ChapterPDF Available

Abstract and Figures

Tea is the world’s favorite beverage; thus, any health-related psychological or physiological consequences of drinking tea could have considerable impact. Although tea is available in many forms, “true” teas all derive from the tea plant, Camellia sinensis: the variety of beverages reflects primarily how the leaves are processed and fermented. For example, green tea is essentially unfermented, whereas black tea is extensively fermented. Tea contains many chemicals with potential for biological activity; in particular, the flavonoids, e.g. catechins, have good antioxidant capability in vitro. In the laboratory, these components, and tea itself, may suppress the damaging activity of free radicals, reduce inflammation and risk of blood clotting, and improve the responsiveness of blood vessel walls to changes in blood flow. Consequently, in studies dissociating other lifestyle factors, tea drinking seems to reduce cardiovascular disease risk.Despite promising laboratory evidence, observational studies of effects of normal tea drinking in large populations and its relation to cancer incidence have been inconsistent. One reason could be that, to protect against cancer, tea may need to be drunk at quite a high level and by populations that eat relatively low amounts of fruit and vegetables, i.e. tea might particularly lower cancer risk in those with an otherwise unhealthy diet.Drinking green tea or tea catechins has been studied for any impact on body weight and body fat: there is evidence that these can be reduced by such treatment in overweight or obese people, potentially by stimulating fat oxidation.Tea appears to have subtle effects on the brain, including aiding recovery from stress, and has been linked to resistance to depression, possibly via effects of the amino acid, theanine, which is known to alter brain electrical activity. This, together with mood and performance effects, suggests that tea may promote a more relaxed state that improves sustained attention. Theanine also interacts with caffeine, so that the combination produced better performance than either alone; theanine suppressed the rise in blood pressure caused by caffeine. In addition to short-term benefits for brain function, tea may protect nerve cells from damage, and promote their growth, suggesting protection against neurodegenerative diseases. Population-based studies show delayed cognitive decline in elderly tea drinkers, and reduced risk of Parkinson’s disease. Therefore, although more research is needed, evidence suggests that habitual tea drinking may benefit both the cardiovascular system and the brain, and improve our physical and psychological health.
Content may be subject to copyright.
621
V.R. Preedy et al. (eds.), Handbook of Behavior, Food and Nutrition,
DOI 10.1007/978-0-387-92271-3_41, © Springer Science+Business Media, LLC 2011
Abbreviations
CVD Cardiovascular disease
EGCG Epigallocatechin gallate
LDL Low-density lipoprotein (cholesterol)
DNA Deoxyribonucleic acid
EEG Electroencephalography
GABA Gamma-aminobutyric acid
CFF Critical flicker fusion test
41.1 Introduction
The beverage tea is second only to water in terms of global consumption of a drink, outstripping all
other drinks put together: in the UK, 77% of adults drink tea, averaging nearly three mugs (540 mL)
per day, with volume increasing with age (Gardner et al. 2007). Moreover, tea is known to most of
the world’s ethnic and cultural groups: therefore, putative effects of tea on health or behavior may
assume considerable importance for public health. This chapter considers the evidence that tea may
affect both these outcomes, through psychological and physiological consequences. There is now a
very substantial literature relating tea to health, but there is only space here to summarize the evi-
dence, concentrating in particular on studies in human beings, and the recent consensus. The impact
of tea on psychological and behavioral outcomes is less thoroughly researched, but nevertheless
several intriguing findings that have emerged in recent years are considered here.
It is important from the outset to define the term “tea” as used in this chapter, since tea can take
many forms across the world. Here, tea refers to the most universally recognized form of beverage,
a hot drink formed from infusing leaves and leaf buds from the shrub Camellia sinensis (familiarly
Chapter 41
Psychological and Physiological Consequences
of Drinking Tea
E.L. Gibson and J.A. Rycroft
E.L. Gibson (*)
Clinical and Health Psychology Research Centre, Department of Psychology,
Whitelands College, Roehampton University, Holybourne Avenue, London SW15 4JD, UK
e-mail: l.gibson@roehampton.ac.uk
622 E.L. Gibson and J.A. Rycroft
known as the tea plant) in hot or boiling water (though once cooled, this beverage can be drunk cold,
as “iced tea”; extracts of tea also form the basis of bottled or canned forms). These tea leaves can be
cultivated, picked, cured, and processed in a variety of ways, resulting in differing fermentation and
oxidation, giving several classes of tea beverage, principally (in order of oxidation): white, green,
oolong, black, and pu-erh teas (Fig. 41.1). In oriental countries, “red tea” is another (arguably more
accurate) term for black tea, although, red tea is also a name used for an infusion of leaves from the
South African “rooibos” (red bush) plant, which thus contains no C. sinensis, or caffeine. Indeed,
infusions of a wide variety of other plants, fruits, and flowers are often referred to as “tea” (or its
equivalent in the local language) in many cultures across the globe, and many of these may have both
psychological and physiological effects relevant to health and well-being (Pardo de Santayana et al.
2005). However, such effects have not been scientifically or extensively researched for most of these
other beverages: indeed, the vast majority of research on tea deals with forms of green or black tea,
which are also the most commonly consumed varieties globally (Table 41.1); therefore, this is the
nature of the evidence summarized in this chapter.
Nevertheless, restricting the scope of the chapter to infusions of the leaf of one plant does not
result in a simple categorization or interpretation of evidence, since the forms of tea from C. sinensis
vary in biochemical content as a result of cultivation of different varieties of the plant, as well as both
preparation of the leaves (Fig. 41.1) and preparation of the infusion (e.g., temperature of the water
and length of brewing time; Astill et al. 2001). Moreover, studies of the potential impact of tea on
health and behavior have often used processed extracts of tea; this has the advantage of controlling
dosage and preparation, but somewhat limits the possibility of generalizing results to any effects of
drinking tea as a beverage.
Fig. 41.1 The production journey for green, oolong, and black tea. The tea journey: a diagram summarizing the
various stages of processing tea leaves, the type of tea produced, and the impact on its key components, the flavonoids
(unpublished figure)
623
41 Psychological and Physiological Consequences of Drinking Tea
The approaches to studying effects of tea, or its components, on health, behavior, and well-being
(a sense of positive health that is more than the absence of illness), vary from in vitro studies of
chemical activity in “test tube” models, through experimental studies of tea dosing in animals and
man, to epidemiological studies of relationships between habitual tea consumption in large populations
and psychological and physiological outcomes. These outcomes are varied, but are grouped here as:
cardiovascular (heart and circulatory) health; cancer risk; body weight and obesity; mental well-
being and mood; and cognitive function or mental performance.
