Fig. 2From: Vitamin D deficiency is associated with respiratory symptoms and airway wall thickening in smokers with and without COPD: a prospective cohort studyTime to exacerbation; Kaplan-Meier curves demonstrating the time to exacerbation in the vitamin D sufficient group (blue line) and the vitamin D deficient group (orange line). There was no significant difference between to two groups (p = 0.095)Back to article page