High-altitude erythrocytosis: mechanisms of adaptive and mal-adaptive responses

Erythrocytosis, or increased production of red blood cells, is one of the most well-documented physiological traits that varies within and among in high-altitude populations. Although a modest increase in blood O 2 -carrying capacity may be beneficial for life in highland environments, erythrocytosis can also become excessive and lead to maladaptive syndromes such as Chronic Mountain Sickness (CMS).