Quercetin reduces residual dysglycemia in postmenopausal women with established coronary artery disease: a randomized double-blind trial

Background Postmenopausal women with chronic coronary artery disease (CAD) remain at high residual cardiometabolic risk despite contemporary therapy. Dysglycemia and insulin resistance contribute to endothelial dysfunction, plaque progression, and recurrent events. Although flavonoid-rich diets are associated with metabolic benefits, randomized evidence supporting the use of isolated flavonoid supplementation in secondary prevention is lacking. Quercetin is a bioactive flavonoid with antioxidant and insulin-sensitizing properties. Purpose To determine whether quercetin supplementation improves glycemic control in postmenopausal women with established atherosclerotic CAD. Methods In this prospective, randomized, double-blind, placebo-controlled trial, 43 naturally postmenopausal women (<70 years) with angiographically documented CAD (≥70% stenosis in ≥1 major epicardial vessel) were randomized to quercetin 500 mg/day (n=22) or placebo (n=21) for 60 days. All participants completed a 40-day washout of lipid-lowering therapy and maintained their habitual diet. Anthropometric, metabolic, and inflammatory parameters were assessed at baseline and 60 days. Results Mean age was similar between groups, being 61±5 years in the placebo group and 60±5 years in the quercetin group. At baseline, anthropometric and metabolic parameters were comparable between the groups. In the placebo group, body mass index, glycemia, HbA1c, lipid profile, and C-reactive protein levels remained unchanged after 60 days of follow-up (p>0.05 for all). In contrast, in the quercetin group, glycemia decreased significantly from 110±17 to 105±13 mg/dL (p=0.024) and HbA1c from 6.0±0.70% to 5.8±0.67% (p=0.016). No significant changes were observed in body mass index, triglycerides, total cholesterol, LDL-C, HDL-C, or C-reactive protein levels during the study period (p>0.05 for all), indicating a glucose-specific metabolic effect independent of weight loss, lipid modulation, or systemic inflammation. No adverse metabolic signals were observed. Conclusions In postmenopausal women with established CAD, short-term quercetin supplementation significantly improved glycemic control without affecting weight or lipids. These findings provide randomized evidence that a single bioactive flavonoid can directly target residual dysglycemia in secondary prevention. Given the central role of hyperglycemia in recurrent cardiovascular events, quercetin may represent a novel adjunctive metabolic strategy in women with CAD. Larger, outcome-driven trials are warranted to determine whether this metabolic signal translates into reduced cardiovascular risk.