Why you may sun need more if you’ve got a big tum

As the government warns more and more of us lack vitamin D...

AFTER the recent heatwave, it seems scarcely believable: one in five adults in Britain has low levels of vitamin D, the sunshine vitamin. This may be because we’re covering up more in the sun — think Nigella Lawson and her ‘burkini’ — and slavishly applying sun cream in response to skin cancer warnings.

Whatever the reason, it has implications for our health. Last week, Public Health England (PHE) announced that the entire population should consider taking vitamin D — 10 micrograms (mcg) a day — throughout the winter months (from October to March) to prevent bone and muscle disease.

Vitamin D is essential for strong bones and teeth. While it’s found naturally in foods such as oily fish and eggs, its main source is UV light — it is ‘manufactured’ in the skin in the presence of sunlight.

Until now, only at-risk groups — including children aged one to five, pregnant and breastfeeding women, adults over 65 and those with darker skins — were advised to take vitamin D daily.

But as Dr Louis Levy, head of nutrition science at PHE, explained last week: ‘Everyone will need to consider taking a supplement in the autumn and winter if you don’t eat enough foods that naturally contain vitamin D or are fortified with it.’

But do we really need vitamin D pills, or can we just spend longer in the garden?

OVER 30 MINUTES OF SUN IS POINTLESS

ExPOsiNg skin to sunlight is the best way to boost vitamin D in the body, and is far more effective than popping a pill. For example, it takes just 30 minutes in the sunshine in the summer months for your skin to make 250mcg of vitamin D— a pill only contains up to 25mcg (this may appear on the label as 1,000 international units, iU).

Wearing sunscreen with an sPF of ten and above can block UV light from penetrating the skin, so you need to expose the skin without it. But you don’t have to go out in the blazing sun to make vitamin D — to avoid burning, get your rays before 11am or after 3pm.

As for how much skin you need to expose every day, the rule of thumb is around 10 per cent (which is the face, neck, back of the hands and arms) for 15-20 minutes in summer.

‘This should be enough to store up an optimum supply,’ says susan Lanham-New, a professor of human nutrition at the University of surrey and a member of the expert committee behind the new guidelines.

in fact, the skin can only make vitamin D for the first 30 minutes of daily exposure, she explains. ‘After that, it stops naturally because it recognises you have all you need.’

WINTER HOLIDAYS DON’T HELP MUCH

THERE is strong evidence that it is impossible for the body to store enough vitamin D during the British summer to last all winter, says Professor Lanham-New.

‘We have carried out studies that show that the body can store vitamin D in the liver for a certain period of time, but the half-life of vitamin D is only five to six weeks. After that, it is no longer able to play an active role in the body.

‘By mid-November, no one who remains in the UK has sufficient vitamin D stores, however much they soaked up the sun through spring and summer.’

Winter sun in the UK is the wrong wavelength to penetrate the skin and make vitamin D. A simple way to tell if the rays are strong enough is to look at your shadow.

‘if your shadow at noon is shorter than your height, the UVB light will be able to trigger the production of vitamin D in your skin. But in the British isles in winter, your shadow is typically twice your height,’ explains Professor Lanham-New.

Taking a winter sunshine break could help to top up your vitamin D levels, but the benefit will be lost within two to three weeks of your return, so you will need to continue with your vitamin D supplement — or take more holidays.

ANOTHER REASON TO LOSE WEIGHT

DARKER-sKiNNED people, such as those of African, Afro-Caribbean and south Asian origin, are naturally protected from strong sunlight because they have large amounts of the pigment melanin. But they therefore need at least three to five times longer in the sun to make the same amount of vitamin D as someone with a white skin tone, a 1982 study in The Lancet found.

For similar reasons, a tan could reduce the amount of vitamin D made. A Brazilian study presented at the Endocrine society in Boston in April found that people who sunbathed regularly could actually be vitamin D deficient because their tans blocked UV light.

More recently, being overweight has been linked to a lack of vitamin D— a 2013 study in the journal PLOs Medicine suggests that vitamin D may become ‘trapped’ inside fat tissue so that less of it is available to circulate inside the blood.

‘Older people are also more at risk of vitamin D deficiency because they become less efficient at making vitamin D in their skin and may also spend more time housebound or indoors,’ explains Professor Lanham-New.

some medications also reduce absorption, such as corticosteroids, used to damp down inflammation such as osteoarthritis.

Professor Lanham-New says people who take statins for high cholesterol may also be at risk from low levels, though more research is needed.

THE LINK TO HEART PROBLEMS

ViTAMiN D is important not only to maintain bones and allow normal growth in children, it’s also vital for muscle function and a healthy immune system, says Dr William Marshall, a consultant clinical biochemist at The London Clinic.

‘it also helps the body to use the calcium and phosphorus from your food and regulates the process where cells change from one type to another, thus helping to prevent cancer. Other associated conditions include an increased risk of diabetes, heart disease and certain cancers.’

But sceptics aren’t convinced vitamin D is the cause — or the solution. When Dr Mark Bolland, with colleagues from the department of medicine at Auckland University, analysed the results of nearly 50 trials involving over 200,000 people in 2013, they found vitamin D supplements had little or no impact on the risk of heart disease, stroke, cancer or bone fractures.

DON’T RELY ON A MULTIVITAMIN

syMPTOMs of vitamin D deficiency may include severe bone pain, lethargy and tiredness, and in older people it can lead to osteoporosis. A blood test can determine if you have low levels of vitamin D, but a gP may start by recommending vitamin D to see if symptoms ease.

Even if you don’t have any symptoms, the latest advice is that we should all consider taking supplements daily, just in case.

Vitamin D can be taken as a single supplement or in a multivitamin. As well as being cheaper, a single vitamin D supplement is preferable, says Professor Lanham-New.

‘Multivitamins may only contain 5mcg of vitamin D and we recommend 10mcg a day. Also, there may be good reasons not to take other vitamins, such as vitamin K, that are found in multivitamins — vitamin K can cancel out the blood thinning properties of warfarin, for instance.’

Buy your supplement in a pharmacy, High street health store or supermarket, she says, rather than over the internet, where doses may exceed safe levels.

IS IT POSSIBLE TO TAKE TOO MUCH?

Although levels of vitamin D in supplements vary, they rarely exceed 25mcg (1,000 international units). The so-called ‘tolerable upper limit’ is 100mcg (4,000iU) per day, above which risk for harm begins to increase.

The problem is that vitamin D is fat-soluble, so it’s hard for your body to get rid of it (unlike watersoluble vitamin C, which can simply be flushed through the kidneys).

With large amounts of vitamin D, your liver produces too much of a chemical that causes high levels of calcium in your blood, leading to a range of symptoms from nausea to muscle weakness, confusion and exhaustion.

Furthermore, a 2004 study found a worrying link between vitamin D supplements and higher risk of mortality — increasing the death rate by 6 per cent compared with people who did not take a vitamin D supplement. The researchers, writing in The Lancet, estimate that for every million people taking the supplements, 9,000 would die prematurely as a result.

However, Peter selby, a professor of metabolic bone disease at Manchester Royal infirmary, says a 10mcg supplement a day wouldn’t cause harm.