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Limitations of Salivary Osmolality as a Marker of Hydration Status


Medicine & Science in Sports & Exercise: June 2011 - Volume 43 - Issue 6 - p 1080-1084
doi: 10.1249/MSS.0b013e3182058643
Applied Sciences

ABSTRACT Salivary osmolality (S osm) is a potentially useful hydration marker but may be confounded by oral artifacts.

Purpose: This study aimed to determine the efficacy of S osm for detecting hypohydration and evaluate the effect of a simple mouth rinse.

Methods: Eight healthy volunteers (six males and two females; age = 22 ± 7 yr, body mass = 83.7 ± 14.9 kg, height = 176.9 ± 9.2 cm) were measured for nude body mass (BM), plasma osmolality (P osm), and S osm when euhydrated (EUH) and again when hypohydrated (HYP) by exercise-heat exposure with fluid restriction. After the initial saliva sample during HYP, a 10-s mouth rinse with 50 mL of water was provided, and saliva samples were obtained 1 min (RIN01), 15 min (RIN15), and 30 min (RIN30) after rinse. The ability of S osm to detect HYP was compared with P osm.

Results: Volunteers were hypohydrated by −4.0% ± 1.2% of BM (range = −2.2% to −5.3%). S osm was elevated above EUH after hypohydration (EUH 58 ± 8 mmol·kg−1 vs HYP 96 ± 28 mmol·kg−1, P < 0.05). S osm baseline and change values displayed more variability than P osm based on ANOVA and regression analyses. After the oral rinse, saliva decreased in concentration (RIN01 = 61 ± 17 mmol·kg−1, P < 0.05) but returned to prerinse values within 15 min (RIN15 = 101 ± 25 mmol·kg−1) and remained similar 30 min after (RIN30 = 103 ± 33 mmol·kg−1).

Conclusions: S osm was remarkably altered 1 min after a brief water mouth rinse. Fifteen minutes proved an adequate recovery time, indicating that the timing of oral artifacts and saliva sample collection is critical when considering S osm for hydration assessment. Given the inherent variability and profound effect of oral intake, use of S osm as a marker of hydration status is dubious.

U.S. Army Research Institute of Environmental Medicine, Natick, MA

Address for correspondence: Brett R. Ely, M.S., USARIEM, Thermal & Mountain Medicine Division, Kansas St., Bldg. 42, Natick, MA 01760-5007; E-mail:

Submitted for publication August 2010.

Accepted for publication November 2010.

©2011The American College of Sports Medicine