As daylight hours grow shorter, incidence of the common cold, flu, and respiratory infections spikes upwards. Scientists have identified reduced Vitamin D levels in winter months as a prime suspect for this increase in infectious disease cases.1-3 Vitamin D from all sources lowers the incidence of respiratory infections.4,5 For example, Dutch children with the least sun exposure are twice as likely to develop a cough and three times more likely to develop a runny nose compared with children with the most sun exposure.6

Children with the lowest Vitamin D serum levels are 11 times more likely to develop respiratory infection.7 When 50,000 IU per week of Vitamin D was administered (for six weeks) to children with frequent respiratory infections, the result was a complete disappearance of such infections in the following six months.In a controlled trial of African-American women, a low dose (800 IU a day) of Vitamin D resulted in a three-fold reduction in cold and flu symptoms compared to those given placebo.Elderly people with low Vitamin D status have been shown to be at increased risk of death from all causes, and are particularly vulnerable to wintertime infections.10-14


1. Korthals Altes H, Kremer K, Erkens C, van Soolingen D, Wallinga J. Tuberculosis seasonality in the Netherlands differs between natives and non-natives: a role for vitamin D deficiency? Int J Tuberc Lung Dis. 2012 May;16(5):639-44.
2. Camargo CA Jr, Ganmaa D, Frazier AL, et al. Randomized trial of vitamin d supplementation and risk of acute respiratory infection in mongolia. Pediatrics. 2012 Sep;130(3):e561-7.
3. Urashima M, Segawa T, Okazaki M, Kurihara M, Wada Y, Ida H. Randomized trial of vitamin D supplementation to prevent seasonal influenza A in schoolchildren. Am J Clin Nutr. 2010 May;91(5):1255-60.
4. Ginde AA, Mansbach JM, Camargo CA Jr. Association between serum 25-hydroxyvitamin D level and upper respiratory tract infection in the Third National Health and Nutrition Examination Survey. Arch Intern Med. 2009 Feb 23;169(4):384-90.
5. Cannell JJ, Vieth R, Umhau JC, et al. Epidemic influenza and vitamin D. Epidemiol Infect. 2006 Dec;134(6):1129-40.
6. Termorshuizen F, Wijga A, Gerritsen J, Neijens HJ, van Loveren H. Exposure to solar ultraviolet radiation and respiratory tract symptoms in 1-year-old children. Photodermatol Photoimmunol Photomed. 2004 Oct;20(5):270-1.
7. Wayse V, Yousafzai A, Mogale K, Filteau S. Association of subclinical vitamin D deficiency with severe acute lower respiratory infection in Indian children under 5 y. Eur J Clin Nutr. 2004 Apr;58(4):563-7.
8. Rehman PK. Sub-clinical rickets and recurrent infection. J Trop Pediatr. 1994 Feb;40(1):58.
9. Cannell JJ, Zasloff M, Garland CF, Scragg, R, Giovannucci E. On the epidemiology of influenza. Virology J. 2008;5:29.
10. Camargo CA Jr, Ganmaa D, Frazier AL, et al. Randomized trial of vitamin d supplementation and risk of acute respiratory infection in mongolia. Pediatrics. 2012 Sep;130(3):e561-7.
11. Pilz S, Dobnig H, Tomaschitz A, et al. Low 25-hydroxyvitamin D is associated with increased mortality in female nursing home residents. J Clin Endocrinol Metab. 2012 Apr;97(4):E653-7.
12. Smit E, Crespo CJ, Michael Y, et al. The effect of vitamin D and frailty on mortality among non-institutionalized US older adults. Eur J Clin Nutr. 2012 Sep;66(9):1024-8.
13. Dobnig H, Pilz S, Scharnagl H, et al. Independent association of low serum 25-hydroxyvitamin d and 1,25-dihydroxyvitamin d levels with al-cause and cardiovascular mortality. Arch Intern Med. 2008 Jun 23;168(12):1340-9.
14. Leow L, Simpson T, Cursons R, Karalus N, Hancox RJ. Vitamin D, innate immunity and outcomes in community acquired pneumonia. Respirology. 2011 May;16(4):611-6.