The effect of zinc supplementation on plasma C-reactive protein concentrations: A systematic review and meta-analysis of randomized controlled trials

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.