F. Ahmadabadi, M. Mirzarahimi, M. Barak, A. Ahadi, and R. Alipour, “The relationship between serum vitamin D level and asthma severity in asthmatic children (aged 1-15 years) in Ardabil, 2012-13”, Int J Res Med Sci, vol. 3, no. 1, pp. 239–243, Jan. 2017.