This proposal will evaluate a potential mechanism of increased risk of lung function impairment, cathelicidin levels, as well as determine if vitamin D replacement can alter this pathway. This study will improve the understanding of factors which can lead to chronic lung disease. If effective, this application would also provide the justification to study vitamin D as a therapy to improve lung health.

Understanding mechanisms leading to decrements in lung function, the physiologic hallmark of obstructive lung diseases including chronic obstructive pulmonary disease (COPD), are necessary to inform interventions to improve lung health. The antimicrobial peptide cathelicidin, and its primary regulator vitamin D, has been implicated in development and progression of chronic lung disease. In this study, the investigators will evaluate the effect of oral vitamin D supplementation on lung cathelicidin levels in humans. Cathelicidin has bactericidal and inflammatory activities in the lung and is regulated by vitamin D levels. The investigators hypothesize that oral vitamin D supplementation will raise cathelicidin levels in the pulmonary compartment, thereby restoring lung cathelicidin deficiency. To test this hypothesis, the investigators will recruit from two ongoing cohort studies: 1) At Johns Hopkins, the Subpopulations and Intermediate Outcome Measures in COPD Study study and 2)at University of North Carolina at Chapel Hill pulmonary and general medicine clinic. The investigators will measure blood and lung lavage cathelicidin levels in 40 vitamin D insufficient individuals (20 from each cohort) before and after eight weeks of oral vitamin D supplementation to determine the effect of vitamin D supplementation on cathelicidin levels.