Effects of Vitamin D 3 Supplementation on Glycaemic Parameters and Insulin Sensitivity in Pre-diabetic Adults: A Prospective Controlled Interventional Study.

Abstract

Pre-diabetes precedes type 2 diabetes mellitus (T2DM) and is characterised by impaired fasting glucose, impaired glucose tolerance or both. Vitamin D deficiency is prevalent in India and implicated in impaired glucose metabolism and insulin resistance, yet interventional data from Indian pre-diabetic populations remain limited. To evaluate the effect of oral Vitamin D 3 supplementation on fasting blood glucose (FBG), post-prandial blood glucose (PPBG) and Homeostatic Model Assessment of insulin resistance (HOMA-IR) in pre-diabetic adults. This prospective controlled interventional study enrolled 90 pre-diabetic adults (aged 18-65 years) at SRM Medical College Hospital and Research Centre, Chennai. Participants were allocated into a Vitamin D group ( n = 45; oral Vitamin D 3 2000 IU once daily for 3 months plus lifestyle advice) and a control group ( n = 45; lifestyle advice alone). FBG, PPBG, HbA1c, fasting insulin, serum 25(OH) D and HOMA-IR were assessed at baseline and 3 months. The Vitamin D group demonstrated significant reductions in FBG (112.6 ± 8.4-102.4 ± 7.3 mg/dL), PPBG (168.5 ± 15.2-150.8 ± 13.6 mg/dL), HOMA-IR (4.38 ± 1.02-3.41 ± 0.89) and HbA1c (6.1% ±0.3% to 5.7% ±0.2%) ( P < 0.001 for all), with significantly greater improvements than controls ( P < 0.001). Serum 25(OH) D rose from 18.4 ± 4.5 to 27.6 ± 2.8 ng/mL ( P < 0.001). Glycaemic normalisation occurred in 40% versus 11% of controls ( P = 0.002). A significant inverse correlation was observed between Δ25(OH) D and ΔHOMA-IR ( r = -0.62, P < 0.001). No serious adverse events were recorded. Vitamin D 3 supplementation significantly improved glycaemic control and insulin sensitivity in pre-diabetic adults, supporting its role as a safe, cost-effective adjunct to lifestyle modification in pre-diabetes management.