Table 41.1 Key facts about tea
Key points Facts
Origins of tea drinking Tea originated in southeast Asia, where it has been drunk for at least 3000 years.
However, tea did not arrive in Europe until the early seventeenth century, finally
becoming fashionable in Britain in the late seventeenth century, whence it spread
to the colonies – the British East India Company established tea plantations in
India in the early nineteenth century.
Types of tea True tea is a drink made by infusing in hot water the leaves from the tea plant,
Camellia sinensis. These tea leaves can be cultivated, picked, cured, and
processed in a variety of ways. However, the main process that differentiates tea
is fermentation (oxidation) of the leaves. Thus, white tea (the youngest leaves), a
Chinese yellow tea, and green tea are not fermented, but undergo steaming,
roasting, and drying, resulting in delicate, light tea. Oolong tea is semi-fer-
mented, giving a tea part way between green and black. Black tea and pu-erh
(“shu” type) tea are fully fermented, although there is a variety of pu-erh tea,
“sheng,” which is unfermented like green tea. Within these broad tea types, there
are numerous varieties.
Global tea production
and consumption
Most tea is produced in East and South Asian countries, including China, Japan,
India, Sri Lanka, Korea, Vietnam, and Indonesia. Other continents produce
substantial amounts of tea including East Africa (especially Kenya), Central and
South America. Turkey is also a major producer. About 70% of production is
black tea, and 22% green tea. These top producers also tend to be big consum-
ers, accounting for at least half of all production: however, the major importers
of tea are (from the highest) Russia, UK, Pakistan, USA, Egypt, Japan, and Iran.
These countries consume very different forms of tea, in terms of processing,
variety, and preparation. Global tea consumption continues to grow, and has
more than doubled since 1970.
Tea preparation Water temperature is important for correct tea preparation, with the more delicate
tea needing lower temperatures than the fermented one. Thus, for white, yellow,
and green tea, water temperature should range from 66°C to 82°C (coolest for
white tea). Oolong tea is best brewed using water at 82–88°C, whereas black and
pu-erh tea require water near boiling point (99°C). Tea should always be steeped
(brewed) for at least 30 s (which allows all the theanine to be released). If
steeping is limited to 2 min or so, then several separate infusions can be obtained
from the same leaves; each will have different flavor characteristics, as well as
chemical components. Longer brewing, for 3–4 min, maximizes the release of
antioxidant polyphenol compounds, although brewing beyond 5 min will tend to
produce a bitter tea.
With or without milk? Adding milk to tea was established early on in its arrival in Europe, although it is
practiced elsewhere, such as Manchuria. It is the most common way to take
tea in Britain, where the popular tea varieties are quite strongly flavored and
astringent. There are mixed findings concerning the impact of milk on tea’s
health benefits, but it is likely that, when added as less than 10% of the
volume, milk will have little impact on tea’s effects.
This table gives key facts about the origins and global distribution of tea drinking, its varieties, production, and prepa-
ration of the tea drink
624 E.L. Gibson and J.A. Rycroft
41.2 Cardiovascular Health
Drinking a daily cup of tea will surely starve the apothecary
(Ancient Chinese proverb)
Earlier epidemiological studies, including prospective studies looking at development of cardiovas-
cular disease (CVD) over several years in large population samples, did not find conclusive evidence
of either a beneficial or harmful effect of drinking tea, but instead, inconsistent results, despite exper-
imental evidence that tea contained potentially beneficial chemicals; however, it was acknowledged
that this may be due to close associations in some populations between tea drinking and other life-
style factors that themselves may be detrimental to cardiovascular health (Hollman et al. 1999). In
other words, in some populations, for example in the UK, frequent black tea drinking is popular in
lower socioeconomic groups in which unhealthy behaviors are also common, and their confounded
influence on heart health may not easily be separated, so that in such populations greater tea intake
may even be associated with poorer cardiovascular health, at least in unadjusted analyses. However,
a recent overall review of many such epidemiological studies, including populations where this
behavioral confounding is not apparent, has concluded that (black) tea clearly has a positive associa-
tion with coronary heart disease, with three mugs per day reducing risk by up to 71%, depending on
the study and population (Gardner et al. 2007). Another meta-analysis of the epidemiological studies
linking tea consumption to incidence of stroke, using data from nine studies involving 4,378 strokes
among 194,965 individuals, also showed that consuming three or more cups of either green or black
tea per day may reduce the risk of ischemic stroke by as much as 21% (Arab et al. 2009).
What properties of tea might benefit the cardiovascular system? The most likely candidates are
the various plant chemicals found in tea, collectively known as polyphenol flavonoid compounds, as
these are known to have antioxidant activity in vitro, which could suppress inflammatory processes
that otherwise contribute to CVD. These components of tea include the catechin flavanols, particu-
larly epigallocatechin gallate (EGCG), their oxidation (fermentation) products, the theaflavins,
thearubigins, as well as the flavonols, quercetin, keampherol, and rutin (Fig. 41.2). Tea also contains
a unique amino acid, theanine, which may have important effects on the brain (see next; refer
Fig. 41.3 for structures of catechins and theanine).
Fig. 41.2 A comparison of
the flavonoid contents of
typical green and black tea.
Pie charts showing the
proportions of different
classes of flavonoid
compounds in average cups
of green and black tea
(% = % dry weight) (Based
on data from Lakenbrink
et al. 2000 and Astill et al.
2001. With permission)
625
41 Psychological and Physiological Consequences of Drinking Tea
In many European populations, tea is the dominant source of flavonoids such as catechins – in the
UK, accounting for as much as 80%, though rather less in the USA – although these are also found in
red wine, chocolate, and apples, for example. It has been estimated that average intake of flavonoids in
Western countries is about 65–250 mg/day (Erdman et al. 2007). Tea’s importance in contributing
catechins to the diet was illustrated by findings from a prospective study of elderly Dutch men, in
whom high habitual dietary catechin intake reduced risk of dying from coronary heart disease by about
50% compared with low catechin intake; in contrast, once the contribution of tea had been statistically
removed, the risk reduction was down to 20% and was not statistically significant (Arts et al. 2001).
