When one of Scotland's leading skin cancer researchers, Professor Rona Mackie, popped out of her city office to buy a lunchtime sandwich last week, she chose to walk on the sunny side of the street. While many other Scots might have done the same, indulging for 15 minutes in some rare Glasgow sunshine, it would be fair to question Mackie's good sense.

For years, the British public have been warned about the health dangers of sun exposure and Mackie, of Glasgow Medical School, surely knows the risks better than most. But the doctor is also aware of a newer, emerging contradiction: that too little sun is bad for our health.

"Nothing is ever black and white in medical research and often there are two sides to a theory," says Mackie, a professor of dermatology. "While it is proven that too much sun exposure increases your risk of skin damage and skin cancers, it is also claimed that a lack of sun is causing serious vitamin D deficiencies among the British population, the consequence of which can be mentally and physically detrimental to many people."

Now we're confused. In Scotland the rate of malignant melanoma, the least common but potentially fatal type of skin cancer, has trebled among Scottish men and doubled among women during the past 30 years. Diagnoses of other, more easily treatable, skin cancers have also risen sharply. Skin cancers are strongly associated with exposure to the sun's UV rays and if the public was to adhere to the most stringent guidelines in this country they would never dare to go out on a summer's day slathered in anything less than factor 15 sun cream.

Indeed, according to the SunSmart campaign backed by Cancer Research UK, even sun lotion should be seen as a last line of defence. The charity's science information officer, Dr Anthea Martin, says: "We'd be advising that when it's sunny, people, especially children and those with fair skin, should be seeking out shade and wearing clothes that cover their skin. Sun lotion often gives people a false sense of protection from harmful UV rays and we would not recommend that people rely wholly on this."

On the other hand, scientists now claim that vitamin D, produced by the bare skin's natural response to sunlight, is good for our health.

"In recent years, scientists have made more and more links between health and vitamin D," says Mackie. "A serious lack of vitamin D is linked to an increased risk of brittle bone problems in the elderly. There is some evidence to suggest that illnesses such as Multiple Sclerosis, Seasonal Affective Disorder, some forms of depression and type 2 diabetes are related to a lack of vitamin D. This is thought to be particularly relevant in Scotland, where winters are dark and dull, and the summers only intermittently sunny.

"Research also appears to reveal that increased levels, or adequate levels, of vitamin D in the blood may have a protective effect against some cancers, such as colon, breast and prostate cancers, because of its ability to regulate the production of cells, a control that is missing in cancer."

This month, two new studies offered a further boost to the powers of vitamin D. German research, reported in the International Journal of Cancer, reveals a reduced risk of lymph system cancers among people who spent a greater number of days on sunny holidays. In addition, Dundee University scientists have concluded that a dose of vitamin D, which can improve blood vessel function, could be the solution to reducing the incidence of heart disease in Scotland.

With two seemingly persuasive, but opposing, arguments perhaps the most pertinent question is: how much sun is enough? "Again the issue is a bit confusing and research into both areas is ongoing," says Mackie. "What we do know though is that there is a strong association between serious episodes of sun burn and a person's chances of later developing skin cancer. People should be avoiding pink or red skin, and skin that peels is definitely not a good idea. Three bad burns in the one place on the body lead to an increased risk of cancer.

"Fair-skinned people must also be much more careful compared to those with darker pigmentations."

Mackie's advice is that people get to know their skin and learn how much is enough for them. "As a dermatologist I wouldn't be saying that the sun should always be avoided and that sun cream is always absolutely necessary. Moderation is the key to a commonsense approach to spending time in the sun," she says. "Sometimes, however, I think some of the advice is too severe for a summer in Scotland. The other day when I was out for 15 minutes in the sun with bare arms I did not have lotion on. I don't believe that spending short periods unprotected in the sun will significantly increase a person's risk of skin cancer."

