The effect of grape seed extract supplementation on oxidative stress and inflammation: A systematic review and meta‐analysis of controlled trials

Background Grape seed extract (GSE) seems to have antioxidant and anti-inflammatory properties due to its high polyphenolic content. Nevertheless, the scientific literature in this field is controversial and inconclusive. Therefore, we aimed to conduct a systematic review and meta-analysis of controlled trials to evaluate the effect of supplementation with GSE on biomarkers of oxidative stress and inflammation. Methods Medline, Scopus, Cochrane Library, Google Scholar and Web of Science databases were searched up to 10 September 2020 using appropriate keywords without restrictions. In the systematic review phase, all biomarkers of oxidative stress and inflammation were considered as outcomes. In the meta-analysis phase, six biomarkers were selected as outcomes, and weighted mean difference (WMD) or standardised mean difference (SMD) with 95% confidence interval (CI) was calculated for them using a random-effects model. Results Twenty-three studies were included in the systematic review, and 19 studies were included in the meta-analysis. GSE supplementation caused a significant decrease in malondialdehyde (SMD: −1.04, 95% CI: −1.65, −0.42), oxidised low-density lipoprotein (SMD: −0.44, 95% CI: −0.75, −0.13) and high-sensitivity C-reactive protein (WMD: −0.48 mg/L, 95% CI: −0.94, −0.03) and a marginally significant increase in total antioxidant capacity (SMD: 0.49, 95% CI: −0.05, 1.04) but did not significantly influence C-reactive protein (WMD: −0.36 mg/L, 95% CI: −1.02, 0.30) and white blood cell count (WMD: 0.12 × 109/L, 95% CI: −0.25, 0.48). Conclusion It appears that GSE supplementation can remarkably modulate the body's redox system, particularly through the inhibition of lipid peroxidation, but has neutral or mildly beneficial effects on inflammatory responses.