Exposure to cigarette smoke has been associated with VD deficiency in healthy patients, older subjects, and patients with chronic rhinosinusitis [42,43], and a few studies have suggested that cigarette smoke could affect VD metabolism by increasing CYP24A1 (24-hydroxylase, catabolizing enzyme that degrades 1,25(OH)D3) [44] and/or decreasing CYP27B1 (1α-hydroxylase, activating enzyme leading to formation of 1,25(OH)D3) [45]. Here, CYP24A1 is linked to chronic rhinosinusitis.