For years, the sun has been public enemy No1, causing skin damage, premature ageing, skin pigmentations and increasing our risk of skin cancer. But before you head for the shade, consider this: those nasty rays are needed in the production of a crucial hormone, vitamin D, and by completely blocking out the sun you are risking a deficiency that could leave you open to all sorts of ailments. An increasing number of scientific studies are now pointing to vitamin-D deficiency as being a factor in a catalogue of illnesses including colds and flu, heart disease, strokes, diabetes, autoimmune disorders, depression, osteoporosis and many cancers. It has even been suggested as a possible cause of autism. At the root of the rate of deficiency is the habit of shunning the sun and using sun block, says the vitamin-D pro-camp. Add to that lifestyle factors that mean we live a much more indoor existence than our ancestors did and you have a population that is not getting enough sunlight to produce the vitamin D their body needs. About half of Americans are believed to have insufficient levels of vitamin D, while a recent study by the Li Ka Shing Faculty of Medicine at the University of Hong Kong revealed that more than 60 per cent of Hong Kong people were deficient. Professor Annie Kung Wai-chee, who led the study, says men fared the worst, possibly because they are likelier to be working long hours indoors. Part of the problem, she says, is the common misconception that because Hong Kong enjoyed a sunny subtropical climate, people got all the sun and vitamin D they needed. In a separate survey, Kung found 76 per cent of middle-aged and elderly women spent less than an hour in the sun over a one-week period. According to Kung, both modern lifestyle and vanity were to blame. 'Asian women like to have fair skin and are more worried about the effect the sun will have on their skin, producing pigmentations and freckles, than skin cancer,' she says. General practitioner Lauren Bramley claims about 70 per cent to 80 per cent of her patients have a vitamin-D level below the healthy benchmark of about 50ng/ml (nanogram of vitamin D per millilitre of blood). 'I had one lady patient with a level of 4ng/ml. She was in a terrible state with a lot of bone pain, depressed mood, all kinds of things,' she says. Vitamin D is a type of hormone that plays an important role in the control of calcium. It has long been known to help strengthen bones, reduce inflammation and prevent rickets in children and osteoporosis later in life. However, some scientists claim the fact that vitamin-D receptors have been found in the liver, kidney, skin, muscle, heart, pancreas, adrenal, brain, reproductive system, lungs, pituitary and thyroid, indicates it has a function to play throughout the body. Since time began, humans have gleaned most of their vitamin D from the sun. Some foods, such as oily fish and eggs, contain some vitamin D, however, the quantity pales into insignificance when compared to the amount produced by just a few minutes of sunlight. Just 15 to 20 minutes in bright sunshine produces 10,000 to 20,000 IU (international units) of vitamin D - some 50 times the amount you can get in many vitamin-D supplements. Once formed, vitamin D passes to the liver and kidneys where it is activated. It then passes into the blood where it controls calcium levels. When levels in blood are sufficient, it moves on into body tissue and into the cells. It is there, says John Cannell of the Vitamin D Council, a non-profit advocacy group based in the United States, that it really goes to work, turning 'genes on and off at a dizzying rate, genes that are either making proteins that are essential to fighting cancer or genes that are making proteins that are promoting diseases like cancer'. With many experts in consensus about the importance of vitamin D, you would think solving the deficiency problem would simply be a matter of going back to worshipping the sun. However, the threat of skin cancer still looms large. In addition, a growing pollution problem that screens out the sun's rays, lifestyle factors that keep us increasingly indoors and the Asian passion for pale complexions and whitening formulas, all make the natural solution less viable. One way around this problem is the vitamin-D supplement, says Bramley who recommends this option to many of her patients. But how much one should take is another dilemma. As with any supplement, there is a risk of overdosing, which can lead to too much calcium in the blood causing liver and bone damage and kidney stones. This is something that doesn't happen when we get our vitamin D through sunlight because our body has an 'overload' mechanism which switches off production when it reaches a certain level. Kung, like the US Food and Nutrition Board, recommends a daily dose 200 IU for children, 400 IU for those aged over 50 and 600 for those over 70. The American Academy of Paediatrics advises 400 IU for children. However, these amounts have been deemed too low by the Vitamin D Council, which recommends levels of between 1,000 IU and 5,000 IU and even higher. In 2007, the Canadian Cancer Society weighed up the pros and cons of sun exposure against vitamin D's role in preventing cancer and advised all Canadians to take 1,000 IU in winter, while those at risk of cancer were advised to take it year-round. Bramley shares the Vitamin D Council's belief in higher doses and recommends 1,000 IU for children under 18 months and then from 2,000 IU up for children and adults. 'I used to do the blood test first, but so many of the results were coming back deficient so now I put patients on a dose of 2,000 units, and encourage them to do a blood test after about three months and adjust the levels if necessary,' she says. 'I love seeing my patients come back after they have been taking the supplements. They look healthier and have lost that greenish white hue that so many people in Hong Kong seem to have. 'I have also seen remarkable results with things like mood and weight loss. It's a hormone and so is very good for those with insulin resistance and weight around the middle. I am also seeing fewer patients with coughs and colds.' However, there is another dilemma for Hong Kong in that vitamin-D supplements are difficult to buy, says Bramley, who ships supplies from the US for her patients. This means until it arrives in pharmacies in Hong Kong, you have to buy overseas, order online or top up your D-levels the way your ancestors did, with regular and careful exposure to sunlight and a diet of vitamin D-rich foods. 'It's a controversial topic as the advice has been so much the other way with 'slip, slop, slap,'' says Bramley. 'But the recommendation is not to get loads of sun. Even 15 minutes of direct exposure can yield great results, even when it is cloudy. 'Start off slowly at low-intensity times of the day and experiment to find what amount of sun works for you. Learn to have brief exposure first and then apply the sun screen.'