ObjectiveOsteoprotegerin (OPG), an inhibitor of osteoclastic bone resorption, has a variety of functions including anti-inflammatory effects and a possible cardiovascular protective role. Both low-grade chronic inflammation and cardiovascular risk are increased in women with the polycystic ovary syndrome (PCOS). We aimed to study serum OPG concentrations in PCOS patients.DesignCase–control study including 40 PCOS patients matched with 40 non-hyperandrogenic women for age and body mass index.MethodsBasal serum sampling and standard oral glucose tolerance test, and measurement of serum OPG concentrations by commercial ELISA.ResultsSerum OPG concentrations were lower in women with PCOS compared with those of controls (304±120 vs 363±105 pg/ml respectively; F=7.641, P=0.007) independently of obesity. No differences were observed in serum receptor activator of nuclear factor-κB ligand (RANKL) levels and in the RANKL/OPG molar ratio. A multivariate linear regression model (R²=0.208, F=6.579, P=0.001) showed that PCOS (β=−0.281, P=0.008), obesity (β=−0.245, P=0.022) and age (β=0.296, P=0.006) were predictive of serum OPG concentrations.ConclusionsSerum OPG concentrations are reduced in PCOS patients independently of obesity. Considering the anti-inflammatory effects of OPG, its reduced serum concentrations might contribute to the proinflammatory state and cardiovascular risk of PCOS patients.