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Could Vitamin D Have a Role in T2DM?

Dec 19, 2020
Editor: David L. Joffe, BSPharm, CDE, FACA

Author: Leyany Feijoo Ramos, PharmD. Candidate, LECOM School of Pharmacy

A recently published meta-analysis evaluates whether vitamin D supplementation could prevent type 2 in patients with prediabetes. 

Vitamin D has been the center of many studies in recent years due to its potential role in treating and preventing many diseases, including diabetes. Evidence suggests that vitamin D modulates insulin synthesis and reduces insulin resistance; however, it remains unclear whether supplementation with vitamin D could reduce the risk of type 2 diabetes. Previously published studies have used mixed interventions and have been insufficiently powered, making it difficult to assess the real effects of vitamin D on glucose regulation. 


A recent meta-analysis sought to determine whether vitamin D would prevent type 2 diabetes in patients with prediabetes. This review used a larger sample size that included eight trials and a total of 4896 participants. Studies included in the analysis were randomized controlled trials published from 2013 to 2019 comparing vitamin D to placebo in those 18 years or older with prediabetes. Baseline characteristics varied across the studies, and participants of different ethnicities were included, which could potentially influence dietary habits and vitamin D response. All trials analyzed included participants with prediabetes; however, two of these studies recruited patients with a vitamin D deficiency, and one trial included those with obesity. The mean age of participants was between 52 and 60 years old, and the duration of followup ranged from 6 months to 5 years. Multiple subgroup analyses were assessed for interactions according to dose, type of vitamin, treatment timing, mean BMI, mean baseline vitamin D level, length of maximum follow-up, and intervention. This analysis’s primary outcome was the diagnosis of new-onset type 2 diabetes, and the secondary outcome was the reversion of prediabetes.  

Researchers reported that 1022 participants across the eight trials were diagnosed with diabetes, which accounted for 20.9% of the study population. The incidence of new-onset diabetes was reduced by 11% in those supplemented with vitamin D (RR= 0.89; 95% CI 0.80-0.99). The three trials that reported a hazard ratio showed a similar decrease in new-onset diabetes in the group receiving vitamin D supplementation (HR=0.88; 95% CI 0.78-0.99). Subgroup analyses found that patients with obesity responded differently to vitamin D supplementation. Investigators reported that in those with a mean BMI of 30kg/m2, vitamin D supplementation only reduced progression to type 2 diabetes by about 5%, which was not considered significant (RR 0.95; 95% CI 0.84-1.08). In contrast, a 27% reduction in type 2 diabetes diagnosis was seen in patients without obesity (RR 0.73; 95% CI 0.57-0.92). Other subgroup analyses evaluating differences in dose, mean baseline vitamin D levels, and follow-up length did not yield a statistically significant difference in effect. 

Reversion of prediabetes was studied in five trials, which accounted for 1080 participants in this meta-analysis. Prediabetes was reversed in 21.2% of participants receiving vitamin D supplementation (116 of 548), compared to 14.1% of patients in the control group (75 of 532). Subgroup analysis showed similar results among the groups, and no statistically significant difference was seen. Researchers concluded that vitamin D supplementation significantly increased the rate of reversion of prediabetes by 48% (RR 1.48).  

This review found that vitamin D supplementation has a significant effect on preventing type 2 diabetes and reversion of prediabetes; however, these findings were only significant in patients without obesity. This study’s limitations include the varied definitions of prediabetes and new-onset diabetes used, the unavailability of individual patient data, and follow-up time. Despite these limitations, the inclusion of a higher number of participants and the rigorous subgroup analyses conducted add credibility to the results obtained in this review. Future studies that include individual patient data and a more extended follow-up period are required to determine the long-term efficacy of vitamin D on different patient subgroups. Specific doses and their impact on glucose levels should also be further studied to determine the optimal dosing that would provide the highest benefit. However, given the results of this study, vitamin D supplementation could soon have an important place in the management of diabetes. 

Practice Pearls: 

  • Vitamin D supplementation reduces the risk of T2DM in patients with prediabetes who do not have obesity. 
  • Reversion from prediabetes to normoglycemia is significantly increased by vitamin D supplementation. 
  • Further studies are needed to determine the optimal dose required and whether vitamin Ds effect is sustained over extended periods. 


Zhang, et al. Effects of Vitamin D Supplementation on Prevention of Type 2 Diabetes in Patients With Prediabetes: A Systematic Review and Meta-Analysis. Diabetes Care 

Leyany Feijoo Ramos, PharmD. Candidate, LECOM School of Pharmacy