Dietary vitamin D deficiency and nasal inflammation Patients with chronic rhinosinusitis with nasal polyps have been shown to be vitamin D deficient, which is associated with worse disease and increased polyp size (1). This study looked at the impact of vitamin D deficiency on this association. Airway function, sinonasal immune cell infiltrate and sinonasal VD3 metabolism profiles were then examined. The results showed that vitamin D deficiency causes changes in sinonasal immunity, while selectively worsening inflammation. Vitamin D deficiency was associated with altered sinonasal vitamin D metabolism, causing reductions in local levels of the active vitamin D3 metabolite, even with adequate circulating levels.