A Comparison of Male and Female Saliva and Plasma Osmolality in Response to Mild Dehydration

Purpose: Firstly, to investigate how changes in whole saliva osmolality (Sosm) compares with changes in plasma osmolality (Posm) during mild dehydration as measured by BML; secondly, to determine whether there are differences between male and female responses and finally, to assess whether Sosm and Posm return to pre-exercise levels following ad libitum re-hydration. Materials and Methods: Thirty-nine healthy volunteers (29 males and 10 females) were dehydrated, resulting in 1.10 - 3.06% body mass loss (BML), by walking on a treadmill for 60 minutes at 40°C and 20% relative humidity. Post-exercise participants were given water ad libitum to drink and post-rehydration samples were collected 30 minutes after the onset of water consumption. Blood and unstimulated whole saliva were collected and analyzed for osmolality pre-exercise, post-exercise and post-rehydration. All data were evaluated for differences between male and female responses. Results: Saliva osmolalities increased from pre- (73.29 ± 15.42) to post-exercise (102.10 ± 25.28) and by a greater percentage than Posm. Generally, Sosm and Posm returned to pre-exercise levels following rehydration. With dehydration, shifts in Posm and Sosm were in the same direction for males and females but females showed morevariability in the response. Conclusion: Although neither Posm nor Sosm correlated closely with BML associated with mild dehydration, Sosm demonstrated sufficient measurable differences, especially in males, and shows potential as a dehydration screening biomarker.