title: The link between obesity and vitamin D in bariatric patients with omega-loop gastric bypass surgery - a vitamin D supplementation trial to compare the efficacy of postoperative cholecalciferol loading (LOAD): study protocol for a randomized controlled trial.
abstract: BACKGROUND
  Beyond its classical role in calcium homoeostasis and bone metabolism, vitamin D deficiency has been found to be associated with several diseases, including diabetes, non-alcoholic fatty liver disease, and even obesity itself. Importantly, there are limited data on therapeutic strategies for vitamin D deficiency in bariatric patients, and the procedure-specific guidelines may not be sufficient. To improve long-term outcomes, nutritional screening and appropriate supplementation to prevent nutrient deficiencies are urgently needed. Therefore, the aim of this study is to examine effects and safety of a forced dosing regimen of vitamin D versus conventional dose supplementation on vitamin D levels and other parameters in bariatric patients.
  
  
  METHODS
  The study includes loading plus repeat dosing compared with repeated administration of vitamin D without a loading dose, according to guidelines, in a prospective, double-blind, randomized controlled trial. Up to a triple oral loading dose is given on day 1, then 2 and 4 weeks after surgery (100,000 IU dose each time), followed by an oral maintenance dose (3420 IU/day). The control group (n = 25) will receive placebo, followed by administration of a standard dose (3420 IU/day). We hypothesize that a significant increase in vitamin D levels will occur in patients in the treatment group (n = 25) by 24 weeks after surgery. Further measurements are aimed at evaluating changes in inflammation, bone turnover, insulin resistance, blood pressure, liver, mental health, and gut microbiota of patients undergoing omega-loop gastric bypass surgery. Furthermore, possible associations between concentrations of vitamin D, the involved enzymes, or vitamin D receptor in adipose and/or liver tissues will be determined.
  
  
  CONCLUSIONS
  To our knowledge, this trial is the first of its kind with this type of vitamin D supplementation in bariatric patients. Its major strength is the design and implementation of evaluation of influencing factors such as liver function, bone health, inflammation, insulin resistance, blood pressure, symptoms of depression, or microbiota. This alternative vitamin D dosing regimen has the potential to be a safe, fast, evidence-based treatment of vitamin D deficiency in bariatric patients. Owing to the increasing number of bariatric patients, it is also of interest to elucidate the link between obesity and vitamin D.
  
