Wearing sunscreen at all times could starve the body of vitamins

Wearing sunscreen at all times when exposed could starve the body of vitamins which protect against various diseases, claim Edinburgh based scientists.

The news is reported in the latest edition of the Royal Society of Chemistry journal Photochemical & Photobiological Sciences.

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 of over-exposure to UV light are well publicised - such as the Australian government's 'slip,slap,slop' campaign to use sunscreen to protect from skin cancer.

But the positive effects of sunlight on the human body are less widely paraded.

Professor Mary Norval and a team from the University of Edinburgh Medical School have studied recent research into effects of the UV light on human health - and the positive and negative implications of ozone depletion.

Non-malignant skin cancers have been shown to be largely attributed to sun exposure, as have the malignant variety though these are also affected by genetic factors.

Eye damage can also occur in two main ways - formation of cataracts, and growths called pterygiums.

Prof Norval said: "Large increases in the occurrences of these two eye conditions are predicted in the future."

While the research supports various government campaigns to get citizens to protect themselves from the sun, scientists are finding more beneficial effects of UV light on humans.

It is well documented that sunlight is needed for the skin to synthesise vitamin D - 90 per cent of the body's supply of this vitamin.

Prof Norval said: "The link between rickets and lack of light has been known for almost a hundred years.

"But 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."

She added: "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."