Mackie's advice also appears to tie in with prevailing views about how the skin manufactures vitamin D. Most experts agree that sun cream inhibits this vital process and various studies have suggested that anywhere between a few minutes a day and half an hour three times a week of sunshine on bare skin is required for adequate vitamin D production. Writing in the British Medical Journal in 2003, Professor Cedric Garland, of the University of California, claimed that 10 to 15 minutes daily without sun cream was enough. One Manchester University study even pinpointed the exact time to be out in the sun, stating: "Calculations have found that the best time if you want to maximise vitamin D production and its benefits, is 10 minutes at midday." Another study at Boston University Medical Centre concluded "in summer a light-skinned person at the beach should get all the vitamin D they need in about five minutes".

The problem for much of the Scottish population, however, is that for many months of the year the sun is almost non-existent. "In northern territories and especially during, for example, a Scottish winter, the amount of sun available is actually not going to be enough to provide adequate levels of vitamin D in the body," says Professor Allan Struthers, who led the recent cardiovascular/vitamin D study at Dundee University. "In a study of 80 people with diabetes living on Tayside during the winter months, 50% were deficient in vitamin D.

"It is one of the reasons why we believe there is a link with higher rates of heart disease in Scotland than in places with more sunlight hours."

However, Struthers does not actually advise people to spend more time in the sun. "The problem is that sun exposure has other dangers like skin cancer so rather than risk too much sun, it might be that we would advocate some people to take a dose of vitamin D in pill form," he says.

And perhaps, then, Professor Struthers has arrived at the solution to the latest health dilemma.

"Certainly we would prefer that the public are encouraged to find other sources to maintain vitamin D levels," says Martin at Cancer Research UK. "Whether it is in pill form, although dosages have not yet been researched enough, or through improved diets, such as eating more oily fish, margarines and fortified cereals, this is better than telling people to get more sun."

Indeed, Mackie believes that vitamin D pills could be the next "must-buy" among UK residents. "Scientists are still not sure how much of a vitamin dose is required for particular health benefits, and for which members of the public. This vitamin D information is still so new and in fact it is hard to find vitamin D pills on sale. But you can certainly see where this line of research is leading."

So what should you do? Common questions answered



If sunlight causes skin cancer how can it protect against other cancers? No-one knows the exact answer to this but it's thought that the clues lie in a vitamin that may play a role in controlling the production of cells - vitamin D, manufactured in the skin when it is exposed to sunlight.

So, are sun creams bad for us? No, sun creams block out the harmful UVA and UVB radiation, reducing the chance of developing skin cancer. They are vital for good skin health. The problem is that by blocking out the UV radiation, they also reduce the skin's ability to manufacture vitamin D.

Can anyone tell me how much time I can sit in the sun unprotected? It depends on your skin type. But common sense says there is no point in taking the risk so it is better to play it safe by wearing higher-factor sun creams.

But how will I get my vitamin D dose? Some experts believe it's enough - and safe - to spend a few minutes in the sun with bare face and hands each day. Others half an hour three times a week wearing less clothing. There is a lot more research to be done before we know, but it is an individual thing.

Do different coloured skins produce more vitamin D? Yes, people with greater amounts of melanin, which result in darker skin, have a reduced ability to produce vitamin D from sunlight. In some case it is recommended they take a supplement in pill form.

Are there any other sources of vitamin D? It can be found in foods including cod liver oil, sardines, herring, salmon, tuna, milk, cheese, eggs, fortified margarine and fortified breakfast cereals. Nutritionists recommend we consume at least two portions of oily fish a week as well as fortified cereals and margarine as part of our diet. But scientists do not believe diet alone can provide us with vitamin D.

Can you overdose on vitamin D? High doses over long periods may weaken bones.

If the sun is so rare in Scotland, why are skin cancer rates increasing? There are two main reasons. When the sun does come out in Scotland we tend to sit out for long periods with little sun protection. This leads to the other reason, which is that Scots holiday abroad in hot climates more often than we did three decades ago.