Abstract
Our previous studies demonstrated that dietary supplementation with tea catechins combined with exercise improved endurance capacity in mice. This study aimed to demonstrate the effect of daily tea catechin consumption on aerobic capacity in humans. Sixteen Japanese non-athlete male subjects (aged 25–47 years) took 500 mL of a test beverage with or without tea catechins (570 mg) daily for 8 weeks and attended a training program twice a week. Aerobic capacity was evaluated by indirect calorimetry and near-infrared spectroscopy during graded cycle exercise. Catechin beverage consumption was associated with a significantly higher ventilation threshold during exercise and a higher recovery rate of oxygenated hemoglobin and myoglobin levels after graded cycle exercise when compared to subjects receiving the placebo beverage. These results indicate that daily consumption of tea catechins increases aerobic capacity when combined with semiweekly light exercise, which may be due to increased skeletal muscle aerobic capacity.
Graphical abstract
Tea catechins improved the recovery rate of oxygenated hemoglobin and myoglobin levels after graded cycle exercise.
Some dietary supplements have been shown to improve aerobic or endurance capacity.Citation1,2) However, to date, these studies have investigated idiosyncratic individuals or exercise. Accordingly, a more effective supplement may be needed to improve aerobic endurance in more common populations or exercise conditions. Prolonged exercise performance can be improved by an increased utilization of fat as energy during exercise, since fat utilization reduces anaerobic carbohydrate consumption in providing energy substrate to the muscle is reduce and minimizes production of lactate in the muscle.Citation3,4)
Our recent studies have demonstrated that dietary supplementation with green tea extract (GTE), when combined with regular exercise, improves running and swimming endurance capacity in mice.Citation5,6) The major component of the GTE is tea catechins, which have been shown to increase fat utilization in the liver and thereby attenuate high-fat diet-induced obesity in mice.Citation7) Our previous studies also revealed that the beneficial effects of dietary GTE on endurance performance were associated with increased fatty acid oxidation not only in the liver but also in the skeletal muscles.Citation8,9) Since skeletal muscular fat utilization is critical for endurance capacity, an increase of skeletal muscular fatty acid oxidation may lead to improvement of endurance capacity. In fact, our study has demonstrated that mice with higher endurance capacity had higher fatty acid oxidation capacity in the skeletal muscle than mice with lower endurance capacity.Citation10)
Our previous randomized control trial also demonstrated that 8-week supplementation with tea catechins combined with semiweekly light aerobic exercise increased whole body fat utilization either in a sedentary condition or during exercise in humans.Citation11) However, whether nutritional supplementation with tea catechins can improve aerobic capacity when combined with low-intensity and low-frequency exercise has yet to be investigated.
Accordingly, the purpose of this study was to demonstrate the beneficial effects of dietary tea catechin supplementation plus semiweekly light exercise on ventilation threshold (VT), which is an indicator of aerobic capacity and a significant predictor of endurance exercise performance in untrained adults.Citation12)
Materials and methods
Subjects
Sixteen healthy male subjects (aged 25–47 years) were enrolled in this study (Table ). Subjects were excluded if they had uncontrolled hypertension, coronary heart disease, food allergies, or motor disorders or if they engaged in resistance training in their daily lives. Signed informed consent was obtained from all subjects after fully informing them about the details and methods of this study. The subjects were instructed not to change their daily exercise and dietary habits during the study period. This study was performed in accordance with the regulations of the Ethics Committee of the Kao Corporation and in conformity with the Declaration of Helsinki.
Table 1. Characteristics of study subjects
Study protocol
The study was designed as a randomized, double-blind, placebo-controlled, crossover trial. Randomization was performed after baseline assessment. The randomization procedure was conducted by a person who was not involved in the study, and the subjects and test staff remained unaware of the assignments throughout the duration of the study. The study period was from November 2010 to August 2011. The subjects were randomly divided into two groups. During the first 8-week intervention period, one group (n = 8) received a placebo beverage, and the other group (n = 8) received a tea catechin beverage. They consumed the test beverages each day during the 8-week period (period 1) and underwent cycle exercise training twice a week. An 8-week washout period was followed by a second 8-week intervention period (period 2) in which the groups were reversed. Physical function tests were performed at the beginning and the end of the 8-week intervention. All subjects abstained from tea catechin-containing supplements and beverages during the study period and alcohol for 2 days before the each physical function test.
Test beverage
Each subject ingested a tea catechin beverage (500 mL) or a placebo beverage (500 mL) daily for 8 weeks. The daily dose of tea catechins (570 mg; equivalent to 6 to 7 cups of regular green tea) was chosen based on what is known about its nutritional safety and efficacy, after converting the minimal effective dose in miceCitation7) to a human equivalent while considering the relative body surface areas. On the exercise training enforcement days, the subjects were instructed to take the beverage within 1 h of the training. On the other days, the subjects were instructed to consume the beverage at the time of their choice during their daily routines.
