Effect of propolis intake on serum C-Reactive Protein (CRP) and Tumor Necrosis Factor-alpha (TNF-a) levels in adults: a systematic review and meta-analysis of clinical trials

Background Propolis is a natural Product and the antioxidant properties of Propolis appear to be principally responsible for its therapeutic effects. However, several studies have shown the positive effect of Propolis on the reduction the levels of inflammatory markers; some others have revealed non-significant impacts on them. Hence, the present systematic review and meta-analysis aimed to investigate the effects of Propolis intake on C-reactive protein (CRP) and tumor necrosis factor-alpha (TNF-a). Methods The systematic search was undertaken in scientific databases that included: PubMed, Embase, Scopus and Web of Science to find studies assessing the effects of Propolis on CRP and TNF-a up to December 2019. Standardized mean difference (SMD) and 95 % confidence intervals (CI) were pooled using a random-effects model. Potential publication bias was tested using Egger’s test. Results Six studies comprising 406 participants were included in the meta-analysis. Compared to controls, Propolis intake significantly reduced serum TNF-a (SMD = -0.48, 95 % CI = [-0.69, -0.26], P < 0.0001, I2 = 66.9 %) and CRP (SMD = -0.38, 95 % CI = [-0.68, -0.07], P = 0.01, I2 = 44.4 %) levels. No evidence of publication bias was found in the meta-analyses. Conclusion The present study concluded in the statistically and clinically reduction of serum CRP and TNF-a levels following Propolis intake.