CYP27B1 and Nasal polyposis: Interestingly, one study did already show that nasal CYP27B1- and 1,25(OH)2D-levels are both reduced in chronic rhinosinusitis (CRS) patients with nasal polyps as compared to CRS-patients without nasal polyps, whereas no difference was found in circulating 1,25(OH)2D-levels (89).