The GTE was prepared from green tea leaves (Camellia sinensis), extracted with hot water, and spray-dried to a powder. The catechin composition (Table ) of the GTE was measured through high-performance liquid chromatography. Each test beverage was prepared in the form of a sterilely bottled sports drink that contained sweeteners (such as sugar or sugar alcohol), acidulants (such as citric acid), electrolytes (such as Na or K salts), antioxidants, and flavor; the beverages were indistinguishable in terms of volume (500 mL), color, taste, and flavor. Both beverages contained the same amount of caffeine (15 mg/500 mL) and energy (17 kcal/500 mL). The catechin beverage contained 570 mg of tea catechins, and the placebo beverage lacked the tea catechins (Table ).
Table 2. Catechin compositions of the test beverages (mg/500 mL).
Table 3. Composition of the test beverages.
Cycle exercise training
Before training, a graded exercise test to determine peak torque was performed. Thereafter, the subjects underwent cycle exercise training twice a week on non-consecutive days during the 8-week study period using the cycle ergometer StrengthErgo 240 (Mitsubishi Electric Corporation, Tokyo, Japan). They conducted 50-rpm light cycle exerciseCitation13) of 3 sessions at 15% peak torque for 60 s followed by 4 sessions at 20% peak torque for 40 s on the cycle ergometer.
Physical function test
The physical function of each subject was examined before and after the 8-week intervention period. From 2 days prior to the physical function test, the subjects were asked to abstain from alcohol and consumed a provided lunch box (661 kcal, carbohydrate:fat:protein = 92.3:19.8:25.6 [g]) before 9 PM the night before the test day, followed by fasting and non-smoking (only water was allowed). On the day of the test, the subjects presented to the test room at 8:30 AM, had a given meal (400 kcal; Calorie Mate; Otsuka phamaceutical, Tokyo, Japan), and remained in a seated position in the room maintained at 25 °C for 60 min until the beginning of the physical function test, which was composed of the following sessions.
Body composition and anthropometric determination
Body weight, body fat ratio, and muscle mass were measured using a bioimpedance body fat analyzer (BC-621, Tanita, Co., Tokyo, Japan). Height was measured only at a single baseline measurement. Body mass index (BMI) was calculated from height and body weight.
Aerobic capacity
Aerobic capacity was measured with graded cycle exercise using an open circuit breath-by-breath gas exchange measurement system (ARCO2000, ARCO SYSTEM, Chiba, Japan). The subjects performed a warm-up cycle exercise on the StrengthErgo 240 (Mitsubishi Electric Corporation, Tokyo, Japan) at 20 W for 3 min followed by graded exercise; the subjects started pedaling at 20 W with heart rate (HR) measurement, and the work rate was increased stepwise at 10 W per min until 70% of the maximal heart rate (HRmax), estimated according to the conventional equation (HRmax = 220 − age), was reached. The graded exercise session finished with a cool down session of 1 min at 20 W.
The calorimetric data were acquired beginning 2 min after the start of the warm-up session (1 min before the beginning of the graded exercise session). Maximal oxygen intake (VO2max) was estimated as the maximal value of VO2 determined using the regression equation in the relationship between VO2 and HR. VT was determined by a single blinded expert reader based on the V-slope analysis of the VO2 and VCO2.Citation14)
Muscle oxygenation
The non-invasive near-infrared spectroscopy (NIRS) method was used for measuring muscle oxygenation. An NIRS probe (Pocket NIRS Duo; Hamamatsu Photonics KK, Japan) was placed on the intermediate portion of the vastus medialis during the aerobic capacity test.Citation15) The oxygenated hemoglobin (Hb) and myoglobin (Mb) (oxy-Hb/Mb) levels were calculated by transforming 3 different wavelengths (735, 810, and 850 nm) and were expressed in arbitrary units. The baseline oxy-Hb/Mb values were recorded prior to the warm-up session while the subject was seated in a chair. During the cool down session after the graded exercise session, the oxy-Hb/Mb recovery rate, which is a function of oxygen delivery and oxygen utilization in muscle,Citation12) was measured for 30 s.
Isokinetic muscle strength
The isokinetic muscle strength of both legs was measured by the cycle ergometer (StrengthErgo 240). Each subject pedaled on the apparatus at maximal power 5 times, and we measured the maximal power for both legs.
Blood analysis
Post-exercise blood was collected from an intermediate vein of the forearm after the aerobic capacity measurement. The blood lactate level was measured using the Lactate-Pro electrochemical test strip (Arkray, Tokyo, Japan). Serum glucose and non-esterified fatty acids were analyzed by SRL Inc. (Tokyo, Japan).
