Vitamin D modulates immune function through effects on both the innate and adaptive components (1). The innate immune system is the first line of defense that infections and includes all mechanisms that prevent invasion without the need for memory from previous pathogen exposure (2). Innate immunity includes the production of antimicrobial peptides that are capable of killing viruses, bacteria, and other organisms. The adaptive immune system is more sophisticated than the innate system. Vitamin D modulates both T-lymphocyte and B-lymphocyte function (1). Among T-lymphocytes the T-helper cell is a principal target. Vitamin D suppresses T-helper cell proliferation and modulates their cytokine production. Cell mediated immunity is promoted in preference to antibody mediated immunity. Vitamin D also has a direct effect on B-lymphocyte proliferation and immunoglobulin production (1).
Additionally, in a study was observed lower serum 25(OH)D levels in cases of acute severe lower respiratory infection requiring admission to hospital compared with controls (3). A Dutch study found that children with low sun exposure were more likely to have a cough and a runny nose, compared to children with most sun exposure (4). The temporal association between seasonal changes in vitamin D levels and winter respiratory virus activity has led to the proposal that low vitamin D levels may have a causal role in the onset of influenza epidemics. Several observational studies have reported on vitamin D status and respiratory infection. A secondary analysis of the U.S. National Health and Nutrition Examination Survey (NHANES) III survey showed that, after adjusting for demographic and clinical characteristics, lower 25(OH)D levels were independently associated with self-reported upper respiratory tract infections (URIs) in the past few days (5). Strong evidence of whether there is a true effect of vitamin D on the risk of infection can only be generated by randomized controlled trials. This point was reinforced in a systematic review, published in 2009 by Yamshchikov et al., who identified 13 clinical trials addressing the effect of vitamin D on treatment and prevention of infectious diseases in humans (6).
1. Hewison M. Vitamin D and immune function: autocrine, paracrine or endocrine? Scand J Clin Lab Invest Suppl 2012;243:92-102.
2. White JH. Vitamin D metabolism and signaling in the immune system. Rev Endocr Metab Disord 2012;13:21-9.
3. 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;58:563-7.
4. Termorshuizen F, Wijga A, Garssen J, Den Outer PN, Slaper H, Van LH. Exposure to solar ultraviolet radiation in young Dutch children: assessment by means of a 6-week retrospective questionnaire. J Expo Anal Environ Epidemiol 2002;12:204-13.
5. 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;169:384-90.
6. Yamshchikov AV, Desai NS, Blumberg HM, Ziegler TR, Tangpricha V. Vitamin D for treatment and prevention of infectious diseases: a systematic review of randomized controlled trials. Endocr Pract 2009;15:438-49.