Diet and Brain Health

Roasted Green Tea May Boost Cognitive Performance

Most of us know have heard that green tea is good for you. Past research has hinted at the traditional beverage’s potential benefits, ranging from lowering cholesterol and stroke risk to alleviating anxiety and managing Type 2 diabetes. But a new study published in Scientific Reports indicates that even a small daily serving of regular or roasted green tea may significantly improve not only mental well-being, but also task performance.

The Research

The recent study, which included 20 healthy male participants from Japan (average age of 23), took place over the course of a single day and then again one month later for a day.

First, the men drank hot water before each of three 5-minute mental arithmetic tasks. After the task, they drank hot water again (for the fourth time) before resting. Later that day, the participants repeated the tasks but swapped out the hot water for either green tea or roasted green tea. One month later, the type of tea was changed to give all the participants experiencing with both kinds. The men who had consumed green tea were given roasted green tea and vice versa.

Throughout the mental arithmetic tasks in all of the experiments, the researchers measured the following physiological responses:

Electrocardiogram: measures electrical activity of the heart

• Respiration: the number of breaths a person takes per minute

Electroencephalogram: measures the electrical activity in the brain

• Photoelectric plethysmogram: detects blood volume changes in the microvascular bed of tissue

• Skin potential level: a measurement of the potential difference between electrodes without current flow

• Continuous blood pressure

• Cardiac output

• Tissue blood volume

• Tissue blood flow

Near infra-red spectroscopy: monitors cerebral oxygenation

In addition, the scientists had participants fill out evaluations on stress, mental workload, fatigue, and workflow.

The Results

Overall, the participants’ task performance was significantly higher with green tea consumption compared to hot water consumption. But specifically, tea consumption resulted in significantly lower:

• tissue blood volume

• tissue blood flow

• near-infrared spectroscopy responses

These positive results suggest that consuming the tea (either regular green tea or roasted green tea) may have improved the participants’ physiological stress responses.

Perhaps most surprising: drinking the roasted green tea appeared to produce an anti-fatigue effect for the participants, despite containing less caffeine than the regular tea. In addition, after drinking the roasted tea, the participants had a greater improvement in response rate and task performance when a higher number of task repetitions was performed.

So, what is it about green tea—especially roasted green tea—that seems to help with cognitive performance?

“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,” explained Alyssa Simpson, RDN, CGN, CLT, and owner of Nutrition Resolution, who was not involved in the study. “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.”

Limitations of the study

Beyond the fact that 20 participants makes for a very small study, there were other limitations that require more research to be done before scientists can confirm the overall impact of green tea on brain health and cognitive performance.

For example, the study was limited to healthy young men from Japan, and there were no follow-up procedures. In addition, the study’s experimental design was limited to one type of task performed over one day.

“This frequent repetition could potentially introduce a practice effect, wherein performance improves with repeated exposure to the task,” noted Thomas M. Holland, MD, MS, a physician-scientist at the RUSH Institute for Healthy Aging, Rush University System for Health, who was not involved in the study. “Practice effects are commonly seen as a source of bias in cognitive assessments.”

Adding green tea to your diet

For most people, adding a cup of green tea to your diet has little risk and the beverage is abundant in flavonoid antioxidants, which can help support healthy blood circulation. However, people on blood thinners or high blood pressure medications, or those with a history of kidney stones, should consult with their doctor before consuming green tea as a regular part of their diet.


Wendy Burt-Thomas writes about the brain, mental health and parenting.

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