Correlation between Subjective Thirst and Properties of Saliva in Humans

Abstract

In this study, the properties of human saliva were analyzed in relation to subjective reports of thirst after exercise. To produce a thirsty state, subjects performed vigorous exercise using an ergometer at high temperature and low humidity. The total volume of saliva secreted, pH, and the concentrations of Na⁺, K⁺, Ca²⁺, Mg²⁺, Cl^-, PO₄^3- and total protein were measured. Subjective thirstiness was evaluated by a questionnaire. Under conditions of thirst, the concentrations of Na⁺, K⁺, Cl^- and total protein were significantly increased in comparison with the resting state. Buffering capacity was also increased. The amount of saliva secreted tended to be reduced, although its pH did not change significantly. After quenching of thirst by drinking mineral water, measures of subjective thirst were restored to the pre-exercise levels, but the concentrations of Na⁺, K⁺, Cl^- and total protein did not recover to their original levels.