The effects of quercetin supplementation on lipid profiles and inflammatory markers among patients with metabolic syndrome and related disorders: A systematic review and meta-analysis of randomized controlled trials

Abstract Aims: This systematic review and meta-analysis of randomized controlled trials (RCTs) was performed to determine the effect of quercetin administration on lipid profiles and inflammatory markers among patients with metabolic syndrome (MetS) and related disorders. Methods: We searched systematically online databases including Cochrane Library, EMBASE, MEDLINE, and Web of Science to identify the relevant RCTs until November 2018. Q-test and I2 statistics were applied to assess heterogeneity among included studies. Data were combined using fixed- or random-effects model and presented as standardized mean difference (SMD) with 95% confidence interval (CI). Results: Out of 591 citations, 16 RCTs were included in the meta-analysis. The pooled findings showed that quercetin consumption significantly decreased total-cholesterol (SMD = −0.98; 95% CI, −1.48, −0.49; p < 0.001; I2: 94.0), LDL-cholesterol (SMD = −0.88; 95% CI, −1.35, −0.41; p < 0.001; I2: 92.7) and C-reactive protein (CRP) levels (−0.64; 95% CI, −1.03, −0.25; p = 0.001; I2: 90.2). While, quercetin supplementation did not significantly affect triglycerides (TG) (SMD = −0.32; 95% CI, −0.68, 0.04; p = 0.08; I2: 84.8), HDL-cholesterol (SMD = 0.20; 95% CI, −0.20, 0.24; p = 0.84; I2: 70.6), interleukin 6 (IL-6) (SMD = −0.69; 95% CI, −1.69, 0.31; p = 0.17; I2: 94.5) and tumor necrosis factor-alpha (TNF-α) levels (SMD = −0.06; 95% CI, −0.25, 0.14; p = 0.58; I2: 35.6) Conclusions: In summary, the current meta-analysis demonstrated that quercetin supplementation significantly reduced total-cholesterol, LDL-cholesterol, and CRP levels, yet did not affect triglycerides, HDL-cholesterol, IL-6 and TNF-α among patients with MetS and related disorders.