When is vitamin D testing appropriate?
The consequences of testing in low-risk individuals is not known. Even though a large proportion of Australians (between 31% and 58%) are estimated to have inadequate vitamin D levels (25-OHD <50 nmol/L) depending on season, severe deficiency is uncommon.1,2 The clinical significance of mild or moderate deficiency is not fully determined and the optimal serum concentration of vitamin D is not established.
A principle of testing is to avoid testing unless there is a plan to deal with possible results. For example what would you do differently if you found out your patient, who was thought to be unlikely to have a severe vitamin D deficiency, was found to have a mild deficiency?
Ensure adequate exposure to sunlight
A major reason for vitamin D deficiency is limited sun exposure. The majority of Australians can get sufficient vitamin D through skin exposure to sunlight. There is a seasonal variation vitamin D levels as production decreases during winter.
For moderately fair-skinned people, a walk with arms exposed for 6–7 minutes mid morning or mid afternoon in summer, and with as much bare skin exposed as feasible for 7–40 minutes (depending on latitude) at noon in winter, on most days, is likely to maintain vitamin D levels.3
Only test people at moderate to severe risk of deficiency
Only consider vitamin D tests for people at risk of moderate to severe deficiency. Moderate to severe deficiency (25-OHD level <25 nmol/L) is uncommon and is present in an estimated 4% of the population.2,4People with 25-OHD levels < 25 nmol/L are truly deficient and have increased risk of developing rickets or osteomalacia. They should receive vitamin D supplements.3
Supplementation without testing may be appropriate in some high-risk groups including housebound, older and/or disabled people, those in residential care and dark-skinned people.3
People at risk of developing vitamin D deficiency
People who are housebound, particularly those over 65 years or resident in aged care facilities3As people age they have reduced ability to synthesise vitamin D from sun exposure. For example, one study demonstrated that 89% of people in residential aged care facility residents had vitamin D deficiency5
People with dark skin3
People with dark skin synthesise less cholecalciferol from sun exposure than people with light skin.1 For example, one study showed that 44% of children from an east African background attending a Melbourne health clinic had vitamin D deficiency2
People who cover themselves for religious or cultural reasons3Limited skin exposure to sunlight can cause deficiency. For example, it is estimated that 68–80% for women who were veiled had vitamin D deficiency.6,7
For more information
- Boyages S, Bilinski K. Seasonal reduction in vitamin D level persists into spring in NSW Australia: implications for monitoring and replacement therapy. Clin Endocrinol (Oxf) 2012;77:515–23. [PubMed]
- Daly RM, Gagnon C, Lu ZX, et al. Prevalence of vitamin D deficiency and its determinants in Australian adults aged 25 years and older: a national, population-based study. Clin Endocrinol (Oxf) 2012;77:26–35. [PubMed]
- Nowson CA, McGrath JJ, Ebeling PR, et al. Vitamin D and health in adults in Australia and New Zealand: a position statement. Med J Aust 2012;196:686–7. [PubMed]
- Bhan A, Rao AD, Rao DS. Osteomalacia as a result of vitamin D deficiency. Rheum Dis Clin North Am 2012;38:81–91, viii–ix. [PubMed]
- Flicker L, MacInnis RJ, Stein MS, et al. Should older people in residential care receive vitamin D to prevent falls? Results of a randomized trial. J Am Geriatr Soc 2005;53:1881–8. [PubMed]
- Diamond TH, Levy S, Smith A, et al. High bone turnover in Muslim women with vitamin D deficiency. Med J Aust 2002;177:139–41. [PubMed]
- Grover SR, Morley R. Vitamin D deficiency in veiled or dark-skinned pregnant women. Med J Aust 2001;175:251–2. [PubMed]