VITAMIN D

Vitamin D is essential for the body to absorb calcium effectively, which is important for bone health and muscle function, and for preventing conditions such as osteoporosis. The main source of Vitamin D is exposure to sunlight, although small amounts can be obtained through some foods, such as fatty fish and fortified margarine and milk.¹

The main consequence of severe Vitamin D deficiency is rickets in children and osteopenia (fragile bones) in older people.¹ There is some evidence to suggest that low Vitamin D levels could also be a risk factor for other chronic conditions, including heart disease, cancer and kidney disease, but more research is needed to better understand these links.^2,3

Measuring Vitamin D In the National Aboriginal and Torres Strait Islander Health Measures Survey (NATSIHMS), Vitamin D levels were measured via a blood test, which measures Vitamin D obtained from both food and sunlight.1 The NATSIHMS used the Liquid Chromatography Mass Spectrometry (LCMS) method to assess Vitamin D status. This method has the highest sensitivity and specificity for measurement of Vitamin D. 4 Given the expensive equipment required for the LCMS method and the lack of standardisation in measurement across laboratories, the LCMS method is not yet widely used in Australia3 and standardised test cut-offs are yet to be developed. In the NATSIHMS, the levels recommended in a recent Australian position statement on Vitamin D2 have been applied to determine Vitamin D deficiency. These cut-offs are: Mild deficiency: 30 – 49 nmol/L Moderate deficiency: 13* – 29 nmol/L Severe deficiency: <13* nmol/L Total deficiency: <50 nmol/L Adequate levels: ≥50 nmol/L# * Note that the cut-off recommended in the position statement is <12.5 nmol/L, but the AATSIHS is unable to output against this cut-off as the Vitamin D data is only available in whole numbers. # Note that the position statement states that levels may need to be 10 to 20 nmol/L higher at the end of summer, to allow for seasonal decrease.

In 2012–13, around one in four (26.5%) Aboriginal and Torres Strait Islander adults had a Vitamin D deficiency (<50 nmol/L), with the majority having a mild deficiency (21.9%) and the remainder a moderate or severe deficiency (4.6%). This pattern was similar for both men and women. After taking age differences into account, Aboriginal and Torres Strait Islander people were more likely to have a Vitamin D deficiency than their non-Indigenous counterparts (rate ratio of 1.1).

In 2012–13, Vitamin D deficiency was much more common among Aboriginal and Torres Strait Islander people living in remote areas, where almost four in ten (38.7%) Aboriginal and Torres Strait Islander people were Vitamin D deficient compared with just over two in ten people living in non-remote areas (23.0%).

Unlike many of the other biomarkers, Vitamin D levels did not vary by age, with similar deficiency rates for all broad age groups (between 25.1% and 29.2%). This was different to the pattern seen in the non-Indigenous population, where rates of Vitamin D deficiency decreased as people got older. This decrease in Vitamin D deficiency in the non-Indigenous population corresponded with an increase in the use of Vitamin D supplements, especially among older age groups.⁵ However information on supplement use was not collected in the AATSIHS, so this comparison is not available for the Aboriginal and Torres Strait Islander population.

As expected, Vitamin D levels varied considerably by season, with overall deficiency rates for Aboriginal and Torres Strait Islander people being much lower in summer (15.3%) and autumn (16.2%) than in winter (36.4%) and spring (34.8%). While this seasonal impact was seen across both non-remote and remote areas, rates of Vitamin D deficiency remained higher among Aboriginal and Torres Strait Islander people in remote areas than in non-remote areas regardless of the time of year.


The Australian position statement² on Vitamin D highlights that obese people may be at higher risk of Vitamin D deficiency because excess body fat can interfere with the absorption of Vitamin D. This was reflected in the NATSIHMS results, with Aboriginal and Torres Strait Islander people who were obese being almost twice as likely to have Vitamin D deficiency as those who were underweight or of normal weight (33.4% and 17.5% respectively). Interestingly though, this relationship was not evident in the non-Indigenous population.⁵


There is some evidence to suggest that low Vitamin D levels are associated with increased risk of certain chronic health conditions, including heart disease and diabetes, although these are yet to be clearly established. ^2,3 In 2012–13, Aboriginal and Torres Strait Islander people with a Vitamin D deficiency were almost twice as likely as those with adequate levels of Vitamin D to have diabetes (16.6% compared with 9.0%). They were also more likely to have chronic kidney disease (26.9% compared with 14.3%). It is important to note however, that the cause and effect of these relationships cannot be determined from this information.

For more information on Vitamin D see Tables 2, 3, 4, 5, 12 and 16 on the Downloads page of this publication.

ENDNOTES

1 Gibson RS, 2005, Principles of Nutritional Assessment, 2nd edition, Oxford University Press, New York.
2 Nowson CA, McGrath JJ, Ebeling PR, Haikerwal A, Daly RM, Sanders KM, Seibel MJ and Mason, RS, 2012, Vitamin D and health in adults in Australia and New Zealand a position statement, Medical Journal of Australia 196(11): 686-687,<https://www.mja.com.au/journal/2012/196/11/vitamin-d-and-health-adults-australia-and-new-zealand-position-statement?0=ip_login_no_cache%3Da474845072622903b6f5567f3a1d71d9>,
3 The Royal College of Pathologists of Australasia, 2013, Position statement; Use and Interpretation of Vitamin D testing, <http://www.aims.org.au/documents/item/347>,
4 Carter GD, Jones JC. 2009 Use of a common standard improves the performance of liquid chromatography-tandem mass spectrometry methods for serum 25-hydroxyvitamin-D. Ann Clin Biochem; 46: 79-81.
5 Australian Bureau of Statistics, July 2014, Australian Health Survey: Biomedical Results for Nutrients, 2011-12, ABS cat. no. 4364.0.55.006, <https://www.abs.gov.au/ausstats/abs@.nsf/Lookup/4364.0.55.006Chapter2002011-12>, Back to top