Rehydration with a Caffeinated Beverage During the Nonexercise Periods of 3 Consecutive Days of 2-a-Day Practices

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1 International Journal of Sport Nutrition and Exercise Metabolism, 2004, 14, Human Kinetics Publishers, Inc. During the Nonexercise Periods of 3 Consecutive Days of 2-a-Day Practices Kelly A. Fiala, Douglas J. Casa, and Melissa W. Roti The purpose of this study was to assess the influence of rehydration with a caffeinated beverage during nonexercise periods on hydration status throughout consecutive practices in the heat. Ten (7 women, 3 men) partially heatacclimated athletes (age 24 ± 1y, body fat 19.2 ± 2%, weight 68.4 ± 4.0 kg, height 170 ± 3 cm) completed 3 successive days of 2-a-day practices (2 h/ practice, 4 h/d) in mild heat (WBGT = 23 C). The 2 trials (double-blind, random, cross-over design) included; 1) caffeine (CAF) rehydrated with Coca- Cola and 2) caffeine-free (CF) rehydrated with Caffeine-Free Coca-Cola. Urine and psychological measures were determined before and after each 2-h practice. A significant difference was found for urine color for the post-am time point, F = 5.526, P = No differences were found among other variables (P > 0.05). In summary, there is little evidence to suggest that the use of beverages containing caffeine during nonexercise might hinder hydration status. Key Words: hydration, urine specific gravity, urine color Caffeine has been demonstrated to enhance sports performance. Because its use is socially accepted and it is banned only in large amounts by various sports associations, it is likely that many athletes would, or do, turn to caffeine for a competitive edge. There have been several recommendations, however, advising athletes to limit caffeine intake before and during sports participation (6). This warning is based on caffeine s diuretic effect at rest which might contribute to a compromise of body fluid homeostasis during exercise. At rest, caffeine exerts its effects by increasing blood flow in the kidneys resulting in an increased glomerular filtration rate (GFR) leading to increased urine production (1). Interestingly, this warning regarding caffeine use and exercise participation has not been adequately supported by research. In fact, several studies have considered the issue of hydration status both at rest and during exercise and reported contradictory results. Although several studies noted a mild diuretic effect of various doses of caffeine in subjects at rest (8, 16-20, 22), Grandjean et al. observed no differences in a 24-h urine collection volume for multiple treatment groups who consumed various combinations of water and both caffeinated and carbonated beverages (12). With respect to exercise, most studies were unable to demonstrate increased urine production with various exercises and various doses of caffeine The authors are with the Dept of Kinesiology in the Neag School of Education at the University of Connecticut, Storrs, CT

