title: Hypovitaminosis D in bariatric surgery: A systematic review of observational studies.
abstract: BACKGROUND
  Obesity is a public health problem that carries global and substantial social and economic burden. Relative to non-surgical interventions, bariatric surgery has the most substantial and lasting impact on weight loss. However, it leads to a number of nutritional deficiencies requiring long term supplementation.
  
  
  OBJECTIVE
  The aims of this paper are to review 25-hydroxyvitamin D [25(OH)D] status pre and post bariatric surgery, describe the dose response of vitamin D supplementation, and assess the effect of the surgical procedure on 25(OH)D level following supplementation.
  
  
  METHODS
  We searched Medline, PubMed, the Cochrane Library and EMBASE, for relevant observational studies published in English, from 2000 to April 2015. The identified references were reviewed, in duplicate and independently, by two reviewers.
  
  
  RESULTS
  We identified 51 eligible observational studies assessing 25(OH)D status pre and/or post bariatric surgery. Mean pre-surgery 25(OH)D level was below 30ng/ml in 29 studies, and 17 of these studies showed mean 25(OH)D levels ≤20ng/ml. Mean 25(OH)D levels remained below 30ng/ml following bariatric surgery, despite various vitamin D replacement regimens, with only few exceptions. The increase in post-operative 25(OH)D levels tended to parallel increments in vitamin D supplementation dose but varied widely across studies. An increase in 25(OH)D level by 9-13ng/ml was achieved when vitamin D deficiency was corrected using vitamin D replacement doses of 1100-7100IU/day, in addition to the usual maintenance equivalent daily dose of 400-2000IU (total equivalent daily dose 1500-9100IU). There was no difference in mean 25(OH)D level following supplementation between malabsorptive/combination procedures and restrictive procedures.
  
  
  CONCLUSIONS
  Hypovitaminosisis D persists in obese patients undergoing bariatric surgery, despite various vitamin D supplementation regimens. Further research is needed to determine the optimal vitamin D dose to reach desirable 25(OH)D levels in this population, and to demonstrate whether this dose varies according to the surgical procedure.
authors.affiliation: Division of Endocrinology, Calcium Metabolism and Osteoporosis Program, WHO Collaborating Center for Metabolic Bone Disorders, American University of Beirut Medical Center, Beirut, Lebanon; Scholars in HeAlth Research Program (SHARP), American University of Beirut Medical Center, Beirut, Lebanon. Electronic address: mc39@aub.edu.lb.
authors.forename: Marlene Toufic
authors.initials: MT
authors.lastname: Chakhtoura
authors.affiliation: Scholars in HeAlth Research Program (SHARP), American University of Beirut Medical Center, Beirut, Lebanon; Division of Endocrinology, American University of Beirut Medical Center, Beirut, Lebanon.
authors.forename: Nancy N
authors.initials: NN
authors.lastname: Nakhoul
authors.affiliation: Scholars in HeAlth Research Program (SHARP), American University of Beirut Medical Center, Beirut, Lebanon.
authors.forename: Khaled
authors.initials: K
authors.lastname: Shawwa
authors.affiliation: Division of Endocrinology, Diabetes and Metabolism, Beth Israel Deaconess Medical Center, Harvard Medical School, Boston, MA, USA.
authors.forename: Christos
authors.initials: C
authors.lastname: Mantzoros
authors.affiliation: Division of Endocrinology, Calcium Metabolism and Osteoporosis Program, WHO Collaborating Center for Metabolic Bone Disorders, American University of Beirut Medical Center, Beirut, Lebanon.
authors.forename: Ghada A
authors.initials: GA
authors.lastname: El Hajj Fuleihan
mesh_terms: D050110:Bariatric Surgery / Q000009:adverse effects*; D019587:Dietary Supplements; D006801:Humans; D009767:Obesity, Morbid / Q000601:surgery; D064887:Observational Studies as Topic; D011183:Postoperative Complications / Q000378:metabolism*; D014807:Vitamin D / Q000627:therapeutic use; D014808:Vitamin D Deficiency / Q000188:drug therapy / Q000209:etiology* / Q000378:metabolism; D014815:Vitamins / Q000627:therapeutic use
chemical_list: D014815:Vitamins; D014807:Vitamin D
keywords: Bariatric surgery; Obesity; Predictor; Vitamin D deficiency; Vitamin D dose