Harmful vitamin D deficiency ‘rare’
Almost a quarter of adults do not have enough vitamin D, but severe deficiency is rare, according to the official statistician.
The Australian Bureau of Statistics has estimated about four million adults do not have sufficient vitamin D, as determined by blood tests carried out as part of the Australian Health Survey, which is based on a sample of 25,000 households.
But the official statistician said that, in the large majority of cases, the deficiency was mild, and was only severe in less than 1 per cent of all adults.
The ABS estimates are significantly lower than those arrived at by other studies. A Baker IDI Heart and Diabetes Institute report estimated 31 per cent of adults had a vitamin D deficiency, while the NSW-based study calculated that almost 60 per cent of adults may have insufficient levels of the nutrient.
The prevalence and severity of vitamin D has become the focus of much debate, with governments and medical experts concerned that the condition has been over-diagnosed, causing a big drain on the health budget and leading many patients to spend large amounts on supplements considered to be unnecessary.
A report published in the Medical Journal of Australia in 2012 found a massive 94-fold increase in the prevalence of vitamin D testing between 2000 and 2010, driving a huge blow-out in the cost of the Medicare rebate for the procedure from around $1 million to almost $97 million over that period.
Last year the Royal College of Pathologists of Australasia and NPS MedicineWise issued updated guidelines advising against routine testing for vitamin D levels. They recommended the test only be carried out on patients showing symptoms of deficiency, or were considered to be at risk.
A similar move in New Zealand has led to a 70 per cent plunge in the number of vitamin D tests since 2010.
Vitamin D is essential in helping the body effectively absorb calcium, and severe deficiency can caused rickets in children and fragile bones in older people.
But NPS MedicineWine clinical adviser Dr Andrew Boyden said the health benefits of routine screening of vitamin D levels were yet to be demonstrated.
“There are limitations with vitamin D immunoassays, debate about optimum vitamin D levels and questions about the clinical significance of mild deficiency,” Dr Boyden said.
For its survey, the ABS used the Liquid Chromatography Mass Spectrometry method to analyse vitamin D levels in the blood. A concentration of 50 nanomoles a litre (nmol/L) or more was considered adequate. A concentration of 30 to 49 nmol/L was defined as mild deficiency, while those with a concentration of less than 13nmol/L were considered to be severely deficient.
The ABS survey found that vitamin D deficiency was greatest in the 18 to 34 years age bracket, while the use of vitamin D supplements increased with age, and was highest among those aged older than 65 years.
As expected, vitamin D levels varied markedly by season and location.
Vitamin D deficiency was greatest among those living in the country’s south-east, and was most marked during the winter months. For example, in Victoria and the ACT almost half of adults (49 per cent) registered a vitamin D deficiency during winter, compared with just 15 per cent of Queenslanders.
Unsurprisingly, rates of deficiency also varied by occupation. During winter, more than a quarter of those who worked predominantly indoors (salespeople, professionals) were found to be deficient, compared with 18 per cent of machinery operators and drivers.
Internationally, Australia has relatively low rates of vitamin D deficiency. While 17 per cent of Australian adults were mildly deficient, in East and Central Asia the rate was between 60 and 70 per cent, and in northern Africa it was 50 per cent – adding to evidence that it is more prevalent among those with darker skin, and those who cover their skin for cultural or religious reasons.
On the health implications of low vitamin D levels, the ABS study was more equivocal.
The ABS reported no evidence that the obese were more prone to deficiency than the rest of the population.
It found that that the links between low vitamin D levels and cancer, heart disease and kidney disease were “yet to be clearly established”.
While those with a vitamin D deficiency were more likely to have diabetes and abnormal levels of HDL cholesterol, “the case and effect of these relationships cannot be determined from this information”.
Similarly, the ABS reported “no significant relationship” between vitamin D and other cardiovascular biomarkers, including total cholesterol and triglycerides.
Indicating the importance of lifestyle factors, the ANS found that smokers were more prone to low vitamin D levels than non-smokers, and the physically active were less likely to be deficient in the vitamin than the sedentary.