Green Tea and Hojicha (Roasted green tea) Affect Physiological Responses, Improve Performance and Help Reduce Fatigue

ITO EN, Ltd. (President: Daisuke Honjo; headquartered in Shibuya-ku, Tokyo) has collaborated with Human, Information and Life Sciences, School of Health Sciences, University of Occupational and Environmental Health, Japan to confirm that the intake of green tea and hojicha (Roasted green tea) affects physiological responses, improves mental task performance and helps reduce the subjective feelings of fatigue. These findings have been published in the academic journal Scientific Reports*¹.

As the expression 日常茶飯 (nichijo sahan, meaning daily occurrence) suggests, tea is a popular beverage that plays essential roles in our lives, such as accompanying our meals, quenching our thirst, relieving fatigue or simply changing our mood. Previous research indicated that the aroma of green tea increased people’s subjective rating of their feeling of relaxation, and therefore that the aroma of green tea can reduce stress*². However, so far, only a few pieces of research were published that objectively evaluated tea’s effects on physiological responses and subjective feelings.

University of Occupational and Environmental Health, Japan and ITO EN research team decided to evaluate the effects of the tea intake on stress reduction and the body’s ability to recover from a multifaceted perspective. Specifically, the joint research team evaluated how the intake of Japanese tea beverages affected people’s physiological responses such as autonomic nervous system activity, mental task performance, and their subjective evaluations, such as feelings of fatigue.

 

Content of Research
Twenty healthy adult male participants rested for five minutes followed by three sets of mental arithmetic tasks, each lasting five minutes. They rested again for five minutes. They drank 50 ml of hot water or commercially available green tea or hojicha four times: before each task and before the final rest. Physiological responses were measured during resting period and performing the mental arithmetic tasks. Before and after each task, the participants were asked to subjectively rate their feelings of fatigue. The hot water/green tea experiment, and the hot water/hojicha experiment were conducted on different days. All participants participated in both experiments.

 

Research Outcomes
The intake of green tea and hojicha improved the percentage of mental arithmetic questions answered correctly more than hot water intake(Figure 1). The results regarding the subjective ratings carried out after the task indicated that hojicha might have anti-fatigue properties (Figure 2). The effects of green tea and hojicha differed in the following aspects : 1) hojicha helped maintain concentration throughout the mental arithmetic task more than green tea, 2) hojicha did not increase the subjective feelings of uneasiness and feelings of local pain or dullness, and 3) hojicha reduced the sense of time pressure, which was not evident with the green tea condition*³.

The intake of green tea and hojicha also affected physiological responses. The responses of tissue blood volume (TBV) of the nose tip, an indicator of peripheral blood constriction*⁴ and the levels of oxyhemoglobin, an indicator of metabolic activity of the brain*⁵, were lower in the tea condition compared to the hot water condition (Figures 3 and 4). They simultaneously increased HF*⁶, CVI*⁷ and BRS*⁸, which are indicators of parasympathetic nervous system activity(Figures 5, 6 and 7). Previous studies have suggested that these physiological responses may be related to the aromatic flavor of green tea/ hojicha.

 

Suggestions of Results
These research results indicate that the intake of green tea and hojicha before or during a task, such as desk work, improves performance and helps reduce the feelings of fatigue. Particularly interesting is that these positive results were obtained within a short duration and in small quantities, similar to amounts consumed daily. Nevertheless, in this research, the repeated mental arithmetic tasks may have allowed participants to familiarize themselves with the process, influencing performance and physiological responses. Further research that disregards the influence of familiarity with tasks is being carried out to obtain more precise results.

People engaged in creative professions, such as working at IT companies, often prefer Japanese tea. In the US, Japanese tea is known as a beverage that inspires creativity. Our research suggested that sipping green tea and hojicha in a “chibidara” fashion*⁹ helps improve task performance and reduce subjective feelings of fatigue. Going forward, as a Health Creation Company, we will continue to contribute to creating healthy and fulfilling lifestyles for customers and a sustainable society from various standpoints, not only conducting research that contributes to the development of products with health appeal, but also actively engaging in research that addresses customers’ concerns and questions about health.

*1 Kurosaka C. et al., Effects of green tea and roasted green tea on human responses. Scientific Reports｜Published: 13 April 2024 (https://doi.org/10.1038/s41598-024-59383-y)
*2 Murao, S., Yoto, A. & Yokogoshi, H. Effect of smelling green tea on mental status and EEG activity. Int. J. Affect. Eng. 12, 37–43 (2013)
*3 Tagata C. et al., Effects of green tea and roasted green tea intake on mental task performance and subjective evaluation. Japanese Pharmacology & Therapeutics vol. 51 no. 9 1377-1388 (2023)
*4 It reflects peripheral vascular constriction (alpha sympathetic nervous sysyem activity) as the nasal tip blood volume is particularly influenced by stress.
*5 Oxidized hemoglobin. Measuring of the levels of hemoglobin in biological tissue using functional near-infrared spectroscopy to evaluate changes in cerebral blood flow. It is an imaging technique that measures blood oxygenation changes in the cerebral cortex located approx. 3 cm below the cortical surface to assess cerebral metabolism.
*6 High-frequency components obtained by the spectral analysis of RRI fluctuations (0.15-0.4 Hz). It is used as a cardiac autonomic index, which is influenced by changes in intrapleural pressure result from breathing and by signals from the respiratory center. It is believed to be controlled mainly by the parasympathetic nervous system (Figure 8). *RRI: The interval between R waves in the electrocardiogram. Heart rate is calculated as the reciprocal of the mean RRI measured in beats per minute (Figure 9).
*7 CVI is calculated from the Poincaré Plot of RRI. It is considered an indicator of parasympathetic nerve activity. The equation required is CVI = log (SD2 x SD1). *SD1: The minor width of the ellipse fitted to the Poincaré plot showing the scatter plot of RRI(i) and RRI(i+1). SD2: The major width of the ellipse (Figure 10).
*8 BRS (Baroreceptor Sensitivity) is a measure of autonomic control of heart activity, which plays an important role in the regulation of blood pressure. It is measured by monitoring the arterial pressure pulse by pulse and is considered a reliable indicator of parasympathetic nervous system activity because only parasympathetic nervous system controls it. BRS is a ratio between heart rate (RRI) change and blood pressure change (BRS=(LF_RRI/LF_SBP)^1/2 [msec/mmHg]). LF_RRI and LF_SBP are low-frequency components of power spectra of RRI fluctuations and SBP fluctuations, respectively. *Low-frequency band = 0.05-0.15 Hz
*9 Sipping a small amount of tea over a long period of time while carrying out desk work.