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The Impact of Vitamin D Supplementation on Fasting Plasma Glucose, Insulin Sensitivity, and Inflammation in Type 2 Diabetes Mellitus: A Systematic Review and Meta-Analysis.

  • 2025-07-30
  • Nutrients 17(15)
    • Enny Probosari
    • Hertanto W Subagio
    • Heri-Nugroho
    • Banundari Rachmawati
    • Siti F Muis
    • Kevin C Tjandra
    • Dwi Adiningsih
    • Tri I Winarni

Study Design

Type
Meta-Analysis
Population
adult patients diagnosed with T2DM
Methods
meta-analysis of clinical trials or randomized controlled trials; sources from five databases; ROB-2 tool for risk of bias; quantitative synthesis with pooled effect sizes and confidence intervals
  • Rigorous Journal
Background/Objectives: Vitamin D supplementation has shown promise in managing type 2 diabetes mellitus (T2DM), while the simultaneous impact on glycemic control and inflammation in T2DM remains poorly understood. This study aimed to investigate the potential role of vitamin D supplementation in managing T2DM using fasting plasma glucose (FPG), insulin levels, HOMA-IR, HOMA-B, HbA1c, and Hs-CRP as the biomarkers. Methods: Original articles from Scopus, Pubmed, Cochrane Library, Epistemonikos, and ScienceDirect published between 2014 and 2024 were the sources. Inclusion criteria included studies conducted as clinical trials or randomized controlled trials involving adult patients diagnosed with T2DM undergoing treatment with vitamin D. The risk of bias was evaluated using the ROB-2 tool and meta-analysis was conducted to quantitatively synthesize the results across the studies using pooled effect sizes and confidence intervals. Results: Nine studies were included in the meta-analysis. Significant differences were found at 12-week follow-up in insulin level (MD(-3.59) [95% CI: -6.93, -0.25]), HOMA-B (MD(-50.35) [95% CI: -92.29, -8.41]), hs-CRP (-2.51 [95% CI: -3.45, -1.57]), and HbA1c level (MD(-0.30) [95% CI: -0.54, -0.06]) and at 24-week follow-up in HOMA-IR (MD(-0.38) [CI: -0.53, -0.24]). The quality of the included studies was generally moderate, with three showing a potential risk of bias. Conclusions: The observed trends in FPG, insulin levels, HOMA-IR, HOMA-B, HbA1c, and hs-CRP indicate that vitamin D may influence glycemic control, insulin sensitivity, and inflammation, but these effects are often modest and may diminish over time. Future studies should explore longer duration randomized trials with standardized dosing and baseline vitamin D status stratification.

Research Insights

  • Vitamin D→Improved Fasting Plasma Glucose

    The observed trends in FPG, insulin levels, HOMA-IR, HOMA-B, HbA1c, and hs-CRP indicate that vitamin D may influence glycemic control, insulin sensitivity, and inflammation, but these effects are often modest and may diminish over time.

    Effect
    Neutral
    Effect size
    Small
  • Vitamin D→Improved Insulin Levels

    Significant differences were found at 12-week follow-up in insulin level (MD(-3.59) [95% CI: -6.93, -0.25])

    Effect
    Beneficial
    Effect size
    Small
  • Vitamin D→Reduced HOMA-B

    HOMA-B (MD(-50.35) [95% CI: -92.29, -8.41])

    Effect
    Harmful
    Effect size
    Small
  • Vitamin D→Reduced HOMA-IR

    at 24-week follow-up in HOMA-IR (MD(-0.38) [CI: -0.53, -0.24])

    Effect
    Beneficial
    Effect size
    Small
  • Vitamin D→Reduced Hemoglobin A1c

    HbA1c level (MD(-0.30) [95% CI: -0.54, -0.06])

    Effect
    Beneficial
    Effect size
    Moderate
  • Vitamin D→Reduced Hs-CRP Level

    hs-CRP (-2.51 [95% CI: -3.45, -1.57])

    Effect
    Beneficial
    Effect size
    Small
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