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Six things you need to know about your vitamin D levels

Vitamin D has emerged as “the vitamin of the decade”, with a long and growing list of maladies supposedly caused through its absence or prevented through its bountiful supply. But is there adequate evidence…

Even if sunscreen is applied very thickly, vitamin D production is reduced but not stopped. Shutterstock

Vitamin D has emerged as “the vitamin of the decade”, with a long and growing list of maladies supposedly caused through its absence or prevented through its bountiful supply.

But is there adequate evidence for the wonders claimed for vitamin D or are we getting a bit carried away?

Before you answer that, here are some common misconceptions about vitamin D that you should know about.

  1. Everybody knows their vitamin D level should be above …?

    It’s a fairly universal agreement that a blood concentration of 25-hydroxyvitamin D (the usual measure of vitamin D status) below 25 nanomoles/litre (nmol/L) should be considered a serious deficiency.

    Anyone who is tested and returns results like that needs to talk to their doctor about proper management. But knowing what levels are sufficient is trickier.

    In 2010, the Institute of Medicine in the United States concluded that bone health is the only condition for which there’s an established causal association with vitamin D. They found:

    health benefits beyond bone health — benefits often reported in the media — were from studies that provided often mixed and inconclusive results and could not be considered reliable.

    So there’s clearly contention about how much is enough. A level of 50nmol/L is sufficient to optimise the bone health of the majority of the population. But other groups recommend 75nmol/L, 100nmol/L or higher (note that US sites provide recommendations in nanograms per millilitre or ng/ml – multiply by 2.5 to convert to nmol/L).

  2. There’s a vitamin D deficiency epidemic in Australia.

    Actually, what is most clear is that there’s an epidemic of vitamin D testing in Australia – a 94-fold increase from 2000 to 2010. Costs to Medicare have gone from $1.3 million in 2000/2001 to $140.5 million in 2012/2013.

    Rather than an epidemic of deficiency, there’s currently an epidemic of vitamin D testing in Australia. Shutterstock

    Some populations are clearly at risk of vitamin D deficiency. People who habitually cover their skin while in public for cultural or other reasons, for instance, and the immobile elderly who are rarely sun exposed. But the evidence of population-wide vitamin D deficiency is thin and unconvincing, at least in part because vitamin D tests are problematic and the desired level is hotly debated.

    If an unreliable test is used and the “sufficient” bar is set too high and more people are tested, then vitamin D “deficiency” will seem more common.

  3. A vitamin D test gives a simple answer and is accurate and reliable.

    This is definitely not so.

    If you take blood from one person and split it up into several samples and test these, you can get very different results between the samples. And it’s not just a little bit different.

    A recent Australian study assessing the consistency and accuracy of vitamin D tests found that between one-in-five and one-in-three participants were misclassified as “deficient”. The vitamin D test results for a single blood sample returned enormously different results depending on which type of test was used and where the sample was analysed.

    Four samples (out of approximately 800) differed by more than 100nmol/L (that’s double the usual “sufficient” level of 50nmol/L) across two different tests, and 10% of the results differed by more than 50nmol/L. These are different measurements of the same sample!

    Fortunately work is underway to improve this abysmal situation. A group of international agencies are developing a reference measurement procedure and laboratories will be able to assess the performance of their test against this new standard.

  4. Vitamin D is the elixir of life, which is sometimes presented as vitamin D deficiency will kill us all.

    Given the challenges of accurately measuring levels of this vitamin and the disagreement on where the goalposts are, doing good consistent research to determine the benefits and detriments of high or low vitamin D is pretty difficult.

    There’s no doubt that severe vitamin D deficiency causes rickets in children, and an equivalent condition known as osteomalacia in adults. Old pictures of children with bowed legs or knock knees were often of children with rickets.

    And there’s pretty good evidence that supplementation with vitamin D and calcium, in combination with weight-bearing exercise, can decrease the risks of fractures in the elderly. Particularly in people who have low levels of vitamain D or calcium (or both) before starting supplementation.

    But most evidence for the other reported benefits of vitamin D comes from weak studies, and there’s little support from better studies.

    There’s good evidence that supplementation with vitamin D and calcium, in combination with weight-bearing exercise, can decrease the risks of fractures in the elderly. Shutterstock

  5. Given it is such good stuff, the higher my vitamin D level, the better.

    Vitamin D has traditionally been thought to be safe, requiring very high levels (greater than 400nmol/L) to reach toxicity. This toxicity cannot occur through sun exposure, but can through excessive supplementation.

    But as we delve more into the vitamin D story, studies are reporting risks to health at even modestly high levels, such as 80-100nmol/L.

    The evidence is not yet strong (much like the evidence of vitamin D’s benefits) but this type of association is typical of many vitamins and nutrients, where both too little and too much are bad for you .

