title: Associations Between Serum 25-Hydroxyvitamin D, Insulin Sensitivity, Insulin Secretion, and β-Cell Function According to Glucose Tolerance Status.
abstract: BACKGROUND
  The objective of this study was to determine whether glucose tolerance status influences the associations between serum 25-hydroxyvitamin D [25(OH)D], insulin sensitivity, insulin secretion, and β-cell function.
  
  
  METHODS
  This cross-sectional study included 112 French Canadian postmenopausal women with normal glucose tolerance (NGT; n = 65) or abnormal glucose tolerance (AGT; n = 47). Estimates of insulin sensitivity [homeostasis model assessment of insulin sensitivity (HOMA %S) and glucose disposal rate (GDR)], insulin secretion [area under the curve of C-peptide (AUC C-peptide)], and β-cell function (GDR × AUC C-peptide) were derived from a 2-hr euglycemic-hyperinsulinemic clamp and a 75-gram 3-hr oral glucose tolerance test (OGTT). Measures of adiposity were taken (waist circumference, body mass index, fat mass by the hydrostatic weighting technique, and computed tomography (CT)-derived total and visceral adiposity), questionnaires on physical activity, dietary calcium, and vitamin D intake were administered, and blood was sampled for measurement of parathyroid hormone, interleukin-6, and adiponectin.
  
  
  RESULTS
  AGT status was significantly associated with lower insulin sensitivity and β-cell function (P ≤ 0.01 for all) but not with insulin secretion. Lower serum 25(OH)D concentrations were significantly associated with lower insulin sensitivity and secretion (P ≤ 0.01 for all) but not with β-cell function. The interaction between glucose tolerance status and serum 25(OH)D concentration was not significant for either insulin sensitivity, insulin secretion, or β-cell function, even after adjustment for potential confounders.
  
  
  CONCLUSIONS
  Vitamin D and glucose tolerance status are both independently associated with measures of insulin sensitivity, insulin secretion, and β-cell function. However, the association between serum 25(OH)D and these surrogate markers of type 2 diabetes mellitus risk is not influenced by glucose tolerance status.
authors.affiliation: 1 Endocrinology and Nephrology Unit, CHU de Québec Research Centre, Laval University , Quebec, Canada .
authors.forename: Anne-Sophie
authors.initials: AS
authors.lastname: Morisset
authors.forename: Vanessa
authors.initials: V
authors.lastname: Tardio
authors.forename: John
authors.initials: J
authors.lastname: Weisnagel
authors.forename: Simone
authors.initials: S
authors.lastname: Lemieux
authors.forename: Jean
authors.initials: J
authors.lastname: Bergeron
authors.forename: Claudia
authors.initials: C
authors.lastname: Gagnon
mesh_terms: D052242:Adiponectin / Q000737:chemistry; D050154:Adiposity; D000368:Aged; D019540:Area Under Curve; D015992:Body Mass Index; D002096:C-Peptide / Q000097:blood; D002170:Canada / Q000208:ethnology; D003430:Cross-Sectional Studies; D003924:Diabetes Mellitus, Type 2 / Q000097:blood; D004032:Diet; D005260:Female; D015309:Glucose Clamp Technique; D005951:Glucose Tolerance Test; D006801:Humans; D007328:Insulin / Q000097:blood* / Q000378:metabolism*; D007333:Insulin Resistance / Q000502:physiology; D000078790:Insulin Secretion; D050417:Insulin-Secreting Cells / Q000502:physiology*; D015850:Interleukin-6 / Q000097:blood; D050152:Intra-Abdominal Fat / Q000473:pathology; D008875:Middle Aged; D012621:Seasons; D014057:Tomography, X-Ray Computed; D014807:Vitamin D / Q000031:analogs & derivatives* / Q000097:blood
chemical_list: D052242:Adiponectin; D002096:C-Peptide; C508600:IL6 protein, human; D007328:Insulin; D015850:Interleukin-6; D014807:Vitamin D; C104450:25-hydroxyvitamin D