Oral Presentation Australian Diabetes Society and the Australian Diabetes Educators Association Annual Scientific Meeting 2017

Vitamin D supplementation has no effect on insulin sensitivity or secretion in vitamin D-deficient, overweight or obese adults: a randomized placebo-controlled trial. (#135)

Barbora de Courten 1 , Aya Mousa 1 , Negar Naderpoor 1 , Helena J Teede 1 , Nicole Kellow 2 , Karen Walker 2 , Robert Scragg 3 , Maximilian PJ de Courten 4
  1. Monash Centre for Health Research and Implementation, School of Public Health and Preventive Medicine, Monash University, Melbourne, VIC, Australia
  2. Department of Nutrition and Dietetics, Monash University, Melbourne, VIC, Australia
  3. School of Population Health, University of Auckland, Auckland, New Zealand
  4. Centre for Chronic Diseases, Victoria University, Melbourne, VIC, Australia

BACKGROUND: Vitamin D supplementation has been proposed as a potential strategy to prevent type 2 diabetes. However, existing clinical trials are limited by short durations, low doses of vitamin D, variability in participants’ vitamin D deficiency status, and use of surrogate measures of body composition, insulin sensitivity, and insulin secretion.

OBJECTIVE: We conducted a double-blind randomised placebo-controlled trial to investigate whether vitamin D supplementation, provided in a sufficient dose and duration to vitamin D-deficient individuals, would improve insulin sensitivity and/or secretion measured by gold-standard methods.

METHODS: Sixty-five overweight or obese (BMI≥25 kg/m2), vitamin D-deficient (25-hydroxyvitamin D (25(OH)D)≤50 nmol/l) adults were randomised to a bolus oral dose of 100,000IU followed by 4,000IU daily of cholecalciferol or matching placebo for 16 weeks. Before and after intervention, participants had gold-standard assessments of body composition (dual X-ray absorptiometry), insulin sensitivity (hyperinsulinemic-euglycemic clamps) and insulin secretion (intravenous glucose-tolerance tests). Additional measurements included BMI, waist-to-hip ratio, blood pressure, serum lipids (ELISA), and high-sensitivity C-reactive protein (highly-sensitive ELISA).

RESULTS: Fifty-four participants completed the study (35M/19F;age=31.9±8.5 years;BMI=30.9±4.4 kg/m2 (mean±SD)). Serum 25(OH)D concentrations increased with vitamin D supplementation compared to placebo (57.0±21.3 versus 1.9±15.1 nmol/l,p=0.02). Vitamin D and placebo groups did not differ in change in insulin sensitivity (0.02±2.0 versus -0.03±2.8 mg/kg/min,p=0.9) or total, first- or second-phase insulin secretion (all p>0.1). There were no differences in changes in anthropometry, blood pressure, serum lipids, or hsCRP (all p>0.1). Results remained non-significant after adjustment for age, sex, and %body fat, and after additional adjustment for sun exposure, physical activity, and dietary vitamin D intake.

CONCLUSIONS: Vitamin D supplementation does not improve insulin sensitivity or secretion in vitamin D-deficient, overweight or obese adults, despite using sufficient doses and robust endpoint measures. It is therefore unlikely that vitamin D supplementation would be an effective strategy for reducing diabetes risk in this population.