There is a lot of discussion, particularly during summer, about the dangers of ultra-violet rays from the sun.
They are implicated in sunburn, cancer and may even play a role in the development of multiple sclerosis. We are told to avoid UV exposure to keep our skin from aging. It seems that the tanned look is no longer fashionable. What most people don’t realize is that UV exposure is vital to our health. If we were to completely avoid it, we would suffer.
UV rays come from the sun, for the most part, but can come from certain electronic equipment, such as sunlamps or so-called black lights. We can get UV rays from welding equipment, some kinds of lasers and even the humble TV remote control.
So, just what are UV rays?
UV rays are light with a short wavelength. Our eyes can distinguish different wavelengths, to a limited degree, as the colours we see. Red light has a long wavelength, whereas blue light has a short one. UV light has an even shorter wavelength than blue. We are not able to see UV light as the wavelength is too short for our eyes. Indeed, the lens in our eyes selectively filters our UV light.
We further subdivide UV light into three wavelength bands. UVA, B, and C.
UVA light has the longest wavelength of 320 to 400 nanometres. It can penetrate deep within our skin and is responsible for quick tanning, as well as being implicated in premature aging and some forms of skin cancer. UVA rays are not stopped by the atmospheres’ ozone layer, a natural protective barrier to UV radiation.
UVB light has a shorter wavelength of 280 – 320 nanometres. It cannot penetrate the skin as deeply as UVA light, but it is not harmless. It causes delayed tanning, sunburns and is responsible for most skin cancers. Fortunately, about 95 per cent of UVB is absorbed by the ozone layer.
Finally, UVC rays are the shortest wavelength – 100 – 280 nanometres. These rays are deadly to almost all life. Because the ozone layer in the atmosphere filters out this radiation, it never reaches the Earth’s surface. UVC rays are generated to sterilize medical equipment and to kill bacteria, a task to which it is admirably suited.
So far, the list of effects of UV radiation is grim.
However, if we do not have UV light exposure, we are likely to develop various illnesses that are associated with a lack of vitamin D. This can include thin or brittle bones, fractures, osteoporosis, muscle weakness, changes in mood and even anxiety and depression. A disease that has disappeared in the developed world, rickets, is caused by a lack of vitamin D, which helps us absorb certain minerals such as calcium and other minerals vital to life.
This vitamin can be produced by the body if it is exposed to a certain level of UV radiation from the sun.
We get less sunlight in winter, especially in the higher latitudes where the length of the day and the low angle of the sun combine to inhibit our vitamin D production. This low level of UV exposure in winter is especially hard on people with darker skin as the pigment in the skin absorbs the UV rays.
Interestingly, the prevalence of low levels of vitamin D in high latitudes also co-relates to the geographical incidence of multiple sclerosis. While it is not clear that there is a causal relationship, low vitamin D levels do appear to play a role in the disease. An exception to this rule appears to be the Inuit. Despite living in an area with low UV rays, they have little trouble with low vitamin D. This is probably related to a diet high in fish, which appear to be rich in vitamin D.
The lesson here appears to be everything in moderation. Too much UV exposure can cause serious health effects but, conversely, too little exposure can lead to different health effects. In Canada, daily moderate exposure to the sun is good and vitamin supplements during the winter may be a good routine to get into.
Tim Philp has enjoyed science since he was old enough to read. Having worked in technical fields all his life, he shares his love of science with readers weekly. He can be reached by e-mail at: email@example.com or via snail mail c/o The Expositor.