2 420 Fiala, Casa, and Roti supplementation (9, 11, 15, 25). In addition to the investigation of potential diuresis of caffeine, the findings showed no differences in physiological measures such as heart rate, rectal temperatures, change in plasma volume, sweat rate, plasma osmolality, and urine osmolality (9, 11, 25). Additional studies have considered caffeinated drinks as rehydration beverages (5, 10). In 1 study, the subjects had similar consumption and urine output volumes (5). In another study, however, urine production was significantly greater for diet cola (DC) than carbohydrate electrolyte solution (CES). In addition, urine volume showed a trend to be greater for DC over water (W). Overall, DC appears to be less effective than W in whole body rehydration, while CES appears somewhat more effective than both W and DC (10). The present study was designed to address hydration status of trained individuals using caffeine during 2-a-day practices across a 3-day period. This is the 1st study to consider successive bouts of exercise simulating 2-a-day practices. As a result of the successive bouts of exercise, a potential diuretic effect of caffeine needs to be explored. Because the experiment is a field study, external validity increases dramatically, and the potential for generalizability to real life situations is possible. Subjects Methods The 10 subjects (7 women and 3 men) were partially heat-acclimatized individuals (age, 24 ± 1 y; body fat, 19.2 ± 2%; weight, 68.4 ± 4.0 kg; height, 170 ± 3 cm). The criteria for participation were as follows: a) no serious chronic health problems, b) no cardiovascular complications, c) not nursing or pregnant, d) no recent history of exertional heat illness, and e) moderate or high fitness level. Following an informal briefing, subjects completed a medical history questionnaire and signed the informed consent identifying the benefits and all potential risks of the study. The University of Connecticut Institutional Review Board approved the research protocol. Trials Each subject completed 2 double-blind, random, cross-over design trials, each 3 d in duration. Subjects consumed a) caffeine trial (CAF)- rehydrated with water during exercise and rehydrated with Coca-Cola during all other times, and b) caffeine-free trial (CF)- rehydrated with water during exercise and rehydrated with Caffeine- Free trial Coca-Cola during all other times. Water and beverages were consumed ad libitum for both trials. Caffeine, other than that provided in the beverage, was prohibited for 4 d before and during each of the trials. Subjects were also required to abstain from foods with high water content such as watermelon and soup during the trial. During the CAF trial, subjects consumed an average 741 ± 171 mg of caffeine (244 ± 78 mg/d). The typical 12-oz. (355 ml) can of Coca-Cola contains 35 mg of caffeine, equivalent to approximately 21 cans of Coca-Cola across the 3-d trial or 7 cans/d. The trials were separated by 4 d. Preliminary Testing Prior to the 2 trials, subjects reported for baseline testing which included measurement of height and weight. In addition, skinfold measurements were taken from the appropriate sites for men (thigh, chest, and abdomen) and women (thigh,

3 421 triceps, and suprailium) to employ the Jackson/Pollock method for the calculation of percent body fat (13, 14). The subjects average caffeine intake in the weeks prior to the research study averaged 57.5 ± 51.3 mg/d. In addition, subjects were told to consume normal meals and fluids prior to the start of each Day 1. We asked subjects to try to be sure they were adequately hydrated the evening before the start of a Day 1. Subjects were encouraged to consume an additional 2 to 3 8-oz. glasses of water at dinner time the night before as an aid to adequate hydration. Laboratory Data Collection On the mornings of Days 1 and 4, subjects reported to the laboratory between 7 and 8 AM. A urine sample was collected and urine specific gravity (USG), color, and osmolality were assessed (2, 3). Urine specific gravity was measured by refractometry (Model A300CL, Spartan, Japan). Urine color was assessed via the urine color chart developed by Armstrong, et al. (2, 3) In addition, a 5-mL blood sample was taken and hematocrit, hemoglobin, and osmolality were analyzed. Hematocrit was measured, in triplicate, from whole blood by microcapillary technique. Hemoglobin was measured, in triplicate, by the cyanmethemoglobin method (Kit 525, Sigma-Aldrich Corp., St. Louis, MO) and a spectrophotometer (Bausch & Lomb Spectronic 88, Rochester, NY). Plasma volume changes were calculated using the Dill and Costill equation (7). Plasma and urine osmolality were measured, in duplicate, via freezing point depression (Model 3DII, Advanced Instruments, Inc., Needham Heights, MA). Finally, body weight was taken via a digital scale (Model BWB-800A, Tanita Corp, Tokyo, Japan). In addition, thirst sensation was recorded using a 9-point thirst scale ranging from 1 (not thirsty) to 9 (very thirsty) (21). Field Data Collection On Days 1 to 3, the subjects completed 3 consecutive days of 2-a-day practices (2 h/practice, 4 h/d) in mild heat (wet bulb globe temperature = 23 C) at an individually selected competitive intensity (see Figure 1). During the morning session, the subjects played soccer, modified rugby, and ultimate Frisbee for 40 min each. The afternoon session consisted of an 80-min hike followed by 40 min of flag football. Prior to and following each exercise session, the following data were recorded: urine color, USG, urine volume, thirst, thermal sensation, rating of perceived exertion (RPE), and body weight. Urine samples were collected at the following time points: prior to the morning practice (pre-am), immediately following the morning practice (post-am), prior to the afternoon practice (pre-pm), and immediately following the afternoon practice (post-pm). Thermal sensation was recorded using a 17-point scale with 0.5 increments ranging from 0.0 (unbearably cold) to 8.0 (unbearably hot) (24). The RPE scale used to assess exertion ranged from 6 (very, very light) to 20 (very, very hard) (4). In addition, subjects were asked to fill out an environmental symptoms questionnaire (ESQ) prior to the morning exercise session and following the afternoon exercise session. The ESQ is a 56-question survey designed to assess on a 0 (not at all) to 5 (extremely) scale whether symptoms exist that might be environment related (23). Subjects had a 1-h break between the 2 practices to collect data and eat their packed lunch. Throughout the duration of each trial, subjects recorded urine production and water and beverage consumption.

