Ozone depletion is not all bad, say an international team of scientists. 

Depletion of the ozone layer over the past four decades has resulted in increased levels of UV light reaching the earth. Meanwhile, worldwide research into the knock-on effects on human health has continued apace. The adverse effects of over-exposure to UV light are well publicised, such as in the Australian government's 'slip, slop, slap' campaign. But the positive effects of sunlight on the human body are less widely paraded. 

Mary Norval from the University of Edinburgh Medical School, UK, and colleagues have looked at recent research into the effects of the UV light on human health, to draw out both the negative and positive implications of ozone depletion. 

The most serious UV damage occurs in the skin and eyes, said Norval. Non-malignant skin cancers have been shown to be largely attributed to sun exposure. Exposure to UV light is a major contributor to the development of malignant melanomas too, although genetic factors do have a large effect. As a result of ozone depletion occurrences of all types of skin cancer are predicted to double over the next ten years, said Norval. 

The sun damages the eye in two main ways; the formation of cataracts, and growths inside the eye called pterygiums. According to Norval, large increases in the occurrences of these two conditions are also predicted in the future. 

This research all supports the various government campaigns that remind citizens to protect themselves from the sun. 

At the same time, researchers are finding more beneficial effects of UV light on humans. It is well known that sunlight is needed for the skin to synthesise vitamin D - 90 per cent of the body's vitamin D is acquired this way - and the link between rickets and lack of light has been known for almost a hundred years. But Norval says that vitamin D is now implicated in the prevention of an increasing number of non-skeletal disorders. These include internal cancers, such as colon, breast, prostate and ovarian cancers, and autoimmune diseases, like multiple sclerosis and insulin-dependent diabetes. 

Sunscreens shield the body from the type of UV light needed to make vitamin D, so covering any exposed skin with sunscreen at all times is not advisable, explained Norval. 

Despite the distinct possibility that the ozone layer will repair itself in the coming decades, the take home message from the research so far is that we should strike a balance between the positive effects of vitamin D formation and the serious negative effects of too much sun exposure, said Norval. 

Nina Athey-Pollard