The science of the mood-changing magic of tea drinks

Researchers are discovering how ingredients in a cup of tea can improve mood, improve concentration, and possibly even prevent depression and memory loss.

For centuries, people worldwide have proven tea’s relaxing and refreshing properties. The traditional calming effects of the Camellia sinensis plant elevate the beverage produced from its leaves to a role beyond quenching thirst – it is taken as a meditation aid, helping to calm the mind. Menstruation or to relax. But while the mental health benefits of C. Sinensis are common knowledge among tea drinkers, scientists are only now beginning to examine how tea works on the mind. Status and awareness.

The science of the mood-altering magic of tea drinks. Credit: Susan Burghart.

For example, researchers have found that drinking tea reduces levels of the stress hormone cortisol. And evidence of long-term health benefits is also emerging: drinking at least 100 millilitres (about half a cup) of green tea daily seems to reduce the risk of developing depression and dementia.

Scientists are also trying to determine the main active compounds that provide the mental health benefits of tea and whether they act alone or in combination with other compounds found in the drink. Tea catechins – antioxidants like epigallocatechin gallate (EGCG) – make up 42% of the dry weight of brewed green tea, and the amino acid L-theanine makes up about 3%. EGCG makes people feel calmer and improves memory and attention when consumed individually. L-theanine was found to have a similar effect when finished in combination with caffeine. Up to 5% of green tea’s dry weight is caffeine, which improves mood, alertness, and cognition.

Andrew Scholey, a pharmacologist at the Swinburne University of Technology in Melbourne, Australia, says the effect of tea on behaviour is somewhat paradoxical. “Tea is soothing, but at the same time warning,” he said, sipping a cup of Earl Gray tea.

The discoveries about tea’s effects on behaviour and mental health come at a time of growing scientific interest in the role of nutrition in mental health and preventive medicine. Physicians need more ways to tackle anxiety, depression, and age-related cognitive decline — conditions that burden the health system and limit treatment options.

“There’s not much out there,” Scholey said. “The idea that maybe dietary agents can help slow the decline could have huge implications for preventive health.”

Stefan Borgwardt, a neuropsychologist at the University of Basel, Switzerland, similarly lamented the lack of available therapies – about a third of people with anxiety and depression never find treatment. Practical, he said.

But he’s cautious about the benefits tea can offer people with clinical depression. “It is important not to overestimate the impacts,” he said. While there is clear evidence of moderate improvement in mood in healthy individuals, studies have yet to prove that tea can help people with mental illness. In addition, researchers need to strengthen their understanding of how tea’s active ingredients affect the body and the dosages required to produce short- and long-term effects.

The benefits of tea

Tea is big business. It is one of the most commonly consumed beverages in the world, and the industry is on the rise. Worldwide, green tea production is expected to grow at an annual rate of 7.5%, reaching 3.6 million tons by 2027, according to projections by the Food and Agriculture Organization of the United Nations. . Given the prominence of tea, surprisingly little is known about its effects on human behaviour, says Scholey. Much of the available evidence comes from epidemiological studies, which often show positive effects on mood and cognitive function. For example, earlier this year, researchers reported that in a healthy Korean community, people drinking green tea had a 21% lower lifetime risk of developing depression than those who drank green tea.

Borgwardt said the Korean study found that tea had a “relatively strong effect,” equivalent to 2.5 hours of exercise per week. Epidemiological studies suggest that regular long-term consumption of green tea may reduce the risk of dementia. For example, a study of over-55s in Singapore found that those who drank at least one cup of tea per week performed better on memory and information processing tasks than those who did not.

But epidemiological studies have limitations. Borgwardt said other genetic or lifestyle factors could be responsible for the positive results.

“A lot of research shows something is happening with tea. But the way the study was done doesn’t shed any light on what’s going on,” said David Kennedy, a biological psychologist at Northumbria University in Newcastle, UK.

One possible confounding factor is that preparing and drinking tea is at work, not the tea itself.

In 2007, Andrew Steptoe, a psychologist at University College London, investigated whether tea’s relaxing effects are a direct biological result or stem from the social context in which the drink is drunk, such as sitting quietly to rest. “Teas are often drunk under conditions conducive to relaxation, which in themselves may be responsible for the obvious benefits,” says Steptoe.

