More than any other people, Australians worry about the risk of skin cancer. But now they're being told by doctors to throw away the sunblock, reports Jeremy Laurance. So who is right?

There is something disturbing about Sydney when you see it, as it were, in the flesh. Australia's premier city sits astride a sparkling harbour under an azure sky. There is the famed opera house, the sunlight glinting off its polished fins, and the magisterial Harbour Bridge linking the northern and southern shores. You see why local estate agents promote Sydney as the city with the matchless lifestyle.

There is something disturbing about Sydney when you see it, as it were, in the flesh. Australia's premier city sits astride a sparkling harbour under an azure sky. There is the famed opera house, the sunlight glinting off its polished fins, and the magisterial Harbour Bridge linking the northern and southern shores. You see why local estate agents promote Sydney as the city with the matchless lifestyle.

Now take a look at the people. They are pasty-faced. Pink necks emerge from pastel polo shirts. The clothes are grey and beige, the skin a pimply shade of pale. To anyone who has holidayed on the shores of the Mediterranean, with its smooth, olive-skinned peoples, vibrant colours and noisy street culture, this comes as a shock - and a disappointment. Here, in one of the most sun-kissed cities of the world, the people look as though they live underground.

In a sense, many of them do. A generation of Australians has been raised to fear the sun, never venturing out without a hat, long-sleeved shirt and Factor 30 sunblock. These people avoid the beach, keep their children covered head-to-toe in summer and go for regular six-monthly check-ups in the ubiquitous skin cancer clinics.

This could be about to change. The Cancer Council Australia has issued new advice on the sun, which, some claim, amounts to a seismic shift in its thinking. After more than two decades of warning people to stay out of the sun, the new advice, to be published in The Medical Journal Of Australia this month, says that a little of it is essential for good health.

Australia has led the world in alerting its population to the damage caused by the sun and the link with skin cancer. So if it is having a re-think, it is time to listen. The reason for this change of heart is that a new problem has emerged in Australia - vitamin D deficiency. Vitamin D is made by the action of the sun on the skin and is essential for good bones, a healthy immune system and possibly also for protection against some forms of cancer. While skin cancer still poses as great a threat as ever, the new advice says that people should remember the benefits, as well as the risks, of the sun.

Spelling out exactly what this means, the advice in MJA says that, in Sydney and southern parts of Australia, people should expose their unprotected face, hands and arms to the sun for five to 10 minutes before 10am or after 3pm on most days of the week in summer to get adequate doses of vitamin D. In winter, they need two to three hours of exposure over a week.

That may not sound like much, but it amounts to a tacit acknowledgement that the warnings about the sun have been overdone. We live in a closeted world, moving between home, car and office, and see too little of it. Some people - the elderly, the housebound, people with dark skin or who wear enveloping clothes such as the chador - are at particular risk.

Bruce Armstrong, professor of public health at the University of Sydney, says: "It is a revolution. I have worked in public health and been preaching sun avoidance for 25 years. But what this statement says is that there are two sides to the story. You need to get enough vitamin D and you need protection from the sun. These two objectives are in conflict and we have to advise people how to do both."

The implications for the pale-skinned British living under grey English skies have yet to be calculated. Professor Armstrong says: "Ideally, we want to give people a sense of how much sun they need according to their latitude and the time of day. Obviously they are going to need more time in the sun if they live in northern Europe than in Australia."

Australia is the skin cancer capital of the world. Pale-skinned immigrants from northern Europe burned under the fierce southern skies and, over the latter half of the last century as the fashion for tanning grew, cases of melanoma, the worst form of skin cancer, soared. Among men in northern Queensland, the rate has risen to 51 cases per 100,000 population - 20 times higher than the rate in Scotland. In response, the country launched the world's most successful sun avoidance strategy. The government's "slip, slap, slop" campaign in the 1980s - slip on a shirt, slap on a hat, slop on the sun cream - was copied around the globe.

On Bondi beach, you can see how the advice has taken hold. While the stretch of golden sand is covered in bronzed bodies soaking up the sun, at least three-quarters of them are foreigners. The few Australians on the beach are mostly well covered or smeared head to toe in sun cream. Karon Caplan, 36, wearing a straw hat and ankle-length black dress, has brought her two children, aged three and four, to the paddling pool. Both are dressed in swimming costumes that cover them from the elbows to the knees and wear hats with flaps protecting their necks.

"I am pretty paranoid about the sun," she says. "I never go out without sunblock and both the kids are not allowed out at school without hats. If someone is burned red here they are probably from the UK."

