Saliva flow rate, total protein concentration and osmolality as potential markers of whole body hydration status during progressive acute dehydration in humans Neil P. Walsh*, Joanna C. Montague, Nichola Callow, Ann V. Rowlands School of Sport, Health and Exercise Sciences, University of Wales, Bangor LL57 2PX, UK Accepted 14 August 2003 Introduction The predominant constituent of saliva is water (97—99.5%) that enters saliva from plasma across acinar cells. 1 Reduced saliva flow rate has been observed during periods of water deprivation 2,3 intense thirst 2 and after hot water immersion. 4 However, these observations were made in only one 2,4 and two 3 subjects. More recently, under laboratory conditions, parotid saliva flow rate was measured by placing a Carlson—Crittenden cup over the orifice of one parotid gland. 5,6 In these stu- dies 5,6 dehydration induced by a 24 h period without food and water was shown to reduce parotid saliva flow rate in both young and older adults. Collec- tively, this evidence suggests that there is a rela- tionship between whole body hydration status and saliva flow rate. A reduction in whole unstimulated saliva flow rate is commonly reported after pro- longed exercise. 7—9 It has recently been suggested 9 Archives of Oral Biology (2004) 49, 149—154 KEYWORDS Salivary flow rate; Osmolality; Total protein; Exercise Summary Objective: To identify whether saliva flow rate, total protein concentration and osmolality are sensitive non-invasive markers of whole body hydration status, we compared changes in these parameters with changes in body mass during progressive acute dehydration. Design: Twelve euhydrated males reported to the laboratory following an overnight fast and cycled on a stationary ergometer at 60% maximal oxygen uptake in an environmental chamber (30 8C and 70% RH) until progressive body mass loss (BML) of 1:1  0:0, 2:0  0:0 and 2:9  0:2%. After exercise, subjects were given a volume of carbohydrate electrolyte solution equivalent to 150% BML to consume within 1 h. Unstimulated whole saliva samples were collected over a 2 min period into pre-weighed tubes at pre-exercise, 1.1, 2.0 and 2.9% BML and then at 75, 135 and 195 min post-exercise. Results: Saliva total protein concentration and osmol- ality increased and flow rate decreased (P < 0:01) during dehydration. Saliva total protein concentration and osmolality correlated strongly with % BML during dehydra- tion (mean r ¼ 0:97 and 0.94, respectively: P < 0:01). The correlation for saliva total protein concentration with % BML was greater (P < 0:05) than the correlation for saliva flow rate with % BML (mean r ¼0:88: P < 0:01) during dehydration. Conclusions: These data show that changes in saliva total protein concentration and osmolality, and to a lesser extent flow rate, are strongly associated with changes in body mass during progressive acute dehydration. ß 2003 Elsevier Ltd. All rights reserved. * Corresponding author. Tel.: þ44-1248-383-480; fax: þ44-1248-371053. E-mail address: n.walsh@bangor.ac.uk (N.P. Walsh). 0003–9969/$ — see front matter ß 2003 Elsevier Ltd. All rights reserved. doi:10.1016/j.archoralbio.2003.08.001