Emrich IE, Dederer J, Kircher A, et al. – Because fibroblast growth factor 23 (FGF23) expression has been shown to be stimulated by hypoxia with a subsequent rise in erythropoietin (EPO) in experimental rodent models, researchers translated these findings into human physiology in this study. They selected 8 healthy volunteers who were then exposed to high altitude (2,656 meters above sea level) for 4 days. Participants were randomized to a low (n = 4) or normal (n = 4) phosphorus diet. A significant increase in plasma EPO was evident due to high-altitude exposure but no consistent rise in plasma c-terminal FGF23 or plasma intact FGF23 was found. After 5 hours of maximal aerobic exercise, a single, intermittent peak in c-terminal FGF23 levels was detected. In this study, a substantial influence of moderate hypoxia alone upon the FGF23 expression was not supported, but it was suggested that FGF23 expression may be temporarily induced by the combination of exercise and high-altitude exposure.