Effects of Oral Vitamin D Supplementation on Vitamin D Levels and Glycemic Parameters in Patients with Type 2 Diabetes Mellitus: A Systematic Review and Network Meta-Analysis.

Xiu Juan ZHANG; Hong Fei WANG; Xia GAO; Yang ZHAO

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Effects of Oral Vitamin D Supplementation on Vitamin D Levels and Glycemic Parameters in Patients with Type 2 Diabetes Mellitus: A Systematic Review and Network Meta-Analysis.

Author: Xiu Juan ZHANG ¹ ; Hong Fei WANG ² ; Xia GAO ¹ ; Yang ZHAO ³
Author Information

1. Department of Endocrinology, Beijing Chao-yang Hospital, Capital Medical University, Beijing 100020, China.
2. Department of Epidemiology and Biostatistics, School of Public Health, Peking University, Beijing 100191, China.
3. Department of Pediatrics, Beijing You'an Hospital Affiliated to Capital Medical University, Beijing 100069, China.
Publication Type:Systematic Review
Keywords: Glycemic biomarkers; Network meta-analysis; Type 2 diabetes mellitus; Vitamin D supplementation
MeSH: Humans; Administration, Oral; Blood Glucose/drug effects*; Diabetes Mellitus, Type 2/blood*; Dietary Supplements; Vitamin D/analogs & derivatives*; Vitamins/administration & dosage*
From: Biomedical and Environmental Sciences 2025;38(6):716-726
CountryChina
Language:English
Abstract: OBJECTIVE:Epidemiological studies have shown that vitamin D status affects glycemic control in individuals with type 2 diabetes mellitus (T2DM). However, findings from intervention studies remain inconsistent. Therefore, a network meta-analysis was conducted to evaluate the comparative efficacy of various vitamin D supplementation strategies on glucose indicators in adults with T2DM.
METHODS:Eligible studies published before September 12, 2024, were retrieved from PubMed, EMBASE, Cochrane Library, and Web of Science. A network meta-analysis of multiple dosage strategies-low (< 1,000 IU/day, LDS), medium (1,000-2,000 IU/day, MDS), high (2,000-4,000 IU/day, HDS), and extremely high (≥ 4,000 IU/day, EHDS)-was performed.
RESULTS:The network meta-analysis of 40 RCTs indicated that, compared with placebo, vitamin D ₃ supplementation increased 25-hydroxyvitamin D [25-(OH)-D] levels, with pooled mean difference ( MD) showing a stepwise increase from LDS to EHDS. Ranking probabilities showed a corresponding rise in 25-(OH)-D levels from LDS (46.7%) to EHDS (91.2%). EHDS reduced fasting blood glucose (FBG) relative to no treatment. LDS significantly decreased hemoglobin A1c (HbA1c), and vitamin D ₂ significantly affected FBG levels. MDS led to a significant change in fasting insulin (FIN) compared to both placebo ( MD: -4.76; 95% CI -8.91 to -0.61) and no treatment ( MD: -7.30; 95% CI -14.44 to -0.17).
CONCLUSION:The findings suggest that vitamin D supplementation may be a viable approach for improving glycemic control in adults with T2DM, with lower doses potentially offering benefit. The analysis also showed a dose-dependent increase in 25-(OH)-D levels.