Vitamin D
Definition
Vitamin D is a hormone that is essential for the body to absorb and retain calcium and phosphorus effectively, which is important for bone health and muscle function. The main source of vitamin D is exposure to sunlight, although small amounts can be obtained through some foods, such as fatty fish, eggs, UV light exposed mushrooms, red and organ meats, and in Australia from fortified margarine, breakfast cereals and milk products (Nowson et al. 2012; Whiting and Gibson 2024; Dunlop et al. 2023). The main consequence of long-term vitamin D deficiency is rickets in infants and children and osteopenia/osteoporosis (fragile bones) in adults (Whiting and Gibson 2024; NIH 2024).
Vitamin D is found in several forms in the body. The IHMHS included a test for vitamin D in the form of calcidiol (25(OH)D) that measured both vitamin D2 and vitamin D3.
In foods and dietary supplements, vitamin D has two main forms, D2 (ergocalciferol) and D3 (cholecalciferol). Both forms increase vitamin D in the blood, but D3 might raise it higher and for longer than D2.
The 2013 National Health and Medical Research Council (NHMRC) Nutrient Reference Values for Australia and New Zealand includes Nutrient Reference Values for vitamin D from the diet in the form of an Adequate Intake (AI) (NHMRC 2013; NIH 2024).
Vitamin D obtained from sun exposure, foods, and supplements is biologically inert and is activated in the body in two ways (via hydroxylation). First, in the liver vitamin D is converted to 25-hydroxyvitamin D [25(OH)D], also known as ‘calcidiol’. Second, vitamin D is converted to 1,25-dihydroxyvitamin D [1,25(OH)2D], also known as ‘calcitriol’, primarily in the kidney (Whiting and Gibson 2024; NIH 2024).
Serum concentration of calcidiol, is the main indicator of vitamin D status. It reflects vitamin D produced from sun exposure and that obtained from foods and supplements. In contrast, calcitriol is generally not a good indicator of vitamin D status (Whiting and Gibson 2024; NIH 2024).
The Royal College of Pathologists of Australia (RCPA) advises vitamin D levels may need to be 10 to 20 nmol/L higher at the end of summer, to allow for seasonal decrease in winter months (Nowson et al. 2012; RCPA 2023a). In Australia, there is a marked difference in exposure to sunlight in the winter months by state and territory (Malcova et al. 2019; Sempos and Binkley 2020).
Higher serum levels of vitamin D in the form of calcidiol >125 nmol/L are linked to potential adverse effects, particularly at levels >150 nmol/L (NIH 2024).
Laboratory test information, including analysis methods and machines used to measure vitamin D, is available from the Downloads page.
Methodology
Vitamin D results were obtained for persons aged 12 years and over who provided a blood sample. Fasting was not required for this test.
Serum vitamin D levels were measured at the Douglass Hanly Moir Pathology (DHM) laboratory using the Liquid Chromatography-tandem Mass Spectrometry (LC-MS/MS) method. The vitamin D test used measures the total amount of vitamin D circulating in the blood at the time of the test, expressed as nmol/L.
Cut-offs for adequate and deficient levels of vitamin D were reported. These cut-offs are based on the current position statement on vitamin D and health in adults in Australia and New Zealand (Nowson et al. 2012; RCPA 2023a).
The following cut-offs were used for serum vitamin D in the form of calcidiol.
- adequate levels ≥50 nmol/L
- deficiency <50 nmol/L
Additional cut-offs were applied to assess the severity of vitamin D deficiency:
- mild deficiency 30–49 nmol/L
- moderate deficiency 13–29 nmol/L
- severe deficiency <13 nmol/L
Users should note that the severe deficiency cut-off recommended in the Australian position statement is <12.5 nmol/L, but it was not possible to output data against this cut-off as the vitamin D data was only available in whole numbers. In most of the ABS output, the moderate and severe vitamin D deficiency categories were combined due to small numbers.
Interpretation
Points to consider when interpreting data for this topic include the following:
- Vitamin D test results do not confirm a specific diagnosis of deficiency without consultation with a health professional.
- All blood samples were analysed for vitamin D by the LC-MS/MS method using standard reference materials. The data from this topic should therefore be used with caution when comparing vitamin D results from other studies using a different test method, unless standardised against the LC-MC/MS method (Whiting and Gibson 2024).
- Vitamin D tests routinely conducted for individuals by pathology laboratories in Australia may only measure serum vitamin D in the form of 25(OH)D3 (RCPA 2023a, b).
Comparison to other vitamin D biomarker data
This is the second time the ABS has collected information on vitamin D levels. Vitamin D was previously collected in the NHMS 2011–12 and the NATSIHMS 2012–13. For information on the potential for time series comparability, see Comparing biomedical collections over time.
Vitamin D data has been collected in other non-ABS surveys. However, caution must be taken when interpreting results due to the differences in scope, assay and the instrument used, and any thresholds applied in the final analysis.
The NHMS 2011–12 and the NATSIHMS 2012–13 were included in the US National Institute of Health (NIH) international Vitamin D Standardization Program (VSDP), which aimed to standardise the measurement of vitamin D across all laboratories to enable the transfer of findings to patient care and public health activities (NIH 2013, 2024, n.d.; Macova et al. 2019; Sempos et al. 2020; Cashman 2022).
References
Cashman KD (2022), 100 YEARS OF VITAMIN D: Global differences in vitamin D status and dietary intake: a review of the data, Endocrine Connections, 11(1):e210282, accessed 20/02/2025.
Dunlop E, Boorman JL, Hambridge HL, McNeill J, James AP, Kiely M, Nowson CA, Rangan a, Cunningham J, Adorno P, Atyeo P, Black LJ (2023), Evidence of low vitamin D intakes in the Australian population points to a need for data-driven nutrition policy for improving population vitamin D status, Journal of Human Nutrition and Dietetics, 36(1):203-215, accessed 20/02/2025.
Malcova E, Cheang P, Dunlop E , Sherriff JL, Lucas RM, Daly RM , Nowson CA & Black LJ (2019), Prevalence and predictors of vitamin D deficiency in a nationally representative sample of adults participating in the 2011–2013 Australian Health Survey, British Journal of Nutrition, 121(8):894–904, accessed 20/02/2025.
National Health and Medical Research Council (NHMRC) (2013), ‘Vitamin D’ Nutrient Reference Values for Australia and New Zealand, Eat for Health website, accessed 20/02/2025.
National Institutes of Health Office of Dietary Supplements (NIH) (2024), Vitamin D, NIH website, accessed 20/02/2025.
National Institutes of Health Office of Dietary Supplements (NIH) (n.d.), Office of Dietary Supplements Vitamin D Initiative 2004-2018, NIH, accessed 20/02/2025.
Nowson CA, McGrath JJ, Ebeling PR, Haikerwal A, Daly RM, Sanders KM Seibel MJ & 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, accessed 20/02/2025.
Royal College of Pathologists of Australasia (RCPA) (2023a), Position Statement: Use and Interpretation of Vitamin D testing, RCPA, accessed 20/02/2025.
Royal College of Pathologists of Australasia (RCPA) (2023), ‘Vitamin D’, RCPA Manual, RCPA website, last accessed 20/02/2025.
Sempos CT, Binkley S (2020), 25-Hydroxyvitamin D Assay Standardisation and Vitamin D Guidelines Paralysis, Public Health Nutrition, 23(7):1153-1164, accessed 20/02/2025.
Whiting RJ, Gibson RS 2024, ‘Vitamin D’, Principles of Nutritional Assessment: 3rd Edition, Nutritional Assessment website, accessed 20/02/2025.