Bronchoalveolar Lavage and Plasma Cathelicidin Response to 25-Hydroxy Vitamin D Supplementation: A Pilot Study

Introduction: Cathelicidin is a vitamin D-regulated, antimicrobial peptide involved in the innate immune response of the airways. Reduced plasma cathelicidin concentrations are independently associated with worse pulmonary outcomes in current and former smokers. This study aimed to determine whether oral vitamin D supplementation in vitamin D-deficient current smokers increases plasma and bronchoalveolar lavage (BAL) cathelicidin levels.

Methods: Vitamin D-deficient (25-hydroxy vitamin D [25-OH vitamin D] <20 ng/ml) smokers (n=17) underwent collection of plasma and BAL for cathelicidin and 25-OH vitamin D measurements before and after 8 weeks of oral supplementation with 50,000 IU vitamin D3 weekly. Differences between baseline and 8-week levels of cathelicidin and 25-OH vitamin D in blood and BAL were assessed along with correlations between serum 25-OH vitamin D, plasma cathelicidin, and BAL cathelicidin.

Results: At baseline, there was no correlation between BAL and plasma cathelicidin. There was a significant increase in 25-OH vitamin D (median 17.0 to 43.3 ng/mL, <0.001) after 8 weeks of vitamin D supplementation. There was no change in plasma cathelicidin (=0.86), BAL cathelicidin (=0.31), or BAL 25-OH vitamin D (0.89). There was no correlation between serum 25-OH vitamin D and either BAL or plasma cathelicidin post-supplementation.

Conclusions: Oral vitamin D supplementation, while increasing serum 25-OH vitamin D levels, does not increase plasma or BAL cathelicidin levels in vitamin D-deficient, active smokers. The lack of increased BAL cathelicidin may be explained by multiple factors related to dosing, smoking effects, or putative mechanisms of engagement. Future studies are needed to determine the effects of vitamin D supplementation on lung and blood functional activity.