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Role of vitamin D in disease prevention questioned

People who take vitamin D supplements in the belief that they protect against heart disease and cancer may be wasting their time, a study suggests.

Scientists who conducted a review of hundreds of studies argued that some of the health benefits attributed to vitamin D were the result of a “chicken and egg” misunderstanding.

Low vitamin D levels were not a cause of chronic conditions such as heart disease, diabetes and cancer but a result of them, they concluded.

The finding challenges the view of many experts - including conventional doctors as well as alternative practitioners - that the vitamin plays a major role in disease prevention.

It is well known that vitamin D promotes the uptake of calcium and bone formation, and children deficient in the vitamin can develop rickets.

What is less clear is the extent to which vitamin D reduces the risk of other major causes of ill-health.

The scientists found that findings from prospective observational studies, which draw inferences from observed phenomena over time, and those from randomly controlled trials did not tally.

Lead researcher Professor Philippe Autier, from the International Prevention Research Institute in Lyon, France, said: “If the health benefits of high vitamin D concentrations shown by data from observational studies are not reproduced in randomised trials then the relation between vitamin D status and disorders are probably the result of confounding or physiological events involved in these disorders.

“What this discrepancy suggests is that decreases in vitamin D levels are a marker of deteriorating health. Ageing and inflammatory processes involved in disease occurrence and clinical course reduce vitamin D concentrations, which would explain why vitamin D deficiency is reported in a wide range of disorders.”

Vitamin D supplements are taken by many thousands of people in the UK, accounting for a sizeable fraction of the £674.6m worth of vitamins and dietary pills sold in 2009.

In the US, annual sales of vitamin D alone are estimated to be worth 600 million dollars (£367m).

The new study, published in the journal The Lancet Diabetes & Endocrinology, analysed the findings of 290 prospective observational studies and 172 randomised trials up to December last year.

A randomised trial is one in which the effects of a drug or supplement are studied in different groups, one of which is unknowingly given a “dummy” placebo.

The observational studies indicated significant benefits from vitamin D, including an up to 58% reduced risk of cardiovascular events such as heart attacks, a 38% reduced risk of diabetes, and a 34% risk of bowel cancer.

However, these improvements were not confirmed by the randomised trials. The pooled analysis of randomised study results failed to identify any effect on non-bone disease of raising vitamin D levels with supplements.

A linked editorial in the journal called for large-scale clinical trials to assess the impact of vitamin D on non-skeletal health outcomes.

The editorial added: “It would be a real boon to patients if the results are positive, but unless effect sizes for clinically important outcomes are large, the results will only confirm the neutral effect reported by most clinical trials thus far.”

Readers' comments (2)

  • I have low vit D levels since weight reducing gastric surgery (sleeve) 3 yrs ago. I try to remember to take a daily A -Z supplement simply to boost and maintain appropriate levels as my food intake is much reduced. Despite this my Vit D is lower than it should be and while I'm fine in nice sunny weather although not necessarily warm weather, I have found that in cold damp weather with little sunshine I suffer aches/pains like a lot of people, and I'm heavilyreliant in painkillers to help me function and I also tend to suffer low mood (eg S.A.D).
    As its classed as the 'sunshine vitamin' due to the fact it can be synthesised in the skin in adequate sunlight I have hypothesised that lack of said sunlight is a contributory factor to the aches and pains particularly around joints and hence low mood. With this in mind I have recently started taking extra calcium/vitamin D (within recommended levels) to see if this will help relieve joint pains/lift my mood. While its a bit too early to say for certain whether it works I do feel it has helped and I don't require so much pain relief. s part of a bariatric follow up I am due to have repeat annual bloods (incl vit D) in February so it will be interesting to see if there has been any improvement.

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  • tinkerbell

    Anonymous | 7-Dec-2013 9:29 am

    Hope it works out for you.

    Likewise my GP informs that I am D3 deficient , another thing to add to what is becoming quite a list:) I wondered what the difference was between the Vit D's and found this on the internet which I thought you might find useful.

    'Vitamin D2 is the form of D that is found in fortified foods like milk, juices or cereals and D3 is the form that is synthesized by the skin when it's exposed to the sun or (ultraviolet light/UVB). D2 (ergocalciferol) can be found, in some plants/fungus. D3 (cholecalciferol) is the sunlight form, and can also be obtained from animals that manufactured it through their skin, like that in fish liver. Since the body can produce this it's actually considered a hormone and not a vitamin. D regulates calcium and phosphorus in the body.


    Some feel that D3 is more effective in humans than D2. D3 can be obtained after 10-15 minutes of sun exposure (without sunscreen) and is recommended 3-4 times a week. For those that can't get this sun exposure, supplements are a recommended substitute. The current RDA on D3 is 1,000 IU's a day for those over the age of 20'.

    I had severe joint stiffness/tenderness following menopause and now take HRT which has made a big (huge) difference as I was coming to a grinding halt. I am taking a D3 supplement at the above dosage which my gp recommended.

    I get SAD also in the dark winter months but from long experience know this will pass when the sunnier, lighter days arrive. Could always get a sun lamp for top ups in the winter.

    Glad to hear you're improving and wish you continued success.

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