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Hydration

HYD: Effect of Caffeinated Beverages on Fluids (2007)

Citation:
Grandjean AC, Reimers KJ, Bannick KE, Haven MC. The effect of caffeinated, non-caffeinated, caloric and non-caloric beverages on hydration. J Am Coll Nutr. 2000 Oct; 19 (5): 591-600. PubMed ID: 11022872
 
Study Design:
Randomized Crossover Trial
Class:
A - Click here for explanation of classification scheme.
Quality Rating:
Positive POSITIVE: See Quality Criteria Checklist below.
Research Purpose:

To examine the effect of five beverage combinations on hydration status in healthy, free-living adult males.

Inclusion Criteria:
  • Male
  • Normal and stable weight
  • Exercise less than four one-hour sessions per week
  • Not participate in sports on a routine and competitive basis
  • Willing to abstain from alcohol on specified days of the testing period
  • Have a usual, average caffeine consumption between 20mg and 1,000mg per day
  • Have normal gastrointestinal function
  • Consume a diet with no extreme food, beverage or dietary supplement intakes
  • Willing to abstain from supplements during the study
  • Take no medications that might influence weight or fluid and electrolyte balance
  • No chronic illnesses
  • Live and work in an ambient temperature environment with no significant temperature and humidity variation
  • Have a fairly routine schedule day to day, including nocturnal sleep patterns.
Exclusion Criteria:
Individuals not meeting inclusion criteria.
Description of Study Protocol:

Recruitment

Males 19 to 39 years old were recruited through flyers, advertisements and mailings distributed throughout the university medical center campus.

Design

A within-subject design was used to evaluate the effect of five different treatments on the variables of body weight, urine and blood parameters. Holding each subject’s total volume constant, treatments A-D were counterbalanced and randomized. The treatments (Tx) were:

  • Tx A: water only
  • Tx B: equal amounts of water and caffeinated, carbonated cola
  • Tx C: equal amounts of water and caffeinated, carbonated non-caloric cola
  • Tx D: equal amounts of water, caffeinated, carbonated cola, caffeinated, carbonated non-caloric cola and instant coffee 

Tx E was not randomized and was undertaken as an ancillary experiment by a subset of 10 volunteers after successful completion of Tx A-D. 

  • Tx E: half water and half carbonated citrus noncaffeinated soft drink

Blinding Used (if applicable)

Not applicable for participants in this study, although brand of beverages was blinded.

Statistical Analysis 

  • Data were analyzed (SPSS 9.0 for Windows) using nonparametric methods since the data was not normal (tested using Kolmogorov-Smirnov methods)
  • To determine differences between all treatments the Friedman test was used and for selected pairs  of treatments the Wilcoxon Signed Rank test was used. Data was not adjusted for multiple comparisons since no P-values were found to be 0.05.
  • To determine which lab measurements were most predictive of dehydration (as measured by weight loss), stepwise regression was used (entry criteria F0.05 and removal criteria F0.100)
  • The level of significance was selected for this study was 0.05
  • Data are presented as mean ±SD unless otherwise noted.
Data Collection Summary:
Timing of Measurements and Procedures

During the two weeks before treatment commenced, subjects received detailed instruction and training.

Subjects received a portable scale accurate to 0.2% at 100gm (Model SR241, SR Instruments, Inc, Tonawanda, NY) and procedures for collection of twice-daily body weight measurements at home for the duration of their participation in the study (seven to eight weeks).

Subjects also received Home Data Booklets in which to record all daily output information, including urination frequency, stool frequency and type, sweating or vomiting. Any variations from the protocol were also recorded in the booklet. Subjects turned in and received booklets each week.

  • Study treatments were conducted over an eight-week period.
  • Tuesday of each week was a stabilization day, whereby subjects consumed the prescribed study diet
  • On Wednesday, treatment day, subjects collected the first urine void upon waking and reported to the laboratory in a fasted state
  • Upon arrival, subjects turned in first void samples and were interviewed regarding any variations from protocol. Subjects then rotated through stations to be weighed, have blood drawn, receive the day’s beverage allotment and receive urine collection containers for the 24-hour urine collection. Subjects followed their study diet, consumed test beverages and collected all urine for the rest of the day. 
  • Thursday morning, upon rising, subjects voided urine in a separate container from the 24-hour collection container, then returned to the lab. After turning in urine samples, the subjects rotated through stations to collect post treatment data and receive supplies for the following week. 
  • The process was repeated each week for a total of eight weeks.

