Vitamin D can reduce the risk of pneumonia following influenza infection William B. Grant, Sunlight, Nutrition and Health Research Center 16 June 2010 A recent paper stated “Influenza may be complicated by bacterial pneumonia. .. At present, antibiotic treatment appears to be the only therapeutic option for postinfluenza pneumonia.”  However, this paper overlooks recent evidence that vitamin D can reduce the risk of both type A influenza and pneumonia. A randomized controlled trial involving school children in Japan found a 64% reduced risk of type A influenza for those taking 1200 IU/day of vitamin D versus 200 IU/day . An ecological study based on case-fatality rates of those infected by influenza in 12 U.S. communities during the 1918-19 pandemic influenza found indices of solar ultraviolet B (UVB) doses explained 50% of the variance . A study in Turkey found childhood pneumonia was frequently associated with rickets, a well-known vitamin D-deficiency disease . A study in Philadelphia found a close association between solar UVB doses and the seasonality of invasive pneumococcal disease . The mechanism whereby vitamin D reduces the risk of both influenza and pneumonia is induction of cathelicidin and defensins by 1,25-dihydroxyvitamin D, which have antimicrobial and antiendotoxin activities . In addition, 1,25-dihydroxyvitamin D shifts the production from proinflammatory T-helper 1 (Th1) cytokines to Th2 cytokines, thereby reducing damage to the epithelial layer of the lungs and, consequently, the risk of invasion by bacteria. References 1. Sluijs KF, Poll TV, Lutter R, Juffermans NP, Schultz MJ. Bench-to-bedside review: Bacterial pneumonia with influenza - pathogenesis and clinical implications. Crit Care. 2010 Apr 19;14(2):219. [Epub ahead of print] 2. 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;91:1255-60. 3. Grant WB, Giovannucci D. The possible roles of solar ultraviolet-B radiation and vitamin D in reducing case-fatality rates from the 1918–1919 influenza pandemic in the United States. Dermato-Endocrinology 2009;1:215-9. 4. Dogan M, Erol M, Cesur Y, Yuca SA, Doğan Z. The effect of 25-hydroxyvitamin D3 on the immune system. J Pediatr Endocrinol Metab. 2009;22:929-35. 5. White AN, Ng V, Spain CV, Johnson CC, Kinlin LM, Fisman DN. Let the sun shine in: effects of ultraviolet radiation on invasive pneumococcal disease risk in Philadelphia, Pennsylvania. BMC Infect Dis. 2009;9:196. Competing interests I receive funding from the UV Foundation (McLean, VA), the Sunlight Research Forum (Veldhoven), Bio-Tech-Pharmacal (Fayetteville, AR), and the Vitamin D Council (San Luis Obispo, CA), and have received funding from the Vitamin D Society (Canada).