Vitamin D is a chemical that is made in the skin when the skin is exposed to sunlight. Vitamin D is converted in the body into a hormone that is very important in ensuring that the levels of calcium in the blood stay within a narrow range. We know that having sufficient vitamin D is very important for growing children so that they have strong bones. Small amounts of vitamin D are found in foods such as sardines, eggs, liver and some meat.
What are the potential benefits of sun exposure?
Sun exposure of the skin is the most important source of vitamin D for most Australians. As well as making vitamin D, exposing the skin to sunlight also triggers the release of a number of other chemicals and molecules that can have overall health benefits. Vitamin D is known to be important for healthy bones. Although some research has suggested that vitamin D might be important to prevent a large range of other diseases, this has not been proven. In particular, vitamin D supplementation does not seem to decrease the risk of these diseases. It is possible that the other molecules produced in the skin when it is exposed to the sun have benefits for these diseases.
What is sensible sun exposure?
Only very small amounts of time in the sun is needed for the production of vitamin D and other molecules that may benefit health. In the summer in Perth and other parts of Western Australia this is only 5-10 minutes on most days of the week. In the winter the time required will be longer and varies according to whether you are in the north of the state (where 5-10 mins will still be enough) or in the south (where up to half an hour will be needed). At all times of the year a longer exposure time is required for people with darker skin and less time is required if more skin is exposed. It is very important not to get sunburnt Gradual exposure to the sun will allow the development of a tan and this provides some sun protection, equivalent to using a sunscreen with an SPF of around 4. Hats provide protection only from direct sun and not from sunlight that is reflected off surfaces. The UV Index, which is published in the newspaper and is available at www.myuv.com.au provides a good guide to how sunny it is and what sun protection you should use. More guidance on sensible sun exposure is available on the Cancer Council WA website.
What are the potential risks of too much sun exposure?
Sun exposure of the skin is the main cause of skin cancers. Two out of three Australians will have a skin cancer removed by the time they reach 70 years of age. There are three main types of skin cancer: basal cell carcinoma (the most common, least likely to kill, but removal can cause scarring and be disfiguring); squamous cell carcinoma (a common cancer in older people with a history of long-term sun exposure and often requiring quite extensive surgery to remove) and melanoma (the most dangerous of the skin cancers). Australia has the highest incidence of melanoma in the world and it is the most common cancer in women aged 15-29 years. Too much sun exposure also damages the eyes causing cataract and a growth on the eye called a pterygium. Flare-ups of cold sores on the lips and sometimes shingles can also occur following too much sun exposure.
What affects vitamin D production?
Most of our vitamin D is produced from sun exposure of the skin. This means that the intensity of the UV radiation, and particularly the UV-B radiation, is very important. UV-B radiation levels are highest in the middle of the day, in summer, and closer to the Equator, i.e. northern WA compared to southern WA. Vitamin D is made most effectively at solar noon (midday in summer), but this is also the time when sunburn occurs most quickly so any sun exposure should be brief. The more skin exposed to the sun, the more vitamin D is made. So exposing a lot of skin for a short time is very effective. Darker skin has inbuilt protection from the sun through higher levels of melanin in the skin. This means that people with darker skin do not make vitamin D as effectively as people with lighter skin - but they don't burn as easily either.
What is the difference between UV-B and UVA?
Ultraviolet radiation is part of the solar spectrum, that includes infrared (wavelengths longer than red light, and we feel this as heat); visible light (from red through the colours of the rainbow - orange, yellow, green, blue, purple - that represent decreasing wavelength); and ultraviolet (wavelengths shorter than purple/violet). Of the ultraviolet wavelengths, UVA are the longest - so after purple/violet, the next shortest is UVA. Then the UV-B wavelengths are shorter than the UVA wavelengths. There is also UVC, but this is stopped in the Earth's atmosphere and doesn't reach the ground. UV-B has higher energy and causes more damage to DNA in our skin, but only penetrates to the very top layer of the skin; UVA doesn't have as much energy, but penetrates further into the deeper layers of the skin and can cause damage to DNA as well as the elastic tissues in skin. We think that photoageing of the skin - the wrinkles that old people get - are largely caused by UVA radiation.
Should my vitamin D levels be tested?
We know from the recent Australian Health Survey that only 6% of the Australian population aged 12 years and over had seriously low vitamin D levels. Most people will have adequate vitamin D if they spend any times outdoors and do not need to be tested. People who never go outdoors, e.g. some office workers, people in aged care homes, or who always wear clothing that fully covers their skin when they are out, are at high risk of vitamin D deficiency and should take vitamin D supplements. There is no real need to test their vitamin D levels because we already know that they will be low. Dark-skinned people in southern latitudes may need to take a vitamin D supplement during winter and early spring, particularly if they are seldom outdoors.
What is the UV Index?
The UV index is a measure of the intensity of UV radiation. It is published in the newspaper, is on TV and can be found at www.myuv.com.au or the website for the Australian Radiation and Nuclear Safety Agency (ARPANSA). The UV Index is a number that is linked to a colour scheme - the higher the number the more intense is the UV and the greater sun protection is required.