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Hydration

HYD: Assessing Hydration Status (2007)

Citation:

Armstrong LE, Soto JAH, Hacker FT, Casa DJ, Kavouras SA, Maresh CM. Urinary indices during dehydration, exercise, and rehydration. International Journal of Sport Nutrition 1998; 8: 345-355.

 

 
Study Design:
Observational
Class:
C - Click here for explanation of classification scheme.
Quality Rating:
Positive POSITIVE: See Quality Criteria Checklist below.
Research Purpose:

To evaluate the validity and sensitivity of Urine color, Urine specific gravity, and Urinary osmolarity as indices of hydration status during 1) marked dehydration (-4% of body mass), 2) a strenuous exercise trial in a hot environment, and 3) a 21-hr period of oral rehydration. 

 

Inclusion Criteria:
Informed consent; no previous heat illnesses, impaired thermoregulation, drug/alcohol abuse, CV, respiratory, metabolic, renal, or endocrine disorders. 
Exclusion Criteria:
not mentioned
Description of Study Protocol:

Recruitment:  not mentioned

Design: Each subject completed 1-42-hr period of observations: Normal hydration (baseline, B):  24-h prior to dehydration (D), consume water/other fluids to ensure proper hydration.  Limit workouts to low-mod intensity during 48-h prior to testing;  hydration measured: Usg, body mass, Posm.

Exercise-induced dehydration (D): Day1: 2-hr mod-intensity cycling, wearing multiple layers of clothing and restricted fluid intake for 21±2 hr to decrease body mass by 4%. 

Strenuous exercise bout in hot environment (E):On day 2, subjects exercised in environmental chamber 36±0.2 C, performed cycling exercise bout to volitional fatigue, no fluids consumed.  Immediately following exercise bout (17.9±7.9 min), body fluid samples collected (Pna, Usg, Ptp, Ucol).

Rehydration period (4H and 21H):  After samples collected, subjects resumed normal fluid and food consumption to begind rehydration phase; body mass, body fluids measured at 4 and 21 hr post-exercise. 

Blinding used (if applicable) - not mentioned 

Intervention (if applicable) - N/a 

Statistical Analysis: outcome variables evaluated for sig across time (Phase B-Phase 21H) via one-way ANOVA w/repeated measures.  Sig level p=0.05; Newman-Keuls post hoc test used to determine specific differences among sample means w/sig F-ratio; Pearson product moment correlation coefficients for selected var across time; r converted into z-scores, which were transformed into value representing mean correlation coefficient for all time points.   

Data Collection Summary:

Timing of Measurements

 

Dependent Variables

  • Body mass - platform scale
  • Body mass change from Phase to phase of the protocol
  • Urine vol - durations (hr) of vol collections were B, 17; E, 0.6; 4H, 4; 21H, 21.
  • Ucol - urine color scale (developed by research team)
  • Pna - ion-specific electrodes
  • Uosm & Posm - freezing point depression technique
  • Usg & Ptp - optical refractometer

Independent Variables

 

Control Variables

 Temperatures/room conditions during each phase of study

Description of Actual Data Sample:

 

Initial N: 9 highly-trained males

Attrition (final N):

Age: 23±3 yoa

Ethnicity: not mentioned

Other relevant demographics: n/a

Anthropometrics:

180± 4cm; 69.8 ±3.0 kg;

13.9± 2.1%BF;

60.3± 3.9 ml/kg/min VO2 Peak

Location: Laboratory (CT, USA)

 

Summary of Results:

 

Variables

Protocol Phase B

Protocol Phase D

Protocol Phase E

 

Protocol Phase 4H Protocol Phase 21H Correlation coefficients across all time points

Statistical Significance of Group Difference

Body mass (kg)

70.77±3.89b

68.13±3.78b

67.09±3.68b 69.87±3.79c 70.17±3.76c  

b:p<0.05-0.001

c:p<0.05-0.005

Body mass change (%)

 0±0b

 -3.7±0.9b

-5.2±1.3b -1.3±0.9c -0.8±1.64c  

 

Urine Vol (L)

 0.87±1.1

 not meas

0.11±0.06 0.38±0.35 1.64±0.84b  

 

Ucol & Usg           0.68  
Ucol & osm           0.72  
Usg & Uosm           0.98 p<0.001
Single vs composite measurements              
Ucol           0.81 p<0.001
Usg           0.64 p<0.001
Uosm           not measured  

 

Other Findings

Mean volume of fluid intake during rehydration phases 4H and 21H was 5.56L, which closely approximated the sum of the mean maximal body weight loss (Phase E, 3.68 kg).  plus the total 21-hr urine vol during rehydration (2.02L).  Thus, after Phase E, ad libitum drinking resulted in nearly complete restoration of body mass at 21H. 

Greatest variance in Ucol, Usg, and Uosm occurred during rehydration phases 4H and 21H. 

