How much sun exposure do we really need?

Fear of skin cancer means many of us may be lacking in the vital vitamin D, so what’s the answer.

WHAT to do when the sun comes out — slap on the sunscreen, head outside to soak up the best source of vitamin D available or avoid the rays out of a fear of sun damage?

It’s a dilemma most of us face when summer finally arrives and it is fuelled by a seemingly never-ending stream of contradictory reports about what is best practice.

A recent study added to the confusion by concluding that women who avoid sunbathing in the belief that they are lessening the risk of skin cancer might be more likely to get the disease than those who lie in the sun every day.

According to Swedish researchers, guidelines telling people to stay out of the sun to reduce exposure to the ultraviolet radiation that is strongly inked to skin melanoma may backfire.

Following a 20-year study of 30,000 women, their findings, published in the Journal of Internal Medicine, suggest that sun avoidance leads to an increased risk not only of melanoma, but also of premature death from any cause, including other forms of cancer.

Dr Pelle Lindqvist, author of the study, said the results “clearly showed that mortality was about double in women who avoided sun exposure compared to the highest exposure group”.

A lack of vitamin D from too little sunlight exposure, suggested the researchers, was probably partly to blame for the adverse health effects in their trial.

It’s not the first time levels of vitamin D have been held up as a barometer of wellbeing. Indeed, if there is a vitamin of the moment, it is this one. Last month, two large studies, both published in the BMJ, showed that people with low levels of vitamin D are more likely to die from cancer and heart disease and to suffer from other illnesses.

Others have suggested that good intakes appear to reduce levels of bad cholesterol, that too little elevates the risk of high blood pressure, osteoarthritis, autoimmune diseases like multiple sclerosis and arthritis.

How much do we need?

For all its importance, however, how much we need and how we should obtain vitamin D remains shrouded in confusion. The only reliable way of finding out if levels of vitamin D are low is to have a blood test. It’s thought that around half the white population, up to 90% of the multi-ethnic population and as many as one quarter of school children in Britain and Ireland are deficient in the vitamin.

“How to get enough vitamin D is simply not that straightforward,” says Professor Dorothy Bennett, a leading vitamin D researcher and head of the molecular cell science research centre at St Georges, University of London. “We can get it from food up to a point, but it is hard to get enough from the diet. So we need other sources and that is where it becomes controversial.”

Indeed, experts cannot seem to agree on precisely how much of the vitamin we need. Nutritionists say around 10mcg of vitamin D a day mainly from food (children under the age of four need 7-8.5mcg) should be enough, but while fortified breakfast cereals, dairy products, egg yolk and oily fish will provide some of that intake, the vitamin is not as widely available in the diet as other nutrients.

Oliver Gillie, author of Sunlight Robbery and a leading vitamin D campaigner, says: “We should aim for at least 2000 IU (50mcg) based on what studies have found although many experts believe 4,000IU per day (100mcg) from all sources — sun, diet, supplements — is best for optimum health.”

Sun is the best source

Nicknamed the sunshine vitamin, the most efficient source is the sun as it is synthesised when chemicals in the skin react to ultraviolet rays. But a lack of direct sunshine, fuelled by growing concerns about its adverse effects, and overuse of high factor sunscreen combined with our increasingly indoor lifestyles are largely to blame for diminishing levels.

Computer games and TV mean that many children are getting so little sunlight that their vitamin D levels have plummeted to the point that they develop bone deformities, an extreme side-effect of deficiency.

“It’s no myth that more of us are deficient,” says Prof Bennett. “Equally it is not really a surprise as nobody is arguing with the fact that the sun’s rays are the main cause of skin cancer. It’s a real dilemma for many people.”

So where should we start?

Experts remain cautious about advocating sun exposure. Professor Kevin Cashman, head of the vitamin D research group at University College, Cork, says that researchers still need to pinpoint the precise level of safe sun exposure that causes minimal skin damage but allows for vitamin D production — if, indeed, it exists.

“With the current lack of such data it is clear why sun awareness campaigns are in place,” Prof Cashman says.

“It may well be that there is no such safe level and so there may be a zero tolerance public health policy in the future.”

As things stand, time spent in the sun but without sunscreen should be minimal but regular. Sun bingeing, says Gillie, could cause more problems than short bouts of regular exposure.

The Irish Cancer Society advises following the WHO’s recommendations of getting five to 15 minutes of casual sun exposure to hands, face and arms two to three times a week during the summer months. People with darker skin will need to spend longer in the sun to produce the same amount of vitamin D. But, it warns, “a little sun exposure goes a long way”.

Without exception, all experts agree the skin should never be allowed to redden or burn and heading out at the hottest time of the day is inadvisable.

However, as a rule of thumb, if shadows are longer than your body then the sun is not strong enough to have an effect.

Are supplements the answer?

For many, a safer option seems to be to pop a pill. Up to one in three people now take the sunshine vitamin in supplement form at some time, its popularity buoyed by some evidence that higher levels offer greater protection against some diseases. Are they doing the right thing?

As a fat-soluble vitamin, there is potential for toxicity if too much vitamin D is consumed and several studies have raised concerns about risks of high-dose vitamins, including vitamin D.

Although recent evidence suggests that even doses upwards of 10,000 IU a day of the vitamin aren’t toxic, experts recommend sticking to supplements containing 1,000 to 2,000 IU.

A review of 462 studies involving more than a million adults carried out at the International Prevention Research Institute in Lyon last year concluded that a lack of vitamin D is not a trigger for many common illnesses and that taking supplements to boost your intake will make little difference to your health.

The debate continues.

VITAMIN D CAN BOOST FITNESS

Boosting your vitamin D intake is not just good for your health, it can also boost your fitness. Dr Graeme Close, a British researcher in sports nutrition and exercise metabolism, says that many of our workout habits compound the lack of vitamin D available to our bodies.

“It’s not just that a lot of people exercise indoors,” he says. “Even those who go outside often run or cycle early in the morning or late in the evening on a commute. Or they wear tight compression-type clothing and a sunscreen that prevents exposure to the sun.”

Combined, these factors mean that “even using conservative guidelines” up to 70% of the recreational and serious athletes tested by Close were found to have worryingly low vitamin D levels.

Steve Simbler, a sports pharmacist who has worked with Olympians, suggests other factors might be at play. “Vitamin D is fat soluble and any we take and don’t need immediately is stored in body fat,” he says.

“Many recreational exercisers and athletes tend to have lower percentages of body fat than the average person, so their ability to store it may be compromised, although research needs to be conducted to prove this to be the case.”

What is clear is the impact that dwindling vitamin D has on many aspects of fitness.“One side-effect of low values is diminished muscle function,” Close says. “It is needed by stem cells for muscle regeneration and recovery after a hard session and there is evidence it might protect immune functions during periods of intensive training.”

Can boosting levels reverse these risks? Close and his team gave a group of footballers either a vitamin D supplement or a placebo and found that, after eight weeks of training, the nutrient group showed significant improvements in two out of six fitness assessments — 10m sprint times and vertical jumps — compared to none among their placebo counterparts.

This year a team of exercise scientists from the University of Kentucky found that giving a vitamin D supplement to a group of swimmers, who trained predominantly indoors, seemed to offer protection against muscle injuries compared with training partners who took a daily placebo.