HYD: Assessing Hydration Status (2007)


Walsh N, Laing S, Oliver S, Montague J, Walters R, Bilzon J. Saliva parameters as potential indices of hydration status during acute dehydration. Med Sci Sports Exerc 2004;36(9):1535-42

PubMed ID: 14693209
Study Design:
Diagnostic, Validity or Reliability Study
C - Click here for explanation of classification scheme.
Quality Rating:
Positive POSITIVE: See Quality Criteria Checklist below.
Research Purpose:
To identify whether saliva flow rate, saliva total protein concentration and saliva osmolality are sensitive non-invasive markers of whole body hydration status by comparing changes in these parameters with changes in body mass during progressive acute dehydration and rehydration.
Inclusion Criteria:
Healthy males, non-smokers and no significant oral, dental or systemic disease and were not taking any medication at the time of the study
Exclusion Criteria:
Description of Study Protocol:


Not described


Study of sensitivity and specificity of a diagnostic test (prospective)

Blinding used (if applicable)


Intervention (if applicable)

  • Subjects were given 30 ml/kg body mass of bottled water to drink between 9:00am and 9:00pm the day before the trial to ensure a euhydrated state.
  • Dehydration protocol: In a exercise chamber of a dry bulb temperature of 30 oC and 70% relative humidity, subjects exercise 10 min of cycling on a stationary cycle ergometer at a power output corresponding to 60% maximal oxygen uptake. Subjects repeated the 10 min of exercise in the chamber followed by 5 min rest periods in the laboratory until progressive body mass loss of 1, 2 and 3% were reached. Subjects received no food or fluid during the dehydration protocol.
  • Recovery: After exercise, subjects were given a volume of carbohydrate (CHO)-electrolyte solution (6% CHO and 25 mmol/l Na+) equivalent to 150% body mass loss to consume within 1 hour. 

Statistical Analysis

  • One-way repeated measures ANOVA (7 saliva collections) with significant differences assessed by applying the post hoc Tukey test.
  • Pearson's correlation coefficient
Data Collection Summary:

Timing of Measurements

Saliva samples were collected at pre-exercise, 1, 2 and 3% body mass loss and then at 75, 135 and 195 min post-exercise.

Dependent Variables

  • Saliva flow: Unstimulated whole saliva samples were collected over a 2 min period using pre-weighed salivette tubes
  • Saliva volume: weighing the salivette tube immediately after collection to the nearest mg and saliva density was assumed to be 1.00 g/ml
  • Saliva flow rate: volume of saliva/collection time
  • Saliva total protein: Coomassie blue technique on a spectrophotometer using protein standards supplied with the kit
  • Saliva osmolality: freezing point depression Osmometer (Model 3 MO, Advanced Instruments, Massachusetts)

Independent Variables

 Dehydration; recovery protocols

Control Variables


Description of Actual Data Sample:

Initial N: 12

Attrition (final N): 12

Age: 21 ±1 years

Ethnicity: ND

Anthropometrics: Mean body weight = 76.2 kg

Location: UK


Summary of Results:
Changes in saliva flow rate, total protein concentration and osmolality during progressive acute dehydration and rehydration


   Pre-excercise 1.1% BML   2.0% BML 2.9% BML   75 min Recovery 195 min recovery
Saliva flow rate (ul/min)  495  400  250*  200*#  550  550
Saliva total protein concentration(mg/ml)  0.75  1.2*  1.7*#  1.75*#  1.0 0.75
Saliva osmolality (mOsmo/kg)  52  80*  100*#  100*#  52  53