In determining likely mechanisms for the impact of tea on cardiovascular health, experimental
studies of tea, or its components, have revealed beneficial effects on vascular physiology that support
probable health benefits of drinking tea on the cardiovascular system, in in vitro laboratory and animal
models, and in clinical trials in human participants (Vita 2005). Several clinical studies have investi-
gated two aspects in particular: (1) activation of blood platelets (assessed as aggregation of platelets
with white blood cells or activated by factors such as adenosine diphosphate), which indicates risk
of clot formation and inflammation of arterial walls, and is a key event leading to coronary heart
disease; (2) responsiveness of the vascular endothelium (cellular lining of blood vessel walls) to
changes in blood flow (i.e., dilatation vs constriction), which is thought to be an important indicator
of the health of the cardiovascular system. In patients with established CVD, 4 weeks of drinking
900 mL of black tea per day did not reduce platelet aggregation compared to water, despite increased
plasma flavonoid content, although the design cannot rule out an interaction with change in caffeine
intake. In contrast, this same group did find that this tea “treatment” improved endothelial function
in these patients (reviewed by Gardner et al. 2007). By comparison, in a recent double-blind, pla-
cebo-controlled study in a larger sample of healthy men, where caffeine intake was equated between
treatment groups, 6 weeks of drinking four mugs of black tea per day was shown to inhibit platelet
activation (aggregation with white blood cells), as well as lowering plasma levels of C-reactive protein,
usually regarded as a general indicator of chronic inflammation (Fig. 41.4; Steptoe et al. 2007a).
Similar evidence is available from studies of effects of green tea, which is higher in levels of
catechins, especially EGCG, than black tea (although the amount consumed will depend on how the
tea is brewed). In epidemiological studies, where potentially confounding lifestyle and other factors
are controlled for, an inverse association has been described between green tea consumption and
CVD, including stroke and hypertension, in oriental populations (Tanabe et al. 2008). Clinical stud-
ies have been short term, but beneficial effects on vascular inflammation and blood lipids, including
Fig. 41.3 The chemical
structures of catechin and
theanine. The chemical
structures for two key
components of tea: (a) the
basic catechin structure and
(b) the structure of the amino
acid, theanine (an analog of
glutamate and glutamine).
Both structures were
downloaded from Wikimedia
Commons (http://commons.
wikimedia.org/ – public
domain images)
626 E.L. Gibson and J.A. Rycroft
reduced oxidation of low density lipoprotein (LDL) cholesterol, have been reported. Indeed, particu-
larly impressive results were found in a recent randomized, double-blind placebo-controlled study
administering decaffeinated green tea extract capsules for 3 weeks to healthy volunteers aged from
21 to 70: the green tea treatment reduced blood pressure, inflammation and oxidative stress (a cellular
process that can damage DNA), and total and LDL cholesterol (Nantz et al. 2009).
However, there is still a need for longer-term placebo-controlled clinical studies. Moreover, it
should be noted that recent ex vivo experimental assessment of tea flavonoid effects on vascular
endothelium vasodilatation found that highly fermented black tea was equally as potent as green tea,
suggesting that the theaflavins and thearubigins in black tea, to which green tea catechins are con-
verted by fermentation, also have beneficial effects on endothelial function (Lorenz et al. 2009).
Similarly, a very recent study showed that black tea dose-dependently improved flow-mediated dila-
tion (a noninvasive measure of endothelial function) in healthy male volunteers (Grassi et al. 2009).
These beneficial cardiovascular effects of tea are reminiscent of similar effects, including lowering
of blood pressure, seen for diets high in fruit and vegetables: similar mechanisms may be involved
and continue to be intensively researched.
41.3 Prevention of Cancer
The ability of components of tea to have physiological activity that benefits cardiovascular health,
either by reducing inflammation or improving arterial vasodilatation, makes it possible that drinking
tea will have other health advantages; key among these could be a reduction in the risk of cancer.
Several mechanisms might account for tea’s anticancer properties, but the principal ones are likely
Fig. 41.4 Change from pretreatment baseline in measures of platelet activation and C-reactive peptide after drinking
four mugs of black tea per day for 6 weeks, or a tea placebo (means adjusted for baseline values). Measures: “Mono-
platelet aggr” = monocyte-platelet aggregation; “Neutro-platelet aggr” = neutrocyte-platelet aggregation; “Leuko-
platelet aggr” = leukocyte-platelet aggregation. *p < 0.05 for significant differences between tea and placebo treatments
(Based on data from Steptoe et al. 2007a. With the authors’ permission)
627
41 Psychological and Physiological Consequences of Drinking Tea
to be reduction of DNA damage by oxidative stress, e.g. by scavenging (deactivation) of reactive
oxygen species (free radicals) and binding of metals, metabolism and detoxification of carcinogens,
modulation of carcinogenic gene expression, and lowering the rate of cell replication (Lambert et al.
2005). In addition, recent evidence suggests that flavonoids in tea may be able to induce apoptosis,
i.e. a process of cell death important in regulating cell proliferation and thus cancer, as well as altering
biochemical intracellular signaling pathways (de Mejia et al. 2009). Furthermore, even theanine may
have anticancer activity (Liu et al. 2009).
Nevertheless, most laboratory studies use higher flavonoid concentrations than those likely to
occur from normal tea drinking. Thus, it is important that this mechanistic evidence should be sup-
ported by evidence of inverse associations between tea consumption and cancer risk at a population
level, i.e. epidemiological studies, where other potentially confounding influences are statistically
adjusted for (Lambert et al. 2005). Although there are promising results from some studies showing
such inverse associations, others have not supported those findings. For example, in prospective stud-
ies in older populations used to assess relations between dietary flavonoid intake and death from
cancer, an inverse association was found in a Finnish cohort but not in two Dutch cohorts (Hollman
et al. 1999). Gardner et al. (2007) recently reviewed epidemiological studies of associations between
specifically black tea and cancer, and concluded that there was little evidence of a consistent protec-
tive effect. For example, in a large sample of Canadian men, no association was found between (mainly
black) tea drinking and prostate cancer (Gardner et al. 2007). Moreover, a recent report from a very
large sample of North American women aged over 45 found no association between total or site-
specific cancer incidence and dietary intake of flavonols and flavones (Wang et al. 2009b). However,
it should be noted that, in this population, tea is likely to be only a minor contributor to the intake of
these flavonoids. In another sample from the USA, no association was found between tea intake and
colorectal cancers (Gardner et al. 2007). In a Japanese sample, frequency of green tea intake was also
not associated with gastric cancer (one of the most common cancers in Japan; Tsubono et al. 2001).
