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"An optimal drink" for stress: drinking tea also strengthens the immune system and cognition.
Dr. Sheena Meredith, MB BS, MPhil
April, 28th, 2022
The first thing many of us tend to say if a friend comes to us in distress is: "I'll put the kettle on and make a cup of tea" – and there are sound scientific as well as psychological reasons for this, according to Louise Dye, professor of nutrition and behaviour at the University of Leeds, also a chartered health psychologist and associate editor of Nutritional Neuroscience.
"There is strong evidence that tea and its constituents seem to be beneficial under conditions of stress," Prof Dye told a virtual audience at the Sixth International Scientific Symposium on Tea and Human Health this week. "That everyday response might actually be very beneficial to reducing our cortisol response."
When animals experience stress, they have a physiological fight-or-flight response, but return to a low stress state once the danger is over, she said. But for humans, "stress doesn’t necessarily go away".
In adult humans, stress occurs as a response to a perceived imbalance between situational demands and the resources needed to cope with them, and this stress activates the hypothalamus and the adrenal cortex to produce a cortisol response. But in most of our everyday situations, it’s more difficult to return to that low stress state.
There is also growing interest in the potential for tea and its constituents to modulate brain activity, Prof Dye said. On an EEG, alpha waves are associated with an alert but relaxed state. Studies of tea, green tea in particular, show it has a capacity to moderate resting state alpha activity.
In a study comparing 50 mg L-theanine - an amino acid found mainly in green and black tea - with a water control, the tea but not the water produced an increasing alpha rate over a period of 105 minutes, showing an increasingly relaxed state.
In addition, epidemiological studies have suggested links between tea consumption and cognitive function, and stress affects multiple dimensions of cognitive function, Prof Dye said.
"When we’re under conditions of stress, that affects our ability to maintain attention, to remember things, to coordinate our motor skills and to exercise executive function, to make judgements and decisions... stress shapes our cognitive function; it shapes how we comprehend, store and use information."
"The most profound cognitive domain that tea seems to act upon is attention and alertness," said Prof Dye. She reported a review she conducted of published research on tea constituents and cognition. After eliminating studies, including participants with some cognitive impairment, she found just seven studies offering good quality methodology: randomised controlled trials with blinded controls employing sensitive cognitive tests in healthy non-impaired people. "Overall, across those seven studies, we saw an improvement in cognition, particularly attention," she said.
Other studies of tea and its constituents have supported the conclusion that tea consumption can produce short-term acute beneficial effects on cognitive performance under stress, measured by objective tests such as an attention switching test.
For example, young adults given 2 g of macha (green tea) daily for 2 weeks were better able to maintain attention in a stressful mental arithmetic task. In another study with older adults aged 50-69, just a single dose of macha improved attention, and repeated dosing over 12 weeks improved work capacity. Another study showed that macha combined with caffeine improved both attention and work capacity when under stress better than caffeine alone. Black tea has been also proven to improve attention.
The mental and psychological effects of tea have been attributed to its unique combination of caffeine and L-theanine, with the latter shown to attenuate cardiovascular as well as cortisol responses to acute stress. Studies also consistently show beneficial effects of the high dose of L-theanine, together with a lower dose of caffeine in tea (compared with coffee), on attention task performance, and the combination may exert different effects from those obtained with caffeine alone.
"Most of these positive effects could be attributed to either the L-theonine in the tea, or the L-theonine and the caffeine," Prof Dye said.
"With these effects on attention, tea is an optimal beverage of choice during a time of elevated stress and burnout worldwide." Subjective reports of alertness also improved among participants in these studies. "Stress is in the eye of the perceiver," Prof Dye said. "It's not just an objective measure, it’s also how those individuals feel."
Speaking to Medscape UK after the symposium, she explained that unlike animals, returning to a resting state after a stressful reaction "doesn’t happen too much in humans".
"The kinds of stresses that we’re confronted with are things that we perceive as stressful and that we can’t necessarily run away from. It’s an imbalance between what’s going on in our situation and how much we can cope with that situation. So stress is a pattern: how you perceive it, your physiological response and then your behavioural tendencies, what you’ve learned in terms of how to cope.