4 422 Fiala, Casa, and Roti Figure 1 Study protocol. Statistical Analysis Data was reported as mean ± standard deviation. A 2-way within-subjects analysis of variance was performed to evaluate the effects of trial and time for the field and laboratory variables. For the field variables, the within-subjects factors were trial with 2 levels (CAF or CF) and time with 3 levels (Day 1, Day 2, and Day 3). (Each of the 4 time points (pre-am, post-am, pre-pm, and post-pm) were evaluated individually in this manner.) For the laboratory variables, the within-subjects factors were trials with 2 levels (CAF or CF) and time with 2 levels (Day 1 or Day 4). Paired-sample t-tests were conducted to follow up significant trial effects, time effects, and interactions. In addition, paired-sample t-tests were conducted on all calculated data including total body weight changes, plasma volume shifts, water consumption, beverage consumption, caffeine ingested, urine produced, and percentage of fluid ingested secreted as urine. All statistical tests were considered significant at the P < 0.05 level with the exception of the follow-up t-tests. Holm s sequential Bonferroni procedure was used to adjust significance levels for the follow-up tests. All statistics were run using Statistical Package for Social Sciences (SPSS) 10.0 for Windows (SPSS Inc., Chicago, IL). Field Variables Results Means and standard deviations of all field variables at the pre-am, post-am, pre- PM, and post-pm time are provided in Tables 1 to 4, respectively.

5 423 Table 1 Field Variables for Pre-AM Day 1 Day 2 Day 3 Variable Caffeine Caffeine-free Caffeine Caffeine-free Caffeine Caffeine-free Body weight (kg) 68.6 ± ± ± ± ± ± 12.4 ESQ 10 ± 6 11 ± 8 11 ± 7 10 ± 8 11 ± 9 13 ± 7 RPE 6 ± 0 7 ± 1 6 ± 0 6 ± 0 7 ± 1 7 ± 1 Thermal 4.0 ± ± ± ± ± ± 0.5 Thirst 3.0 ± ± ± ± ± ± 1.0 USG ± ± ± ± ± ± Urine color 4 ± 2 3 ± 2 6 ± 1 6 ± 2 5 ± 2 5 ± 2 Note. Values are mean ± standard deviation. Table 2 Field Variables for Post-AM Day 1 Day 2 Day 3 Variable Caffeine Caffeine-free Caffeine Caffeine-free Caffeine Caffeine-free Body weight (kg) 68.1 ± ± ± ± ± ± 12.4 RPE 15 ± 1 15 ± 2 15 ± 1 15 ± 1 14 ± 3 16 ± 1 Thermal 5.5 ± ± ± ± ± ± 1.0 Thirst 5.0 ± ± ± ± ± ± 1.0 USG ± ± ± ± ± ± Urine color 6 ± 2 6 ± 1 6 ± 2 6 ± 2 7 ± 1 5 ± 2 Note. Values are mean ± standard deviation.

