Effects of vitamin D supplementation on glycemic control, inflammation, and oxidative stress in individuals with type 2 diabetes mellitus: A systematic review

The objective of this study was to analyze the effect of vitamin D supplementation on glycemic control parameters and markers of inflammation and oxidative stress in people with type 2 diabetes mellitus. The protocol used was registered under number CRD42024557570. Articles from randomized or non-randomized controlled clinical trials, longitudinal studies, or parallel group studies involving individuals with type 2 diabetes supplemented with vitamin D were included. In addition, studies involving animals, randomized controlled crossover trials, quasi-randomized trials, and those in which vitamin D supplementation was combined with any other nutrient were excluded. The PICO strategy was used. The Risk of Bias 2 (RoB 2) tool was applied to assess the risk of bias. The search for articles was performed in the PubMed, Embase, SciELO, Web of Science, and Science Direct databases, with no restriction on the year of publication. The search was last performed on December 12, 2025. Eleven articles were included in the review, of which 10 evaluated glycemic control, two evaluated markers of oxidative stress, and three analyzed markers of inflammation. In addition, three studies evaluated the three parameters of interest together. Vitamin D supplementation may improve the metabolic profile of these patients by increasing insulin sensitivity and reducing markers of inflammation and oxidative stress, especially when combined with physical exercise. Inflammation markers showed a negative correlation with vitamin D concentrations. Further studies are still needed to elucidate the metabolic effects, as well as to define doses, intervention time, and form of supplementation in different age groups and sexes.