title: A randomized, placebo-controlled trial of vitamin D supplementation to improve glycaemia in overweight and obese African Americans.
abstract: OBJECTIVE
  Vitamin D deficiency may increase the risk for type 2 diabetes. African Americans tend to have poor vitamin D status and increased risk of diabetes, but effects of vitamin D supplementation on components of diabetes risk have not been tested in this group. This study was conducted to determine whether vitamin D supplementation improves insulin secretion, insulin sensitivity and glycaemia in African Americans with prediabetes or early diabetes.
  
  
  METHODS
  In this randomized, placebo-controlled trial, we examined the effect of 4000 IU/day vitamin D(3,) on glycaemia and contributing measures including insulin secretion, insulin sensitivity and the disposition index over 12 weeks in 89 overweight or obese African Americans with prediabetes or early diabetes. Outcome measures were derived from oral glucose tolerance testing.
  
  
  RESULTS
  Mean plasma 25-hydroxyvitamin D was about 40 nmol/l in the placebo and vitamin D groups at baseline and increased to 81 nmol/l with supplementation. Insulin sensitivity decreased by 4% in the vitamin D group compared with a 12% increase in the placebo group (p = 0.034). Insulin secretion increased by 12% in the vitamin D group compared with a 2% increase in the placebo group (p = 0.024), but changes in the disposition index were similar across groups. There was no effect of supplementation on post-load glucose or other measures of glycaemia.
  
  
  CONCLUSIONS
  Supplementation with 4000 IU/day vitamin D(3) successfully corrected vitamin D insufficiency and had divergent effects on insulin secretion and sensitivity with no overall effect on disposition index or glycaemia. In this study, vitamin D supplementation for 3 months did not change the pathophysiology of prediabetes in overweight and obese African Americans.
authors.affiliation: Jean Mayer USDA Human Nutrition Research Center on Aging at Tufts University, Boston, MA 02111, USA. susan.harris@tufts.edu
authors.forename: S S
authors.initials: SS
authors.lastname: Harris
authors.forename: A G
authors.initials: AG
authors.lastname: Pittas
authors.forename: N J
authors.initials: NJ
authors.lastname: Palermo
mesh_terms: D001741:Black or African American / Q000208:ethnology*; D001786:Blood Glucose / Q000378:metabolism*; D002762:Cholecalciferol / Q000008:administration & dosage*; D003924:Diabetes Mellitus, Type 2 / Q000097:blood / Q000208:ethnology; D019587:Dietary Supplements; D005260:Female; D006801:Humans; D007328:Insulin / Q000378:metabolism; D007333:Insulin Resistance / Q000208:ethnology / Q000502:physiology; D000078790:Insulin Secretion; D008297:Male; D008875:Middle Aged; D009765:Obesity / Q000097:blood / Q000208:ethnology; D050177:Overweight / Q000097:blood* / Q000208:ethnology; D011236:Prediabetic State / Q000097:blood; D014807:Vitamin D / Q000031:analogs & derivatives / Q000097:blood; D014808:Vitamin D Deficiency / Q000188:drug therapy* / Q000208:ethnology; D014815:Vitamins / Q000008:administration & dosage*
chemical_list: D001786:Blood Glucose; D007328:Insulin; D014815:Vitamins; D014807:Vitamin D; D002762:Cholecalciferol; C104450:25-hydroxyvitamin D