Eroglu, Cemal, et al. “The Relation Between Serum Vitamin D Levels, Viral Infections and Severity of Attacks in Children With Recurrent Wheezing”. Allergologia Et Immunopathologia, vol. 47, no. 6, Dec. 2019, pp. 591-7, https://all-imm.com/index.php/aei/article/view/274.