VDR and Recurrent upper respiratory tract infections: Vitamin D is an immunomodulatory hormone whose active form, 1,25 dihydroxy vitamin D (1,25(OH)D), binds to the vitamin D receptor (VDR) to exert anti-inflammatory and immunomodulatory effects, prevent inflammatory response, and accelerate the healing process in affected areas, and it acts mainly in lung tissue with proven effectiveness against various upper respiratory tract infections (Mohan et al., 2020).