Water turnover and body composition during long-term exposure to high altitude (4,900-7,600 m).

Thirteen healthy subjects (11 men and 2 women; 30.2 +/- 5.4 yr; 73.5 +/- 10.3 kg; 178.9 +/- 10.4 cm; body mass index, 22.9 +/- 1.6 kg/m2) participated at the 62-day expedition to the Broad Peak (8,047 m), Pakistan. Weight, body water, and water turnover (deuterium dilution and elimination) were measured eight times to assess long-term changes. Body weight fell during the ascent to the base camp [from 73.2 +/- 9.8 (baseline) to 71.7 +/- 9.7 kg; P < 0.05] and decreased until the end of the base camp stay (66.7 +/- 7.2 kg; P < 0.0001). Body compartments changed at different rates. Total body water decreased during the ascent (from 43.1 +/- 7.3 to 41.0 +/- 7.7 liters; P < 0.05) and remained unchanged until the base camp was reached (41.2 +/- 6.9 liters; P < 0.01) but decreased further during the base camp stay (40.6 +/- 5.2 liters). Water content of the body (total body water-to-body weight ratio) fell during the ascent (from 58.6 +/- 3.4 to 55.8 +/- 4.4%; P < 0.01), approached the baseline value during the base camp (57.4 +/- 4.0 and 58.3 +/- 5.1%), and increased again until the end of the base camp (60.6 +/- 3.4 and 60.9 +/- 4.3%). The compartment of the solids increased during the ascent (from 30.2 +/- 3.4 to 32.2 +/- 4.9 kg; P < 0.01) and approached the baseline value on arrival at the base camp (30.5 +/- 4.7 kg). Until the end of the base camp, the compartment of the solids fell (26.9 +/- 2.6 and 26.1 +/- 4.0 kg), indicating that weight loss was due to a loss of body solids, presumably mostly fat mass. Water turnover during the pretest period (sea level) was 45 +/- 7 ml.kg-1.day-1; it increased during the ascent (56 +/- 11 and 60 +/- 10 ml.kg-1.day-1) but remained constant during the base camp stay (63 +/- 12, 58 +/- 9, and 56 +/- 10 ml.kg-1.day-1). It increased during the ascent to Broad Peak (73 +/- 20 ml.kg-1.day-1; P < 0.05) and even more during the descent to civilization (83 +/- 17 ml.kg-1.day-1; P < 0.05).