The Journal of Clinical Endocrinology and Metabolism Journal Article

Vitamin D and Insulin Sensitivity and Secretion

January 25, 2022

Neda Rasouli, Irwin G Brodsky, Ranee Chatterjee, Sun H Kim, Richard E Pratley, Myrlene A Staten, Anastassios G Pittas, D2d Research Group
The Journal of Clinical Endocrinology & Metabolism, Volume 107, Issue 1, January 2022, Pages 230–240
https://doi.org/10.1210/clinem/dgab649

Abstract

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%S_cpep) 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%S_cpep, or C-peptide response between the 2 groups. Among participants with baseline 25(OH)D level <12 ng/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.