Effects of Vitamin D 3 Supplementation on Glycaemic Parameters and Insulin Sensitivity in Pre-diabetic Adults: A Prospective Controlled Interventional Study.
Ganesan S, Vidvath V, Vidya T • The Nigerian postgraduate medical journal • 2026
Vitamin D3 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.
Key Findings
Results
Three months of oral vitamin D3 (2000 IU daily) plus lifestyle advice significantly reduced fasting blood glucose in pre-diabetic adults.
In the Vitamin D group (n = 45), FBG fell from 112.6 ± 8.4 to 102.4 ± 7.3 mg/dL (P < 0.001).
The improvement was significantly greater than in the control group, which received lifestyle advice alone (n = 45; P < 0.001).
This was a prospective controlled interventional study of 90 adults aged 18-65 years at SRM Medical College Hospital and Research Centre, Chennai.
PPBG in the Vitamin D group fell from 168.5 ± 15.2 to 150.8 ± 13.6 mg/dL (P < 0.001).
The reduction was significantly greater than in controls (P < 0.001).
Results
Vitamin D3 supplementation improved insulin resistance as measured by HOMA-IR.
HOMA-IR decreased from 4.38 ± 1.02 to 3.41 ± 0.89 in the Vitamin D group (P < 0.001).
The improvement was significantly greater than in controls (P < 0.001).
Fasting insulin was measured at baseline and 3 months to derive HOMA-IR.
Results
HbA1c decreased significantly in the Vitamin D group.
HbA1c fell from 6.1% ± 0.3% to 5.7% ± 0.2% (P < 0.001).
Improvements were significantly greater than in controls (P < 0.001).
Results
Serum 25(OH)D increased with supplementation, but mean levels remained below 30 ng/mL.
Serum 25(OH)D rose from 18.4 ± 4.5 to 27.6 ± 2.8 ng/mL (P < 0.001).
Baseline levels indicated vitamin D insufficiency/deficiency, consistent with the stated high prevalence in India.
Results
A higher proportion of the Vitamin D group achieved glycaemic normalisation than controls.
Glycaemic normalisation occurred in 40% of the Vitamin D group versus 11% of controls (P = 0.002).
Results
Increases in 25(OH)D were inversely correlated with changes in HOMA-IR.
The correlation between Δ25(OH)D and ΔHOMA-IR was r = -0.62 (P < 0.001).
This suggests greater vitamin D repletion was associated with greater improvement in insulin resistance.
Results
No serious adverse events were recorded with vitamin D3 supplementation.
The dose was 2000 IU once daily for 3 months.
The authors conclude it is a safe and cost-effective adjunct to lifestyle modification in pre-diabetes.
What This Means
This study looked at whether taking vitamin D supplements could help adults with pre-diabetes, a stage where blood sugar is higher than normal but not yet diabetes. Ninety adults in Chennai, India, were split into two groups of 45. One group took 2000 IU of vitamin D3 daily for three months along with lifestyle advice, while the other group received lifestyle advice only.
After three months, the vitamin D group had lower fasting and after-meal blood sugar, lower HbA1c (a measure of average blood sugar over several months), and lower insulin resistance, and these improvements were larger than in the lifestyle-only group. About 40% of those taking vitamin D returned to normal blood sugar levels, compared with 11% of the lifestyle-only group. People whose vitamin D blood levels rose more also tended to show larger improvements in insulin resistance. No serious side effects were reported.
This research suggests vitamin D supplementation may be a helpful, low-cost addition to lifestyle changes for people with pre-diabetes who have low vitamin D levels. However, the study was fairly small, lasted only three months, and was a controlled interventional study rather than a randomized trial as described, so larger and longer studies are needed to confirm the results and to see whether they reduce progression to type 2 diabetes.
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Ganesan S, Vidvath V, Vidya T. (2026). Effects of Vitamin D 3 Supplementation on Glycaemic Parameters and Insulin Sensitivity in Pre-diabetic Adults: A Prospective Controlled Interventional Study.. The Nigerian postgraduate medical journal. https://doi.org/10.4103/npmj.npmj_230_26