Conversely, green tea was associated with almost a 50% reduction in risk of gastric cancer in a
Chinese population (Setiawan et al. 2001), and black tea was strongly protective against gastric cancer
in an Indian population (Rao et al. 2002). Moreover, in a Japanese population, drinking more than ten
cups per day of green tea reduced the risk of developing any cancer in both men and women by at least
40%, and onset of cancer was delayed, compared with low intake of green tea (Nakachi et al. 2000).
These studies are dependent on accuracy of information concerning both tea intake and confounding
factors: importantly, in a prospective study of Chinese men, urinary tea polyphenols were measured
to estimate tea intake; high tea intake protected against gastric and esophageal cancers, but only in
men who had a low intake of carotene, suggesting low consumption of vegetables (Sun et al. 2002).
This could suggest that any protective effect of tea against cancer may be obscured if the diet is gener-
ally healthy. Such complex interactions are also indicated by a study of Dutch men and women, where
protective effects of dietary flavonoids against colorectal cancers depended on the body size of partici-
pants, i.e. protection was only evident in overweight men and normal weight women (Simons et al.
2009), which suggests subtle interactions with other lifestyle, and perhaps genetic, factors.
In summary, despite very promising evidence from mechanistic laboratory studies suggesting
that tea flavonoids could reduce the risk of cancer, epidemiological studies of relations between tea
(or dietary flavonoid) intake and cancer incidence have produced inconsistent findings. The US Food
and Drug Administration previously assessed all the epidemiological data available on green tea and
cancer prevention and concluded that it is highly unlikely that green tea reduces the risk of prostate
cancer and that there is no credible evidence to support a relationship between green tea consump-
tion and a reduced risk of gastric, lung, colon/rectal, esophageal, pancreatic, ovarian, and combined
cancers (FDA 2005). One reason could be that, to protect against cancer, tea intake may need to be
both high and in populations that eat relatively low amounts of fruit and vegetables.
628 E.L. Gibson and J.A. Rycroft
41.4 Body Weight, Appetite, and Obesity
Tea’s proper use is to amuse the idle, and relax the studious, and dilute the full meals of those who cannot use
exercise, and will not use abstinence.
Samuel Johnson (1757) “Essay on tea.”
Anecdotally, tea has long been believed to alter appetite; however, scientific evidence has been scarce
until recently. Laboratory studies investigating potential cardiovascular benefits of black and green
tea flavonoids revealed physiological effects that could be of benefit to obese humans at risk of insu-
lin resistance and unhealthy blood lipid profiles (Ramadan et al. 2009). Consistent with this, the
green tea flavanol EGCG, was found to promote postprandial insulin secretion in human beings
(Weber 2004): this latter result is particularly interesting, as insulin is known to promote satiety and
so constrain food intake (see Sect. 1.3 and 1.7 of this publication). In addition, short-term adminis-
tration of green tea extract plus caffeine to ten healthy men increased fat oxidation and energy expen-
diture, through stimulation of the sympathetic nervous system (probably by inhibiting enzymatic
degradation of the neurotransmitter noradrenaline), whereas caffeine alone was ineffective (Dulloo
et al. 1999). Likewise, in 12 healthy men performing a 30-min cycling exercise, green tea extract
(without caffeine) increased fat oxidation rate compared with placebo (Venables et al. 2008).
Eleven long-term clinical studies have recently been reviewed and meta-analyzed by Hursel et al.
(2009): some of those are summarized here (but not cited, if included in that review). In a study of
104 obese Dutch men and women undergoing severe energy restriction for weight loss, the effect of
green tea on weight regain after the restricted period was compared to placebo: there was no differ-
ence between groups; however, there was evidence that caffeine may reduce weight regain in habitu-
ally low consumers of caffeine. This shows that it is important to design studies that distinguish
between effects of caffeine and the flavonoid components of tea. In another study by these same
investigators, caffeine was standardized to 300 mg/day for both a green tea extract treated group and
a placebo group, during a weight loss diet in women. There was no benefit from green tea on weight
or fat loss; in fact, the women given green tea actually became hungrier than those on placebo.
However, in normal and overweight Japanese men and women, taking a drink containing green tea
catechins twice or thrice a day for 12 weeks resulted in greater weight and fat loss than placebo
(Kajimoto et al. 2005). During this period, participants were asked to maintain their usual diet; even
so, the catechin drink also reduced total and LDL cholesterol. Similar results were found in a study of
Japanese men comparing 12 weeks of drinking either oolong tea once per day or the same tea supple-
mented with green tea extract; body weight and fat loss, and reduction in LDL cholesterol, were great-
est for the green tea extract group. Furthermore, in obese Thai men and women on a calorie-controlled
diet (8.4 MJ/day) for 12 weeks, green tea treatment reduced body weight and increased resting energy
expenditure compared to placebo. By comparison, in Taiwanese obese women taking green tea extract
or placebo capsules for 12 weeks, there was no difference in weight loss, but blood cholesterol profiles
were markedly improved by the tea extract. Despite these somewhat mixed findings, a meta-analysis
of such studies concluded that evidence supports a small effect of green tea or catechins (or combined
with caffeine) in enhancing weight loss or weight maintenance (Hursel et al. 2009).
Since then, another study monitored the effects of green tea consumption on body weight, body
fat mass, as well as the distribution of fat (Wang et al. 2009a). A total of 182 moderately overweight
Chinese subjects, aged between 18 and 55 years, were divided into four groups, with each group
allocated a regular dose of green tea containing a different quantity of catechins. Amounts consumed
ranged from 30 mg to almost 900 mg; an average cup of green tea contains between 50 and 100 mg
of catechins. Participants in the study drank their designated tea divided in two daily doses. On days
0, 30, 60, and 90, measurements of body composition were taken to assess the effects that the pre-
scribed tea had on body mass and fat.
