title: Seasonal variation in the deficiency of 25-hydroxyvitamin D(3) in mildly to extremely obese subjects.
abstract: BACKGROUND
  Vitamin D deficiency is a common finding in obese subjects even before any bariatric operation. However, most previous studies reporting on high rates of vitamin D deficiency in obese subjects have not systematically controlled for seasonal variations. Furthermore, the existence of seasonal variation in serum 25-hydroxyvitamin D(3) levels has not been well documented in obese subjects so far.
  
  
  METHODS
  Serum 25-hydroxyvitamin D(3) levels were measured in 248 obese subjects (body mass index: range, 30.1-68.9 kg/m(2)). Fat mass was determined using standard bioelectrical impedance analysis.
  
  
  RESULTS
  Serum 25-hydroxyvitamin D(3) levels decreased with the increasing body mass index and fat mass (both P < 0.001) and showed a marked variation across the seasons of the year (P < 0.001), which was not affected by the degree of obesity. According to the variation in absolute levels, the prevalence of vitamin D deficiency (<50 nmol/l) was 3.8-fold higher during winter than during summer (91.2% vs. 24.3%; P < 0.001).
  
  
  CONCLUSIONS
  Data show a marked seasonal variation in absolute serum 25-hydroxyvitamin D(3) concentrations and prevalence of vitamin D deficiency in subjects with mild to extreme obesity. Considering the increasing number of studies reporting on vitamin D deficiency in obesity, the present finding points to season as a crucial factor that should not be neglected when assessing serum levels of this vitamin in obese subjects.
authors.affiliation: Interdisciplinary Obesity Center, Kantonsspital St. Gallen, Heidener Strasse 11, CH-9400, Rorschach, Switzerland.
authors.forename: Barbara
authors.initials: B
authors.lastname: Ernst
authors.affiliation: Interdisciplinary Obesity Center, Kantonsspital St. Gallen, Heidener Strasse 11, CH-9400, Rorschach, Switzerland.
authors.forename: Martin
authors.initials: M
authors.lastname: Thurnheer
authors.affiliation: Department of Internal Medicine I, University of Luebeck, 23538, Luebeck, Germany.
authors.forename: Sebastian M
authors.initials: SM
authors.lastname: Schmid
authors.affiliation: Department of Internal Medicine I, University of Luebeck, 23538, Luebeck, Germany.
authors.forename: Britta
authors.initials: B
authors.lastname: Wilms
authors.affiliation: Interdisciplinary Obesity Center, Kantonsspital St. Gallen, Heidener Strasse 11, CH-9400, Rorschach, Switzerland. bernd.schultes@kssg.ch.|Department of Internal Medicine I, University of Luebeck, 23538, Luebeck, Germany. bernd.schultes@kssg.ch.
authors.forename: Bernd
authors.initials: B
authors.lastname: Schultes
mesh_terms: D000293:Adolescent; D000328:Adult; D000368:Aged; D001823:Body Composition; D015992:Body Mass Index; D005260:Female; D006801:Humans; D006887:Hydroxycholecalciferols / Q000097:blood*; D008297:Male; D008875:Middle Aged; D009767:Obesity, Morbid / Q000097:blood* / Q000150:complications* / Q000175:diagnosis; D012621:Seasons; D012720:Severity of Illness Index; D014808:Vitamin D Deficiency / Q000097:blood / Q000150:complications* / Q000175:diagnosis; D055815:Young Adult
chemical_list: D006887:Hydroxycholecalciferols