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 examine the effect of heat-induced dehydration (2.9% weight loss as lean body mass) on peak urinary caffeine concentration, following the consumption of a very strong soluble coffee (five mg caffeine per kg)
The study also evaluated sweat as a quantitative route for the non-metabolic clearance of caffeine.

Inclusion Criteria:

Males
Healthy
Non-smokers
Experienced sauna users.

Exclusion Criteria:

Use caffeine-containing medication
Biliary lithiasis
Liver disease
Hyper- or hypotension.

Description of Study Protocol:

Recruitment

Not described.

Design

30 hours before the trial, subjects followed their habitual diet, but abstained from caffeine-containing products
On the morning of each trial, subjects consumed a normal breakfast prior to reporting (breakfast was replicated on the second trial day)
Baseline urine and saliva samples were taken to confirm compliance with caffeine abstinence
During two trials, subjects drank 300ml hot coffee containing 6.4±0.0mg caffeine per kg lean mass (calculated to provide a group average of 4.9±0.1mg caffeine per kg total body weight, which equated to roughly three to four European cups of coffee drunk in succession). After drinking the coffee, subjects rinsed their mouth in preparation for later saliva sampling.

Dehydration Trial (DEH)

Subjects were dehydrated (target, 3% loss of lean body mass) through intermittent sauna exposure (temperature, 80-90°C, 20% to 30%) for 2.5 hours.

No drinking was allowed between coffee and lunch, when 600ml of fluid was ingested (300ml water and 300ml orange juice)
Subjects showered with soap prior to entering sauna
Body weight was recorded at the start and after every bout of approximately 12 minutes in the sauna
Heat exposure ended when target loss was achieved or at 2.5 hours, whichever came first.

Euhydration Trial (EUH)

Subjects remained clothed and quiet at neutral temperature (approximately 20°C) for 2.5 hours. Subjects drank 300ml water at 1.5 hours to ensure euhydration and 300ml orange juice at lunch.

In Both Treatments

Fluid volume consumed between -0.5 and 4.0 hours was 900ml
From lunch onwards, caffeine-free foods and drinks were allowed ad libitum (not recorded)
Subjects abstained from non-sedentary activities and continued to collect their total urine production until the next morning, when they returned the last voids to complete the 24-hour collection
The order of the trials was random, with four to six subjects testing simultaneously.

Statistical Analysis

C_max of urinary caffeine was assessed with Wilcoxin’s signed ranked test
Lognormal distribution modeling was used to evaluate the probability of one dehydrated subject having a C_max of 12µL per ml with the given coffee dose
The trapezoidal rule from the area under the concentration curve was used to calculate urinary caffeine recovery. Total caffeine was obtained from the sum of urine and sweat losses.
Paired T-test was used to evaluate treatment effects at different time points
Linear correlation coefficients were calculated between C_max and weight loss or urine flow
Significance was set at P<0.05.

Data Collection Summary:

Timing of Measurements

Following ingestion of coffee, subjects were intermittently exposed to heat in a sauna until they had lost 2.9% of lean mass
On a separate occasion, they consumed the same amount of coffee, but remained quiet and euhydrated (control).

Dependent Variables

Caffeine and its primary metabolites, paraxanthine, theobromine and theophylline, were measured using high-performance liquid chromatography from the following sample sources. Extraction was completed in duplicate and repeated if the difference exceeded 5%. Analytical precision was 0.18µL per ml. See paper for detailed caffeine extraction and analytical methods.
Urine: Pooled at study times 2.5 hours (end of sauna or control), 3.5, 4.5, 7.5 and 24 hours following coffee ingestion. Other measured urine indices were: Creatinine (Boehringer 124192, automated method), pH and density (optical refractometry).
Saliva: Sampled at 1.0, 2.5, 3.5 and 4.5 hours. A sterile cotton cylinder was placed in the mouth for two minutes without chewing to collect unstimulated saliva. Sample was put into a tube and frozen.
Sweat: Collected from the DEH subjects’ backs at 1.0 and 2.5 hours during heat exposure. Collection process was gently rolling a cotton cylinder on the skin using powder-free latex gloves. Samples were frozen.
Weight loss: Calculated from pre- and post-weights.