629
41 Psychological and Physiological Consequences of Drinking Tea
The results showed that, relative to the control group consuming no green tea catechins, body
weight, waist circumference, intra-abdominal fat, and the total lean mass all decreased after 90 days
in the group that drank the tea with the highest concentration of catechins. The authors concluded
that regular consumption of green tea with very high catechin content can, over a 90-day period,
reduce body weight, body fat mass, and waist size in moderately overweight Chinese individuals.
41.5 Mental Well-being and Mood
If you are cold, tea will warm you; if you are too heated it will cool you. If you are depressed, it will cheer you;
if you are excited, it will calm you.
W. E. Gladstone (British Prime Minister 1865)
In many cultures, it is an accepted folklore that drinking tea can acutely improve one’s state of
well-being, especially the ability to calm oneself, to relax, and escape for a moment from life’s many
pressures. However, there has been very little scientific investigation to support this notion. Of course
tea normally contains caffeine, and, as described in the next section, this explains some, but not all, of
the arousing potential of a regular cup of tea (Hindmarch et al. 2000). Yet, other aspects of tea may have
important effects on mood: for example, drinking tea, but not coffee, was associated with feeling more
relaxed, for women with high social support at work (see Steptoe et al. 2007b). Furthermore, the amino
acid, l-theanine, unique to tea, has been shown to increase a psychophysiological measure of relaxation
in human beings, i.e. increased electrical alpha-wave activity on the brain surface, as detected by elec-
tro-encephalographic (EEG) recording of brain electrical potential changes, or “brain waves” (Nobre
et al. 2008), and to improve relaxation during restful conditions (Lu et al. 2004). However, another
study measuring EEG after theanine-enriched green tea intake found evidence of increased attention
but not relaxation (Dimpfel et al. 2007). Furthermore, several studies have found that theanine and caf-
feine can interact in affecting mental function (see below), and one study reported that theanine can
ameliorate the increase in blood pressure seen after acute caffeine intake (Rogers et al. 2008).
If theanine aids relaxation, one might expect theanine to be of benefit during stress, as seems
anecdotally to be the case for tea. There is evidence that this is indeed the case: thus, in participants
who were acutely stressed by having to complete a difficult mental arithmetic task, theanine reduced
the heart rate response to stress, and also reduced a well-known stress-sensitive response, a rise in
salivary immunoglobulin A antibody levels, compared to placebo (Kimura et al. 2007).
One study has looked at the impact of drinking black tea (without milk) four times a day for 6 weeks
on responses to stress in healthy men (Steptoe et al. 2007b). This was a randomized double-blind pla-
cebo-controlled study, where effects of caffeine were controlled by equating caffeine levels between tea
and placebo drink groups. Participants underwent stressful laboratory tasks (role-play speech and mir-
ror tracing tasks) at baseline, after a 4-week wash-out phase on placebo tea, and finally after 6 weeks
on either active or placebo tea: 75 men completed the study. Blood samples were taken before and after
the stress; heart rate and blood pressure were measured continuously during each session, and the hor-
mone cortisol, known to increase under stress, was measured at several time points in saliva samples.
The main findings were that, compared to placebo (a) tea treatment did not alter the stress-induced
increases in heart rate and blood pressure; (b) tea drinking resulted in a faster poststress recovery of the
cortisol response (Fig. 41.5); (c) participants given the active tea were more relaxed after stress than
those given placebo (Fig. 41.6). Thus, drinking tea for 6 weeks did not alter the acute physiological
responses during stress, but improved the hormonal and psychological recovery from stress.
If tea benefits mood and coping with stress, it might be expected to show some ability to protect
against depression. There is indeed some support for this: a cross-sectional study of over 2000
630 E.L. Gibson and J.A. Rycroft
Finnish people found that respondents reporting daily tea drinking were significantly less depressed
than those drinking tea less frequently, and there was no depression among those drinking five or
more cups per day (Hintikka et al. 2005). This finding may also be relevant to the evidence that tea
has neuroprotective effects (see next). A similar finding has been reported for a Japanese population,
in relation to green tea and psychological well being (Hozawa et al. 2009): in over 42,000 Japanese
over 40 years old, those drinking green tea at least five times per day were 20% less likely to report
being psychologically distressed than those drinking tea less than once a day, after controlling for
other lifestyle and demographic factors.
What could be the mechanisms by which tea benefits mood and psychological well-being?
Animal studies have shown that the catechins in tea can act in the brain via type-A receptors for
Fig. 41.6 Effect of 6-week
tea drinking vs. placebo on
change in relaxation from
before performing stressful
tasks to after post-task
recovery. Change in rated
relaxation from before
performing stressful tasks to
after posttask recovery, 50
min later. Participants were
less relaxed after stress
following placebo treatment
(dashed line), but more
relaxed after drinking active
tea for 6 weeks (solid line)
(The figure is reproduced
from Steptoe et al. 2007b.
With the permission of the
authors)
Fig. 41.5 Changes in salivary cortisol before, after, and during recovery from, stressful tasks, after either 6 weeks of
drinking black tea or a placebo drink. Levels of the stress hormone, cortisol, in saliva samples taken before and after per-
forming psychologically stressful tasks, and during subsequent poststress recovery. Cortisol levels fell more rapidly during
recovery from stress (50 min later) for the group drinking black tea for 6 weeks (solid line), compared to the group drinking
placebo tea (dashed line) (The figure is reproduced from Steptoe et al. 2007b. With the permission of the authors.)
631
41 Psychological and Physiological Consequences of Drinking Tea
gamma-aminobutyric acid (GABA-A), a major inhibitory neurotransmitter known to be involved in
the calming, sedative, and anti-anxiety actions of benzodiazepine drugs like Valium (Vignes et al.