Dependent Variables

Body weight: Pre- and post-treatment fasted early-morning body weights of each subject were measured by a trained investigator on a digital scale accurate to 0.1% at 100g. 

  • Subjects voided before weighing and wore only shorts that were provided, with the weight of the shorts being subtracted to obtain true body weight
  • Subjects also weighed (in the nude, after voiding) twice each day, upon rising and before retiring. They used a provided portable scale and recorded the weight in the Home Data Booklet.

Urine collection and analysis: For each treatment, each subject collected three urine samples.

  • Pre-Tx was the first voided urine on test day, before treatment began 
  • Post-Tx urine was the first voided urine on Thursday morning 
  • Pre- and post-urine samples were analyzed for chloride, sodium, potassium, creatinine, osmolality and specific gravity 
  • The 24-hour urine was analyzed for chloride, sodium, potassium, creatinine, osmolality, specific gravity and volume 
  • To monitor compliance to Tx A (water), urine caffeine was analyzed using a 5ml aliquot from the 24-hour urine.

Blood Collection and Analysis

Independent Variables

  • Beverage allotment: The mean volume of test beverages consumed was 1,745±408ml (range=1,202 to 2,879ml). Participant’s fluid allotments were calculated as follows: 
    • Total daily fluid requirement was estimated using 35ml per kg body weight per day 
    • Subtracted from this total was water from study diet foods and 300ml for metabolic water 
    • The remainder was determined to be the beverage quantity for each subject.
  • Based on each subject’s calculated fluid requirement, individual beverage allotments were weighed to the nearest gram on a digital bench scale (Model XL 6100, Denver Instruments, Arvada, CO)
  • The amounts to be consumed were marked on sequentially numbered bottles to guide the subject regarding the amount to drink in each time period. Except for Tx D, equal amounts of each beverage were consumed in four-hour periods between 6:00 a.m. and 10:00 p.m.
  • In Tx D, the entire allotment of coffee (one-fourth of the day’s fluid) was consumed at the time of the subject’s usual consumption, which for all subjects was between 6:00 and 10:00 a.m. The other three beverages were consumed in equal volumes in each of the three remaining periods of the day. All beverages were commercially available and represented commonly consumed products.
  • All soft drinks were provided in glass bottles and spring water was provided in plastic bottles. Both were unlabeled (except for a code number) as delivered by a commercial bottler.
  • Instant coffee was purchased by the investigator and was prepared the morning of the study using bottled water and provided in thermoses
  • Diet: Based on subjects’ three-day food records and subject interviews, a registered dietitian developed a personalized one-day menu for each subject
  • Diets were designed to reflect normal eating habits
  • On a self-selection basis, in a free-living environment, subjects followed the diet for two days each week: The pre-treatment day (Tuesday) and the treatment day (Wednesday). The same foods and quantity of fluid were consumed each Tuesday and Wednesday throughout the study period.
  • Beverages consumed Tuesday were assigned based on the subjects’ usual consumption and included juice, soft drinks, milk, coffee and tea.
  • On Wednesday, the assigned beverage treatment replaced the usual beverages
  • Subjects were given printed copies of the daily menus on which they verified consumption and recorded any variations.
Description of Actual Data Sample:
  • Initial N: 18 males; the authors did not state the number of initial recruitment respondants who were subsequently interviewed via phone to determine eligibility
  • Attrition (final N): 18 males
  • Age: 24 to 39 years
  • Ethnicity: Not stated
  • Other relevant demographics: All subjects described as healthy. Most were graduate students in health professions or medical students.
  • Anthropometrics
    • Height (cm) 181.7±8.2; range=162.6–193.0
    • Weight (kg) 80.1±12.2; range=62.7–113.5
    • Percent body fat 16.6±5.1; range=8.5–24.2
    • Body surface area (m2) 2.0±0.2; range=1.8–2.4.
  • Location: University of Nebraska, Omaha, Nebraska.
Summary of Results:

Results were insignificant for all indices in the tables below:

  • Friedman’s test was performed on to detect differences between groups
  • Paired comparisons of Tx A with Tx B, C, D and E were made using Wilcoxon Signed Rank Test.

