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

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.