Tea has been praised for its relaxing and rejuvenating properties by people worldwide for centuries. The traditional soothing effects of the Camellia sinensis plant have elevated tea to a role that goes beyond quenching thirst. It is used to aid in meditation, soothe nerves, or relax. Although the mental-health benefits C. Tea drinkers are familiar with the mental-health benefits of C. Sinensis, scientists are just beginning to study how tea affects mood and cognition.

For example, researchers have shown that tea can lower cortisol levels. Evidence is also emerging that green tea has long-term health benefits. Studies show that drinking 100ml (roughly half a cup) per day of green tea reduces the likelihood of developing depression or dementia.

Scientists are also trying to identify the main active compounds in tea that confer mental-health benefits. They want to know if they can be used alone or in combination. Tea catechins, antioxidants like epigallocatechin gallate (EGCG), can account for 42% of the brewed green-tea weight. L-theanine accounts for around 3%. EGCG can be used alone to calm people and improve attention and memory. L-theanine, also known to improve attention and memory, has a similar effect when combined with caffeine. Green tea can contain as much as 5% caffeine. This is believed to increase mood, alertness, and cognition.

Andrew Scholey, a psychiatrist at Swinburne University of Technology, Melbourne, Australia, believes that tea’s effect on behaviour is somewhat paradoxical. While sipping Earl Grey tea, he said, “Tea is calm but alerting at the same time.”

Research into the effects tea has on mental and behavioural health comes when there is increasing scientific interest in nutrition and its role in preventative and mental health. These conditions are extremely burdensome for health systems, and physicians need to find more effective ways to treat them.

Scholey says, “There’s not much out there.” “The possibility that dietary agents could slow down the decline could have huge implications for preventative healthcare.”

Stefan Borgwardt is a neuropsychiatrist from the University of Basel in Switzerland. He also laments the absence of effective therapies. Around one-third of people suffering from anxiety or depression don’t find a treatment that works.

He is careful about what tea can do for those who are clinically depressed. He says, “It is important not to overestimate its effects.” There is evidence that tea can improve mood in healthy people, but studies have not shown that tea can benefit those with mental illnesses. Researchers need to improve their understanding of the effects of active ingredients in tea on the body and the dosages required to achieve these effects.

Benefits of a brew

Tea is big business. The industry is growing rapidly, and green tea is one of the most popular drinks in the world. According to the Food and Agricultural Organization of the United Nations, green tea production worldwide will grow at 7.5% per year and reach 3.6 million tonnes by 2027. Scholey says that despite tea’s popularity, very little is known about its effects on human behaviour. Many epidemiological studies show that tea positively affects mood and cognitive function. Researchers reported earlier this year that green tea drinkers were 21% less likely than non-drinkers to develop depression in a healthy population.

Borgwardt claims that the Korean study proves that tea has a “relatively strong effect”, comparable to 2.5 hours of daily exercise. Studies suggest that green tea consumption may reduce dementia risk if it is continued for a long time. One study of people aged over 55 in Singapore, for example, found that those who drank as little as one cup of tea per week performed better at the memory and information-processing tasks than did non-tea-drinkers2.

However, epidemiological studies are limited. Borgwardt suggests that other lifestyle factors and genetics could also be responsible for positive results.

“Lots and lots of research show that something is happening to tea. However, the method of research doesn’t reveal what is going on,” said David Kennedy, a Northumbria University biological psychologist in Newcastle, UK.

One possibility is that the effect of the preparation and consumption of tea is the confounding factor, not the actual tea.

 A University College London psychologist, explored whether the relaxing properties of tea are biologically derived or if they can be attributed to the context in which it is consumed. For example, Steptoe studied the effects of sitting still for a break and sitting down for a while. Steptoe states that tea is often consumed in conditions that promote relaxation, which may be responsible for its apparent benefits.

Steptoe and his colleagues compared the effects of black tea to a placebo. To mask the differences between the tea and placebo, the tea was presented in the form of fruit-flavoured powders that were coloured as tea. Researchers found that people recovered faster from stressful tasks. The tea-drinking group saw their saliva levels of stress hormone cortisol drop to 53% within 50 minutes, while the baseline level was 73% for those who drank a placebo. Tea drinkers reported feeling more relaxed than those who had drank a placebo.

Brain-boosting ingredients

Researchers are now beginning to investigate which compounds give tea its health benefits. The key components L-theanine, EGCG and EGCG, have been tested and found equally effective when combined with caffeine.

Scholey and his coworkers reported in 2022 that volunteers who drank a nutrient drink with 200 mg of L-theanine, which is roughly the same amount as eight cups of tea, had lower cortisol levels. They also reported feeling less stressed after performing tasks that involved stress. The researchers also used magnetoencephalography (MEG) to assess changes in brain activity associated with the drink. The alpha oscillatory activity, a higher frequency brainwave associated with people who are naturally more anxious, was seen in those who were naturally more anxious. Alpha brainwaves can be associated with relaxation and lack of active cognitive processing.

Scholey previously found that L-theanine had a greater effect on memory and reaction times when consumed with caffeine. Scholey says that L-theanine’s contrast effects result in a “relaxed and capable state of mind” — you are “in the zone”. Scholey believes that L-theanine relaxes only those brain areas not required to perform tasks. This is evident in the MEG analysis. He says that L-theanine improved the signal to noise ratio not by increasing the signal but by decreasing the noise. This allows for better focus and attention.