Effects of dietary sodium on body and muscle potassium content during heat acclimation

Summary

It has been suggested that renal conversion of sodium (Na⁺) during training in hot environments results in potassium (K⁺) deficiencies. This investigation examined the influence of two levels of dietary Na⁺ intake (399 vs 98 mmol · d⁻¹) on intramuscular, urinary, sweat, and whole body K⁺ homeostasis. Nine unacclimated, untrained males underwent heat acclimation during two 8 day dietary-exercise regimens (40.1±0.1‡ C, 23.5±0.4%RH). Both diets resulted in depressed urinary K⁺ excretion. Sweat K⁺ and muscle K⁺ concentrations were not altered by diets or acclimation. The whole body stores of Na⁺ increased 31.1% (+ 916.8 mmol) during the high Na⁺ diet and decreased 7.8% (−230.4 mmol) during the low Na⁺ diet; whole body stores of K⁺ increased 4.1% (+ 137.6 mmol) during the high Na⁺ diet and increased 3.4% (+ 113.6 mmol) during the low Na⁺ diet. This dietary-acclimation protocol did not result in whole-body or intramuscular K⁺ deficits and offers no evidence to support previous claims that dietary sodium levels affect K⁺ balance.