"In the current climate, people are very stressed," she said. "They have been very isolated; they’ve been at home, trying to do jobs and manage kids, all that sort of thing. We’ve all had much more stressful lives of the past couple of years, and it’s been an unfamiliar kind of stress, because we've all been put in this very novel situation where we may not have all the resources to cope as well."
In terms of the beneficial effects of tea on cognition and stress, in order to show cause and effect, we need to know what the mechanisms are, and we don't have enough high quality evidence as yet.
"It seems likely that those positive effects are due to the L-theonine content of the tea or that combination of L-theonine and caffeine". The caffeine content of tea is much lower than in coffee, so the combination, the synergistic effect seems to be what’s important.
However: "It’s the feeling of being more alert that’s probably going to drive consumption, rather than evidence of performing ever so slightly better.
"There might be something physiological that’s driving the subjective feeling; it could also be something that’s related to your memory of events, of how you respond to situations.
"The other point I made during the symposium is that it’s not just about the active ingredients in these drinks, it's also the psychological thing... there is an association between consuming that drink, that food, and feeling calmer.... you can’t separate out the psychological aspects of that. We’ve grown up drinking it, we have a strong association with it."
Nor is this just an English thing. "There are an awful lot of cultures that drink tea... a lot of culture and tradition centres around tea-drinking. So it's very difficult to separate out, and that’s where that subjective feeling comes from as well.
"Some ingredients do seem to have effects on our ability to perform in stressful situations, and also seem to make us feel more relaxed and less stressed." So there remains "an association between something [bad] happening and putting the kettle on".
Tea is the second most consumed beverage in the world next to water, and other evidence presented at the symposium revealed benefits on immune function, cardiometabolic disease, cognitive decline, and cancer prevention.
"There is a growing body of research from around the world demonstrating that drinking tea can enhance human health in many ways," said symposium chair, Jeffrey Blumberg, PhD, professor emeritus at the Friedman School of Nutrition Science and Policy at Tufts University.
"There may be other herbals and botanical products that can deliver health benefits, but none of them are as systematically studied as Camellia sinensis – true tea," said Mario Feruzzi, PhD, professor and chief of the section of developmental nutrition in the Department of Pediatrics at the University of Arkansas for Medical Sciences. "With true teas – white, green, black, and oolong - you’re dealing with thousands of years of traditional use, 60-70 years of systematic study which, in the last 15-20 years, has ramped up to the point where we have very definitive data."
The symposium heard that, as well as L-theanine, tea contains flavonoids, which have strong antioxidant properties to neutralise free radicals and have been shown in experimental studies to have anti-carcinogenic properties, which may explain why higher tea consumption had been associated with a reduced risk of some cancers, particularly biliary tract, breast, endometrial, liver, and oral cancer.
Flavonoids also have antioxidant, anti-angiogenesis, and anti-inflammatory mechanisms as well modifying the profile of gut microbiota.
"Tea may help support your immune system and increase your body's resistance to illnesses," said Dr Dayong Wu of the Nutritional Immunology Laboratory in the USDA Jean Mayer Human Nutrition Research Center on Aging at Tufts University. He presented data from a comprehensive review showing that the catechins in green tea help to decrease a pathogen's ability to infect the host and to enable the immune system spring into action.
"In the event you do become sick, tea can help your body respond to illness in a more efficient way by ridding itself of the infection, and may also alleviate its severity when [infections] happen."
Green tea and catechins have also been shown to improve autoimmune disorders by promoting self-tolerance, suppressing autoantigen-induced inflammatory attack, and enhancing tissue repair.
Further evidence of the benefits of tea on cognition were revealed by Jonathan Hodgson, PhD, professor at the Institute for Nutrition Research at Edith Cowan University.
"There is growing evidence that as little as one to two cups of tea daily could significantly reduce risk of vascular dementia and potentially Alzheimer’s disease," he said. High-quality data from long-term, prospective cohort studies also show that moderate intakes of the flavonoids present in tea are associated with reduced risk for cognitive decline and particularly vascular dementia, with maximal benefit from as little as two to four cups per day.