2006). Moreover, these catechins have recently been found to inhibit activity of neurones in the brain
stem nucleus, the locus coeruleus (Chang et al. 2009). As the locus coeruleus is involved in brain
arousal systems, this might indicate a mechanism for the calming effects of tea, although it is not
clear that catechins absorbed from drinking tea could affect the brain in this way. Theanine also
appears to act in the brain via another inhibitory amino acid transmitter, glycine, and via modulation
of dopamine release (involved in attention and motivation, as well as motor control). Theanine is a
structural analog of glutamate and glutamine, two neurotransmitters involved in excitatory brain
transmission. As such, theanine is able to compete with glutamate and glutamine for their transporters,
receptors, and metabolizing enzymes. By attenuating the action of glutamate and glutamine, theanine
might affect cognitive function, or mood (Bryan 2008). There remains much to be learnt about the
potentially complex mechanisms by which tea may modulate brain activity and so mental well-being.
41.6 Cognitive Function
My dear, if you could give me a cup of tea to clear my muddle of a head, I should better understand your affairs.
Charles Dickens (1894)
This section will consider two sorts of evidence in relation to tea and brain function: (a) that tea can
acutely modulate cognitive function, i.e. as assessed by mental performance after short-term dosing
with tea or its components; (b) that drinking tea, or ingesting its components, is associated with
neuroprotective effects, i.e. effects on neuronal structure and function that prevent or ameliorate
neurodegeneration and associated cognitive decline or dementia.
41.6.1 Acute Effects on Cognitive Function
More than a decade ago, it was shown that drinking black tea improved alertness acutely (within 10
min; Critical Flicker Fusion test, CFF) – an effect that was not matched by 100 mg caffeine and was
more reliable than the effect of coffee on repeated testing over the day (Hindmarch et al. 1998).
Nevertheless, that study also found no acute benefit of tea, coffee, or caffeine on tests of short-term
memory. Subsequently, in a comparison of tea and coffee over a day, tea improved alertness (CFF)
more than coffee (which had twice as much caffeine), whereas coffee showed some additional ben-
efit for reaction times in a choice reaction time task (Hindmarch et al. 2000). Additionally, both these
caffeinated drinks delayed and disrupted sleep, although tea less so than coffee. Finally, there are
preliminary reports that black tea may improve focused attention, i.e. the ability to select and process
only relevant sensory information from among multiple stimuli, although it is not clear to what
extent that effect is independent of caffeine (Lipton Institute of Tea Factsheet, “Black tea and mental
performance,” 2009, Unilever; de Bruin et al. unpublished data).
Thus, there is some evidence that beneficial effects of tea on alertness may differ from those of caf-
feine per se. It is also worth noting here that there is increasing evidence that apparently beneficial
effects of caffeine may largely be due to removal of cognitive impairment following overnight with-
drawal from caffeine. Thus, unlike the positive effects seen in overnight withdrawn participants, no
beneficial effects of caffeine on performance were found in participants who had abstained from
632 E.L. Gibson and J.A. Rycroft
caffeine for 3 weeks prior to testing, and among those receiving placebo, these long-term withdrawn
participants performed better than overnight withdrawn participants (Rogers et al. 2005). However, it
is not known whether beneficial effects of tea, as distinct from caffeine, depend on acute withdrawal.
How might tea improve alertness and attention, other than via caffeine? One possibility is via the
activity of theanine: as already mentioned, EEG recordings of brain activity after theanine adminis-
tration suggest that it is able to produce a relaxed state without drowsiness that might improve sus-
tained attention (Nobre et al. 2008; Gomez-Ramirez et al. 2009). One group examined the impact on
performance of caffeine (150 mg) or theanine (250 mg) alone or in combination (Haskell et al.
2008). As expected, caffeine improved performance on several measures; however, theanine alone
did not, and even impaired performance on a demanding mental arithmetic task, as well as increasing
headaches 90 min later. Yet, the combination of caffeine and theanine improved performance above
caffeine alone on more complex verbal tasks, and also caused the greatest increase in alertness.
However, these effects on mood were not replicated by another group who used 250 mg of caffeine
and 200 mg of theanine, alone or in combination (Rogers et al. 2008). In that study, theanine seemed
to prevent the increase in alertness caused by caffeine, as well as the increase in blood pressure. The
authors noted that this might help to explain why tea is often perceived to be more relaxing than cof-
fee, and it is in line with changes in EEG activity described above. However, it is important to note
that these doses of theanine and caffeine are considerably greater than would normally be found in a
cup of tea. Nevertheless, when lower doses of caffeine (50 mg) and theanine (100 mg) were tested in
another study, the combined treatment showed some improvement in attention and memory over
caffeine alone and placebo (theanine was not tested alone), whereas the caffeine-related increase in
alertness was again weaker in the presence of theanine (Owen et al. 2008). The effects of these same
doses of caffeine and theanine have subsequently been shown to improve attention on a switch task
but not to improve intersensory attention or subjective alertness (Einöther et al. 2010).
Could the flavonoid components of tea, especially the catechins, also contribute to any acute effects
of tea on cognitive function? It may be plausible, given the animal evidence discussed in the previous
section that catechins do alter brain neurotransmitter systems – indeed, the inhibition of locus ceoruleus
neuronal activity by catechins (Chang et al. 2009) would be compatible with a more relaxed frame of
mind after tea, though not obviously with improved attention – though they may not reach the brain in
sufficient amounts. Furthermore, catechins and other flavonoids could improve blood flow in active
areas of the brain via their vascular epithelial effects (see above). There are also several studies in rodents
demonstrating that chronic consumption of catechins improves memory and other aspects of neuronal
function (de Mejia et al. 2009), as well as promising results from human interventions administering
some types of dietary flavonoids (mainly isoflavones) for weeks or months (Macready et al. 2009).
Nevertheless, there do not appear to be any studies demonstrating short-term effects of tea flavonoids on
cognitive performance, so the question of their contribution to any such effects from tea remains open.
41.6.2 Chronic Effects on Cognition and Brain Function
There is growing evidence from animal studies that various flavonoids, including tea catechins, can
benefit neuronal growth and function, and furthermore act as neuroprotective agents, counteracting neu-
rodegenerative processes, such as oxidative stress, that otherwise lead to dementia, Parkinson’s disease,
etc. (de Mejia et al. 2009; Macready et al. 2009). Moreover, theanine also appears to have neuroprotec-
tive effects in animals (Il Kim et al. 2009). To date, there do not appear to be any controlled interventions
examining the impact of chronic tea intake (or tea components) on cognitive function in human beings.
