On the fatigue reducing effects of Japanese green tea (Camellia sinensis (L.) Kuntze) from Uji
Green tea is consumed in Japan since more than a thousand years for its alleged ability to reduce mental fatigue and for its general health improving effects, which are mainly attributed to its prominent phenolic constituents such as epigallocatechin gallate. However, comprehensive parallel examinations of its psychological, physiological, and immunological effects in humans have not been conducted up to now. In this randomized cross-over human trial – conducted with green tea from the famous plantations of Uji in Kyoto – we monitored all these effects in a coordinated way. After 120 min of highly fatigue inducing computer work, subjects were randomized into two groups. Group 1 conducted the green tea trial on the first day and the water control on the second day. In group 2, the order was reversed. Otherwise, all procedures were carried out identically. Data were collected by means of blood sampling for natural killer (NK) cell activity, electrocardiography (ECG) with power spectrum analysis for heart rate variability – especially for both high frequency (HF) values and the average ratios between low and high frequencies (LF/HF) – as an indicator for the function of the autonomic nervous system, electroencephalography (EEG) for P300 event related potentials (ERP), and a questionnaire for assessing subjective psychological reactions. All measurements were executed three times: before and after the computer fatigue inducing task as well as 30 min after drinking either green tea or water. The heart rate variability results indicate that green tea induces dominance of the parasympathetic nervous system, while the P300 data demonstrate an improvement in attentiveness. Furthermore, NK activity was also notably elevated and fatigue scores were improved by green tea intake. Thus, this study comprehensively demonstrates the fatigue reducing effect of Uji green tea in psychological, physiological, and immunological parameters.