Vitamin D supplementation reduces insulin resistance in South Asian women living in New Zealand who are insulin resistant and vitamin D deficient - a randomised, placebo-controlled trial

Br J Nutr. 2010 Feb;103(4):549-55. doi: 10.1017/S0007114509992017. Epub 2009 Sep 28.

Abstract

Low serum 25-hydroxyvitamin D (25(OH)D) has been shown to correlate with increased risk of type 2 diabetes. Small, observational studies suggest an action for vitamin D in improving insulin sensitivity and/or insulin secretion. The objective of the present study was to investigate the effect of improved vitamin D status on insulin resistance (IR), utilising randomised, controlled, double-blind intervention administering 100 microg (4000 IU) vitamin D(3) (n 42) or placebo (n 39) daily for 6 months to South Asian women, aged 23-68 years, living in Auckland, New Zealand. Subjects were insulin resistant - homeostasis model assessment 1 (HOMA1)>1.93 and had serum 25(OH)D concentration < 50 nmol/l. Exclusion criteria included diabetes medication and vitamin D supplementation >25 microg (1000 IU)/d. The HOMA2 computer model was used to calculate outcomes. Median (25th, 75th percentiles) serum 25(OH)D(3) increased significantly from 21 (11, 40) to 75 (55, 84) nmol/l with supplementation. Significant improvements were seen in insulin sensitivity and IR (P = 0.003 and 0.02, respectively), and fasting insulin decreased (P = 0.02) with supplementation compared with placebo. There was no change in C-peptide with supplementation. IR was most improved when endpoint serum 25(OH)D reached > or = 80 nmol/l. Secondary outcome variables (lipid profile and high sensitivity C-reactive protein) were not affected by supplementation. In conclusion, improving vitamin D status in insulin resistant women resulted in improved IR and sensitivity, but no change in insulin secretion. Optimal vitamin D concentrations for reducing IR were shown to be 80-119 nmol/l, providing further evidence for an increase in the recommended adequate levels. Registered Trial No. ACTRN12607000642482.

Publication types

  • Randomized Controlled Trial
  • Research Support, Non-U.S. Gov't

MeSH terms

  • Adult
  • Asia / ethnology
  • Asian Continental Ancestry Group
  • C-Reactive Protein / metabolism
  • Cholecalciferol / administration & dosage
  • Cholecalciferol / pharmacology
  • Cholecalciferol / therapeutic use*
  • Dietary Supplements
  • Double-Blind Method
  • Female
  • Humans
  • Insulin / metabolism*
  • Insulin Resistance* / ethnology
  • Insulin Secretion
  • Middle Aged
  • New Zealand
  • Nutritional Status
  • Vitamin D / analogs & derivatives*
  • Vitamin D / blood
  • Vitamin D Deficiency / blood
  • Vitamin D Deficiency / drug therapy*
  • Vitamin D Deficiency / ethnology
  • Vitamins / pharmacology
  • Vitamins / therapeutic use*

Substances

  • Insulin
  • Vitamins
  • Vitamin D
  • Cholecalciferol
  • C-Reactive Protein
  • 25-hydroxyvitamin D