Nevertheless, there are several epidemiological studies that have examined relationships between
long-term tea consumption and brain or cognitive function. In a cross-sectional study of elderly
633
41 Psychological and Physiological Consequences of Drinking Tea
Japanese, higher green tea consumption, but not coffee, was associated with lower cognitive impair-
ment (Kuriyama et al. 2006). In an elderly French population, risk of dementia after 5 years was
reduced by 51% in those having the highest intake of dietary flavonoids at baseline (Commenges
et al. 2000). In an American population, drinking two or more cups of tea per day was associated
with a reduced risk of Parkinson’s disease, independently of smoking or coffee drinking (Macready
et al. 2009). In Chinese adults aged 55 or over, tea (mainly black or oolong) consumption at baseline
was clearly associated with lower cognitive impairment or decline 1–2 years later (Ng et al. 2008).
Finally, in 70–74-year-old Norwegians, habitual intake of tea, wine, and chocolate (all of which are
rich in flavonoids including catechins) was dose-dependently and additively associated with better
cognitive performance (Nurk et al. 2009). Taken together, these findings support beneficial effects on
brain function from habitual consumption of tea.
41.7 Conclusions
It is becoming increasingly clear that tea, the beverage made from infusions of leaves from C.
sinensis, can have both physiological and psychological effects that may benefit health. Tea con-
tains plant chemicals known as flavonoids that have antioxidant properties and have been shown
to benefit indicators of cardiovascular health in laboratory studies measuring effects on inflamma-
tion and vascular function, and in clinical trials administering fixed doses of tea or tea extracts.
Population-based studies also, on balance, support a positive relationship between tea drinking
and cardiovascular health.
Laboratory studies suggest that tea and its components, especially catechins, can have effects on
cellular processes that might reduce the risk of developing cancer. However, results from population-
based studies have been inconsistent, and currently it is not possible to conclude that tea reliably
reduces cancer risk.
There is some evidence that high doses of catechins from green tea may promote weight loss,
potentially by stimulation of fat oxidation. In terms of psychological effects, tea can improve cogni-
tive function acutely, and to some extent independently of its caffeine content. One reason may be
due to effects on the brain of the amino acid, theanine, which has been shown to alter brain electrical
activity. Theanine seems to improve relaxation and aspects of attention, without overstimulation.
Possibly related, tea can also ameliorate physiological responses to stress and help poststress relax-
ation. This might explain population evidence that links tea drinking with resistance to depression.
Finally, laboratory and animal studies suggest that tea and its components, both flavonoids and
theanine, can have neuroprotective effects, suggesting resistance to neurodegeneration. This possi-
bility is further supported by prospective epidemiological evidence indicating that populations drink-
ing tea regularly show slower declines in cognitive function, or less risk of dementia with aging,
while cross-sectional studies have found a positive association between tea consumption and cogni-
tive function in the elderly.
In conclusion, there have been a large number of scientific studies investigating physiological and
psychological effects of drinking tea. Overall, a number of health benefits may arise from tea, but the
strongest evidence is for cardiovascular and neurological health.
41.8 Applications to Other Areas of Health and Disease
Gardner et al. (2007) have recently reviewed areas of health that may be affected by drinking tea, in
addition to those discussed before.
634 E.L. Gibson and J.A. Rycroft
41.8.1 Dental Health
The tea plant naturally accumulates fluoride from the soil, and so drinking tea can contribute to the
beneficial effect that fluoride can have on preventing or treating damage to teeth enamel caused by
dental caries, for example. The high levels of catechins in green tea may also protect against caries
by inhibiting growth of oral bacteria.
41.8.2 Bone Health
It has been suggested that compounds in tea including fluoride, phytoestrogens, and caffeine may
influence bone mineral density, especially in older people. There is limited evidence that drinking
four or more cups per day may increase bone mineral density, and reduce the risk of hip fractures,
independently of whether milk is added – although adding milk clearly contributes a significant
amount of calcium in regular drinkers.
41.8.3 Hydration
Although high doses of caffeine can be diuretic, i.e. stimulating the kidneys to increase secretion of
water, eventually leading to dehydration, there is no evidence that such an effect occurs at the levels
of caffeine normally drunk in tea. On the contrary, it has been demonstrated that tea has a beneficial
effect on hydration.
41.8.4 Iron Status
Polyphenols in tea can inhibit the absorption of iron from non-heme sources (i.e., plants). This
appears only to be of concern to those who may already be at risk from low iron status: in such cases,
drinking tea should be avoided within 1 h of meals.
Summary Points
From a health point of view, the key components of tea are likely the flavonoid group of chemi-•
cals, including catechins, such as EGCG (high in green tea), their metabolites the theaflavins and
thearubins (high in black tea), and the flavonols, as well as the amino acid, theanine.
The flavonoids have antioxidant, as well as other biochemical effects, and these reduce inflamma-•
tion and improve blood vessel dilatation, which may lead to better cardiovascular health.
Despite laboratory evidence suggestive of cancer preventive properties of tea components, find-•
ings from population-based studies have been inconsistent, so it is not clear whether chronic tea
drinking reliably reduces cancer risk.
Green tea catechins, at least at high doses, appear to aid weight loss in overweight people, probably •
by increasing oxidation of fat.
Tea can relieve effects of stress, and help with poststress recovery, both physiologically and •
psychologically.
635
41 Psychological and Physiological Consequences of Drinking Tea
Tea can benefit acute cognitive performance, possibly by the action of theanine in the brain, •
where it appears to aid relaxation but also improves some forms of attention.
Tea may protect the brain against degeneration: tea components are neuroprotective in the labora-•
tory, and tea drinking is associated with less dementia in the elderly.
References
Arab L, Liu W, Elashoff D. Stroke. 2009;40:1786–92.
Arts IC, Hollman PC, Feskens EJ, Bueno de Mesquita HB, Kromhout D. Am J Clin Nutr. 2001;74:227–32.
Astill C, Birch MR, Dacombe C, Humphrey PG, Martin PT. J Agric Food Chem. 2001;49:5340–7.
Bryan J. Nutr Rev. 2008;66:82–90.
Chang KC, Yang JJ, Wang-Hsu ECH, Chiu TH, Hsu FC. Neurosci Lett. 2009;452:141–5.
Commenges D, Scotet V, Renaud S, Jacqmin-Gadda H, Barberger-Gateau P, Dartigues JF. Eur J Epidemiol.
