Six healthy, heat-acclimatized subjects were exposed to different hot and humid environments in a climatic chamber and sodium, potassium, and chloride concentrations in their sweat, urine, and blood were determined. The concentration of potassium in sweat was found to be considerably higher than that in the plasma, whereas that of sodium and chloride was very much lower. The concentration of potassium in urine was also 8-12 times higher than that in the plasma as compared to 0.5 to 1.5 times higher for sodium and chloride. The total daily computed losses of potassium in sweat and urine, of a person working in severe heat in the tropics, can be about 116 mEq as against a dietary intake of 97 mEq/d, thereby resulting in negative potassium balance. The potassium depletion in sweat, even in acclimatized Indians, is thus heavy and is likely to play an important role in the causation of heat-illness.
Malhotra MS, Sridharan K, Venkataswamy Y. Potassium losses in sweat under heat stress. Aviat Space Environ Med. 1976 May