Effects of Quercetin Supplementation on Cardiovascular Risk Factors and Inflammatory Biomarkers in Patients with Type 2 Diabetes

Quercetin is found in a wide range of food sources. Previous research has reported inconsistent findings about the effects of quercetin on inflammation and heart disease. Hence, the present study evaluated the effects of quercetin intake on blood pressure, lipid profile, and inflammatory biomarkers of patients with type 2 diabetes. This double-blind randomized clinical trial assessed 72 women for 10 weeks. Subjects were assigned to quercetin and placebo groups using permuted-block randomization with a block size of two. A 500 mg quercetin capsule was given to the quercetin group every day. Biochemical variables were measured at baseline and the end of the study and changes were compared using appropriate statistical methods. Quercetin intake decreased systolic blood pressure significantly (-8.8 ± 9.3 in the quercetin group vs. -3.5 ± 11.7 in the control group, P = 0.04). However, changes in diastolic blood pressure in two groups were not significantly different (P = 0.19). While high density lipoprotein cholesterol (HDL-c) was significantly decreased in both groups, there were no significant with group or intragroup differences in changes in total cholesterol, low density lipoprotein cholesterol (LDL-c), triglycerides (TG), and ratio of TG/HDL-c and LDL-c/HDL-c. Quercetin supplementation significantly reduced serum concentration of tumor necrosis factor alpha (TNFα) and interleukin-6 (IL-6) (P = 0.01 and P < 0.01, respectively). Nevertheless, the mean changes in serum levels of IL-6, TNFα, and high sensitivity C-reactive protein (hs-CRP) were not significantly different between groups. Although quercetin supplementation significantly reduced systolic blood pressure, it had no effects on other cardiovascular risk factors and inflammatory biomarkers. Considering the biological effects of quercetin in vitro, more studies with stronger design, larger sample size, and different doses of quercetin are warranted.