Values in the tables were estimated from figures.
*P<0.01, significantly different from pre-exercise
#P<0.01, significantly different from 1.1% BML (body mass loss)
  • Saliva total protein concentration and osmolality correlated strongly with %BML during dehydration (mean r=0.97 and 0.94 respectively: P<0.01).
  • Saliva flow rate negatively correlated with %BML during dehydration (mean r=-0.88: P<0.01).
Author Conclusion:
Changes in saliva total protein concentration, osmolality, and flow rate, are strongly associated with changes in body mass during progressive acute dehydration.
Funding Source:
University/Hospital: University of Wales
Reviewer Comments:
Quality Criteria Checklist: Primary Research
Relevance Questions
  1. Would implementing the studied intervention or procedure (if found successful) result in improved outcomes for the patients/clients/population group? (Not Applicable for some epidemiological studies) N/A
  2. Did the authors study an outcome (dependent variable) or topic that the patients/clients/population group would care about? Yes
  3. Is the focus of the intervention or procedure (independent variable) or topic of study a common issue of concern to dieteticspractice? Yes
  4. Is the intervention or procedure feasible? (NA for some epidemiological studies) Yes
Validity Questions
1. Was the research question clearly stated? Yes
  1.1. Was (were) the specific intervention(s) or procedure(s) [independent variable(s)] identified? Yes
  1.2. Was (were) the outcome(s) [dependent variable(s)] clearly indicated? Yes
  1.3. Were the target population and setting specified? Yes
2. Was the selection of study subjects/patients free from bias? Yes
  2.1. Were inclusion/exclusion criteria specified (e.g., risk, point in disease progression, diagnostic or prognosis criteria), and with sufficient detail and without omitting criteria critical to the study? Yes
  2.2. Were criteria applied equally to all study groups? N/A
  2.3. Were health, demographics, and other characteristics of subjects described? Yes
  2.4. Were the subjects/patients a representative sample of the relevant population? Yes
3. Were study groups comparable? Yes
  3.1. Was the method of assigning subjects/patients to groups described and unbiased? (Method of randomization identified if RCT) N/A
  3.2. Were distribution of disease status, prognostic factors, and other factors (e.g., demographics) similar across study groups at baseline? N/A
  3.3. Were concurrent controls or comparisons used? (Concurrent preferred over historical control or comparison groups.) N/A
  3.4. If cohort study or cross-sectional study, were groups comparable on important confounding factors and/or were preexisting differences accounted for by using appropriate adjustments in statistical analysis? N/A
  3.5. If case control study, were potential confounding factors comparable for cases and controls? (If case series or trial with subjects serving as own control, this criterion is not applicable.) N/A
  3.6. If diagnostic test, was there an independent blind comparison with an appropriate reference standard (e.g., "gold standard")? Yes
4. Was method of handling withdrawals described? Yes
  4.1. Were follow-up methods described and the same for all groups? N/A
  4.2. Was the number, characteristics of withdrawals (i.e., dropouts, lost to follow up, attrition rate) and/or response rate (cross-sectional studies) described for each group? (Follow up goal for a strong study is 80%.) N/A
  4.3. Were all enrolled subjects/patients (in the original sample) accounted for? N/A
  4.4. Were reasons for withdrawals similar across groups? N/A
  4.5. If diagnostic test, was decision to perform reference test not dependent on results of test under study? Yes
5. Was blinding used to prevent introduction of bias? No
  5.1. In intervention study, were subjects, clinicians/practitioners, and investigators blinded to treatment group, as appropriate? N/A
  5.2. Were data collectors blinded for outcomes assessment? (If outcome is measured using an objective test, such as a lab value, this criterion is assumed to be met.) N/A
  5.3. In cohort study or cross-sectional study, were measurements of outcomes and risk factors blinded? N/A
  5.4. In case control study, was case definition explicit and case ascertainment not influenced by exposure status? N/A
  5.5. In diagnostic study, were test results blinded to patient history and other test results? No
6. Were intervention/therapeutic regimens/exposure factor or procedure and any comparison(s) described in detail? Were interveningfactors described? Yes
  6.1. In RCT or other intervention trial, were protocols described for all regimens studied? N/A
  6.2. In observational study, were interventions, study settings, and clinicians/provider described? N/A
  6.3. Was the intensity and duration of the intervention or exposure factor sufficient to produce a meaningful effect? Yes
  6.4. Was the amount of exposure and, if relevant, subject/patient compliance measured? N/A
  6.5. Were co-interventions (e.g., ancillary treatments, other therapies) described? N/A
  6.6. Were extra or unplanned treatments described? N/A
  6.7. Was the information for 6.4, 6.5, and 6.6 assessed the same way for all groups? N/A
  6.8. In diagnostic study, were details of test administration and replication sufficient? Yes
7. Were outcomes clearly defined and the measurements valid and reliable? Yes
  7.1. Were primary and secondary endpoints described and relevant to the question? Yes
  7.2. Were nutrition measures appropriate to question and outcomes of concern? Yes
  7.3. Was the period of follow-up long enough for important outcome(s) to occur? Yes
  7.4. Were the observations and measurements based on standard, valid, and reliable data collection instruments/tests/procedures? Yes
  7.5. Was the measurement of effect at an appropriate level of precision? Yes
  7.6. Were other factors accounted for (measured) that could affect outcomes? Yes
  7.7. Were the measurements conducted consistently across groups? Yes
8. Was the statistical analysis appropriate for the study design and type of outcome indicators? Yes
  8.1. Were statistical analyses adequately described and the results reported appropriately? Yes
  8.2. Were correct statistical tests used and assumptions of test not violated? Yes
  8.3. Were statistics reported with levels of significance and/or confidence intervals? Yes
  8.4. Was "intent to treat" analysis of outcomes done (and as appropriate, was there an analysis of outcomes for those maximally exposed or a dose-response analysis)? N/A
  8.5. Were adequate adjustments made for effects of confounding factors that might have affected the outcomes (e.g., multivariate analyses)? N/A
  8.6. Was clinical significance as well as statistical significance reported? Yes
  8.7. If negative findings, was a power calculation reported to address type 2 error? N/A
9. Are conclusions supported by results with biases and limitations taken into consideration? Yes
  9.1. Is there a discussion of findings? Yes
  9.2. Are biases and study limitations identified and discussed? Yes
10. Is bias due to study's funding or sponsorship unlikely? Yes
  10.1. Were sources of funding and investigators' affiliations described? Yes
  10.2. Was the study free from apparent conflict of interest? Yes