EEG measurement can be used to assess brain activity after drinking tea. Credit: Swinburne Neuroimaging

Steptoe and his team examined the effects of drinking black tea in healthy men compared with a caffeinated placebo. The tea and the placebo were presented as fruit-flavoured powders, coloured like tea, to mask any differences between the two beverages. Researchers found that tea helped people recover faster from a stressful job. Saliva levels of the stress hormone cortisol dropped to 53% of baseline within 50 minutes of the task for the tea group, compared with 73% of baseline for the placebo drinkers. Medicine. The tea drinkers also reported feeling more relaxed than the placebo drinkers.

Brain Booster Ingredients

Researchers are also beginning to look at which compounds confer the beneficial properties of tea. Tests on the main ingredients – L-theanine and EGCG – show that they contribute alone and in combination with caffeine.

In 2016, Scholey and his colleagues reported that volunteers who consumed a nutritional drink containing 200 milligrams of L-theanine — about the amount found in eight cups of tea — had lower cortisol levels and said they felt more comfortable after doing stressful tasks than when they don’t. Placebo users 4. The researchers also used electroencephalogram (MEG) recording to assess changes in brain activity related to drinks. People who are naturally more anxious show an increase in lower frequency brain waves, known as alpha fluctuating activity. Alpha brain waves are associated with relaxation and a lack of active cognitive processing.

In a previous study, Scholey found that L-theanine improved memory and reaction time when consumed with caffeine, which was more significant than caffeine or L-theanine5 alone. Scholey says that the end result of L-theanine’s contrasting effects is “a relaxed, energized state of mind — you’re in the zone.” He suspects that this meditative state is partially achieved because L-theanine relaxes only areas of the brain that are not needed to perform tasks, as the MEG analysis has shown. “It improved the signal-to-noise ratio — not by increasing the signal, but by reducing noise,” he says. “This allows for improved concentration and attention.”

Borgwardt says L-theanine can affect brain chemicals in several ways. This compound crosses the blood-brain barrier, so it may directly benefit brain plasticity, the brain’s self-renewal process. It can also act on the pituitary-adrenal axis (the body’s stress response system), reducing cortisol and stress levels. Animal tests show that L-theanine enhances the neurotransmitter GABA (γ-aminobutyric acid), reducing anxiety.

Green tea’s other primary ingredient, EGCG, contributes to the drink’s mental health benefits. In a detailed study, Scholey used an EEG to compare the brain activity of people who consumed a nutritional drink containing EGCG or a placebo. Those taking EGCG experienced increased brain activity across all frequency bands: alpha waves; theta waves, which are associated with quiet alertness; and beta waves, which increase concentration and attention. Research shows that EGCG drinks foster a relaxed state of mind and attention6. Animal and test-tube studies7 have shown that EGCG can cross the blood-brain barrier to act directly on the brain and improve the health of blood vessels and enhance nitric oxide delivery. Together can benefit cognitive function.

Although research on the mental health benefits of tea is accelerating, much is still unknown. Researchers still need to understand how the compounds that make up tea work together. Caffeine is known to benefit mood and cognition, and its biochemistry is widely understood – it prevents the sleep-regulating chemical adenosine from binding to its receptors, which helps maintain nerve activity. and makes caffeine drinkers feel more alert. But little is known about how caffeine interacts with EGCG. Likewise, it is unclear whether caffeine enhances the cognitive effects of L-theanine or vice versa. It will be necessary to resolve such uncertainties before researchers can more accurately determine the long-term benefits of tea and its potential use in people with mental illness. And for some researchers, including Scholey, tea’s effects on mood and cognition raise even more profound and more esoteric questions. For instance, why didn’t the brain evolve to function optimally without consuming chemical beers?

For now, there’s no reason not to encourage healthy people to drink tea to improve their mood and focus, says Borgwardt. Drinking tea can provide a leisurely supplement, or even an alternative, to the mood-enhancing effects of exercise, he says. “Why not have a good cup of tea?” he says. “It’s easier than running three times a week!”

Nature 566, S8-S9 (2019)
doi: https://doi.org/10.1038/d41586-019-00398-1