6 424 Fiala, Casa, and Roti Table 3 Field Variables for Pre-PM Day 1 Day 2 Day 3 Variable Caffeine Caffeine-free Caffeine Caffeine-free Caffeine Caffeine-free Body weight (kg) 68.8 ± ± ± ± ± ± 12.4 RPE 7 ± 1 6 ± 1 7 ± 1 7 ± 1 6 ± 1 7 ± 1 Thermal 3.0 ± ± ± ± ± ± 1.0 Thirst 2.0 ± ± ± ± ± ± 0.5 USG ± ± ± ± ± ± Urine color 5 ± 2 5 ± 2 5 ± 2 5 ± 3 5 ± 2 6 ± 2 Note. Values are mean ± standard deviation. Table 4 Field Variables for Post-PM Day 1 Day 2 Day 3 Variable Caffeine Caffeine-free Caffeine Caffeine-free Caffeine Caffeine-free Body weight (kg) 68.7 ± ± ± ± ± ± 12.5 ESQ 19 ± 9 15 ± 9 18 ± 9 16 ± 7 21 ± ± 11 RPE 14 ± 1 13 ± 2 14 ± 1 14 ± 2 15 ± 1 14 ± 1 Thermal 4.0 ± ± ± ± ± ± 1.0 Thirst 4.0 ± ± ± ± ± ± 2.0 USG ± ± ± ± ± ± Urine color 4 ± 2 4 ± 2 4 ± 3 4 ± 3 5 ± 2 5 ± 2 Note. Values are mean ± standard deviation.

7 425 Urine Values. A significant interaction was found for urine color for the post- AM time point, F(1, 9) = 5.526, P = 0.031, partial η 2 = Follow-up testing demonstrated a difference between the change from Day 1 to Day 3 for CAF ( 0.70 ± 1.2) and CF (1.3 ± 1.8), t(9) = 3.354, P = 0.008, η 2 = The mean urine color for the CAF group increased just less than 1 unit while the CF group s urine color decreased over 1 unit from Day 1 to Day 3. Interactions were not observed for pre-am, pre-pm, and post-pm time points. In addition, a significant trial main effect was found for urine color for the pre-pm time point, F(1, 9) = 7.826, P = 0.021, partial η 2 = Follow-up tests, however, revealed no pair differences. Trial main effects were not observed for pre-am, post-am, and post-pm time points. Finally, time main effects were observed for pre-am, F(2, 8) = 7.953, P = 0.013, partial η 2 = time points for urine color. For the pre-am time point, follow-up tests indicated differences between Day 1 (3.7 ± 1.7) and Day 2 (5.8 ± 1.0), t(9) = 3.993, P = 0.003, η 2 = No time main effects were observed for post-am, pre-pm, and post-pm time points. There were no time, trial, and interaction effects for any time point for both urine volume and USG. Perceptual Data. No significant interactions or time effects were observed for thirst ratings at any time point. A significant trial effect was found, however, for thirst for the pre-pm time point, F(1, 9) = 8.308, P = 0.018, partial η 2 = Follow-up tests, however, failed to reveal any pair differences. No significant trial effect was found at pre-am, post-am, or post-pm time points. No significant interactions or trial effects were observed for thermal ratings at any time point. A significant time effect was found for thermal for both the pre-pm [F(2, 8) = , P = 0.007, partial η 2 = 0.716] and post-pm [F(2, 8) = , P = 0.004, partial η 2 = 0.756] time points. For the pre-pm time point, follow-up tests indicated differences between Day 1 (3.4 ± 0.6) and Day 2 (4.2 ± 0.4), t(9) = 3.416, P = 0.008, η 2 = 0.565, and Day 1 and Day 3 (4.5 ± 0.5), t(9) = 4.646, P = 0.001, η 2 = For the post-pm time point there was a significant difference between Day 1 (4.5 ± 0.4) and Day 3 (5.5 ± 0.5), t(9) = 5.119, P = 0.001, η 2 = 0.744, Day 1 and Day 2 (5.1 ± 0.5), t(9) = 3.091, P = 0.013, η 2 = and Day 2 and Day 3, t(9) = 3.207, P = 0.011, η 2 = No significant time effects were observed at the pre-am and post-pm time points for thermal sensation. No significant interactions or trial effects were observed for thermal ratings at any time point. A significant time effect was found, however, for RPE for the post-pm time point, F(2, 8) = 6.720, P = 0.019, partial η 2 = Followup testing demonstrated a difference between Day 2 (13.8 ± 0.9) and Day 3 (14.4 ± 1.1), t(9) = 3.881, P = 0.004, η 2 = Pre-AM, post-am, and pre-pm yielded no significant time effect. There were no time, trial, and interaction effects for any time point for ESQ at any time point. Body Weight. No significant interaction, time, or trial effects were observed for the body weight variable at the pre-am, post-am, or pre-pm time points. Laboratory Variables. Means and standard deviations of all laboratory values are provided in Table 5 for Days 1 and 4. There were no significant interaction effects for any of the laboratory variables. There was a significant trial main effect for hematocrit, F(1, 9) = 8.226, P = 0.019, partial η 2 = Follow-up testing, however, failed to reveal differences between the 2 trials at any time point. All

