HYD: Effect of Caffeinated Beverages on Fluids (2007)

Citation:
 
Study Design:
Class:
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Quality Rating:
Research Purpose:
To assess the effectiveness of two common rehydration beverages, a caffeinated diet cola and a 6% carbohydrate-electrolyte solution, compared with water for whole body rehydration, gastric emptying and blood volume restoration during a two-hour rehydration period following exercise-induced dehydration.
Inclusion Criteria:
  • College students
  • Exercised routinely
Exclusion Criteria:
None noted.
Description of Study Protocol:

Recruitment

Not described.

Design

  • First Study: Following exercise-induced dehydration, subjects sat for two hours in a thermoneutral environment while rehydrating with one of four treatments: water (W), caffeinated diet cola (DC), carbohydrate-electrolyte solution (CE) or no fluid.  Each of the four trials was separated by one week. It appears that all of the subjects received the same treatment on the same day. The authors do not mention treatment randomization or sequence.  
  • Second Study: Mirrored the first study, but included only two treatments, carbohydrate-electrolyte solution (CE) and water (W).

Blinding used (if applicable)

None noted.

Treatment

  • DC: A caffeinated diet cola (Diet Coke, Coca Cola Co.); 128mg caffeine per liter, weight 1ml=0.987g
  • CE: A 6% carbohydrate-electrolyte solution (Gatorade, Quaker Oats Co.); weight 1ml=1.024g.
  • W: Regular tap water; weight 1ml=1.000g

All beverages were eight to 10 degrees C.

Statistical Analysis

  • Two-way ANOVA with repeated measures (treatment by time), used to compare the treatments
  • Tukey's post-hoc analysis of blood volume and osmolality was used to compare the rehydration treatments with the "no-fluid" treatment
  • Significance was set at P<0.05.
Data Collection Summary:

Timing of Measurements

  • Prior to reporting to the lab, subjects consumed a standardized breakfast (two to three hours prior) and 500ml water (90 minutes prior)
  • Upon reporting, subjects voided their bladder and sat quietly for 30 minutes. Then a blood sample and nude body weight were obtained (euhydrated state).
  • For both studies and all four treatments, subjects exercised at 60-80% VO2max (140-160 beats/min) in a heated environmental chamber (32 degrees C, 40% relative humidity) until they lost ~2.5% (1.95±0.12 kg) of their body weight (BW); ~80-100 minutes of running or cycling were required to reach the 2.5% dehyration level.
  • First Study (N=10)
    • After the exercise/dehydration period, subjects' sweat was collected using the washdown technique described by Costill et al.
    • Then subjects sat in a thermoneutral environment (21 degrees C; 60% relative humidity)
    • After 30 minutes of sitting (45 minutes post exercise), a blood sample was obtained (dehydrated state)
    • At this point, the two-hour rehydration period began with one of four treatments. For the three fluid treatments, the volume of DC, W or CE was equal to the amount of fluid lost (difference between euhydrated and dehydrated body weight).
    • Fluids were consumed in two boluses, at 0 and 45 minutes into the period; bolus 1=53% of fluid loss and averaged 1,046±198ml, bolus 2=47% of fluid loss and averaged 912±186ml.
    • Each bolus was consumed in ~300ml increments over a five- to eight-minute period.  The average DC bolus consumption took ~two minutes longer because of the carbonation.
    • The procedures for the no-fluid treatment mirrored the other treatments without the fluid consumption
    • At the end of the two-hour period, nude body weight and urine output were obtained
    • Gastric volume was determined using epigastric impedance at the beginning of the two-hour rehydration and again at 15, 30, 45, 60, 70 and 120 minutes
    • Additionally, during the rehydration period, at five, 40, 50, 80 and 115 minutes, subjects completed a questionnaire (1-5 scale) regarding their sensations of taste, stomach fullness and pressure.
  • Second Study (N=9, data from first and second studies were combined for a total N=19)
    • This study mirrored the first study, but compared only two treatments, carbohydrate-electrolyte solution and water.

Dependent Variables

  • Percent rehydration: The percentage body weight loss that was regained was used as an index of whole body rehydration.  Calculated as: percentage rehydration=body weight lost during exercise minus (euhydrated body weight-rehydrated body weight in kg)x100 per fluid intake (kg). 
  • Gastric volume: Determined using epigastric impedance as described by McClelland and Sutton, 1985.  Measurements were made while subjects were seated in a vertical position with legs extended horizontally.
  • Urine volume during rehydration: Collection method not described
  • Urine sodium, potassium and chloride losses in urine formed during rehydration period: Method not described
  • Percentage change in blood volume: Calculated from hemoglobin concentration changes determined from blood samples obtained pre- and post-treatment at 0, 45, 60, 90, 120 minutes. Cyanmethemoglobin technique determined in triplicate after microcentrifugation.
  • Serum osmolality, sodium, potassium and chloride: Blood samples were centrifuged, separated, serum removed, frozen and later analyzed for osmolality using freezing point method (Advance Micro-osmometer, 3MO) and electrolyte concentrations (Nova 5)
  • Feelings of stomach fullness, gas and pressure: Questionnaire described above.

