Effects of Vitamin D Supplementation on Insulin Sensitivity and Secretion in Prediabetes

Document Type


Publication Date



Endocrinology & Diabetes

Journal Title

The Journal of clinical endocrinology and metabolism

MeSH Headings

Aged; Blood Glucose (metabolism); Cholecalciferol (administration & dosage); Diabetes Mellitus, Type 2 (diagnosis, epidemiology, metabolism, prevention & control); Dietary Supplements; Female; Follow-Up Studies; Glucose Tolerance Test; Humans; Incidence; Insulin (metabolism); Insulin Resistance; Insulin-Secreting Cells (metabolism); Male; Middle Aged; Overweight (blood, complications, diet therapy, metabolism); Prediabetic State (blood, diagnosis, diet therapy, metabolism); Treatment Outcome; Vitamin D (analogs & derivatives, blood); Vitamin D Deficiency (blood, diagnosis, diet therapy, metabolism)


CONTEXT: Vitamin D regulates glucose homeostasis pathways, but effects of vitamin D supplementation on β-cell function remain unclear. OBJECTIVE: To investigate the effects of vitamin D3 supplementation on insulin sensitivity and β-cell function. METHODS: This is a prespecified secondary analysis of the Vitamin D and Type 2 Diabetes study. Overweight/obese adults at high risk for type 2 diabetes (prediabetes) were randomly treated with vitamin D3 4000 IU or matching placebo daily for 24 months. MAIN OUTCOME: Disposition index (DI), as an estimate of β-cell function, was calculated as the product of Homeostasis Model Assessment 2 indices derived from C-peptide values (HOMA2%Scpep) and C-peptide response during the first 30 minutes of a 75-g oral glucose tolerance test (OGTT). RESULTS: Mean age was 60.5 ± 9.8 years and body mass index was 31.9 ± 4.4 kg/m2. Mean serum 25(OH)D level increased from 27.9 ± 10.3 ng/mL at baseline to 54.9 ng/mL at 2 years in the vitamin D group and was unchanged (28.5 ± 10.0 ng/mL) in the placebo group. The baseline DI predicted incident diabetes independent of the intervention. In the entire cohort, there were no significant differences in changes in DI, HOMA2%Scpep, or C-peptide response between the 2 groups. Among participants with baseline 25(OH)D level /mL, the mean percent differences for DI between the vitamin D and placebo groups was 8.5 (95% CI, 0.2-16.8). CONCLUSIONS: Supplementation with vitamin D3 for 24 months did not improve an OGTT-derived index of β-cell function in people with prediabetes not selected based on baseline vitamin D status; however, there was benefit among those with very low baseline vitamin D status.

First Page


Last Page