Sex Differences in Hydration Biomarkers and Test-Retest Reliability Following Passive Dehydration

Area of Science:

• Exercise Physiology
• Sports Science
• Human Physiology

Background:

• Accurate hydration status monitoring is crucial for athletes and military personnel.
• Existing hydration biomarkers may exhibit sex-specific responses and reliability.
• Understanding these differences is key to optimizing hydration strategies.

Purpose of the Study:

• To investigate sex-based differences in serum, tear, and urine osmolality, hematocrit, and urine specific gravity changes following acute passive dehydration.
• To assess the test-retest reliability of these hydration biomarkers in males and females separately.

Main Methods:

• Fifteen males and fifteen females underwent a sauna protocol twice to induce approximately 4% body mass loss (BML).
• Serum, tear, and urine samples were collected pre- and post-dehydration for biomarker analysis.
• Change scores and intraclass correlation coefficients (ICCs) were calculated to determine differences and reliability.

Main Results:

• Males achieved significantly greater BML than females in both trials.
• Changes in hematocrit were significantly different between sexes, regardless of BML.
• Sex was a significant predictor for changes in hematocrit and serum osmolality, independent of BML.
• Biomarker reliability was generally poor to moderate and lower in males compared to females.

Conclusions:

• Hydration biomarker responses and reliability are sex-specific.
• Hematocrit and serum osmolality changes are influenced by sex, even after controlling for body mass loss.
• Current hydration biomarkers exhibit limited test-retest reliability, necessitating careful consideration of sex and individual variability.