Roasted green tea (Hojicha) may boost brain function. Adobe AI-Generated Image
A small-scale clinical trial revealed that Japanese subjects who consumed roasted Hojicha performed better on mental tasks than when consuming green tea or warm water.
The findings reinforce the theory that drinking small quantities of green tea daily boosts brain function, concluding that “it is not only reasonable but also advisable to include green tea in one’s diet,” say researchers.
In their conclusion, researchers found that aromatic stimulation from tea consumed in small quantities over a short duration may also exert positive physiological and subjective effects.
The research was published in the April 13 issue of the peer-reviewed journal Scientific Reports. The study compared the performance of 20 adult males who completed mental performance tests after drinking warm water and again after drinking green tea. Subjects completed five-minute mental arithmetic tasks six times during two sessions on the same day.
In the first session, the men, aged 18-30 (average 23), consumed hot water before completing three tasks, then rested and drank hot water before completing a fourth task. In the second session, the subjects were given a different type of tea, either green or roasted green tea (Hojicha), before completing three tasks. They rested and drank another cup of tea before completing a fourth task, ensuring a rigorous and balanced study design.
One month later, the same subjects were tested, but those who drank green tea on the first day switched to roasted tea so that every subject consumed equal amounts of green tea and hojicha during two sessions.
Eleven specific physiological responses, including tissue blood volume (TBV), tissue blood flow (TBF), and near-infrared spectroscopy assessments, were recorded. Participants also completed a self-evaluation describing their fatigue, stress level, mental workload, and ease of workflow. Results suggest that drinking green tea or roasted green tea helped moderate stress responses.
Drinking roasted green tea also demonstrated greater anti-fatigue properties despite being lower in caffeine than green tea.
The journal article highlights the role of aromatic stimulation in tea. Researchers concluded that tea intake improved mental arithmetic task performance compared to hot water. Inhaling the pyrazines in roasted green tea may also directly affect brain activity and influence mood, relaxation, and alertness.
The researchers observed that “By scrutinizing various indicators, we found that aromatic stimulation of Japanese tea beverages has the potential to induce positive effects, enhance mental task performance, promote refreshment, and alleviate feelings of fatigue.”
Limitations to the study include the fact that the subjects were all males and young. The results may have been biased by repeating the tasks over a short period. In follow-up studies, the researchers suggested that the tea’s aroma should be evaluated without drinking the tea.
Kurosaka, C., Tagata, C., Nakagawa, S. et al. Effects of green tea and roasted green tea on human responses. Sci Rep 14, 8588 (2024).