Why are the high altitude inhabitants like the Tibetans shorter and lighter?
High altitude inhabitants (HAI) are generally smaller than low altitude inhabitants (LAI). This anthropological observation has recently been confirmed in the Tibetan refugees who have settled in India since 1950s. Those settled at lower altitudes (970 m) are taller and muscular than compatriots settled at higher altitudes (3500 m). While lower socioeconomic status is implicated in growth retardation at higher altitudes, the smaller stature in adults in well-off communities says otherwise. Hypobaric hypoxia (HH) is the main challenge at high altitudes, which the long established HAI have overcome via biological adaptations, including larger chests, raised blood hemoglobin, and producing more nitric oxide (NO), which deliver similar levels of oxygen to tissues, as LAI. The Tibetans produce 10-fold more NO than LAI. NO is a potent inhibitor of steroidogenesis. Therefore I hypothesize that the short stature and lower musculature in HAI results from steroid deficiency precipitated by NO, which HAI produce to cope with HH.
Panesar
N S
NS
Department of Chemical Pathology, The Chinese University of Hong Kong, Shatin, New Territories, Hong Kong. nspanesar@cuhk.edu.hk
D000220:Adaptation, Biological / Q000502:physiology*; D000531:Altitude; D001827:Body Height / Q000502:physiology*; D001835:Body Weight / Q000502:physiology*; D005006:Ethnicity; D006801:Humans; D009569:Nitric Oxide / Q000378:metabolism*; D012959:Socioeconomic Factors; D018609:Tibet
D009569:Nitric Oxide