The Science Bit: Part 4 – Sunlight – Friend or Foe?

2 09 2010

At this time of year, when the sun is (hopefully) shining and we’re looking forward to our summer holidays, messages about sun safety abound. In this seasonal Science Bit, Lisa Martin examines new research that suggests some of us play a little too safe in the sun.

In Australia, the oft-quoted “Slip, slap, slop” slogan, reminds us to slip on a t-shirt, slap on a hat and slop on the sunscreen in an effort to educate the public about the dangers of too much exposure to ultra-violet light. It’s common knowledge that this is the single most frequent cause of skin cancer, and has a premature ageing effect as well, but less well known it seems, are the positive effects of exposure to sunlight.

Vitamin D, actually a group of chemicals called secosteroids, is vital for our health.  Vitamin D is used to activate a hormone that performs a number of essential roles in the body, the most significant of which is to fix calcium in the bones, thus making them hard and strong.  A very small amount of vitamin D can be taken in through the diet, but in order to gain enough, we’d have to eat oily fish – even the skin – 3 times a day, every day! I don’t know many people who like sardines that much! Instead, the majority of our vitamin D is actually made as the result of a chemical reaction that uses sunlight.

A substance called 7-dehydrocholesterol, found naturally in the epidermis of the skin, absorbs UV light and is then broken down into vitamin D. If we do not obtain enough vitamin D, a deficiency can lead to several bone disorders, most notably, osteoporosis (brittle bones) and Ricketts (soft bones). People who spend all day indoors, those who work night shifts and those who cover their whole bodies for religious or cultural reasons, as well as children and the elderly, are most at risk of vitamin D deficiency.

A recent article in the Independent newspaper revealed that Cancer Research UK, the country’s leading cancer research and education body, is currently drafting a new position statement to reflect emerging research findings in this high profile area. Traditionally, the advice has always been to avoid going out in the sun between the hours of 11am and 3pm when the intensity of UV radiation from sunlight is strongest, to cover up and to wear a high factor sunscreen. All of these things however, are a barrier to vitamin D production in the skin.

Is it estimated that more than half of the UK population produce insufficient levels of vitamin D. We’re not helped by the fact that the UK is located in the far north of the hemisphere, where the UV radiation in sunlight is weak, but according to health writer and vitamin D campaigner Oliver Gillie, inappropriate sun safety advice is also largely to blame for the state of the nation’s vitamin D levels.

Recent research has shown that vitamin D deficiency could be a major contributing factor to several serious diseases, including heart disease, arthritis and susceptibility to infections. Gillie even believes that multiple sclerosis and insulin-dependent diabetes could both be completely eradicated if breastfeeding mothers took vitamin D supplements or spent enough time in the sun.

Clearly, recommending that people go out in the midday sun without sunscreen is dangerous advice if not communicated properly. It is still more pertinent than ever to prevent burning and the risks of skin cancer and premature ageing should not be underestimated. It only takes a few minutes of unprotected exposure to sunlight in order to make enough vitamin D, so for most people sitting outside for 3 or 4 minutes a day before applying sunscreen will be more than enough to maintain your vitamin D levels and keep you healthy.

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