Independent Variables

Coffee: 300ml, provided 6.4±0.0mg caffeine per kg lean mass
Lean mass (body mass – fat mass): Used to calculate the target weight loss for the dehydration trial and to standardize the individual dose of coffee.
Coffee: 300ml, provided 6.4±0.0mg caffeine per kg lean mass
Heat exposure: Described above.

Description of Actual Data Sample:

Initial and final N: 10 males, no attrition noted
Age: 34±2 years
Ethnicity: Not described.

Other Relevant Demographics

Usual coffee consumption

None: One subject
Two to six cups per day: Eight subjects
15 cups per day: One subject.

Anthropometrics

Body mass: 74.4±2.5kg
Body fat: 24±2%, estimated from skinfold thickness

Location

Study location was not described, however the authors were employed at the Nestle Research Center in Lausanne Switzerland.

Summary of Results:

Dehydration

During dehydration treatment, sweat loss amounted to 1.68±0.05kg (2.91±0.25% of lean body mass)
Dehydration treatment reduced urine flow seven-fold (under 30ml per hour). Urine flow returned to normal five hours later.

Urinary Caffeine

Peak urinary caffeine (was 7.6±0.4µg per ml in dehydration and 7.1±0.2µg per ml in the control (P>0.05). The variability was relatively high in the dehydration group, 17% vs. 8% in controls.
At these low excretion rates (under 30ml per hour), caffeine concentration was negatively correlated with flow. This corresponded to an increase in density and acidification (see Figure One in paper).
Compared with the control, dehydration delayed peak urinary caffeine by one hour, maintained higher saliva caffeine concentration (6.1 vs. 5.2mcg per ml, P<0.05) and a lower saliva paraxanthine-caffeine ratio (P<0.001)
The amount of caffeine recovered in 24-hour-urine was reduced (1.2 vs. 2.8% of dose, P<0.001), however at least 2.6% of dose was lost in sweat
Mean caffeine concentration at the 1.0 and 2.5 time points was more than 50% higher in sweat (DEH 9.6±0.7µg per ml, uncorrected for the evaporated water fraction) than in saliva (or urine) over the corresponding period.
The ratio of salivary to sweat caffeine was 0.62±0.04µg per ml.

Mean caffeine concentration in saliva at the 1.0 and 2.5 time points was higher in the dehydrated than in the euhydrated state (5.7±0.3µg per ml vs. 4.8±0.2µg per ml, P<0.01).

[Note: Baseline urinary caffeine was not zero, as three subjects (the same in both treatments) were either less compliant or had slow caffeine metabolism.]

Author Conclusion:

Heat dehydration did not lead to higher caffeine concentration in urine, when compared to normally hydrated controls
Following the consumption of very strong coffee (five mg per kg body weight), peak urinary caffeine (C_max) was 7.6±0.4µg per ml, which is far below the legal International Olympic Committee (IOC) limit of 12µg per ml. Therefore, caffeine should not be considered a doping solution when ingested at normal doses via coffee consumption.
Results suggest that the rise in circulating caffeine, due to delayed metabolic clearance, was partially offset by a sizeable elimination of caffeine in sweat
The 24-hour urine recovery in the dehydrated condition was less than the normally hydrated condition.

Funding Source:

Industry:

Nestle Research Center

Food Company:

Reviewer Comments:

Fluid intake was not the same at certain time points in the two treatments. The authors did state that this asymmetry may have enlarged the difference in urine flow between treatments and increased the difference in C_max.
The authors did discuss reasons for variability in urinary caffeine levels
This was a very small study population. Additional discussion of anthropometrics and demographics may have been useful to the reader.
The study may have benefited from two additional cross-over groups: Caffeine-free dehydrated and caffeine-free euhydrated.

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?	???
	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?	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.)	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?	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