Salivary Biomarkers for Field Assessment of Hydration in Sport

Dehydration is defined as the state in which the total body water content falls below a constant standard. Attempts to objectively quantify hypohydration using salivary samples have been reported. However, previous studies have been confined to laboratory settings and have not extended to competitive athletes or children. This study aimed to evaluate the utility of salivary indices in assessing dehydration in real-world sports settings. Ten collegiate triathletes provided stimulated whole saliva and urine samples before and after a duathlon (approximately 2 h). Salivary flow rate, salivary osmolality, and urine specific gravity (USG) were measured. Twelve elementary school soccer players underwent the same measurements before and after a 90-minute training session. In collegiate triathletes, post-race increases in USG ( < .01), a decrease in salivary flow rate, and an increase in salivary osmolality (both < .01) were observed, suggesting that salivary indices may be useful for dehydration assessment. In contrast, among child soccer players, the USG increased ( < .01), but the salivary indices showed no significant change ( > .05). These differences may reflect differences in hydration behavior, exercise conditions, and age-related physiological characteristics. Future work should establish context- and age-appropriate salivary indices and standardize measurement protocols to enhance the accuracy of these assessments.