EAL

HYD: Effect of Caffeinated Beverages on Fluids (2007)

Citation:

Study Design:

Class:

- Click here for explanation of classification scheme.

Quality Rating:

Research Purpose:

To assess hydration status of trained athletes using a caffeinated beverage for rehydration during two-a-day practices across a three-day period in warm conditions.

Inclusion Criteria:

Male or female
Moderate to high fitness level
Heat acclimatized

Exclusion Criteria:

Chronic health problems
Cardiovascular complications
Pregnant or nursing
History of exertional heat illness

Description of Study Protocol:

In two double-blind, randomized, cross-over design trials, subjects completed three successive days of two-a-day practices (two hours per practice, four hours per day) in mild heat (WBGT=23C). During practices, all subjects rehydrated with water. During all other times, they rehydrated with the designated trial beverages:

Caffeine trial (CAF) rehydrated with Coca-Cola
Caffeine-free trial (CF) rehydrated with Caffeine-Free Coca-Cola.

Other than in the trial beverage, caffeine was prohibited for four days before and during each trial. Water and other beverages were consumed ad libitum for both trials.

Subjects also abstained from high water-content foods such as soup and watermelon during the trial.

Data Collection Summary:

Timing of Measurements

Trials were separated by four days. Other timing noted below.

Dependent Variables

Laboratory Data Collection: The following urine and blood indices (5ml sample) were collected on Days 1 and 4 in a laboratory setting.

Urine specific gravity: Measured by refractometry (Model A300CL, Spartan)
Urine color: Assessed using Armstrong Color Chart
Hematocrit: measured in triplicate by microcapillary technique
Hemoglobin: Measured in triplicate by cyanmethemoglobin technique (Kit 525, Sigma-Aldrich Co.) and spectrophotometer (Bausch % Lomb Spectronic 88)
Plasma volume: Changes calculated using Dill and Costill equation
Plasma and urine osmolality: Measured in duplicate using freezing point depression (Model 3DII, Advanced Instruments Inc.)
Thirst sensation: Recorded on a nine-point scale ranging from 1 (not thirsty) to 9 (very thirsty)

Field Data Collection

Urine and psychological measures were determined in a field setting before and after each two-hour practice.

Control Variables

Caffeine trial (CAF): Subjects rehydrated with Coca-Cola; a 12-oz. can of contains 35mg caffeine
Caffeine-free trial (CF): Subjects rehydrated with Caffeine-Free Coca-Cola

Description of Actual Data Sample:

Initial N: Not described
Attrition (Final N): Ten (seven women, three men)
Age: 24±1 year
Ethnicity: Not described
Other relevant demographics
- Partially heat- acclimated athletes
- Prior to the study, subjects' average caffeine intake was 57.5±51.3mg caffeine per day
Anthropometrics
- Weight 68.4±4.0kg
- Height 170±3cm
- Body fat 19.2±2% (Jackson/Pollock skinfold method)
Location: University of Connecticut, Storrs, CT.

Summary of Results:

During the Caffeine trial (CAF), subjects consumed an average of 741±171mg caffeine (244±78 mg per day), ~21 12-oz cans during the three-day trial period (~7 cans per day).

A significant difference was found for urine color for the post-AM time point, F=5.526, P=0.031. No differences were found among other variables (P>0.05).

Author Conclusion:

This study found no difference in hydration status (or “potential diuresis of caffeine”) for caffeine and placebo groups. However, the hydration status of both groups were compromised for both trials.

The study results suggest that the use of beverages containing caffeine during non-exercise periods do not hinder rehydration.

Funding Source:

University/Hospital:

University of Connecticut

Reviewer Comments:

Authors' affiliations were identified, but the source of funding was not.

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?	Yes
	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?		No
	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%.)	No
	4.3.	Were all enrolled subjects/patients (in the original sample) accounted for?	???
	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?		Yes
	5.1.	In intervention study, were subjects, clinicians/practitioners, and investigators blinded to treatment group, as appropriate?	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
	5.4.	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?	N/A
	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)?	Yes
	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