Effects of salt loading during exercise in a hot dry climate.

Strenuous work or sports activities in a hot environment can cause significant fluid and salt losses due to excessive sweating. Fluid replacement is commonly accepted to be beneficial, but controversy surrounds the necessity of adding salt to the dietary intake in hot climates. Five healthy young men participated in a self-controlled experiment designed to investigate the effects of salt loading on acclimatized people exercising under controlled laboratory conditions. The additional salt ingestion was found to cause an increase in body weight, rectal temperature, heart rate, urinary sodium and potassium concentrations and in the total amounts of sodium and chloride excreted in urine during the exercise. Furthermore, it decreased plasma aldosterone level and sweat chloride excretion, but did not affect fluid intake, urine output, sweat rate, skin temperature, excretion of sodium and potassium in sweat or urinary potassium content and chloride concentration. Neither did the additional salt intake affect plasma electrolyte levels, renin activity or acid base balance. It is concluded that acclimatized people living in a hot dry climate need no supplementary salt to their daily dietary intake while engaging in physical exercise or sports activities up to two hours a day. Salt loading has no beneficial effects in these conditions and may even be hazardous.