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A cup of green tea or roasted green tea before undergoing a mental task could help improve performance, a new study shows. Image credit: Costfoto/NurPhoto via Getty Images.
  • Roasted green tea is a traditional Japanese tea that is roasted over charcoal.
  • A new study suggests that drinking modest amounts of regular and roasted green tea may improve mental task performance.
  • Although the research has limitations, starting a daily green tea habit is worthwhile, according to experts.

Roasted green tea, also known as houjicha, is a type of Japanese green tea roasted over charcoal to give the tea a unique smoky flavor and dark brown color.

Previous research has highlighted the cognitive benefits of green tea consumption, though the research has often focused on long-term effects, individual compounds in isolation, or high consumption.

Now, a recent study published in Scientific Reports explored the potential acute impacts of roasted green tea and green tea consumption on mental task performance compared to plain water.

The findings suggest that even small daily servings of green tea or roasted green tea may significantly improve task performance and mental well-being.

This study’s participants included 20 healthy adult men from Japan, with an average age of 23. They were tasked with completing a 5-minute mental arithmetic task six times across two sessions in a single day.

In the first session, they consumed hot water before the first three tasks and then hot water again before a rest period, totaling four water intakes.

In the second session, participants either drank green tea or roasted green tea before tackling the remaining three tasks and prior to another rest period, also totaling four tea intakes.

This process was repeated on a second day, 1 month later, with the type of tea being switched so that all participants experienced both teas.

During these tasks, the researchers measured 11 different physiological responses to assess the impact of drinking hot water, green tea, or roasted green tea on their mental task performance.

They also gathered participants’ self-evaluations on fatigue, stress, mental workload, and workflow to complement their physiological data.

Compared to drinking hot water, tea consumption during tasks resulted in significantly lower tissue blood volume (TBV), tissue blood flow (TBF), and near-infrared spectroscopy responses (NIRS) in participants.

These results suggest that drinking green tea or roasted green tea may have helped moderate the participants’ physiological stress responses.

Aromatic compounds present in green tea, known to have relaxation effects, appeared to play a significant role in these positive outcomes.

“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,” wrote the study authors.

Throughout all sessions, task performance was significantly higher with tea consumption than water.

However, only the roasted green tea seemed to have anti-fatigue properties despite being lower in caffeine content than regular green tea.

Particularly in the sessions where roasted tea was used, a higher number of task repetitions also led to a greater improvement in response rate and task performance.

Importantly, these benefits were observed with small amounts of tea and within a short time frame, which aligns with typical daily tea consumption habits.

To gain insight into the mechanisms behind this study’s results, Medical News Today spoke with Alyssa Simpson, RDN, CGN, CLT, owner of Nutrition Resolution, and Eliza Whitaker, MS, RDN, a registered dietitian and medical nutrition advisor at Dietitian Insights, who were not involved in the study.

Simpson explained:

“The study highlights the role of aromatic stimulation from tea, particularly compounds like pyrazines in roasted green tea, in influencing mood, relaxation, and alertness by directly affecting brain activity. Additionally, tea consumption induces peripheral vasoconstriction, potentially contributing to feelings of refreshment and increased alertness. “

“The study also suggests that aromatic stimulation activates the parasympathetic nervous system, leading to relaxation and reduced stress responses, ultimately enhancing task performance and reducing subjective feelings of fatigue,” she said.

Whitaker agreed, noting: “When comparing roasted green tea and green tea, roasted green tea contains more pyrazine and aromatic components which could contribute to the mechanism behind the benefits of this study; however, further research is needed to confirm this.”

Thomas M. Holland, MD, MS, physician-scientist at the RUSH Institute for Healthy Aging, Rush University System for Health, not involved in the study, clarified that despite green tea’s demonstrated effect on mental task performance, “[a]ssessing the overall impact on brain health in this study presents some challenges.”

He explained that “[t]he study’s demographics, including the number of participants, follow-up procedures, and age and sex distribution, are quite limited, making it difficult to generalize the findings to any other populations.”

Holland also expressed potential issues with study’s experimental design. “One notable concern is the repetition of the mental arithmetic task six times within a single day,” he told us.

“This frequent repetition could potentially introduce a practice effect, wherein performance improves with repeated exposure to the task. Practice effects are commonly seen as a source of bias in cognitive assessments,” cautioned Holland.

Jane Ujoatu, DrPH, RDN, a registered dietitian and owner of Encore Nutrition and Public Health Consulting, who was not involved in the research, highlighted the need for future research to compare the effects of different teas, such as black or oolong tea, on mental tasks and to include diverse participants, those with health conditions, and women.

Factors including age, diet, and lifestyle may also affect green tea’s effectiveness in enhancing mental performance.

Ultimately, Holland said, “[f]urther research is needed to explore the long-term implications and to address potential confounding factors such as practice effects.”

“Incorporating green tea and roasted green tea into your routine can provide numerous health benefits, but it’s essential to be mindful of certain considerations,” said Simpson.

She recommended trying various brands and brewing methods and advises keeping it to a few cups daily to avoid any adverse effects.

People on medication, particularly for high blood pressure or on blood thinners, should be careful of potential interactions, and those with kidney stone history should also be cautious of green tea’s oxalate content, she said.

Whitaker suggested that green tea, containing less caffeine than coffee or black tea, can be a suitable alternative for those wanting improved focus with lower caffeine intake.

Regarding whether individuals should incorporate green tea, Holland concluded:

“Considering that green tea is abundant in flavan-3-ols — comprising multiple catechins among other flavonoids — and flavonols, both of which have been linked to enhanced brain health, it is not only reasonable but also advisable to include green tea in one’s diet.”