Statistical analysis
Numerical data are expressed as the means ± SD. The differences in each study endpoint or the changes from the baseline between the interventions were analyzed using a linear mixed model. We included the fixed effects of group, period, period baseline, and the interaction of group and period. We also included the subject as a random effect. The pairwise comparison between the interventions was performed with a Bonferroni analysis. In a separate analysis, the change from the baseline to the endpoint was evaluated using the paired t-test for intragroup comparisons, and the changes were considered significant for all p < 0.05. For statistical analysis, SPSS for Windows, release 23.0 (SPSS, Chicago, IL) was used.
Results
Effects of the intervention on anthropometric variables
The subjects’ baseline characteristics were similar between the groups (Table ). There was no report of adverse side effects derived from the test beverages and the exercise training. Two subjects were unable to complete the intervention period due to personal reasons unrelated to the intervention.
No overall changes in body weight, body fat ratio, or whole body and leg muscle mass were observed during the intervention period (Table ).
Table 4. Changes in anthropometric variables before and after the intervention.
Effects of catechin and exercise on aerobic capacity and muscle strength
A significant (p = 0.006) difference between the groups was observed in VT (Table ). After the 8-week intervention period, the VT, an indicator for aerobic capacity,Citation16) was significantly increased from baseline in the catechin beverage group (p < 0.05) but not in the placebo beverage group and was significantly higher in the catechin beverage group than in the placebo beverage group. The VO2max was significantly (p < 0.05) increased in both the catechin and the placebo groups from the baseline, but there was no statistically significant difference between the groups.
Table 5. Physical performances of the subjects before and after the intervention.
The leg extension strength was significantly increased only in the catechin group, and tended to be higher in the catechin beverage group than in the placebo beverage group after the 8-week intervention period (Table ).
Near-infrared spectroscopy
The NIRS signal decreased during the aerobic capacity test in both the placebo and catechin beverage groups, and the magnitude of the decrease was not significantly different (data not shown). During the cool down session, the muscle oxy-Hb/Mb level increased with time. The recovery rate of oxy-Hb/Mb, an indicator for oxygen delivery and utilization in muscle,Citation12) was significantly (p < 0.05) increased from the baseline in the catechin beverage group but not in the placebo beverage group (Fig. ).
Fig 1. Recovery rate of oxygenated hemoglobin/myoglobin (oxy-Hb/Mb) level of the exercising muscle during the cool down after the graded exercise session during the aerobic capacity test in the placebo group (A) and the catechin group (B). Values are means ± SD. * p<0.05, significant difference compared with the baseline by using the paired t-test.
Blood analysis
After the 8-week intervention period, the blood lactate level after aerobic exercise was significantly lower in the catechin beverage group compared to the baseline (Table ). Other blood variables did not differ within the group or between two groups (Table ).
Table 6. Changes in post-exercise blood variables before and after the intervention.
Discussion
The major finding of the present study is that supplementation with dietary tea catechins increased aerobic capacity in healthy male non-athletes who conducted semiweekly light exercise. To our knowledge, this is the first to demonstrate the beneficial effect of tea catechins on aerobic endurance capacity in untrained adults. Maximum oxygen consumption, but not muscle strength, was significantly increased after the 8-week semiweekly exercise alone, suggesting that the exercise was aerobic training rather than resistance training. The results in this study are compatible with our previous findings in animals that dietary tea catechins, when combined with light aerobic exercise, improved endurance capacity; these findings indicate that the beneficial effects of dietary tea catechins extend to physical performance in humans.
In a review, Lynch et al. (2007) suggested that aerobic training is the most effective exercise for improving endurance capacity and increasing cardiovascular fitness, whereas resistance training is effective for maintaining or improving muscle strength.Citation17) Sjödin et al. showed that aerobic training increased the VT in trained athletes.Citation18) The lack of efficacy of semiweekly exercise alone on the VT in the present study may be due to the moderate intensity and/or frequency of the exercise program used in this study. Interestingly, when semiweekly aerobic exercise was combined with dietary supplementation of tea catechins for 8 weeks, the VT, which is a common indicator for aerobic capacity during exercise, significantly increased without any change in the overall body composition or muscle mass. These results may indicate that tea catechin supplementation boosts the beneficial effects of light aerobic exercise in humans, which is compatible with our previous finding that dietary tea catechins plus regular exercise improved endurance performance in mice.Citation5,6)
A previous study evaluated the effect of tea catechin intake and endurance training on aerobic capacity in healthy men, and showed the VT increased by 24% after a 10-week intervention, with no significant difference compared to the placebo group.Citation19) In contrast, we demonstrated that the VT increased by 14% after an 8-week intervention, with significant difference compared to the placebo group. This difference might be related to the difference in the experimental protocol between the two studies. First, the exercise training was performed 3 times per week for 60 min each in the previous study, whereas the training was performed 2 times per week for 10 min each in this study. Second, the graded cycle exercise test was performed with the work rate increased stepwise at 20 W per min in the previous study, whereas the work rate was increased at 10 W per min in this study. Therefore, in this study, the mild change in aerobic capacity due to catechin intake might be detected.
