Plasma interleukin 6 levels are elevated in polycystic ovary syndrome independently of obesity or sleep apnea

Premenopausal women with polycystic ovary syndrome (PCOS) are at a much higher risk for excessive daytime sleepiness, fatigue, and insulin resistance than control women. Elevated levels of interleukin 6 (IL-6) and tumor necrosis factor α (TNF-α) are presumably part of the pathogenesis of these clinical manifestations. Forty-two obese women with PCOS, 17 body mass index-comparable obese controls, and 15 normal-weight controls free from apnea participated in the study that included one 8-hour nighttime polysomnography, single morning cytokine plasma concentrations, and insulin resistance indices. Women with PCOS exhibited higher plasma concentrations of IL-6 than obese controls, who had intermediate values, or normal-weight controls, who had the lowest values (4.75 ± 0.5 vs 3.65 ± 0.4 vs 1.84 ± 0.3 pg/mL, P < .01). Tumor necrosis factor α values were higher in PCOS and obese controls compared with normal-weight controls, but the difference was not statistically significant (4.05 ± 0.3 vs 3.79 ± 0.2 vs 3.14 ± 0.2 pg/mL, P = .103). Based on backward regression analysis, IL-6 levels had a stronger association with the PCOS group than with the obese group, and the sleep or hypoxia variables did not make a significant contribution to either IL-6 or TNF-α. Both IL-6 and TNF-α correlated positively with body mass index (P < .01) in obese controls but not in women with PCOS. Furthermore, within the PCOS group, IL-6 and TNF-α correlated more strongly with indices of insulin resistance than obesity. We conclude that IL-6 levels are elevated in obese women with PCOS independently of obesity or sleep apnea and may represent a pathophysiologic link to insulin resistance.