Taylor Wallace, PhD, a professor in the Department of Nutrition and Food Studies at George Mason University told the symposium that tea consumption has the potential to mitigate cardiometabolic disease risk and progression in adults, and may be inversely associated with adverse cardiometabolic outcomes. Population studies have demonstrated that each daily cup of unsweetened tea was associated with an average 1.5% lower risk of all-cause mortality, 4% lower risk of cardiovascular disease mortality, 2% lower risk of CVD events, and 4% lower risk of stroke events.
"When you look at all the different biomarkers and mechanisms that tea is affecting, this bountiful beverage is one which consumers can easily add to better their diet and create a healthier and longer life for themselves," he said.
The Sixth International Scientific Symposium on Tea and Human Health was co-sponsored by the American Cancer Society, American Institute for Cancer Research, American Nutrition Association, American Herbal Products Association, Osher Center for Integrative Medicine at the Harvard Medical School and the Linus Pauling Institute at Oregon State University.
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„Ein optimales Getränk“ gegen Stress: Teetrinken stärkt zudem das Immunsystem und die Kognition.
Dr. Sheena Meredith, MB BS, MPhil
12. Mai 2022
Das Erste, was viele von uns sagen, wenn ein Freund in Not zu uns kommt, ist: "Ich setze den Kessel auf und mache eine Tasse Tee" - und dafür gibt es sowohl wissenschaftliche als auch psychologische Gründe, wie Louise Dye, Professorin für Ernährung und Verhalten an der Universität Leeds, Gesundheitspsychologin und Mitherausgeberin von Nutritional Neuroscience, erklärt.
"Es gibt eindeutige Beweise dafür, dass Tee und seine Inhaltsstoffe unter Stressbedingungen vorteilhaft zu sein scheinen", sagte Prof. Dye diese Woche vor einem virtuellen Publikum auf dem Sechsten Internationalen Wissenschaftlichen Symposium über Tee und menschliche Gesundheit. "Diese alltägliche Reaktion könnte tatsächlich sehr vorteilhaft sein, um unsere Cortisolreaktion zu reduzieren."
Wenn Tiere Stress erleben, haben sie eine physiologische Kampf-oder-Flucht-Reaktion, kehren aber in einen niedrigen Stresszustand zurück, sobald die Gefahr vorüber ist, sagte sie. Aber beim Menschen geht der Stress nicht unbedingt weg".
Bei erwachsenen Menschen tritt Stress als Reaktion auf ein wahrgenommenes Ungleichgewicht zwischen den Anforderungen der Situation und den zu ihrer Bewältigung erforderlichen Ressourcen auf, und dieser Stress aktiviert den Hypothalamus und die Nebennierenrinde, um eine Cortisolreaktion zu erzeugen. In den meisten unserer alltäglichen Situationen ist es jedoch schwieriger, zu diesem niedrigen Stresszustand zurückzukehren.
"Wir können nicht vor einem wütenden Chef davonlaufen - und wir sollten uns auch nicht gegen ihn wehren -, aber eine Tasse Tee könnte tatsächlich von Vorteil sein, denn das im Tee enthaltene L-Theonin reduziert die Cortisolreaktion auf akuten Stress.
Tee fördert die Alphawellen-Aktivität
Es gebe ein wachsendes Interesse daran, dass Tee und seine Inhaltsstoffe die Gehirnaktivität modulieren können, sagte Dye. In einem EEG werden Alphawellen mit einem wachen, aber entspannten Zustand in Verbindung gebracht. Studien über Tee, insbesondere über grünen Tee, zeigen, dass er die Alpha-Aktivität im Ruhezustand moderieren kann.
In einer Studie, in der 50 mg L-Theanin – eine Aminosäure, die vor allem in grünem und schwarzem Tee enthalten ist – mit einer Wasser-Kontrollgruppe verglichen wurden, führte der Tee, nicht aber das Wasser, über einen Zeitraum von 105 Minuten zu einem Anstieg der Alpha-Aktivität, was einen zunehmend entspannten Zustand anzeigt.
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Zu zitieren: Dr. Sheena Meredith, MB BS, MPhil. Eine Tasse Tee kann wirklich Stress abbauen - Medscape News UK - 28 April 2022