title: Hypovitaminosis D is associated with insulin resistance and beta cell dysfunction.
abstract: BACKGROUND
  Although the role of vitamin D in type 2 diabetes is well recognized, its relation to glucose metabolism is not well studied.
  
  
  OBJECTIVE
  We investigated the relation of 25-hydroxyvitamin D [25(OH)D] concentrations to insulin sensitivity and beta cell function.
  
  
  METHODS
  We enrolled 126 healthy, glucose-tolerant subjects living in California. Insulin sensitivity index (ISI) and first- and second-phase insulin responses (1stIR and 2ndIR) were assessed by using a hyperglycemic clamp.
  
  
  RESULTS
  Univariate regression analyses showed that 25(OH)D concentration was positively correlated with ISI (P < 0.0001) and negatively correlated with 1stIR (P = 0.0045) and 2ndIR (P < 0.0001). Multiple regression analyses confirmed an independent correlation between 25(OH)D concentration and ISI (P = 0.0007). No independent correlation was observed between 25(OH)D concentration and 1stIR or 2ndIR. However, an independent negative relation of 25(OH)D concentration with plasma glucose concentration was observed at fasting (P = 0.0258), 60 min (P = 0.0011), 90 min (P = 0.0011), and 120 min (P = 0.0007) during the oral-glucose-tolerance test. Subjects with hypovitaminosis D (<20 ng/mL) had a greater prevalence of components of metabolic syndrome than did subjects without hypovitaminosis D (30% compared with 11%; P = 0.0076).
  
  
  CONCLUSIONS
  The data show a positive correlation of 25(OH)D concentration with insulin sensitivity and a negative effect of hypovitaminosis D on beta cell function. Subjects with hypovitaminosis D are at higher risk of insulin resistance and the metabolic syndrome. Further studies are required to explore the underlying mechanisms.
authors.affiliation: Division of Clinical Epidemiology and Preventive Medicine, Department of Medicine, University of California-Los Angeles School of Medicine, 924 Westwood Boulevard, Los Angeles, CA 90024, USA. kchiu@mednet.ucla.edu
authors.forename: Ken C
authors.initials: KC
authors.lastname: Chiu
authors.forename: Audrey
authors.initials: A
authors.lastname: Chu
authors.forename: Vay Liang W
authors.initials: VL
authors.lastname: Go
authors.forename: Mohammed F
authors.initials: MF
authors.lastname: Saad
mesh_terms: D000328:Adult; D001786:Blood Glucose / Q000378:metabolism*; D005260:Female; D015309:Glucose Clamp Technique; D005951:Glucose Tolerance Test; D006801:Humans; D007333:Insulin Resistance / Q000502:physiology*; D007515:Islets of Langerhans / Q000503:physiopathology*; D008297:Male; D024821:Metabolic Syndrome / Q000453:epidemiology / Q000378:metabolism; D012044:Regression Analysis; D014807:Vitamin D / Q000031:analogs & derivatives* / Q000097:blood / Q000378:metabolism*; D014808:Vitamin D Deficiency / Q000097:blood / Q000378:metabolism* / Q000503:physiopathology
chemical_list: D001786:Blood Glucose; D014807:Vitamin D; C104450:25-hydroxyvitamin D