8 426 Fiala, Casa, and Roti Table 5 Laboratory Variables Day 1 Day 4 Caffeine- Caffeine- Variable Caffeine free Caffeine free Hematocrit 45.5 ± ± ± ± 3.0 (%) Hemoglobin ± ± ± ± 1.11 (g/dl) Plasma osmolality 284 ± ± ± ± 6 (mosmo/kg) USG ± ± ± ± Urine color 4 ± 2 5 ± 1 6 ± 1 6 ± 1 Urine osmolality 649 ± ± ± ± 238 (mosmo/kg) Thirst 4.0 ± ± ± ± 2.0 Note. Values are mean ± standard deviation. Table 6 Time Effects for Laboratory Variables Repeated measures Follow-up t-test ANOVA (Days 1 and 4) Variables F p t p η 2 Hematocrit Hemoglobin Plasma osmolality USG Urine color Urine volume Thirst other laboratory variables showed no significant trial main effects. As expected, however, all variables (except urine osmolality) had time main effects, as shown in Table 6. Total Fluid Calculations. Paired sample t-tests showed no differences between trials for fluid consumption: beverage, water, and total fluid. As expected, a paired sample t-test demonstrated caffeine ingestion differences between the trials. In

9 427 Table 7 Total Fluids Ingested and Produced, and Resultant Body Weight and Plasma Volume Changes for 3 Days Fluid Caffeine Caffeine-free t(9) P Soda 5.60 ± 1.54 L 5.39 ± 1.53 L Caffeine 741 ± 171 mg 0 ± 0 mg Water 6.26 ± 2.27 L 6.02 ± 1.78 L Total fluid ± 1.83 L ± 1.39 L Urine volume 5.08 ± 1.71 L 5.01 ± 2.47 L Urine percent a 43.7 ± 15.1% 44.2 ± 21.6% Weight changes 0.31 ± 0.76 kg 0.06 ± 0.26 kg % change plasma ± 10.61% ± 9.15% volume Note. Values for caffeine and caffeine-free are mean ± standard deviation. a Urine percent = urine volume/total fluid 100%. addition, there were no significant differences between urine production, percentage of fluid ingested excreted as urine, plasma volume, and body weight changes (see Table 7). Discussion As expected, time main effects were observed in many of the variables. This reinforces the fact that it only takes 3 d of 2-a-day-practices to induce the effects of dehydration. The most interesting result was the interaction of trial and time across Day 1 and Day 3 for urine color at the post-am time point. Urine color value increased, indicating a less-than-optimal hydration status, for the caffeine group and decreased for the caffeine-free group. It is important to note that this was not true for any other time point. Prior to the post-am time point, all subjects were rehydrating with water. The subjects, however, had been undergoing different hydration methods throughout the 3-d period prior to this result. Although consumption of caffeine at rest has been shown to have a diuretic effect (8, 16-20), the overall results of this study were not surprising. They are consistent with the previously described exercise studies that found no differences in hydration status for caffeine and placebo groups (9, 11, 15, 25). Kovacs et al. had subjects complete a 20-min warm-up cycle followed by a break and then a time trial. The treatment groups included placebo, placebo and carbohydrate-electrolyte solution (CES), CES and 150 mg caffeine, CES and 225 mg caffeine, and CES and 320 mg caffeine (15). There were no differences in urine volume before or after the exercise, however. Wemple et al. had subjects complete 3 h of cycling at 65% VO 2max followed by a performance trial at 85% VO 2max (25). They observed no differences in urine volume between the placebo and caffeine trials. Caffeine consumption was 25 mg/dl of carbohydrate electrolyte drink and each subject received 35 ml of drink per kg of body weight. In addition to the investigation of potential diuresis of caffeine, this study showed no differences in physiological measures such as heart

