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Previous studies have shown zinc has potential anti-inflammatory and anti-oxidative effects. However, findings from clinical trials about the effect of zinc on plasma C-reactive protein (CRP) appeared inconsistent and uncertain. Therefore, the aim of this meta-analysis was to summarize the effect of zinc supplementation on plasma CRP concentrations in adults. The literature search through PubMed, SCOPUS, and Google Scholar were done to find published studies up to October 2017. Random or fixed-effects model depending on the results of heterogeneity tests were used to estimate the pooled effect size. Between-study heterogeneity was assessed using Cochran's Q test and I 2 index. Funnel plot and Egger's regression test were used to assess publication bias. Our search found 1505 publications, of which 8 randomized controlled trials (RCTs) were eligible to be included in the analysis. The results of the meta-analysis displayed a significant reduction in circulating CRP levels (WMD: − 1.68 mg/l; 95% CI: − 2.4 to − 0.9, P = <0.001) following zinc supplementation. In the subgroup analysis, supplementation dosage, study quality, study population, and baseline CRP level were the potential sources of heterogeneity. Participants took equal to 50 mg/d zinc (WMD: − 1.97 mg/l; 95% CI: − 2.28 to − 1.67, P = <0.001), low quality studies (WMD: − 2.9 mg/l; 95% CI: − 3.68 to − 2.12, P = <0.001) and those with renal dysfunction (WMD: − 7.43 mg/l; 95% CI: − 12.57 to −2.29, P = 0.005) showed greater improvement in CRP levels. In conclusion, zinc supplementation may have a beneficial effect on the serum CRP, especially at doses equal to 50 mg/d and in renal insufficiency patients compared with healthy subjects. [ABSTRACT FROM AUTHOR]

Oxidative stress is a contributing factor to many chronic diseases. It has been investigated that zinc (Zn) may enhance the antioxidant defense. The current dose-response and time-response meta-analysis aims to determine the efficacy of Zn supplementation in improving antioxidant defense. Scopus, PubMed/Medline, Web of Science, and Embase databases were searched systematically up to December 30, 2020. Meta-analysis was performed on human controlled clinical trials using random effects method. To find any source of heterogeneity, subgroup analysis and meta-regression were performed. Trim and fill analysis was used for adjusting the publication bias. To find any non-linear relationship between variables and effect size, dose-response and time-response analyses were performed. Cochrane Collaboration's tool was used for evaluating the quality assessment. A total of 23 controlled clinical trials were analyzed. The range of Zn supplementation duration in various studies was within 4–24 weeks. Zn supplementation did not have beneficial effects on glutathione peroxidase (GPx) activity (SMD = −0.34 U/g; 95% CI: -0.93, 0.25; P = 0.258). There were significant increasing effects of Zn supplementation on glutathione (GSH) (SMD = 1.28 μmol/l; 95% CI: 0.42, 2.14; P = 0.003) and total antioxidant capacity (TAC) levels (SMD = 1.39 mmol/l; 95% CI: 0.44, 2.35; P = 0.004). Zn had ameliorative effects on superoxide dismutase (SOD) activity after elimination of publication bias (SMD: 0.84 U/g; 95% CI: 0.12, 1.56, P < 0.05). Zn could also elevate GSH and TAC levels, plus SOD activity after modifying the publication bias. Finally, Zn had no significant effect on GPx activity. [ABSTRACT FROM AUTHOR]