Abstract：
OBJECTIVE: Maintaining an appropriate hydration level by ingesting fluid in a hot environment is a measure to prevent heat-related illness. Caffeine-containing beverages, including green tea (GT), have been avoided as inappropriate rehydration beverages to prevent heat-related illness because caffeine has been assumed to exert diuretic/natriuretic action. However, the influence of caffeine intake on urine output in dehydrated individuals is not well documented. The aim of the present study was to examine the effect of fluid replacement with GT on body fluid balance and renal water and electrolyte handling in mildly dehydrated individuals.
METHODS: Subjects were dehydrated by performing three bouts of stepping exercise for 20 min separated by 10 min of rest. They were asked to ingest an amount of water (H2O), GT, or caffeinated H2O (20 mg/100 ml; Caf-H2O) that was equal to the volume of fluid loss during the dehydration protocol; fluid balance was measured for 2 h after fluid ingestion.
RESULTS: The dehydration protocol induced hypohydration by ~ 10 g/kg body weight (~ 1% of body weight). Fluid balance 2 h after fluid ingestion was significantly less negative in all trials, and the fluid retention ratio was 52.2 ± 4.2% with H2O, 51.0 ± 5.0% with GT, and 47.9 ± 6.2% with Caf-H2O; those values did not differ among the trials. After rehydration, urine output, urine osmolality, and urinary excretions of osmotically active substances, sodium, potassium and chloride were not different among the trials.
CONCLUSIONS: The data indicate that ingestion of GT or an equivalent caffeine amount does not worsen the hydration level 2 h after ingestion and can be effective in reducing the negative fluid balance for acute recovery from mild hypohydration.
BACKGROUND: ISRCTN53057185; retrospectively registered.
METHODS: Subjects were dehydrated by performing three bouts of stepping exercise for 20 min separated by 10 min of rest. They were asked to ingest an amount of water (H2O), GT, or caffeinated H2O (20 mg/100 ml; Caf-H2O) that was equal to the volume of fluid loss during the dehydration protocol; fluid balance was measured for 2 h after fluid ingestion.
RESULTS: The dehydration protocol induced hypohydration by ~ 10 g/kg body weight (~ 1% of body weight). Fluid balance 2 h after fluid ingestion was significantly less negative in all trials, and the fluid retention ratio was 52.2 ± 4.2% with H2O, 51.0 ± 5.0% with GT, and 47.9 ± 6.2% with Caf-H2O; those values did not differ among the trials. After rehydration, urine output, urine osmolality, and urinary excretions of osmotically active substances, sodium, potassium and chloride were not different among the trials.
CONCLUSIONS: The data indicate that ingestion of GT or an equivalent caffeine amount does not worsen the hydration level 2 h after ingestion and can be effective in reducing the negative fluid balance for acute recovery from mild hypohydration.
BACKGROUND: ISRCTN53057185; retrospectively registered.
摘要：
目的：通过在热环境中摄取液体来保持适当的水合水平是预防与热有关的疾病的措施。含咖啡因的饮料，包括绿茶（GT），已避免作为不适当的补液饮料，以防止与热有关的疾病，因为咖啡因已被认为发挥利尿/利钠作用。然而,咖啡因摄入对脱水个体尿量的影响尚不清楚.本研究的目的是研究用GT替代液体对轻度脱水个体的体液平衡以及肾脏水和电解质处理的影响。
方法：通过进行3次20分钟的踏步运动，间隔10分钟的休息，使受试者脱水。他们被要求摄取一定量的水（H2O），GT,或含咖啡因的H2O（20mg/100ml；Caf-H2O），等于脱水方案中的失水量；摄入液体后2小时测量液体平衡。
结果：脱水方案诱导约10g/kg体重（约1％体重）的水合不足。在所有试验中，摄入液体后2小时的液体平衡均呈阴性，H2O的液体滞留率为52.2±4.2%，GT为51.0±5.0%，和47.9±6.2％的Caf-H2O；这些值在试验中没有差异。补液后,尿量,尿液渗透压,和尿液中渗透活性物质的排泄物，钠,钾和氯化物在试验中没有差异。
结论：数据表明，摄入GT或同等量的咖啡因不会使摄入后2小时的水合水平恶化，并且可以有效降低液体负平衡，以从轻度水合不足中急性恢复。
背景：ISRCTN53057185；回顾性注册。
方法：通过进行3次20分钟的踏步运动，间隔10分钟的休息，使受试者脱水。他们被要求摄取一定量的水（H2O），GT,或含咖啡因的H2O（20mg/100ml；Caf-H2O），等于脱水方案中的失水量；摄入液体后2小时测量液体平衡。
结果：脱水方案诱导约10g/kg体重（约1％体重）的水合不足。在所有试验中，摄入液体后2小时的液体平衡均呈阴性，H2O的液体滞留率为52.2±4.2%，GT为51.0±5.0%，和47.9±6.2％的Caf-H2O；这些值在试验中没有差异。补液后,尿量,尿液渗透压,和尿液中渗透活性物质的排泄物，钠,钾和氯化物在试验中没有差异。
结论：数据表明，摄入GT或同等量的咖啡因不会使摄入后2小时的水合水平恶化，并且可以有效降低液体负平衡，以从轻度水合不足中急性恢复。
背景：ISRCTN53057185；回顾性注册。
