Villafuerte et al. (2016) also showed that mean sleep SpO2, total sleep time below 80% SpO2, and the Epo-to-soluble Epo receptor ratio (an Epo availability index) were significant predictors of Hct in men. Finally, Julian et al. (2013) found that men with excessive erythrocytosis had lower nocturnal SpO2 as well as higher levels of the oxidative stress marker 8-iso-PGF2alpha. The results presented here demonstrate that the relationships between sleep SpO2 and Hct previously identified in men are present in women as well. Here, EPO is linked to polycythemia.