From The Times
London, UK
30 May, 2009
Quote:
Is vitamin D the new wonder supplement?
Most of us don’t get enough of it. But the solution — spending more time in the sun — is also the problem
The dramatic news this week that cases of the deadliest form of skin cancer have reached a record high drove home the message that we all know: protect your skin as much as possible from the sun’s damaging ultraviolet rays. But there is a problem behind the urgent simplicity of this warning. There is increasing evidence that if we do just that our health may suffer in other ways.
The reason is vitamin D, an essential nutrient almost wholly provided to the body by dint of a chemical reaction that occurs when ultraviolet rays hit the skin. A swath of recent research shows how beneficial vitamin D is to our health and wellbeing, and how harmful deficiency can be. Results from an international study on ageing, published last week, showed that high vitamin D levels are associated with greater mental agility in men aged 40 to 79.
Vitamin D, a product of sun exposure, is rapidly taking up the status of wonder nutrient. But having been primed for decades about the importance of covering up, what are we to do?
For years scientists have known that vitamin D deficiency raises the risk of bone problems such as osteoporosis and rickets. But, recently, a firm link has been made with bowel cancer, and, in the past five years, with breast cancer, diabetes, heart disease, joint disease, multiple sclerosis, dementia, birth difficulties and autism.
Given that some research indicates that 60 per cent of us are vitamin D-deficient — 90 per cent in winter — this could be important. In the past few weeks papers have come out in reputable journals suggesting that low levels are linked with severe asthma and that a daily dose of the vitamin may slow prostate cancer.
Now, with a potential flu pandemic on our doorsteps, the belief of an American doctor and psychiatrist, John Cannell, that vitamin D deficiency makes us more vulnerable to influenza is certain to grab the limelight. His theory, published recently in the reputable journal Epidemiology and Infection, hinges on the mysterious seasonality of flu, which hits us mainly in colder months.
The reason, Cannell says, is that lack of sun deprives us of vitamin D, which has been shown to stimulate the production of antimicrobial chemicals that kill flu viruses. Less sun equals more viral infection.
Not only that, but there is also evidence that vitamin D can damp down our immune response so that it doesn’t get out of control. This is important as far as flu is concerned because in the 1918 flu pandemic many young and healthy people died as a result of an overreaction by their immune system, not the infection itself.
How much of this new research should we believe? The case for vitamin D as a wonder nutrient is on a spectrum of credibility with Cannell’s work at one end of the scale: fascinating, but a plausible theory lacking research evidence to back it up. At the other end is strengthening evidence of a firm link with specific illnesses.
Take multiple sclerosis. Five years ago, scientists who pointed out a link between vitamin D and MS — because, looking globally, hours of sunlight exposure (and therefore vitamin D production) tallied almost exactly with distribution of the disease — were regarded as maverick.
But in February The Times reported that George Ebers, Professor of Clinical Neurology at the University of Oxford, had discovered that vitamin D affects a particular genetic variant, which increases the risk of developing multiple sclerosis. This, he says, suggests that lack of sunlight and vitamin D deficiency in pregnancy and early childhood increases the risk of developing MS. The MS Society welcomed the findings as “remarkable”.
A World Health Organisation report published late last year said that there was “strong evidence that increased daily intake of vitamin D could significantly improve health”. The problem is that the strength of evidence varies from condition to condition (see panel overleaf), which is why it also calls for more large research studies.
Why should vitamin D have such a beneficial effect? We know that it is needed by the body to help it to absorb calcium and phosphorous, which are essential for bone and tooth growth. Now there is some understanding that it can affect the way that genes express themselves.
And in a new paper published in a specialist mineral metabolism journal recently, researchers from the University of California propose that vitamin D is essential in preventing cancer because it holds layers of cells together, preventing their multiplication from getting out of control.
If evidence that vitamin D improves your health is good, and if studies show that most of us are deficient, why aren’t we all being given official advice to take vitamin D supplements? Or to eat foods rich in vitamin D, such as oily fish, eggs and breakfast cereals? There is a problem.
At least 90 per cent of the vitamin D in the body comes from sunlight exposure. Scientists agree that by far the best way of boosting the nutrient is to expose your body to sunlight, without sunscreen, at times when ultraviolet radiation is at its strongest: noon and early afternoon in spring and summer. This also builds up a reserve for winter.
Research has indicated that the skin produces about 10,000 international units (IU) of vitamin D in response to 20-30 minutes of summer sun exposure. In comparison, the recommended daily dose of a vitamin D supplement is 400 IU (10 micrograms); any more of this synthetic (as opposed to skin-manufactured) version is considered risky by authorities because too much can, in theory, cause kidney damage. One portion of oily fish contains 320 IU (8 micrograms).
In other words, the amount you can eat in your diet, or is judged safe for a daily supplement tablet, is unlikely to dent the problem of deficiency. Even conservative estimates about deficiency, from the Government’s National Diet and Nutrition Survey, say that 30-40 per cent of people in some groups, such as older people, 19-24-year-olds and those with dark skins, are consistently low on vitamin D. But the alternative — encouraging people to sun themselves — is fraught with danger given concerns about skin cancer.
Cancer organisations understandably tread a cautious line on the issue. They do, however, acknowledge the importance of not covering up all the time. And everyone agrees that burning is bad.
“Obviously vitamin D is important for health, but the amount you need from the Sun is always less than for tanning or burning,” says Ed Yong, the health information manager at Cancer Research UK. “We know that casual exposure is enough for vitamin D production and recommend 10 to 15 minutes a day.”
Meanwhile, the Human Nutrition Research Centre (of the Medical Research Council), which informs the Government on diet and nutrients, acknowledges that vitamin D deficiency is a policy poser. Dr Inez Schoenmakers, the senior scientist leading work on vitamin D metabolism, says that it is possible, but difficult, to get all our vitamin D requirement from food. Fortifying foods is another option that has been pursued in the US and other countries, but not in the UK, where only cereals, margarine and some flours have added vitamin D.
The problem with this broad approach is that it does not target those who need vitamin D most, Dr Schoenmakers says. She also recommends careful and limited unprotected sun exposure in the middle of the day. But for elderly, teenage or dark-skinned people who can’t do this she advises taking a vitamin D supplement. Her research has indicated that it is circulated and used by the body more effectively than has previously been acknowledged.
In other words, getting the right levels of vitamin D without damaging our bodies at the same time requires us to eat, take supplements or seek the sun sensibly; to behave responsibly. Governments are not renowned for putting out public health messages that trust us to do that.
http://www.timesonline.co.uk/tol/li...icle6373802.ece
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