Dark color hair and eye iris are also determined by melanin.
Ultraviolet light has one important benefit for your health. UVB light promotes the formation of previtamin D3 in the skin that later is transformed into the active form in liver and kidneys. Vitamin D (also known as calcitriol) is important for calcium metabolism promoting calcium absorption in the digestive tract. Calcium is important for bone strength, heart and muscle work. Deficiency of D3 causes several bone-softening diseases, i.e. rickets in children. By the way, UVB light cannot penetrate the glass. That’s why melanocytes cannot synthesize vitamin D in your skin if you spend a lot of time inside. You need to go outside to get the direct contact of your skin with the sun UVB radiation because several minutes a day are pretty enough for a moderate amount of vitamin D production. If you eat calcium-rich products, go out and have a sunbath but do not overdose.
The main purpose of sun tanning nowadays is cosmetic effect – the darker the skin is, the prettier and healthier most of us look since the renaissance pale skin is no longer trendy. At the same time, UV light promoting this effect can cause some unpleasant feelings or even diseases. At first, the great amount of sun radiation cannot be blocked with melanin. Some rays pass through it and cause sunburns and skin aging. A lot of heat and UV light can activate immune cells and cause allergic reactions to the sunlight (photosensitivity).
Furthermore, dangerous UV light promotes DNA damage: formation of intramolecular bonds in DNA structure and production of oxygen radicals. These factors are the main reasons of mutations and development of skin cancers. Tanning bed producing UV radiation has the same effect as sun UV light and isn’t safe. Interestingly, sun rays can even cause the addiction: researches have shown that sun tanning stimulates endorphin synthesis causing dependence on sun tanning. So, the more time you spend under the sun, the more you wish to stay there. Scientists suggest that it is an evolutionary trick: you should like the feeling under the sun because it is the source for vitamin D producing.
Several types of skin are very sensitive to sunlight when melanin production is not enough to protect skin from great amounts of UV radiation. Thus, it is dangerous to be on a beach whole day long. Do wear sun protecting clothes or use sunscreens containing organic or inorganic compounds that absorb, scatter or reflect UV radiation. The latter decrease sunburns and risk of cancer diseases if used correctly. Mind that the same color of skin can be achieved by eating a lot of carrots and tomatoes containing carotenoids – yellow pigments and vitamin A precursors. Besides, vitamins C, E and A, serving as antioxidants, increase skin protection from dangerous oxygen radicals.
Overall, sunlight, like all physical, chemical and biological factors surrounding us, has both benefits and negative effects. Moderate amount of UV radiation as an essential component of sunlight stimulates synthesis of melanin, endorphins and vitamin D. At the same time, great amounts of the sun UV radiation cause unpleasant feeling of sunburns and increase risk of skin cancers. So, dear friend, try to avoid spending time under the sun in very hot days, or use cloth or sunscreens. And have a look how to have fun protecting your skin from the sun… even partially.