  
  BACKGROUND
  ClinicalTrials.gov identifier: NCT02092376 . Registered on 17 March 2014.
authors.affiliation: Division of Endocrinology and Metabolism, Department of Internal Medicine III, Medical University of Vienna, Währinger Gürtel 18-20, 1090, Vienna, Austria. maria.luger@meduniwien.ac.at.|Special Institute for Preventive Cardiology and Nutrition - SIPCAN, Guggenbichlerstraße 8/15, 5026, Salzburg, Austria. maria.luger@meduniwien.ac.at.
authors.forename: Maria
authors.initials: M
authors.lastname: Luger
authors.affiliation: Division of Endocrinology and Metabolism, Department of Internal Medicine III, Medical University of Vienna, Währinger Gürtel 18-20, 1090, Vienna, Austria. renate.kruschitz@meduniwien.ac.at.
authors.forename: Renate
authors.initials: R
authors.lastname: Kruschitz
authors.affiliation: Clinical Institute for Medical and Chemical Laboratory Diagnostics, Department of Laboratory Medicine, Medical University of Vienna, Währinger Gürtel 18-20, 1090, Vienna, Austria. rodrig.marculescu@meduniwien.ac.at.
authors.forename: Rodrig
authors.initials: R
authors.lastname: Marculescu
authors.affiliation: Clinical Institute for Medical and Chemical Laboratory Diagnostics, Department of Laboratory Medicine, Medical University of Vienna, Währinger Gürtel 18-20, 1090, Vienna, Austria. helmuth.haslacher@meduniwien.ac.at.
authors.forename: Helmuth
authors.initials: H
authors.lastname: Haslacher
authors.affiliation: Special Institute for Preventive Cardiology and Nutrition - SIPCAN, Guggenbichlerstraße 8/15, 5026, Salzburg, Austria. office@sipcan.at.
authors.forename: Friedrich
authors.initials: F
authors.lastname: Hoppichler
authors.affiliation: Department of Pathophysiology and Allergy Research, Medical University of Vienna, Währinger Gürtel 18-20, 1090, Vienna, Austria. enikoe.kallay@meduniwien.ac.at.
authors.forename: Enikö
authors.initials: E
authors.lastname: Kallay
authors.affiliation: Division of Gastroenterology and Hepatology, Department of Internal Medicine III, Medical University of Vienna, Währinger Gürtel 18-20, 1090, Vienna, Austria. christian.a.kienbacher@meduniwien.ac.at.
authors.forename: Christian
authors.initials: C
authors.lastname: Kienbacher
authors.affiliation: Division of Endocrinology and Metabolism, Department of Internal Medicine III, Medical University of Vienna, Währinger Gürtel 18-20, 1090, Vienna, Austria. n0748048@students.meduniwien.ac.at.
authors.forename: Carmen
authors.initials: C
authors.lastname: Klammer
authors.affiliation: Division of Gastroenterology and Hepatology, Department of Internal Medicine III, Medical University of Vienna, Währinger Gürtel 18-20, 1090, Vienna, Austria. melanie.kral@akhwien.at.
authors.forename: Melanie
authors.initials: M
authors.lastname: Kral
authors.affiliation: Division of General Surgery, Department of Surgery, Medical University of Vienna, Währinger Gürtel 18-20, 1090, Vienna, Austria. felix.langer@meduniwien.ac.at.
authors.forename: Felix
authors.initials: F
authors.lastname: Langer
authors.affiliation: Institute of Social Medicine, Centre for Public Health, Medical University of Vienna, Kinderspitalgasse 15/1, 1090, Vienna, Austria. eva.luger@meduniwien.ac.at.
authors.forename: Eva
authors.initials: E
authors.lastname: Luger
authors.affiliation: Division of General Surgery, Department of Surgery, Medical University of Vienna, Währinger Gürtel 18-20, 1090, Vienna, Austria. gerhard.prager@meduniwien.ac.at.
authors.forename: Gerhard
authors.initials: G
authors.lastname: Prager
authors.affiliation: Division of Gastroenterology and Hepatology, Department of Internal Medicine III, Medical University of Vienna, Währinger Gürtel 18-20, 1090, Vienna, Austria. michael.trauner@meduniwien.ac.at.
authors.forename: Michael
authors.initials: M
authors.lastname: Trauner
authors.affiliation: Division of Gastroenterology and Hepatology, Department of Internal Medicine III, Medical University of Vienna, Währinger Gürtel 18-20, 1090, Vienna, Austria. stefan.traussnigg@meduniwien.ac.at.
authors.forename: Stefan
authors.initials: S
authors.lastname: Traussnigg
authors.affiliation: Department of Pathology, Medical University of Vienna, Währinger Gürtel 18-20, 1090, Vienna, Austria. tanja.wuerger@meduniwien.ac.at.
authors.forename: Tanja
authors.initials: T
authors.lastname: Würger
authors.affiliation: Division of Endocrinology and Metabolism, Department of Internal Medicine III, Medical University of Vienna, Währinger Gürtel 18-20, 1090, Vienna, Austria. karin.schindler@meduniwien.ac.at.
authors.forename: Karin
authors.initials: K
authors.lastname: Schindler
authors.affiliation: Division of Endocrinology and Metabolism, Department of Internal Medicine III, Medical University of Vienna, Währinger Gürtel 18-20, 1090, Vienna, Austria. bernhard.ludvik@meduniwien.ac.at.
authors.forename: Bernhard
authors.initials: B
authors.lastname: Ludvik
mesh_terms: D000284:Administration, Oral; D015415:Biomarkers / Q000097:blood; D002762:Cholecalciferol / Q000008:administration & dosage* / Q000009:adverse effects; D002985:Clinical Protocols; D019587:Dietary Supplements / Q000009:adverse effects; D004311:Double-Blind Method; D004334:Drug Administration Schedule; D005260:Female; D015390:Gastric Bypass / Q000009:adverse effects / Q000379:methods*; D006801:Humans; D008297:Male; D009765:Obesity / Q000175:diagnosis / Q000601:surgery*; D011182:Postoperative Care; D011446:Prospective Studies; D012107:Research Design; D013997:Time Factors; D016896:Treatment Outcome; D014807:Vitamin D / Q000031:analogs & derivatives / Q000097:blood; D014808:Vitamin D Deficiency / Q000097:blood / Q000175:diagnosis / Q000188:drug therapy*
chemical_list: D015415:Biomarkers; D014807:Vitamin D; D002762:Cholecalciferol; C104450:25-hydroxyvitamin D