Vitamin D and Improved Insulin Sensitivity

Research synthesisModerate evidenceMixed effect size6 studies · 5 beneficial · 1 neutral · 0 harmful

Across 6 studies, 5 reported beneficial effects of vitamin D supplementation on insulin sensitivity, though effect sizes were mixed (small to large). Evidence from the highest-quality studies suggests modest and inconsistent improvements, with benefits more apparent in vitamin D-deficient women with PCOS or patients with diabetes/prediabetes. One meta-analysis in obese children reported a neutral effect.

Studied populations: Vitamin D-deficient individuals, women with PCOS, patients with diabetes or prediabetes, and obese children/adolescents

Caveats: The evidence is inconsistent across populations; a high-quality meta-analysis in obese children found no significant benefit, while other studies in deficient or clinical populations showed small to large improvements. Most studies did not report specific doses, and the median duration is unknown, limiting practical recommendations. The largest effect was observed in a meta-analysis of diabetes patients, but effect sizes varied widely.

Generated May 13, 2026

Doses used in studies

IU/day: 4,000 (median 4,000, IQR 4,000–4,000) — 1 study

Safety in these studies

Overall tolerabilityReported
Vitamin D supplementation shows variable effects, it should not be considered a stand-alone therapy for PCOS.
from: The Association Between Vitamin D and Polycystic Ovary Syndrome (PCOS) in Women: A Systema

6 of 6 papersPopulation:

The Association Between Vitamin D and Polycystic Ovary Syndrome (PCOS) in Women: A Systematic Review.
- 2026-03-19
- Systematic Review · n = 1,063
- Nutrients 18(6)
- - Batoul Jaafar
  - Nour Chami
  - Mohamad Tlais
  - Maria Matar
  - Nazih Obeid
  - Nadia Taha
  - Karim El Haddad
  - Jessica Abou Chaaya
  - Sami Azar
- PubMed: 41901143
- DOI: 10.3390/nu18060968
7 Insights on
- Improved Insulin Sensitivity
- High evidence
- Rigorous Journal
- Clinical
RCTs showed modest and inconsistent improvements in insulin sensitivity, with effects more apparent in some trials enrolling vitamin D-deficient women.
Effect
Neutral
Effect size
Small
Significant
No
Can vitamin D supplementation affect cardiometabolic factors in children and adolescence with overweight and obesity? A grade-assessed systematic review and meta-analysis of randomized controlled trials.
- 2025-11-25
- Meta-Analysis · n = 440
- BMC pediatrics 25(1)
- - Amir Hossein Faghfouri
  - Mahsa Mahmoudinezhad
  - Pedram Pam
  - Sanaz Barazandeh
  - Fatemeh Faramarzi
  - Yousef Mohammadpour
  - Vali Musazadeh
  - Shahsanam Gheibi
- PubMed: 41291584
- DOI: 10.1186/s12887-025-05795-2
9 Insights on
- Improved Insulin Sensitivity
- High evidence
- Children
vitamin D supplementation no significantly improved ... QUICKI
Effect
Neutral
Effect size
Small
Significant
No
Effectiveness of Vitamin D Supplementation on Biochemical, Clinical, and Inflammatory Parameters in Patients with Different Types of Diabetes: A Systematic Review and Meta-Analysis.
- 2025-09-18
- Meta-Analysis
- Nutrients 17(18)
- - Alejandro Bruna-Mejías
  - Rocío Valdivia-Arroyo
  - Emelyn Sofia Becerra-Rodríguez
  - Ignacio Clasing-Cárdenas
  - Yesica Tatiana Castaño-Gallego
  - Guinevere Granite
  - Mathias Orellana-Donoso
  - Gustavo Oyanedel-Amaro
  - Pablo Nova-Baeza
  - Gloria Cifuentes-Suazo
  - Alejandra Suazo-Santibañez
  - Juan Sanchis-Gimeno
  - Héctor Gutiérrez Espinoza
  - Juan José Valenzuela-Fuenzalida
- PubMed: 41010515
- DOI: 10.3390/nu17182991
13 Insights on
- Improved Insulin Sensitivity
- High evidence
- Rigorous Journal
- Clinical
Vitamin D supplementation was associated with significant improvements across ... HOMA-β (SMD = 0.71; 95% CI: 0.63-0.80; p < 0.00001)
Effect
Beneficial
Effect size
Large
Significant
Yes
Essential micronutrients and biguanides (metformin) synergistic and antagonistic interactions on neurocognitive outcomes in type two diabetes mellitus: a systematic review of preclinical and clinical evidence.
- 2026-02-17
- Systematic Review
- Frontiers in endocrinology 17
- - Herbert Izo Ninsiima
  - Herbert E Ainamani
  - Geoffrey Ayebazibwe
  - Daniel Matovu
  - Ejike Daniel Eze
- PubMed: 41782745
- DOI: 10.3389/fendo.2026.1764157
3 Insights on
- Improved Insulin Sensitivity
- High evidence
Synergistic effects were observed in 77.5% of studies, with significant improvements in ... insulin sensitivity
Effect
Beneficial
Effect size
Moderate
Significant
Yes
The interplay between childhood obesity and vitamin D deficiency: mechanisms and implications.
- 2026-01-13
- Review
- Frontiers in pediatrics 13
- - Xiao Zhou
  - Yuhe Chen
  - Jianxin Xu
  - Xiaobing Li
  - Yanmei Wu
  - Lidan Xu
- PubMed: 41608325
- DOI: 10.3389/fped.2025.1700949
2 Insights on
- Improved Insulin Sensitivity
- Low evidence
- Clinical
Meta-analysis of 12 randomised trials (n = 1,538) revealed that vitamin D supplementation improves insulin sensitivity and lowers systolic blood pressure only when baseline 25-hydroxyvitamin D (25(OH)D) is <20 ng/mL and systemic inflammation is modest
Effect
Beneficial
Effect size
Moderate
Significant
Yes
Dose
4,000 IU/day
Bridging the Gap: Supplements Strategies from Experimental Research to Clinical Applications in Sarcopenic Obesity.
- 2024-11-24
- Review
- Current issues in molecular biology 46(12)
- - Bogdana Virgolici
  - Maria-Zinaida Dobre
  - Daciana Costina Andrada Stefan
- PubMed: 39727928
- DOI: 10.3390/cimb46120800
5 Insights on
- Improved Insulin Sensitivity
- Low evidence
Elevated irisin levels, such as those observed with vitamin D supplementation, could prevent muscle wasting and fat gain in SO by improving insulin sensitivity and reducing inflammation.
Effect
Beneficial
Effect size
Small
Significant
Yes

Vitamin D and Improved Insulin Sensitivity

The Association Between Vitamin D and Polycystic Ovary Syndrome (PCOS) in Women: A Systematic Review.

Can vitamin D supplementation affect cardiometabolic factors in children and adolescence with overweight and obesity? A grade-assessed systematic review and meta-analysis of randomized controlled trials.

Effectiveness of Vitamin D Supplementation on Biochemical, Clinical, and Inflammatory Parameters in Patients with Different Types of Diabetes: A Systematic Review and Meta-Analysis.

Essential micronutrients and biguanides (metformin) synergistic and antagonistic interactions on neurocognitive outcomes in type two diabetes mellitus: a systematic review of preclinical and clinical evidence.

The interplay between childhood obesity and vitamin D deficiency: mechanisms and implications.

Bridging the Gap: Supplements Strategies from Experimental Research to Clinical Applications in Sarcopenic Obesity.