Vitamin D and Microbiota in Cystic Fibrosis

Inclusion Criteria: * Presenting to the Cystic fibrosis clinic for routine follow up of cystic fibrosis * Serum 25(OH)D concentrations obtained within 2 months of enrollment * Able to tolerate oral medications Exclusion Criteria: * Inability to obtain or declined informed consent from the subject and/or legally authorized representative * Pregnancy or plans to become pregnant in the next 3 months * History of disorders associated with hypercalcemia including parathyroid disease * Current hypercalcemia (albumin-corrected serum calcium \>10.8 mg/dL or ionized calcium \>5.2 mg/dL) * History of nephrolithiasis with active symptoms within the past two years * Chronic kidney disease worse than stage III (\<60 ml/min) * Current significant hepatic dysfunction total bilirubin \> 2.5 mg/dL with direct bilirubin \> 1.0 mg/dL * Current use of cytotoxic or immunosuppressive drugs * History of AIDS * History of illicit drug abuse (defined as history of enrollment into a drug rehabilitation program or hospital visits due to drug use within the past 3 years or any use of the following drugs in the past 6 months (cocaine, opiates, amphetamines, marijuana) or any positive toxicology screen for (cocaine, opiates, amphetamines, marijuana) * Too ill to participate in study based on investigator's or study team's opinion * Current enrollment in another intervention trial * In addition we amended our study with three additional criteria 11) systemic antibiotic use in the last 4 weeks, 12) use of probiotics and, 13) inflammatory bowel disease, four months after the start of the study and after 12 subjects were randomized, as we considered that these factors may also influence our study endpoints. Of the 12 subjects who were randomized, only 4 would have been excluded.