 

 

Tx A
(N=18)

Tx B
(N=18)

Tx C
(N=18)

Tx D
(N=18)

Tx E
(N=10)

Body Weight (kg)

Pre

80.01±12.34

80.29±12.19

80.18±12.42

80.23±12.32

85.00±12.29

Post

79.86±12.19

79.95±12.20

79.89±12.27

79.93±12.27

84.88±12.34

Selected 24-hour Urine Values

 

 

 

 

 

Urine Volume (ml)

1424±395

1424±410

1403±431

1575±524

1421±437

Creatinine (mg/24h)

1996.7±285.3

1982.3±401.6

1937.7±270.7

1954.1±248.6

1935.8±532.6

Osmolality
(mOsm/kg) 

664.9±200.4

666.4±159.7

676.0±181.8

644.9±200.4

 663.8±196.5

Specific Gravity

1.018±0.005

1.018±0.004

1.018±0.004

1.017±0.005

1.018±0.005

Urine Pre & Post-Tx AM Voids

 

 

 

 

 

Cl (mmol/L)

 

Pre

70.9±44.6

85.9±38.5

77.9±48.0

85.0±46.0

88.0±40.0

Post

69.2±37.4

75.8±34.6

75.1±34.6

78.6±42.2

80.9±41.5

Na (mmol/L)

 

Pre

99.7±51.2

114.3±39.8

111.4±38.0

124.6±53.7

114.0±39.8

Post

98.3±41.3

106.2±39.4

103.5±39.3

112.3±58.4

110.3±57.0

K (mmol/L)

 

Pre

30.17±15.57

34.78±20.79

35.28±20.70

29.50±16.49

38.70±19.91

Post

29.33±13.81

31.22±12.35

30.28±13.39

33.22±16.82

28.60±12.09

Na/K

 

Pre

3.954±2.831

3.855±1.754

4.245±2.442

5.335±3.601

4.074±3.195

Post

3.794±1.953

3.791±1.642

4.003±2.067

4.307±2.598

4.028±1.566

Creatinine (mg/dL)

Pre

166.67±62.49

164.72±71.19

172.28±75.75

152.00±66.36

170.40±71.72

Post

177.78±61.60

170.61±52.89

176.94±62.86

186.22±75.48

155.20±37.60

Osmolality

(mOsm/kg) 

Pre

652.2±212.4

713.8±234.0

725.5±263.7

681.4±242.9

704.2±158.2

Post

682.6±221.1

692.8±187.6

712.3±221.4

717.8±231.4

661.8±178.2

Specific Gravity

Pre

1.019±0.006

1.019±.007

1.020±.009

1.018±.007

1.019±.005

Post

1.019±0.006

1.019±.005

1.020±.006

1.019±.007

1.018±.004

Pre- and Post-Tx
Blood Indices

 

 

 

 

 

Hemoglobin (g/dL)

Pre

14.8±0.9

14.8±1.1

14.7±0.9

14.7±0.9

14.6±0.9

Post

14.8±1.0

14.9±0.9

14.7±0.9

15.0±1.0

14.8±0.9

Hematocrit (%)

Pre

43.8±2.5

43.4±2.6

43.4±2.3

43.4±2.7

42.9±2.4

Post

43.4±2.5

43.5±2.6

43.5±2.3

43.9±2.3

43.6±2.2

Serum Osmolality 

Pre

291.9±2.2

291.1±2.9

291.6±3.7

290.6±3.0

289.5±2.1

Post

291.7±2.7

290.8±2.8

291.8±2.8

290.3±2.5

290.9±2.8

Plasma Cl (mmol/L)

Pre

102.6±1.7

102.4±1.8

102.1±1.8

101.9±1.5

102.1±1.2

Post

102.8±1.8

102.6±2.1

102.9±1.2

102.7±1.6

103.1±1.5

Author Conclusion:

This pilot study found no significant differences in the effect of various combinations of beverages on hydration status of healthy adult males.

  • Advising people to disregard caffeinated beverages as part of the daily fluid intake is not substantiated by the results of this study
  • The across-treatment weight loss observed, when combined with data on fluid-disease relationships, suggests that optimal fluid intake may be higher than common recommendations. Further research is needed to confirm these results and to explore optimal fluid intake for healthy individuals.
  • The intent of this pilot study was to evaluate multiple measures used to document hydration to determine any treatment effect and to assess the sensitivity of the assays. As is the nature of a pilot study, no single hypothesis was proposed for formal evaluation, and thus neither sample size nor power were calculated prospectively.
Funding Source:
Industry:
Coca-cola
Food Company:
Reviewer Comments:
This study was supported by a grant from The Coca-Cola Company.
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? N/A
  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? No
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? 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? 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? 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.) 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? Yes
  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? 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)? N/A
  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