Do we need additional electrolytes at high altitude?

Exposure to high altitude causes significant changes in fluid and electrolyte balance, even in healthy individuals. During the first several days at moderate altitudes, people commonly experience a reduction in total body water, plasma volume, and body weight. This temporary dehydration is largely driven by increased urine output (diuresis), reduced thirst, and lower fluid intake. Researchers also found that alterations in fluid balance often occur before symptoms of altitude-related illnesses, such as acute mountain sickness (AMS), suggesting that fluid regulation may play an important role in the development of these conditions.

The body's fluid response to altitude is influenced by several factors, including hypoxia, physical activity, hormonal changes, and kidney function. While acute exposure to altitude generally promotes fluid loss, exercise soon after ascent appears to have the opposite effect, encouraging sodium and water retention. Hormones involved in fluid regulation, such as aldosterone, antidiuretic hormone (ADH), and catecholamines, may contribute to these changes, particularly in individuals who are susceptible to AMS. Additionally, kidney blood flow tends to decrease at altitude, which may further alter the body's ability to regulate fluid balance and electrolyte concentrations. Because electrolyte needs can vary based on altitude, training volume, sweat losses, and individual physiology, working with a registered dietitian or sports nutritionist can help determine an appropriate hydration and electrolyte replacement strategy.

Over longer periods of exposure, the initial dehydration seen at altitude often resolves and may shift toward fluid retention. Studies of individuals living for months at high elevations found increases in total body water despite continued reductions in body weight and plasma volume. At extreme altitudes above 6,000 meters, prolonged exposure can result in substantial salt and water retention, sometimes leading to serious conditions such as subacute mountain sickness, characterized by edema and fluid accumulation. The authors conclude that although acute altitude exposure generally causes transient dehydration, chronic exposure may promote fluid retention, and further research is needed to better understand the interactions among altitude, exercise, hormones, kidney function, and fluid regulation.

Reference:

Institute of Medicine (US) Committee on Military Nutrition Research; Marriott BM, Carlson SJ, editors. Nutritional Needs In Cold And In High-Altitude Environments: Applications for Military Personnel in Field Operations. Washington (DC): National Academies Press (US); 1996. 18, Fluid Metabolism at High Altitudes. Available from: https://www.ncbi.nlm.nih.gov/books/NBK232881/