Seasonal and Regional Variations of Asthma and Association with Osteoporosis: Possible Role of Vitamin D in Asthma

Background. Based on the evidence that vitamin D is involved in the development of immune system and vitamin D receptor gene is associated with asthma, we supposed that vitamin D is related to the development of asthma. Methods. Asthma patients were identified from the Swedish Hospital Discharge Register and the hospitalization rate was examined by different seasons and regions. Standardized incidence ratios (SIRs) for asthma were examined among patients hospitalized for osteoporosis compared with the general population. Results. A total of 172,384 patients were hospitalized for asthma in Sweden during 1965-2007. More patients were hospitalized in winter and North Sweden than in summer and South Sweden. The risk of asthma after osteoporosis was significantly increased, giving an overall SIR of 2.93. The risk was higher in male patients when compared with female subjects. Patients hospitalized for osteoporosis at age younger than 55 showed a high risk. Reversing the analyses and examining the risk of osteoporosis after hospitalization of asthma, SIR was significantly increased (3.54). Conclusion. Our study suggests that vitamin D, as indicated by the high risk of asthma after osteoporosis and the seasonal and regional variations of hospitalization, could play an important role for the development of asthma.