RESEARCH ARTICLE The effects of quercetin supplementation on metabolic and hormonal parameters as well as plasma concentration and gene expression of resistin in overweight or obese women with polycystic ovary syndrome Masoud Khorshidi 1 | Ashraf Moini 2,3 | Elham Alipoor 4 | Neda Rezvan 5 | Sattar Gorgani‐Firuzjaee 6 | Mehdi Yaseri 7 | Mohammad Javad Hosseinzadeh‐Attar 1,8 1 Department of Clinical Nutrition, School of Nutritional Sciences and Dietetics, Tehran University of Medical Sciences (TUMS), Tehran, Iran 2 Department of Endocrinology and Female Infertility, Reproductive Biomedicine Research Center, Royan Institute for Reproductive Biomedicine, ACECR, Tehran, Iran 3 Department of Obstetrics and Gynecology, Arash Women's Hospital, Tehran University of Medical Sciences, Tehran, Iran 4 Department of Nutrition, School of Public Health, Iran University of Medical Sciences, Tehran, Iran 5 Department of Clinical Nutrition, School of Nutritional Sciences and Dietetics, International Campus, Tehran University of Medical Sciences, Tehran, Iran 6 Department of Medical Laboratory Sciences, School of Allied Health Medicine, AJA University of Medical Sciences, Tehran, Iran 7 Department of Epidemiology and Biostatistics, School of Public Health, Tehran University of Medical Sciences (TUMS), Tehran, Iran 8 Centre of Research Excellence in Translating Nutritional Science to Good Health, The University of Adelaide, Adelaide, Australia Correspondence Mohammad Javad Hosseinzadeh‐Attar, Department of Clinical Nutrition, School of Nutritional Sciences and Dietetics, Tehran University of Medical Sciences (TUMS), Tehran, Iran. Email: hosseinzadeh.md.phd@gmail.com; mhosseinzadeh@tums.ac.ir Funding information Tehran University of Medical Sciences and Health Services, Grant/Award Number: 33057 The aim of this study was to investigate the effect of quercetin on metabolic and hormonal parameters as well as plasma concentration and gene expression of resistin in overweight or obese women with polycystic ovary syndrome (PCOS). In this ran- domized, double‐blind, placebo‐controlled trial, 78 overweight or obese women (25 ≤ BMI ≤ 40 kg/m 2 , 20–40 years) with PCOS were recruited. Patients were ran- domized to receive 1,000 mg/day quercetin or placebo for 12 weeks. Resistin plasma concentration and gene expression in peripheral blood mononuclear cells, parameters of glucose homeostasis, circulatory testosterone, luteinizing hormone (LH), and sex hormone‐binding globulin, and anthropometries were assessed at baseline and at the end of the study. Following supplementation, quercetin significantly decreased resistin concentration (2.07 ± 0.23 vs. 2.88 ± 0.40 ng/ml, p < 0.001) and mRNA level (0.64 ± 0.58 vs. 1 ± 0.56 fold change, p = 0.008), compared with placebo group. More- over, testosterone (0.72 ± 0.15 vs. 0.76 ± 0.12 ng/ml, p = 0.001) and LH (8.05 ± 2.88 vs. 8.77 ± 1.99 mIU/ml, p = 0.035) concentrations were significantly lower in querce- tin compared with placebo group. Fasting blood glucose (p < 0.001), insulin (p = 0.02), and homeostatic model assessment of insulin resistance (p = 0.009) decreased within the quercetin group; however, no significant differences were observed compared with the placebo group (p = 0.074, p = 0.226, p = 0.22, respectively). Quercetin supplementation decreased resistin plasma levels and gene expression, and testoster- one and LH concentration in overweight or obese women with PCOS. KEYWORDS obesity, polycystic ovary syndrome, quercetin, resistin Received: 8 April 2018 Revised: 19 June 2018 Accepted: 3 July 2018 DOI: 10.1002/ptr.6166 Phytotherapy Research. 2018;1–8. © 2018 John Wiley & Sons, Ltd. wileyonlinelibrary.com/journal/ptr 1