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 the effects of controlled chronic and acute caffeine ingestion on fluid-electrolyte, physiological and thermoregulatory responses during an exercise heat tolerance test (EHT).

Inclusion Criteria:

Male
Healthy
Not taking medications that affect caffeine metabolism or the physiological variable measured.

Exclusion Criteria:

Varsity athlete status
Participation in prolonged or intense exercise
Excercise less that twice per week
History of heat illness
Consumes over 600mg caffeine per day
Consumes no caffeine (caffeine naïve)
Cardiovascular, metabolic or respiratory disease.

Description of Study Protocol:

Recruitment

Subjects were volunteers
No further description.

Design

Subjects were stratified and matched by age, body weight and body composition, into three groups. The study began with a six-day equilibrium period, during which all subjects consumed three mg caffeine per kg body weight per day.
On Days Seven through 12, subjects were randomized into one of three treatment levels of caffeine
On Day 12, subjects participated in an exercise-heat tolerance test (EHT), which consisted of 90 minutes walking, 1.56m x s(-1), 5% grade; dry bulb temperature, 37.7±0.1 degrees C; relative humidity, 56.3±1.5%.

Blinding Used

Caffeine treatment was blinded from investigators and subjects.

Statistical Analysis

Used commercial software, SPSS Base 10.0 Software, SPSS Inc.
Anthropometric characteristics and caffeine consumption prior to the study were analyzed by analysis of variance (ANOVA)
Dietary components analyzed using a 3x11 (group x day) repeated-measures ANOVA
Post-hoc paired sample T-tests were applied where appropriate and evaluated with Bonferroni adjustment
Significance was set at P<0.05.

Data Collection Summary:

Timing of Measurements

Days One to Six: All subjects consumed caffeine at three mg per kg per day
Days Seven to 12: Subjects consumed a treatment
- G0: Zero mg caffeine (placebo)
- G3: Three mg caffeine per kg body weight per day
- G6: Six mg caffeine per kg body weight per day.
Day 12: Thirty minutes after consuming the 12- to 14-hour caffeine ingestion, subjects donned exercise clothing, inserted rectal thermometer to 10cm and provided a urine sample. Then they entered the environmental chamber where weight, skin and rectal temperatures were recorded. Subjects exercised 90 minutes, to exhaustion or when rectal temperature reached 39.5 degrees C.

Dependent Variables

Blood analyses

Hematocrit: Measured in triplicate, following microcentriguation
Hemoglobin: Determined spectrophotometrically, using cyanmethemoglobin technique (Spectronic 410, Spectronic Instruments)
Percentage change in plasma volume: Calculated using Dill and Costill method
Total plasma protein: Measured in duplicate with a hand-held refractometer (model A300CL, Atago Co.).

Urine analyses

Urine color: Used hand-held refractometer (Model A 300CL, Atago Co.)
Specific gravity: Used hand-held refractometer (Model A 300CL, Atago Co.)
Osmolality (mOsm per kg): Measured with freezing point-depression osmometer (Model 3DII, Advanced Digimatic)
Sodium and Potassium (total daily electrolyte loss): Analyzed using ion-sensitive electrodes (model 4003, alectrolyte analyzer, Medica Corp.).

Other variables

Heart rate: Used monitor transmitter on chest (Polar Electro, Kempele, Finland)
Body weight: Measured on platform scale (±100g) (Model DS44L, Ohaus Co.)
Skin and rectal temperatures: Digital monitors
Perceived exertion: Used visual scale to rate; values recorded every 15 minutes during exercise
Sweat rate: Calculated from pre- and post-exercise weights x 60 minutes of exercise time.

Independent Variables

Caffeine treatment described above.

Control Variables

Serum caffeine levels verified on Days Six, 11 and 12: Analyzed using high-performance liquid chromatography at the Pennington Biomedical Research Center, Baton Rouge, LA
Exercise-heat tolerance test (EHT): Consisted of approximately 90 minutes walking on a motorized treadmill, 1.56 meters per step, 5% grade; dry bulb temperature, 37.7±0.1 degree C; relative humidity, 56.3±1.5%
VO₂: Measured online between Minutes 15 and 30 to verify moderate intensity state. (Medical Graphics Corp)
Diet: Analyzed using Nutritionist Pro Software (Version 1.2, N-Squared Computing).

Description of Actual Data Sample:

Initial N: 60 males
Final N: 59 males, one withdrew for personal reasons
Age: 21.6±0.4 year

Ethnicity: Not described

Other relevant demographics

Weekly activity score (WAS): 15.7±3.2
Pre-investigation coffee intakes: 98±17mg per day (equated to 1.3mg per kg per day)

Anthropometrics

Height: 177.9±0.8cm
Weight: 75.4±1.0kg
Body fat: 11.1±0.7%

Location: Human Performance Lab, Department of Kinesiology, University of Connecticut, Storrs, CT.

Summary of Results:

Serum caffeine level on Days Six, 11 and 12, indicated that all subjects were in compliance
Exercise-heat tolerance time was significantly greater in treatment G3 (three mg caffeine per kg) 86±2.0 minutes, as compared to G0 (no caffeine) 75±3.3 minutes (P<0.05)
There were no significant between-group differences in pre- and post-EHT for plasma, urinary, thermoregulatory, cardiovascular or perceptual variables across time (P<0.05). Although, as expected, some of these variables increased significantly over time (P<0.05). [See bar charts in paper.]
Body weight loss, corrected for urinary losses, was not significantly different among groups:

G0: 1.4±0.09kg
G3: 1.4±0.09kg
G6: -1.2±0.09kg.

Dietary consumption: Mean ad libitum values (Days One to 11), no significant differences throughout duration of study.

Energy intake: 2,782±90Kcal
Carbohydrate: 52±1% of total Kcal
Fat: 31±1% of total Kcal
Protein: 18±1% of total Kcal
Sodium: 205±7mEq
Potassium intake: 76±3mEq.

Author Conclusion:

This investigation found no significant differences in fluid-electrolyte, exercise endurance or thermoregulatory responses among the three treatment groups
The results demonstrated no evidence of hypohydration or impaired thermoregulation during an exercise-heat tolerance test after six days of chronic caffeine consumption (three mg and six mg per kg per day)
Both caffeine groups were able to exercise longer than the no-caffeine group, but only the G3 group (three mg per kg) was significant
Caffeine appears to be a safe strategy for enhancing physical or cognitive performance.

Funding Source:

Not-for-profit

Foundation associated with industry:

Reviewer Comments:

This study appeared to be an extension of the Armstrong, 2005, study, which examined three caffeine treatments over a 12-day period
The treatments in this study occured on Day 12 following completion of the Armstrong study.

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?	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)	Yes
	3.2.	Were distribution of disease status, prognostic factors, and other factors (e.g., demographics) similar across study groups at baseline?	Yes
	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?		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%.)	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
	4.5.	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?	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)?	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?	Yes
9.	Are conclusions supported by results with biases and limitations taken into consideration?		Yes
	9.1.	Is there a discussion of findings?	Yes
	9.2.	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