Effects of supplementation with quercetin on plasma C-reactive protein concentrations: a systematic review and meta-analysis of randomized controlled trials

Abstract

Promising experimental studies suggest that quercetin has potential anti-inflammatory effects. However, the results of current clinical trials on quercetin's effects on the C-reactive protein (CRP), a sensitive inflammatory biomarker, are ambiguous. We conducted a meta-analysis of available randomized controlled trials (RCTs) to resolve this inconsistency and quantify the net effect of quercetin on circulating CRP concentrations. A systematic search was performed in several databases including SCOPUS, PubMed-Medline and Google Scholar until 16 June 2016. We used a random-effects model in combination with weight mean difference (WMD) and 95% confidence intervals (CI) for data analysis. Standard methods were used for the assessment of heterogeneity, meta-regression, sensitivity analysis and publication bias. The meta-analysis of seven RCTs (10 treatment arms) showed a significant reduction of circulating CRP levels (WMD: -0.33 mg/l; 95% CI: -0.50 to -0.15; P<0.001) following quercetin supplementation. In the subgroup analysis, a significant reducing effect was observed in trials with ⩾500 mg/day dosage (WMD: -0.34 mg/l; 95% CI: -0.52, -0.16; P⩽0.001) and in those with CRP <3 mg/l (WMD: -0.34 mg/l; 95% CI: -0.51, -0.18; P⩽0.001). In meta-regression, there was no association between changes in CRP concentrations, dose of supplementation and CRP baseline values. Our findings showed a significant effect of quercetin supplementation on the C-reactive protein-especially at doses above 500 mg/day and in patients with CRP <3 mg/l.

Therapeutic Potential of Flavonoids in Pain and Inflammation: Mechanisms of Action, Pre-Clinical and Clinical Data, and Pharmaceutical Development

“…A meta-analysis of clinical studies evaluating quercetin actions on cardiovascular protection concludes that quercetin supplementation should be considered as an add-on therapeutic approach [241]. Quercetin doses above 500 mg/day show effects on the C-reactive protein levels [242], and in women with polycystic ovary syndrome, 1g quercetin intake for 12 weeks improved adiponectin-mediated insulin resistance and hormonal profiles [242]. Moreover, in 50 rheumatoid arthritis (RA) patients, 500 mg quercetin supplementation during 8 weeks ameliorates clinical symptoms such as early morning stiffness and pain, disease activity, and TNFα plasma levels [200].…”

Supplementation with a Mango Leaf Extract (Zynamite®) in Combination with Quercetin Attenuates Muscle Damage and Pain and Accelerates Recovery after Strenuous Damaging Exercise

“…Although the administration of antioxidants to prevent muscle damage is controversial [3][4][5], some recent studies indicate that ingestion of polyphenol-rich extracts for at least three days before exercise and during the following hours/days may improve recovery [6]. Zynamite ® , a mango leaf extract rich in the natural polyphenol mangiferin, and quercetin have antioxidant and anti-inflammatory properties [7][8][9][10], which may prevent EIMD and facilitate recovery [11]. Nevertheless, these two polyphenols have not been studied in combination and the effect of quercetin has been only assessed after chronic administration and with large daily doses (∼1000 mg), which could impair exercise performance or blunt part of the adaptations to training [12].…”

Effects of quercetin supplementation on glycemic control among patients with metabolic syndrome and related disorders: A systematic review and meta‐analysis of randomized controlled trials

“…Prior studies in diabetic rats showed quercetin intake decreases hyperinsulinemia, insulin resistance, inflammatory factors, blood pressure, and hyperlipidemia (Mahmoud, Hassan, El Bassossy, & Fahmy, 2013;Rivera, Moron, Sanchez, Zarzuelo, & Galisteo, 2008). In addition, recent meta-analyses have reported the beneficial influences of quercetin administration on inflammation, blood pressure, and serum triglycerides levels in humans (Mohammadi-Sartang, Mazloom, Sherafatmanesh, Ghorbani, & Firoozi, 2017;Sahebkar, 2017;Serban et al, 2016). Some randomized controlled trials (RCTs) have investigated the effects of quercetin on glucose homeostasis in patients with metabolic disorders, whereas the results are conflicted.…”