Efficacy of vitamin D supplementation as an adjunct therapy for improving inflammatory and oxidative stress biomarkers: An umbrella meta-analysis

Vitamin D supplementation has attracted a lot of attention as a potential modulator of inflammation and oxidative stress, while some studies have reported controversial findings. In this regard, the purpose of this study was to summarize existing systematic reviews and meta-analyses of clinical trials that determined the effects of supplementation with vitamin D on inflammatory and oxidative biomarkers. The following international databases were systematically searched till March 20 th , 2022: PubMed, Scopus, Embase, Web of Science, and Google Scholar. A random-effects model was applied to evaluate the effects of vitamin D on inflammatory and oxidative stress biomarkers. Overall, 23 meta-analyses were qualified in this umbrella meta-analysis. Our findings revealed that the vitamin D supplementation significantly reduced serum C-reactive protein (CRP) (ES = -0.42; 95% CI: -0.55, -0.29, p <0.001), tumor necrosis factor-α (TNF-α) (ES = -0.27; 95% CI: -0.42, -0.12; p<0.001), and malondialdehyde (MDA) concentrations (ES = -0.37; 95% CI: -0.48, -0.25, p <0.001). However, no significant changes were illustrated regarding interleukin-6 (IL-6) (ES = -0.35, 95% CI: -0.80, 0.10; p = 0.125), total antioxidant capacity (TAC) (ES = 0.68; 95% CI: -0.31, 1.66, p = 0.179), and glutathione (GSH) activity (ES = 0.08; 95% CI: -0.44, 0.60, p = 0.757). The present umbrella meta-analysis indicated that supplementation of vitamin D in adults can improve CRP, TNF-α, and MDA levels under various health conditions. Vitamin D could be considered an adjuvant therapy for relieving inflammation and oxidative stress.