Control Variables

  • Sweat and urine sodium, potassium and chloride losses during exercise: Measure of internal validation across the trail periods

 Independent Variables

  • Loss of body weight by dehydration: Excercise to reduce weight via sweat loss equalling 2.5% initial weight
  • Fluid intake: Treatments described above

 

Description of Actual Data Sample:
  • Initial and final N: 19 subjects (16 male, three female) 
    • Ten subjects participated in the first study, which compared DC, W, CE and no fluid replacement 
    • An additional group of nine subjects was tested to further examine the comparison between DE and W
  • Age: 22.8±2.8 years
  • Ethnicity: Not described
  • Anthropometrics
    • Body weight: 73.9±12.8kg
    • VO2 Max: 4.2±0.6l per minute
  • Location: Univ. of Texas, Austin, TX

Summary of Results:

At the end of the two-hour rehydration period, epigastric impedance indicated that no fluid remained in the stomach during any of the trials. However, in all trials, subjects were somewhat hypohydrated (range 0.62 to 0.94kg BW below euhydrated BW; P<0.05) after the two-hour rehydration period.

First study: average dehydration weight loss and rehydration fluid consumption=1.95±0.12kg (two boluses)

  • Bolus 1=53% of fluid loss and averaged 1,046±198ml
  • Bolus 2=47% of fluid loss and averaged 912±186ml

Note: See Figure 1, pg. 401 for bar chart showing fate of ingested treatment volumes. 

 

Caffeinated Diet Cola

(DC)

Water

(W)

Carbo-Electrolyte

(CE)

p

First Study N=10

Weight loss during rehydration period

230±20 g,

110±20 g,

140±20 g,

<0.05

Percent rehydration - % BW loss that was regained

54±5%

64±5%

69±5%

<0.05

Urine Volume

710±100mL

600±90mL

480±90mL

DC/CE p<0.05

DC/W = Not Sig

Blood Volume

 

-2.6±0.9%

p<0.05

 

-2.1±0.8%

p<0.05

 

0.7±0.9%

NS

No Fluid Tx

-1.8±0.8%

NS

Urine Sodium

60±12mEq

78±15mEq

53±12mEq

NS

Urine Chloride

97±15mEq

119±19mEq

95±16mEq

NS

Urine Potassium

38±8mEq

57±14mEq

41±10mEq

NS

Second Study N=19 (Group of nine pooled with original 10)

Weight loss during rehydration period

n/a

150±2g

150±20g

<0.05

Percent rehydration

n/a

65±3%

73±3%

<0.05

Urine Volume

n/a

500±60mL

340±60ml

<0.05

There was a trend for percentage rehydration from W to be less than CE (P=0.09):

  • Difference in rehydrated body weight between treatments:
    • Between DC and CE: 328±73g (N=10; P<0.05)
    • Between DC and W: 226±79g (N=10; P<0.05)
    • Between CE and W: 156±39g (N=19; P<0.05)
  • Gastric volume from subset (N=6)
    • After the first bolus, at rehydration+15 minutes, the volume of W was significantly less than DC; 41±2% vs. 54±4%, respectively (P<0.05); no statistical differences were observed at 45 minutes.
    • After the second bolus, at rehydration+70 min, the volume of W was significantly less than both DC and CE (no values given).  However, in all trials, epigastric impedance values had returned to baseline at rehydration+120 minutes.
  • Serum osmolality: There were no significant differences between pre- and post-trial serum osmolalities for any of the trials. However during the second hour of rehydration, CD levels were significantly higher than DC and W.
  • Serum sodium, potassium, chloride: There were no significant differences observed among the three rehydration beverages.  Two serum concentrations increased significantly (P<0.05) sodium increased ~3mEq per liter and chloride increased ~6mOsm per kg.
  • Urine Electrolytes: There was a trend for the total electrolyte losses to be greater during W than DC and CE.
  • Stomach fullness and the sensation of gas or pressure was greater with DC compared with CE and W.

Second study: Average dehydration weight loss and rehydration fluid consumption=1.95±0.12kg

  • Serum osmolality: From rehydration +60 to +120 minutes, CE levels remained significantly higher compared with W (P<0.05).

 

Author Conclusion:
  • Caffeinated diet cola was less effective than water or a carbohydrate-electrolyte beverage for whole body rehydration during a two-hour period after exercise.
  • The 6% carbohydrate-electrolyte solution was a more effective rehydrator that plain water. This was largely due to less urine formation and greater blood volume restoration, probably as a result of its salt and sugar content, which elevated serum osmolality.
  • Differences in whole body rehydration and blood volume restoration were not due to differing amounts of gastric emptying.
Funding Source:
University/Hospital: University of Texas at Austin
Reviewer Comments:

While the subjects' body weights were measured each week prior to initiation of treatment, the paper did not mention analyzing the weights for change or stability over the four-week study period.  Since the percentage dehydration and the volume of rehydration for each treatment was based on body weight, an increasing or decreasing trend over the span of the study would have influenced these values.

Question:  Would treatment randomization improve the study's validity regarding this issue? Or with N=10, would randomizing treatment days introduce another form of bias?

Question:  Rehydration beverages were administered on a weight rather than volume basis. Although not reported, this would have equated to a relative difference in total fluid volume administered between the treatments.

The study may have benefited from the addition of two common beverages: caffeinated regular cola (osmolality more similar to Gatorade) and unsweetened cool tea or coffee (uncarbonated).

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
  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? Yes
  2.3. Were health, demographics, and other characteristics of subjects described? No
  2.4. Were the subjects/patients a representative sample of the relevant population? ???
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) Yes
  3.2. Were distribution of disease status, prognostic factors, and other factors (e.g., demographics) similar across study groups at baseline? ???
  3.3. Were concurrent controls or comparisons used? (Concurrent preferred over historical control or comparison groups.) Yes
  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")? 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
  4.2. 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
  4.4. 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? N/A
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? No
  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.) No
  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? N/A
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? Yes
  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? Yes
  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? Yes
  6.8. In diagnostic study, were details of test administration and replication sufficient? N/A
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? ???
  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? No
  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? ???
  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)? ???
  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? No
  10.2. Was the study free from apparent conflict of interest? Yes