  6. Sunscreen stops vitamin D production.

    The majority of vitamin D your body needs comes through exposure to the sun, specifically from shorter wavelength UVB radiation that is also the main cause of skin cancers. It may seem logical that if sunscreen stops the damaging UVB reaching sensitive skin cells, it will also stop vitamin D production by those same cells.

    But even if sunscreen is applied very thickly, vitamin D production is reduced but not stopped. And, of course, who puts it on that thickly?

    Most of us apply sunscreen because we are going to be in the sun. We put on a thin layer that is not too icky. Under these conditions, sunscreen actually doesn’t seem to make a lot of difference to vitamin D production.

There’s a lot we don’t know about vitamin D. But we do know that Australia has the highest skin cancer incidence in the world: hundreds of thousands of skin cancers are removed each year at a cost of more than $700 million and there are over 2,000 deaths from it.

Excessive sun exposure is the main cause of that problem. Getting the balance between vitamin D levels and sun protection right is an important health goal.

More research is needed and it should be Australian research because our circumstances are different to those in the United States and Europe. We can’t just take results from there and use them here.

While a simple solution would be nice, an evidence-based one is preferable and worth pursuing. Stories about our epidemic of vitamin D deficiency drive excessive testing at high cost and unknown value. And they probably just end up selling more vitamin supplements.

But they also create confusion and diminish people’s confidence and resolve to reduce excessive UV exposure.

Join the conversation

9 Comments sorted by

  1. Rosemary Stanton

    Nutritionist & Visiting Fellow at UNSW Australia

    Thank you for this excellent article. A 7th myth (which also applies to levels of many other nutrients) is that we all need to be at the top of the 'normal' range.

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  2. Rosemary Stanton

    Nutritionist & Visiting Fellow at UNSW Australia

    It might also be good to look at the funders of various studies and accompanying publicity. For example, in the USA, one company with a prominent online presence sells not only vitamin D supplements but also a kit that promotes 'home testing'.

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    1. Gary Goland

      Researcher

      In reply to Rosemary Stanton

      Agree with both comments Rosemary. Would also like to add that we should also be able to have confidence that the market will deliver products that will not contain contaminants that have popped up from time to time in supplements. Independent public review standards and product assessment within our system have produced some historical critical achievements in pharmacy lines. Not so in pollution evaluation and exposure to risks in other dysciplines.

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  3. John Doyle

    architect

    I read somewhere that sun exposure to get vitamin D only happens when the sun is above 55 degrees from the horizon. The atmosphere cuts out the UVB rays at lesser angles.
    There are many parts of the planet where the sun is never higher than 55 degrees at any time.
    What's the truth?

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  4. Gordon Angus Mackinlay

    Clinical Psychologist

    It is always good to see on this electronic pages something of relevance, and for which the Conversations was originally intended, rather than a de facto Labor Party re-election mouth piece.

    Whilst of course their risk of skin carcinoma's is greatly than the general public, there is a great deal of anecdotal evidence that daily short term exposure to mid-day, early afternoon sun is of great benefit to those suffering from psychiatric problems.

    And this is quite marked in the in patient treatment…

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    1. Gordon Angus Mackinlay

      Clinical Psychologist

      In reply to Gordon Angus Mackinlay

      For some reason the last sentence in the 3rd paragraph lost some words, it should read :
      "Plenty of anecdotal evidence records it does seem so, but, I have never seen any enthusiasm for a study." Yours, Mackinlay with my apologies.

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    2. Gary Goland

      Researcher

      In reply to Gordon Angus Mackinlay

      Maybe competition for research funding in Australia now has such access very difficult Gordon. Perhaps study could be undertaken in a clinical setting. Environmental access and approval might not be easy, but some scientific evidence to support the anecdotal would be great to see.
      Like all managed health activities and medication, we do need to keep in mind the existing individual subject levels, and potential biological relevance of the additions sought. I point to some discussion on this in articles freely available in Google Scholar at; http://scholar.google.com.au/scholar?hl=en&q=health+benefits+of+exposure+to+the+sun&btnG=&as_sdt=1%2C5&as_sdtp=

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  5. Sue Ieraci

    Public hospital clinician

    Great article - thank you!

    Your comment ''Getting the balance between vitamin D levels and sun protection right is an important health goal.'' is particularly relevant.

    Our society seems to have the tendency to go into a spin about the purported risks of a multitude of individual influences in our lives, without taking the wider view. As Rosemary Stanton says, we eat foods, not individual chemicals. Similarly, we walk in the world, not in concentrations of chemicals in air and water.

    We are too focused on tests and not enough on health and well-being - which is about function and not about numbers.

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  6. Brooke Berry

    logged in via Facebook

    Thanks for an excellent article. I'll be sharing this so my Mum might believe me now - apparently my formal qualifications, experience and access to expert colleagues are no match for the tele.

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