Author Conclusion:

1) Ucol may be used as index of hydration durin daily exercise - tracks body water changes as well or better than Uosm, Usg, Posm, Ptp. 

2)Exercise, large gains or losses of body water and intake of variety of rehydration fluids do not alter the validity of Ucol, Usg, Uosm as indices of hydration status. 

3) Uosm and Usg may be used interchangably  in lab studies to assess hydration status during dynamic periods of water turnover.

Funding Source:
Industry:
General Nutrition Inc.
Food Company:
University/Hospital: University of Connecticut
Reviewer Comments:
Ucol is a useful index of hydration status during various periods of and situations in which hydration should be assessed. 
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) Yes
  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) Yes
  2. Did the authors study an outcome (dependent variable) or topic that the patients/clients/population group would care about? Yes
  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
  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
  4. Is the intervention or procedure feasible? (NA for some epidemiological studies) Yes
 
Validity Questions
  1. Was the research question clearly stated? Yes
1. Was the research question clearly stated? Yes
  1.1. Was (were) the specific intervention(s) or procedure(s) [independent variable(s)] identified? Yes
  1.1. 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
  1.2. Was (were) the outcome(s) [dependent variable(s)] clearly indicated? Yes
  1.3. Were the target population and setting specified? Yes
  1.3. Were the target population and setting specified? Yes
  2. Was the selection of study subjects/patients free from bias? 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
  2.1. 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? Yes
  2.2. Were criteria applied equally to all study groups? Yes
  2.3. Were health, demographics, and other characteristics of subjects described? Yes
  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? No
  2.4. Were the subjects/patients a representative sample of the relevant population? No
  3. Were study groups comparable? N/A
3. Were study groups comparable? N/A
  3.1. Was the method of assigning subjects/patients to groups described and unbiased? (Method of randomization identified if RCT) N/A
  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
  3.2. 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.) ???
  3.3. Were concurrent controls or comparisons used? (Concurrent preferred over historical control or comparison groups.) ???
  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
  3.4. 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
  3.5. 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
  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? N/A
4. Was method of handling withdrawals described? N/A
  4.1. Were follow-up methods described and the same for all groups? N/A
  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
  4.2. 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? Yes
  4.3. Were all enrolled subjects/patients (in the original sample) accounted for? Yes
  4.4. Were reasons for withdrawals similar across groups? 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
  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? ???
5. Was blinding used to prevent introduction of bias? ???
  5.1. In intervention study, were subjects, clinicians/practitioners, and investigators blinded to treatment group, as appropriate? N/A
  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.) Yes
  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.) Yes
  5.3. In cohort study or cross-sectional study, were measurements of outcomes and risk factors blinded? 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
  5.4. 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? ???
  5.5. In diagnostic study, were test results blinded to patient history and other test results? ???
  6. Were intervention/therapeutic regimens/exposure factor or procedure and any comparison(s) described in detail? Were interveningfactors described? N/A
6. Were intervention/therapeutic regimens/exposure factor or procedure and any comparison(s) described in detail? Were interveningfactors described? N/A
  6.1. In RCT or other intervention trial, were protocols described for all regimens studied? N/A
  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? Yes
  6.2. In observational study, were interventions, study settings, and clinicians/provider described? Yes
  6.3. Was the intensity and duration of the intervention or exposure factor sufficient to produce a meaningful effect? Yes
  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? ???
  6.4. Was the amount of exposure and, if relevant, subject/patient compliance measured? ???
  6.5. Were co-interventions (e.g., ancillary treatments, other therapies) described? 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
  6.6. 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
  6.7. 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
  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. 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
  7.1. 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
  7.2. 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
  7.3. 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
  7.4. 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? ???
  7.5. Was the measurement of effect at an appropriate level of precision? ???
  7.6. Were other factors accounted for (measured) that could affect outcomes? No
  7.6. Were other factors accounted for (measured) that could affect outcomes? No
  7.7. Were the measurements conducted consistently across groups? 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. 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
  8.1. 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
  8.2. 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
  8.3. 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
  8.4. 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)? No
  8.5. Were adequate adjustments made for effects of confounding factors that might have affected the outcomes (e.g., multivariate analyses)? No
  8.6. Was clinical significance as well as statistical significance reported? ???
  8.6. Was clinical significance as well as statistical significance reported? ???
  8.7. If negative findings, was a power calculation reported to address type 2 error? N/A
  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. Are conclusions supported by results with biases and limitations taken into consideration? Yes
  9.1. Is there a discussion of findings? Yes
  9.1. Is there a discussion of findings? Yes
  9.2. Are biases and study limitations identified and discussed? 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. Is bias due to study's funding or sponsorship unlikely? Yes
  10.1. Were sources of funding and investigators' affiliations described? Yes
  10.1. Were sources of funding and investigators' affiliations described? Yes
  10.2. Was the study free from apparent conflict of interest? Yes
  10.2. Was the study free from apparent conflict of interest? Yes