A large meta-analysis of 25 high quality, double-blind randomised control trials involving 10,933 individuals showed that daily and weekly vitamin D supplementation was safe and effective in reducing the incidence of respiratory infection in all participants, including those with 'adequate' levels of vitamin D. The study also demonstrated a profound effect in those who were vitamin D deficient. Those with vitamin D levels less than 25nmol/L who received daily or weekly supplementation with vitamin D experienced a 70% reduction in incidence of cold and flu. The body of evidence contributing to this meta-analysis was considered to be of high quality, meaning the randomised trials were well designed, therefore increasing the power of these results.
Vitamin D deficiency is very common, affecting nearly a third of all Australians and up to 60% of women over the period of winter-spring. In fact, in the United States of America, it is estimated that only 10% of the US population has a vitamin D level greater than 100nmol/L which has been identified in multiple studies as the target range for enhanced immuno-protection.
Taking a vitamin D supplement is much safer than excessive sun exposure which can significantly increase your risk of developing skin cancer.
1. 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.bmj.com/content/356/bmj.i6583
2. 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/