title: The Apparent Relation between Plasma 25-Hydroxyvitamin D and Insulin Resistance is Largely Attributable to Central Adiposity in Overweight and Obese Adults.
abstract: BACKGROUND
  Research indicates that plasma 25-hydroxyvitamin D [25(OH)D] is associated with insulin resistance, but whether regional adiposity confounds this association is unclear.
  
  
  OBJECTIVE
  This study assessed the potential influence of adiposity and its anatomical distribution on the relation between plasma 25(OH)D and insulin resistance.
  
  
  METHODS
  A secondary analysis of data from middle-aged overweight and obese healthy adults [n = 336: 213 women and 123 men; mean ± SD (range); age: 48 ± 8 y (35-65 y); body mass index (BMI; in kg/m2): 30.3 ± 2.7 (26-35)] from West Lafayette, Indiana (40.4 °N), were used for this cross-sectional analysis. Multiple linear regression analyses that controlled for multiple covariates were used as the primary statistical model.
  
  
  RESULTS
  Of all participants, 8.6% and 20.5% displayed moderate [20.1-37.5 nmol/L plasma 25(OH)D] to mild (37.6-49.9 nmol/L) vitamin D insufficiency, respectively. A regression analysis controlling for age, sex, race, plasma parathyroid hormone concentration, season of year, and supplement use showed that 25(OH)D was negatively associated with fasting insulin (P = 0.021). Additional regression analyses showed that total and central adiposity but not peripheral adiposity predicted low plasma 25(OH)D [total fat mass index (FMI): P = 0.018; android FMI: P = 0.052; gynoid FMI: P = 0.15; appendicular FMI: P = 0.07) and insulin resistance (homeostasis model assessment of insulin resistance: total and android FMI, P <0.0001; gynoid FMI, P = 0.94; appendicular FMI, P = 0.86). The associations of total and central adiposity with insulin resistance remained significant after adjusting for plasma 25(OH)D. However, adjusting for central adiposity but not other anatomical measures of fat distribution eliminated the association between plasma 25(OH)D and insulin resistance.
  
  
  CONCLUSIONS
  Central adiposity drives the association between plasma 25(OH)D and insulin resistance in overweight and obese adults. The trial was registered at clinicaltrials.gov as NCT00812409.
authors.affiliation: Department of Nutrition Science, Purdue University, West Lafayette, IN; and.
authors.forename: Christian S
authors.identifier: http://orcid.org/0000-0002-9594-2759
authors.initials: CS
authors.lastname: Wright
authors.affiliation: Department of Nutrition Science, Purdue University, West Lafayette, IN; and.
authors.forename: Eileen M
authors.identifier: http://orcid.org/0000-0001-5408-0024
authors.initials: EM
authors.lastname: Weinheimer-Haus
authors.affiliation: Department of Nutrition Science, Purdue University, West Lafayette, IN; and.
authors.forename: James C
authors.identifier: http://orcid.org/0000-0002-0142-9517
authors.initials: JC
authors.lastname: Fleet
authors.affiliation: Department of Medicine, Indiana University, Indianapolis, IN.
authors.forename: Munro
authors.initials: M
authors.lastname: Peacock
authors.affiliation: Department of Nutrition Science, Purdue University, West Lafayette, IN; and campbellw@purdue.edu.
authors.forename: Wayne W
authors.identifier: http://orcid.org/0000-0002-7847-7242
authors.initials: WW
authors.lastname: Campbell
mesh_terms: D000328:Adult; D000368:Aged; D001823:Body Composition; D015992:Body Mass Index; D003430:Cross-Sectional Studies; D004311:Double-Blind Method; D005260:Female; D006801:Humans; D007196:Indiana; D007333:Insulin Resistance / Q000502:physiology*; D016014:Linear Models; D008297:Male; D008875:Middle Aged; D009765:Obesity / Q000503:physiopathology*; D056128:Obesity, Abdominal / Q000097:blood / Q000503:physiopathology*; D050177:Overweight / Q000503:physiopathology*; D010919:Placebos; D014807:Vitamin D / Q000031:analogs & derivatives* / Q000097:blood
chemical_list: D010919:Placebos; D014807:Vitamin D; C104450:25-hydroxyvitamin D
keywords: 25(OH)D; adiposity; body composition; central adiposity; insulin resistance; vitamin D status