Is insulin resistance an intrinsic defect in Asian polycystic ovary syndrome?

Purpose: Approximately 50% to 70% of women with polycystic ovary syndrome (PCOS) have some degree of insulin resistance, and obesity is known to worsen insulin resistance. Many metabolic consequences of PCOS are similar to those of obesity; therefore, defining the cause of insulin resistance in women can be difficult. Our objective was to clarify the factors contributing to insulin resistance in PCOS. Materials and Methods: We consecutively recruited 144 women with PCOS [age: 26±5 yr, body mass index, body mass index (BMI): 24.4±4.0 kg/m²] and 145 controls (age: 25±5 yr, BMI: 23.0±3.6 kg/m²), and divided them into overweight/obese (ow/ob, BMI ≥23 kg/m²) and lean (BMI <23 kg/m²) groups. Anthropometric measures and a 75-g oral glucose tolerance test were performed, and insulin sensitivity index (ISI) was calculated as an index of insulin sensitivity. Factors predictive of ISI were determined using regression analysis. Results: ISI was significantly lower in both lean and ow/ob women with PCOS compared to BMI-matched controls (p<0.05). Increasing BMI by 1 kg/m² decreased ISI by 0.169 in PCOS patients (p<0.05) and by 0.238 in controls (p<0.05); there was no significant difference between these groups. In lean PCOS patients and lean controls, BMI had no effect on ISI. Multiple regression analysis revealed that PCOS status (β=-0.423, p<0.001) and BMI (β=-0.375, p<0.001) were significantly associated with ISI. Conclusion: Insulin resistance is an intrinsic defect of PCOS, and a high BMI could exacerbate insulin resistance in all women, irrespective of whether they have PCOS.