title: Serum 25-hydroxyvitamin D and parathyroid hormone are independent determinants of whole-body insulin sensitivity in women and may contribute to lower insulin sensitivity in African Americans.
abstract: BACKGROUND
  Circulating 25-hydroxyvitamin D [25(OH)D] and parathyroid hormone (PTH) concentrations have been shown to be associated with insulin sensitivity; however, adiposity may confound this relation. Furthermore, African Americans (AAs) have lower insulin sensitivity and 25(OH)D concentrations than do European Americans (EAs); whether these differences are associated in a cause-and-effect manner has not been determined.
  
  
  OBJECTIVE
  The objectives of this study were to examine the relation of 25(OH)D and PTH concentrations with whole-body insulin sensitivity and to determine whether lower 25(OH)D concentrations in AAs compared with EAs contribute to the lower insulin sensitivity of AAs relative to that of EAs.
  
  
  METHODS
  This was a cross-sectional study of 25 AA and 25 EA women. We determined the whole-body insulin sensitivity index (S(I)) with an intravenous glucose tolerance test and minimal modeling. Percentage body fat was determined with dual-energy X-ray absorptiometry, and intraabdominal adipose tissue (IAAT) was determined with computed tomography.
  
  
  RESULTS
  Multiple linear regression analysis indicated that 25(OH)D and PTH concentrations were independent determinants of S(I) [standardized β = 0.24 (P = 0.04) and -0.36 (P = 0.002), respectively] after adjustment for age, race, and IAAT. The mean ethnic difference in S(I) decreased from 2.70 [· 10(-4) · min⁻¹/(μIU/mL)] after adjustment for IAAT and percentage body fat to 1.80 [· 10(-4) · min⁻¹/(μIU/mL)] after further adjustment for 25(OH)D and PTH concentrations.
  
  
  CONCLUSIONS
  25(OH)D and PTH concentrations were independently associated with whole-body insulin sensitivity in a cohort of healthy women, which suggested that these variables may influence insulin sensitivity through independent mechanisms. Furthermore, ethnic differences in 25(OH)D concentrations may contribute to ethnic differences in insulin sensitivity.
authors.affiliation: Department of Nutrition Sciences and the Department of Pediatrics/Division of Pediatric Endocrinology and Metabolism, The Children's Hospital, University of Alabama at Birmingham, Birmingham, AL, USA. jalvar2@uab.edu
authors.forename: Jessica A
authors.initials: JA
authors.lastname: Alvarez
authors.forename: Ambika P
authors.initials: AP
authors.lastname: Ashraf
authors.forename: Gary R
authors.initials: GR
authors.lastname: Hunter
authors.forename: Barbara A
authors.initials: BA
authors.lastname: Gower
mesh_terms: D015502:Absorptiometry, Photon; D000328:Adult; D001741:Black or African American; D003430:Cross-Sectional Studies; D005260:Female; D005951:Glucose Tolerance Test; D006801:Humans; D007333:Insulin Resistance / Q000208:ethnology; D016014:Linear Models; D008875:Middle Aged; D010281:Parathyroid Hormone / Q000097:blood*; D012044:Regression Analysis; D012307:Risk Factors; D012737:Sex Factors; D014807:Vitamin D / Q000031:analogs & derivatives* / Q000097:blood; D055815:Young Adult
chemical_list: D010281:Parathyroid Hormone; D014807:Vitamin D; C104450:25-hydroxyvitamin D