To the Editors

Abstract

There is additional support for a vitamin D–COPD link. Indeed, frequent cases of acute bronchitis increase the risk of COPD 3. Respiratory syncytial virus (RSV) is an important risk factor for acute bronchitis. Solar ultraviolet (UV)B has been found to explain some of the seasonal and latitudinal variation in RSV activity. In a recent study, solar UVB explained 13% of the RSV activity in Miami (FL, USA), 5% in Buffalo (NY, USA) and 0.6% in Winnipeg (MB, Canada) 4. The relevant action of vitamin D is the induction of human cathelicidin, LL-37 5. LL-37 is an important component of the innate immune system and vitamin D supplementation was demonstrated to reduce the risk of viral infections in a post hoc analysis of a randomised controlled trial. Black postmenopausal women living in the state of New York (USA) had one-tenth the incidence rate of seasonal influenza and common cold when taking 2,000 IU·day⁻¹ of vitamin D3 compared with those taking a placebo; those taking 800 IU·day⁻¹ had 40% the incidence rate of those taking a placebo 6.