The bottom line:
- Vitamin D deficiency is common, affecting nearly one third of Australians
- Routine vitamin D3 supplementation has also been shown to be safe and effective in preventing acute respiratory tract infections such as common cold and flu.
- If you’d like to know more about your vitamin D status and dose requirements, we recommend talking to your doctor
Vitamin D deficiency has been recognised as a global public health concern with nearly a third of Australians over the age of 25 shown to have low levels of vitamin D. This finding was demonstrated in a large population-based study conducted in 2012 which assessed vitamin D levels in more than 11,000 Australians. Vitamin D deficiency was found to affect 31% of Australians, with the highest incidence in women (39% were deficient in vitamin D overall). Even more astonishing was the finding that nearly sixty percent of women were shown to be deficient in vitamin D over the period of winter to spring(1). So what is the link between vitamin D and immunity? And could all this deficiency be putting people at risk?
The role of vitamin D in regulating immune function has been described in various literature reports. Vitamin D receptors have been identified on various immune cells including macrophages, monocytes, dendritic cells, and T and B lymphocytes, all of which are vital to enable direct killing of pathogens and development of long standing immunity through production of antibodies(2).
Routine vitamin D3 supplementation has also been shown to be safe and effective in preventing acute respiratory tract infection. This was concluded from a large meta-analysis of 25 high quality randomised, double-blind placebo-controlled trials including 10,933 subjects. Vitamin D supplementation reduced the incidence of respiratory infection in all participants, including those with ‘adequate’ levels of vitamin D. It also had a profound effect in those who were vitamin D deficient. It is important to know that daily and weekly supplementation is effective, but larger infrequent doses (e.g. once a month) are not effective(3).
So how much vitamin D do you need?
The bottom line is that the only way to know if you are deficient in vitamin D is to see your doctor and get a simple blood test which will help determine the dose of vitamin D required to maintain healthy levels. In Australia, vitamin D deficiency refers to levels lower than 50nmol/L (or 20ng/mL for those readers in the USA) with levels greater than 75nmol/L considered optimal(4). Daily vitamin D3 doses of 1000IU (25mcg) per day can maintain people in the healthy range provided they are not already deficient in vitamin D. However, there is some evidence that optimal health benefits of vitamin D may be obtained in the range of 100-150 nmol/L which may require daily dosing of 4000-6000IU per day. Toxicity from excessive oral intake of vitamin D is possible, however, no evidence of vitamin D toxicity has been shown with doses of up to 4000IU per day. In Australia, the maximum daily dose of vitamin D recommended for general use is 1000IU per day unless advised otherwise by your doctor(5).
Ultimately, the decision to take vitamin D supplements or not rests with you. If you’d like to know more about your vitamin D status and dose requirements, we recommend talking to your doctor.
- Daly R, Gagnon C, Lu Z, Magliano D, Dunstan D, Sikaris K et al. Prevalence of vitamin D deficiency and its determinants in Australian adults aged 25 years and older: a national, population-based study. Clinical Endocrinology [Internet]. 2012;77(1):26-35. Available from: https://pubmed.ncbi.nlm.nih.gov/22168576/
- Charoenngam N, Holick M. Immunologic Effects of Vitamin D on Human Health and Disease. Nutrients [Internet]. 2020;12(7):2097. Available from: https://www.mdpi.com/2072-6643/12/7/2097/htm
- Martineau A, Jolliffe D, Hooper R, Greenberg L, Aloia J, Bergman P et al. Vitamin D supplementation to prevent acute respiratory tract infections: systematic review and meta-analysis of individual participant data. BMJ [Internet]. 2017:i6583. Available from: https://www.ncbi.nlm.nih.gov/pmc/articles/PMC5310969/
- RCPA - Vitamin D [Internet]. Rcpa.edu.au. 2020 [cited 4 December 2020]. Available from: https://www.rcpa.edu.au/Manuals/RCPA-Manual/Pathology-Tests/V/Vitamin-D
- Vitamin D deficiency in adults [Internet]. NPS Medicinewise. 2010 [cited 4 December 2020]. Available from: https://www.nps.org.au/australian-prescriber/articles/vitamin-d-deficiency-in-adults-1