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Introduction: Current evidence is debatable regarding the feasible effects of zinc supplementation on the inflammation and oxidative stress status of adults. This systematic review and meta-analysis aimed to clarify this inconclusiveness. Methods: Literature search was conducted via online databases such as PubMed, Scopus, ISI Web of Science, Cochrane Library, and Google Scholar until June 2020. The overall effect was presented as the weighted mean difference (WMD) at 95 % confidence interval (CI) in a random-effects meta-analysis model. Publication bias was also assessed using Egger's and Begg's statistics Results: In total, 25 clinical trials (n = 1428) were reviewed, which indicated that zinc supplementation significantly affects the concentration of C-reactive protein (WMD: -0.03 mg/l; 95 % CI: -0.06, 0.0; P = 0.029), interlukin-6 (WMD: -3.81 pg/mL; 95 % CI: -6.87, -0.76; P = 0.014), malondialdehyde (WMD: -0.78 µmol/l; 95 % CI: -1.14, -0.42; P < 0.001), and total antioxidant capacity (WMD: 95.96 mmol/l; 95 % CI: 22.47, 169.44; P = 0.010). In addition, a significant between-study heterogeneity and a non-significant increment was reported in nitric oxide (WMD: 1.47 µmol/l; 95 % CI: -2.45, 5.40; P = 0.461) and glutathione (WMD: 34.84 µmol/l; 95 % CI: -5.12, 74.80; P = 0.087). Conclusions: According to the results, zinc supplementation may have beneficial antiinflammatory and anti-oxidative effects in adults. [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]

We carefully read the meta -analysis by Hosseini et al. (1) on the effects of Zinc supplementation on inflammation and oxidative stress markers, which was recently published in Cytokine journal. The authors show that Zinc supplementation significantly decreased CRP, TNF, and MDA while having no significant effect on IL-6. Although respecting the authors' efforts, we are concerned about different aspects of the current review: the inadequate search strategy, the methodological flaws, the interpretation of data, and the reporting of the results that might lead to biased results. [ABSTRACT FROM AUTHOR]

• Zinc (Zn) is a trace metal that is considered to have an impact on chronic inflammation. • Zn supplementation improved serum C-reactive protein (CRP), tumor necrosis factor-alpha (TNF-α) and malondialdehyde (MDA). • Through meta-regression, treatment duration was found as the source of inter-study heterogeneity. Zinc (Zn) is a trace metal that is considered to have an impact on chronic inflammation. However, findings of clinical trials have been inconsistent. The present systematic review and meta -analysis aimed to provide a more robust examination of the evidence on the effectiveness of Zn supplements on markers of inflammation and oxidative stress. A systematic search in PubMed, Scopus, Web of Science and Cochrane Library was undertaken to identify relevant randomized controlled trials (RCTs) assessing the impact of Zn on inflammation and oxidative stress until 17 August 2020. We applied a random-effects method to obtain effect sizes (ES) and 95% confidence intervals (CIs). Meta-regression was used to detect the potential source of between-study heterogeneity. Twenty-one eligible RCTs comprising 1321 participants were included in the meta -analysis. In comparison with the control groups, serum C-reactive protein (CRP) (ES = −0.92 mg/L, 95% CI = [−1.36, −0.48], P < 0.001, I 2 = 90.2%), tumor necrosis factor-alpha (TNF-α) (ES = −0.49 pg/mL, 95% CI = [−084, −0.14], P = 0.006, I 2 = 34.6%) and malondialdehyde (MDA) (ES = −0.42, 95% CI = [−083, −0.01], P = 0.04, I 2 = 76.1%) were significantly reduced in the groups receiving Zn. Serum interleukin 6 (ES = −1.02 pg/mL, 95% CI = [−2.06, 0.02], P = 0.05, I 2 = 92.3%) was marginally reduced following Zn supplementation. Moreover, treatment duration was found as the source of inter-study heterogeneity. This meta-analysis suggests that Zn supplements reduce serum concentrations of markers of inflammation and oxidation: CRP, TNF-α and MDA. [ABSTRACT FROM AUTHOR]