"Slip, slap, slop" was replaced in the 1990s because research suggested that most people were only picking up the third part of the message about slopping on sun cream. The new campaign, called Sunsmart, was launched in the 1990s and stressed the importance of seeking shade in the heat of the day. "Between 11 and 3, slip under a tree. The best sunscreen of all is absolutely free." Meanwhile, melanoma rates continued to rise.

Against this background, the latest statement from the Cancer Council Australia - that some sun exposure is good for you - has provoked fevered debate among specialists. It has been agreed by the Australian and New Zealand Bone and Mineral Society, Osteoporosis Australia and the Australasian College of Dermatologists. The cancer specialists and dermatologists are the most surprising signatories, as they are the doctors most aware of the damaging effects of the sun on the skin. Unsurprisingly, they are anxious that they might undermine the sun protection message, and are playing down the importance of the change.

Craig Sinclair, the chairman of the national Skin Cancer Committee for the Cancer Council Australia, says: "It is not so much a re-think as about understanding that there are both risks and benefits from the sun. We need to recognise that some groups are vitamin D-deficient and they need sun exposure or vitamin D supplements. But the sun-protection message is as relevant as it was 20 years ago.

"It's simply that, during some parts of the year, you don't need sun protection. We can now say how much exposure people need to get adequate vitamin D so they can understand that easily."

Robin Marks, professor of dermatology at the University of Melbourne and a member of the Skin Cancer Committee, is more outspoken. He says: "We have always known it was necessary to have sunlight for healthy growth and development. All we are doing is trying to spell out exactly what that means. Nothing has changed."

If there is a problem of vitamin D deficiency in Australia it is likely to be multiplied in Britain. Grey skies and short days from October to March mean that 60 per cent of the population are deficient in the vitamin by the end of the winter, according to a survey last year. However, more foods in Britain, such as margarine, are fortified with vitamin D than in Australia, which helps to counter any deficiency.

A shortage of vitamin D leads to rickets in children, which has made a comeback in Britain among Asian and Afro-Caribbean families, and osteomalacia (weak bones) in adults, contributing to the epidemic of fractures among the elderly. Studies have also linked lack of the vitamin to the incidence of multiple sclerosis - the condition is commoner in countries furthest from the equator, which get less sun - and there is accumulating evidence that it may play a role in other autoimmune diseases such as Type 1 diabetes, and in cancers of the colon, breast, prostate and ovary.

Graham Bentham, professor of environmental sciences at the University of East Anglia, says: "The survey showed that a substantial proportion of the population has levels of vitamin D by the end of the winter that are insufficient. They are not low enough to cause osteomalacia, but they are bad for the bones and may increase the risk of other diseases."

New findings by researchers from the University of Sydney led by Professor Armstrong, published in the International Journal of Cancer in December last year, have added to the controversy. They show that people who spend more time in the sun have a lower risk of the cancer non-Hodgkin's lymphoma. The finding was confirmed last month in a second study by researchers from Sweden and Denmark, and published in the Journal of the National Cancer Institute (JNCI).

Most remarkable of all, however, was a study published in the same issue of the JNCI, which found that people with greater lifetime exposure to the sun were more likely to survive melanoma. The researchers, the same team from the University of Sydney, say that the finding is independent of increased skin awareness and earlier diagnosis, and suggest that vitamin D, melanin (the pigment that darkens the skin) and DNA repair may all be stimulated by the sun and help protect against the cancer.

Some dermatologists are now starting to challenge the view that there is "no such thing as a safe tan", arguing instead that the real risk is from sunburn. But this is still heresy. Michael Holick, a professor of dermatology, lost his post at Boston University for saying as much in a book, The UV Advantage, published last year.

In the UK, Dr Neil Walker, chairman of the UK Skin Cancer Prevention Working Party, ruffled feathers when he described warnings to avoid the sun entirely as "draconian and unnecessary". His view was backed by Professor Brian Wharton, chairman of the British Nutrition Foundation, who said: "We do need some sensible use of the sun and we have been swinging too strongly against it." Oliver Gillie, author of Sunlight Robbery, which spells out the dangers of insufficient vitamin D, has asked the government and Cancer Research UK to alter the offiical SunSmart message in the UK. "The present message is putting the health of the public at risk and should be changed before the summer starts. In our climate, we need to sunbathe whenever we can in order to get enough vitamin D for optimum health, but of course it is important to avoid burning."

The war over the sun is far from over. But it looks as though those who regard it as the enemy may be in retreat.