As the government calls for more people to take vitamin D Peta Bee investigates why we all need a little more of this sunny supplement in our diet

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With warmer weather finally here, we can say hello not only to long evenings but to our most reliable supplier of vitamin D: sunshine. Such has been the rise in prominence of this nutrient that we all know we need it to stay healthy. High levels have been linked to protection against heart disease and cancer, osteoporosis and a wide range of health problems.

A recent article in the British Medical Journal  even linked vitamin D defiency to coronavirus, with deficiency in the vitamin a factor in the progression, severity and mortality of those with covid-19 and it has been reported that Public Health England will advise this week that everyone should supplement 10µg Vitamin D daily during the lockdown period.

Yet confusion surrounds where it comes from and how we can boost our stores to the extent that many of us fall woefully short of getting anywhere near enough. It’s estimated that around half the white population, up to 90 per cent of the multi-ethnic population and as many as one quarter of British children display deficiencies. So what should we be doing and what’s the safest way to boost stores? We asked a panel of experts and reviewed the evidence:

How much vitamin D do we really need?

There is no recommended daily amount of the vitamin in the UK although around 600 IU (15mcg) is generally recommended and if your levels are found to be inadequate then safe, sensible exposure to sunlight is advised as a starting point. 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 4,000 IU per day (100mcg) from all sources — sun, diet, supplements — is best for optimum health.”

How are we missing out?

By far, the most efficient source is the sun as it is synthesised when chemicals in the skin react to ultraviolet rays. But growing concerns for adverse effects of direct sunlight, coupled with overuse of high factor sunscreen combined with our increasingly indoor lifestyles are largely to blame for diminishing levels. One recent study suggested 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.

The Swedish researchers said that guidelines telling people to stay out of the sun to reduce the risk of developing skin melanoma may backfire. After following 30,000 women over 20 years, their findings showed that sun avoidance led to an increased risk not only of melanoma, but also of premature death from any cause, including other forms of cancer. Children who spend too much time on computer and video games 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. At Southampton General Hospital, experts uncovered evidence to suggest a resurgence of rickets, a problem previously linked to Victorian poverty that is caused by low levels of vitamin D.

MORE GLOSS: Kids' health - fitness from 1 to 10

Gyms and trendy workout clothing aren’t helping matters

Dr Graeme Close, a researcher in sports nutrition and exercise metabolism at Liverpool John Moores University says many of our workout habits compound the lack of vitamin D available to our bodies. “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 fitting compression-type clothing and an SPF that prevents exposure to the sun.” Combined, these factors mean that “even using conservative guidelines” up to 70 per cent of the recreational and serious athletes tested by Dr Close are found to have worryingly low vitamin D levels. Gwyneth Paltrow, known for her dedication to fitness almost as much as for her acting, is among those to have been diagnosed as vitamin D deficient a few years ago. And among the gym generation, it is increasingly widespread.

How much sunlight is needed?

Experts remain cautious about advocating sun exposure because, of course, too much raises the risk of some forms of cancer. As things stand, the time spent in the sun but without sunscreen should be minimal but regular. Cancer Research UK  recommends “only a few minutes in the summer sun in the middle of the day without sun protection” between April and September as sufficient to ensure you boost levels. “Photobiologists say 15 minutes of UK sun is about right and that exposure to your face and arms is all that’s needed,” says Professor Dorothy Bennett, a leading vitamin D researcher and head of the molecular cell science research centre at St George's, University of London .

Children generally need less time due to their smaller body size, around 10-12 minutes daily without sunscreen. People with darker skin will need to spend longer in the sun to produce the same amount of vitamin D. All experts agree that the skin should never be allowed to redden or burn. Sun bingeing could cause more problems than short bouts of regular exposure. And at all other times, wearing sunscreen is imperative.

Is food a good source?

Not as good as you might think, says Professor Bennett. “We can get it from food up to a point, but it is hard to get enough from the diet.” Emma Williams, a nutrition scientist at the British Nutrition Foundation , says that on average, we need around 10 mcg of vitamin D a day from food (children under the age of 4 need 7-8.5mcg) 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.

Vegans may be more likely to suffer from deficiency too, as the main food sources of vitamin D are off limits in a plant-based diet.

Should we pop a pill?

Worried about deficiencies, up to one in three people now take the sunshine vitamin in supplement form  at some time during the year. It’s not without risk. Vitamin D is fat-soluble so there is potential for toxicity if too much is consumed. Most studies suggest that even doses upwards of 10,000 IU a day of the vitamin aren’t toxic, but the advice is to stick to supplements containing 1,000 to 2,000 IU if you go down that route.

Not everyone is convinced it’s worth the expense. Researchers at the University of Auckland reported in the Lancet Medical Journal that there is little reason to prescribe vitamin D supplements to adults looking to reduce the risk of fractures or disease as they offer no significant protection against either.

MORE GLOSS: Should you be taking a pre-workout supplement?

Get enough and you might find you are fitter

Health benefits are expected when you correct your vitamin D status, but an unexpected bonus could be that you get more out of your workouts in the long term. The vitamin is more like a steroid hormone in the way it acts on the body and one side-effect of low value is diminished muscle function. 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. Dr Close and his team gave a group of footballers either a vitamin D supplement or a placebo and found that, after 8 weeks of training, the nutrient group showed significant improvements in two out of six fitness assessments - 10 metre sprint times and vertical jumps - compared to no change among their placebo counterparts.

Want to know more? Here are  10 things worth knowing about vitamin D

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