10 428 Fiala, Casa, and Roti rate, rectal temperatures, change in plasma volume, sweat rate, plasma osmolality, and urine osmolality. Graham et al. had their subjects run at 85% VO 2max after they consumed 4.45 mg of caffeine per kg of body weight in a volume of liquid equivalent to 7.15 ml/kg body weight (11). Again, there were no differences in urine volume for the caffeine groups, coffee or caffeine and water, and the placebo. Falk and colleagues had subjects exercise at 70 to 75% VO 2max to self-determined exhaustion. The investigators observed no differences in total water loss or sweat rate (9). In addition, heart rate, rectal temperature, and sweat rates were not shown to be different for the placebo and caffeine trials. This lack of alteration in hydration status could be the result of caffeine s diuretic effect being offset by alterations to the renin-angiotensin-aldosterone cascade and increases in catecholamines followed by increases in solute reabsorption and water conservation that occur during exercise (25). The interaction for post-am urine color, however, might indicate a potential for altered hydration status after use of caffeine for consecutive days. No other study has addressed this issue. This potential alteration of hydration status with caffeine use should be investigated further before making recommendations regarding the use of a caffeinated beverage over consecutive days. This study has great potential for generalization given that it was a field study; however, internal validity would be stronger in a laboratory study. It is clear that the use of caffeine needs to be investigated further as both a hydration beverage during exercise and a rehydration beverage following exercise. It is very important that these studies be conducted across several days, because that is more applicable to real life situations. Also, most of the studies have considered effects of a single dose of caffeine prior to an exercise bout. It is important to consider the effects of multiple doses across days prior to and during exercise, which is more realistic given that caffeinated beverages are consumed by many athletes outside the confines of practice and competition. In summary, there is little evidence to suggest that the use of beverages containing caffeine during nonexercise might hinder hydration status. However, of concern is the fact that hydration status at the end of 3 d was compromised for both trials. Acknowledgments The authors would like to thank Tutita Casa, Eric Combs, Michael D Alfonso, Nora Decher, Aya Felling, James Fernandes, Catie Fuller, Lynn Harvey, and Breanne Smith for their participation as research assistants in the project. In addition, we would like to extend our appreciation to the town of Mansfield, CT for the use of their park as the primary research site. References 1. Armstrong, L.E. Caffeine, body fluid-electrolyte balance, and exercise performance. Int. J. Sports Nutr. Exerc. Metab. 12: , Armstrong, L.E., C.M. Maresh, J.W. Castellani, M.F. Bergeron, R.W. Kenefick, K.E. La Gasse, and D. Riebe. Urinary indices of hydration status. Int. J. Sports Nutr. 4: , Armstrong, L.E., J.A.H. Soto, F.T. Hacker, D.J. Casa, S.A. Kavouras, and C.M. Maresh. Urinary indices during dehydration, exercise, and rehydration. Int. J. Sports Nutr. Exerc. Metab. 8: , 1998.

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