Abstract
A negative water and sodium balance develops during the first hours to days after reaching a high altitude. The fluid and sodium balance does not alter in cases of altitude sickness, or may even become positive. This is attributed to a decreased diuresis and natriuresis in those who develop altitude sickness, while their fluid intake is no different to that of people who do not suffer from altitude sickness. This is a consequence of stimulation of the renin-angiotensin-aldosterone system (RAAS) and an increased secretion of antidiuretic hormone (ADH) combined with a higher than normal sympathetic activity. Therefore there is no argument for an increased fluid intake for the prevention of altitude illness. In theory this might even be harmful.
