Effect of grape polyphenols on selected inflammatory mediators: A systematic review and meta-analysis randomized clinical trials

Grapes contain different polyphenols and might prevent inflammation by reducing Nitric Oxide (NO) inactivation through antioxidative enzymes. The aim of this article was to demonstrate the effects of grape polyphenols on the selected inflammatory mediators, such as interleukin-6 (IL-6), tumor necrosis factor-alpha (TNF-a), and high-sensitivity C-reactive protein (hs-CRP). To find papers assessing the effects of grape polyphenols on inflammatory mediators, electronic data bases, including ISI web of science, PubMed/Medline, SCOPUS, and Google scholar, were searched up to March 2019. Delphi checklist was used for evaluating the qualities of the included articles. The protocol was registered in PROSPERO (No. CRD42019116695). The mean changes in the intervention and control groups were calculated by subtracting the end values from the baselines. Then, the difference between the two changes was measured and utilized as the effect size in meta-analysis. 9 and 8 articles were included in the systematic review and meta-analysis, respectively. Our results indicated that grape polyphenols did not reduce hs-CRP levels, but omission of one article could lead to a significant reduction in hs-CRP (Weight Mean Difference (WMD): −0.54 mg/L, 95 % CI: −1.02, -0.06; P=0.026, I(2)=0.0 %). Regarding IL-6 and TNF-α, no significant changes were observed in the intervention compared to the control group (WMD: 0.04 pg/mL, 95 % CI: −0.02, 0.28; P=0.744, I(2)=0.0 %, WMD: -0.10 pg/mL, 95 % CI: −0.25, 0.05; P=0.183, I(2)=0.0 %, respectively). We found no beneficial effects of grape polyphenols on the selected inflammatory mediators. Still, more studies with higher doses of polyphenols, longer treatment durations, different sources of grape polyphenols, and larger numbers of participants are required.