Research

Hormonal

Acute exercise-heat-induced dehydration without fluid replacement increases sweat sodium and chloride concentrations in men, likely due to elevated extracellular fluid sodium, plasma aldosterone, and sympathetic nervous activity.

If you exercise for more than an hour in hot conditions, your sweat becomes saltier if you don't drink. This means you lose more sodium than you would if you stayed hydrated. To maintain performance and health, consider replacing fluids with electrolytes, especially sodium, rather than just plain water, to match the increased loss.

GoodSupportsHIGH confidence
Acute exercise-heat stress without fluid replacement resulted in a greater sweat [Na+] and [Cl-] which was potentially related to greater extracellular fluid [Na+], plasma aldosterone or sympathetic nervous activity.
Rhian Morgan et al. · Acta Physiologica Scandinavica · 2004

Why this rating

Randomized controlled trial with clear intervention and measurement, though small sample size (n=8).

Source

Acute effects of dehydration on sweat composition in men during prolonged exercise in the heat

Rhian Morgan et al. · Acta Physiologica Scandinavica · 2004

DOI 10.1111/j.1365-201x.2004.01305.x

crossover · n=8Cited 190×
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DOI resolved against Crossref · corpus check 2026-06-10

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