Background. Cystic fibrosis (CF) is a chronic catabolic disease often requiring hospitalization for acute episodes of worsening pulmonary exacerbations. Limited data suggest that vitamin D may have beneficial clinical affects, but the impact of vitamin D on systemic metabolism in this setting is unknown. Objective. We used high-resolution metabolomics (HRM) to assess the impact of baseline vitamin D status and high-dose vitamin D-3 administration on systemic metabolism in adults with CF with an acute pulmonary exacerbation. Design. Twenty-five hospitalized adults with CF were enrolled in a randomized trial of high-dose vitamin D-3 (250,000 IU vitamin D-3 bolus) versus placebo. Age-matched healthy subjects served as a reference group for baseline comparisons. Plasma was analyzed with liquid chromatography/ultra-high resolution mass spectrometry. Using recent HRM bioinformatics and metabolic pathway enrichment methods, we examined associations with baseline vitamin D status (sufficient vs. deficient per serum 25-hydroxyvitamin D concentrations) and the 7-day response to vitamin D-3 supplementation. Results. Several amino acids and lipid metabolites differed between CF and healthy control subjects, indicative of an overall catabolic state. In CF subjects, 343 metabolites differed (P < 0.05) by baseline vitamin D status and were enriched within 7 metabolic pathways including fatty acid, amino acid, and carbohydrate metabolism. A total of 316 metabolites, which showed enrichment for 15 metabolic pathways-predominantly representing amino acid pathways-differed between the vitamin D-3- and placebo-treated CF subjects over time (P < 0.05). In the placebo group, several tricarboxylic acid cycle intermediates increased while several amino acid-related metabolites decreased; in contrast, little change in these metabolites occurred with vitamin D-3 treatment. Conclusions. Numerous metabolic pathways detected by HRM varied in association with vitamin D status and high-dose vitamin D-3 supplementation in adults with CF experiencing a pulmonary exacerbation. Overall, these pilot data suggest an anti-catabolic effect of high dose vitamin D-3 in this clinical setting. (C) 2017 Elsevier Inc. All rights reserved.