Umemoto and Otsuki demonstrated that dietary supplementation of Chlorella powder that contained multiple nutrients such as amino acids, carbohydrates, lipids, minerals, and vitamins for 4 weeks significantly increased peak oxygen uptake in young individuals, most of whom engaged in regular exercise (more than 30 min/day on 3 days/week); however, the active components and underlying mechanism for this compound are still unclear.Citation1) Our previous studies in mice suggested that tea catechins, especially epigalocatechin galate, might be one of the active components of GTE promoting fatty acid oxidation in the liverCitation20) and, when combined with habitual aerobic exercise, in skeletal muscles.Citation5) Therefore, tea catechins seem to be responsible for the beneficial effects of dietary GTE on aerobic performance in humans. In addition, green tea has some components such as caffeine and theanine besides catechins. It was shown that the combination of these components increased lipid metabolism.Citation21) Thus, the increase of in aerobic capacity by due to the catechin beverage might be caused by the synergy effect of catechins, caffeine, and theanine contained in green tea.
Further, dietary tea catechin supplementation plus semiweekly aerobic exercise increased the leg extension strength, an indicator of muscle strength, whereas aerobic exercise alone did not change the muscle strength. Muscle strength is highly related to the muscle mass.Citation22) However, dietary tea catechin supplementation increased the muscle strength without changing the muscle mass. The results agree with our previous findings in animals that dietary tea catechins attenuated the unloading-induced decrease in force in isolated an soleus muscle compared with the control group without a change in muscle mass.Citation23) Our previous study in mice also suggested that this effect was partly due to decreased oxidative modifications of myofibrillar proteins through the antioxidant activity of tea catechins.Citation23)
Our NIRS study suggested that dietary catechin supplementation increased the recovery rate of oxygen consumption after aerobic exercise, which represents mitochondrial aerobic capacity in the skeletal muscle.Citation12) In addition, the blood lactate increase during exercise was significantly decreased after 8-week catechin supplementation, which also supports that dietary catechin plus semiweekly light exercise increased whole-body aerobic capacity in untrained adults. Our previous studies in mice demonstrated that dietary supplementation with catechins combined with habitual exercise increased the activity and the gene expression of fatty acid oxidation in the skeletal muscles and played a significant role in increasing aerobic and endurance capacity in mice.Citation10) The results in the present study agree with our previous findings in animals and suggest that nutritional and exercise interventions may be effective for increasing aerobic capacity in humans. Although we did not directly examine endurance performance, dietary catechins plus semiweekly light exercise increased VT, which is a well-known indicator of endurance capacity.Citation16) A higher VT indicates higher endurance performance in trainedCitation18) and untrainedCitation24) adults. Accordingly, we speculate that dietary supplementation with catechins combined with semiweekly light-intensity aerobic exercise improved endurance performance in untrained adults.
Several limitations of the present study should be considered. First, our sample size was small. Second, the endurance performance was not directly investigated. Third, the type and intensity of the exercise were also limited. Therefore, the effects of dietary catechins alone compared to the effects when combined with exercise of various types or intensities still needs to be clarified. In addition, the dose-dependent nature of the beneficial effects of catechins on physical performance and muscles still requires investigation. Since skeletal muscular metabolism varies with exercise intensity and type,Citation25) we expect that dietary catechins and exercise would improve muscle function additively or synergistically. Finally, the physical functions were investigated in only male subjects in order to reduce the variation factors in this study. In future, studies of larger populations including both male and female subjects are needed to clarify the effect of tea catechins on physical functions.
In conclusion, the present study demonstrates that dietary catechins plus semiweekly aerobic exercise enhances the VT compared to exercise alone. Therefore, daily intake of tea catechins might improve the aerobic capacity. Furthermore, the results suggest that increased mitochondrial aerobic capacity plays a significant role in the beneficial effects of the treatment on aerobic performance in non-athletes. The findings will increase our understanding of the role of dietary supplementation in increasing physical performance and muscle strength. Studies are also in progress to clarify the mechanism underlying the beneficial actions of catechin supplementation plus aerobic exercise on skeletal muscles. Nutritional intervention combined with exercise might be important for enhancing physical performance in non-athlete individuals.
Authors’ contributions
SS and NO managed the study, analyzed and interpreted the data, and drafted the manuscript. AS was involved in the study conception, managing the research expenses, and drafted the manuscript. All authors contributed to the study design and critical revision of the manuscript.
Disclosure statement
No potential conflict of interest was reported by the authors.
Funding
This study was supported by Kao Corporation, and there was no other funding/outside support.
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