2000;16:357–63.
de Mejia EG, Ramirez-Mares MV, Puangpraphant S. Brain Behav Immun. 2009;23:721–31.
Dimpfel W, Kler A, Kriesl E, Lehnfeld R, Keplinger-Dimpfel IK. Nutr Neurosci. 2007;10:169–80.
Dulloo AG, Duret C, Rohrer D, Girardier L, Mensi N, Fathi M, Chantre P, Vandermander J. Am J Clin Nutr.
1999;70:1040–5.
Einöther SJL, Martens VEG, Rycroft JA, De Bruin EA. Appetite. 2010;54, 406–09.
Erdman JW Jr, Balentine D, Arab L, Beecher G, Dwyer JT, Folts J, Harnly J, Hollman P, Keen CL, Mazza G, Messina
M, Scalbert A, Vita J, Williamson G, Burrowes J. J Nutr. 2007;137:718S–37S.
FDA Green Tea and Reduced Risk of Cancer Health Claim (Docket no. 2004Q-0083) Centre for Food Safety and
Applied Nutrition. Silver Spring: US FDA, 2005.
Gardner EJ, Ruxton CH, Leeds AR. Eur J Clin Nutr. 2007;61:3–18.
Gomez-Ramirez M, Kelly SP, Montesi JL, Foxe JJ. Brain Topog. 2009;22:44–51.
Grassi D, Mulder TP, Draijer R, Desideri G, Molhuizen HO, Ferri C. J Hypertension 2009;27:774–81.
Key Terms
Polyphenol antioxidants: A group of chemicals based on a polyphenolic substructure, widely
available in fruits and vegetables. These compounds show strong antioxidant activity in labora-
tory tests, although the extent to which dietary sources reach target sites in sufficient concentra-
tions is debated. They may benefit health by deactivating reactive oxygen species (free radicals),
so reducing inflammation and cell damage.
Flavonoids: A subclass of polyphenol antioxidants, some of which are common in tea, espe-
cially the catechins (strictly, flavonols) such as EGCG.
Reactive oxygen species: Often called free radicals, these are small molecules that are highly
reactive due to the presence of oxygen ions with unpaired (free) electrons. They are a normal
byproduct of oxygen metabolism in cells, but if levels rise (a state known as oxidative stress),
reactive oxygen species can damage cell structures including DNA.
Electroencephalography: Recording of brain surface electrical activity through electrodes
placed around the scalp. The electrical potentials reflect the sum of activity of millions of neu-
rones, and result in rhythmic activity (brain waves) with frequencies between 1 and 20 Hz; these
are classified (in increasing frequencies) as delta, theta, alpha, beta, and gamma waves, reflecting
different brain states.
Cortisol: A steroid hormone produced in the cortex (outer shell) of the adrenal glands, in
response to activation of the hypothalamic–pituitary–adrenal–neuroendocrine axis. Cortisol levels
in blood or saliva rise rapidly in response to psychological stress, although they also display an
underlying circadian rhythm (high in the early morning and low in the evening).
636 E.L. Gibson and J.A. Rycroft
Haskell CF, Kennedy DO, Milne AL, Wesnes KA, Scholey AB. Biol Psychol. 2008;77:113–22.
Hindmarch I, Quinlan PT, Moore KL, Parkin C. Psychopharmacol. 1998;139:230–8.
Hindmarch I, Rigney U, Stanley N, Quinlan P, Rycroft J, Lane J. Psychopharmacol. 2000;149:203–16.
Hintikka J, Tolmunen T, Honkalampi K, Haatainen K, Koivumaa-Honkanen H, Tanskanen A, Viinamaki H. Eur J
Epidemiol. 2005;20:359–63.
Hollman PCH, Feskens EJM, Katan MB. Proc Soc Exp Biol Med. 1999;220:198–202.
Hozawa A, Kuriyama S, Nakaya N, Ohmori-Matsuda K, Kakizaki M, Sone T, Nagai M, Sugawara Y, Nitta A,
Tomata Y, Niu K, Tsuji I. Am J Clin Nutr. 2009;90:1390–6.
Hursel R, Viechtbauer W, Westerterp-Plantenga MS. Int J Obes. 2009;33:956–61.
Il Kim T, Lee YK, Park SG, Choi IS, Ban JO, Park HK, Nam SY, Yun YW, Han SB, Oh KW, Hong JT. Free Radic Biol
Med. 2009;47:1601–10.
Kajimoto O, Kajimoto Y, Yabune M, Nakamura T, Kotani K, Suzuki Y, Nozawa A, Nagata K, Unno T, Sagesaka YM,
Kakuda T, Yoshikawa T. J Health Sci. 2005;51:161–71.
Kimura K, Ozeki M, Juneja LR, Ohira H. Biol Psychol. 2007;74:39–45.
Kuriyama S, Hozawa A, Ohmori K, Shimazu T, Matsui T, Ebihara S, Awata S, Nagatomi R, Arai H, Tsuji I. Am J Clin
Nutr. 2006;83:355–61.
Lakenbrink C, Lapczynski S, Maiwald B, Engelhardt UH. J Agric Food Chem. 2000;48:2848–52.
Lambert JD, Hong J, Yang GY, Liao J, Yang CS. Am J Clin Nutr. 2005;81:284s–91s.
Liu Q, Duan HY, Luan JL, Yagasaki K, Zhang GY. Cytotechnol. 2009;59:211–7.
Lorenz M, Urban J, Engelhardt U, Baumann G, Stangl K, Stangl V. Basic Res Cardiol. 2009;104:100–10.
Lu K, Gray MA, Oliver C, Liley DT, Harrison BJ, Bartholomeusz CF, Phan KL, Nathan PJ. Human Psychopharmacol
Clin Exp. 2004;19:457–65.
Macready AL, Kennedy OB, Ellis JA, Williams CM, Spencer JP, Butler LT. Genes Nutr. 2009;4:227–42.
Nakachi K, Matsuyama S, Miyake S, Suganuma M, Imai K. Biofactors. 2000;13:49–54.
Nantz MP, Rowe CA, Bukowski JF, Percival SS. Nutrition. 2009;25:147–54.
Ng TP, Feng L, Niti M, Kua EH, Yap KB. Am J Clin Nutr. 2008;88:224–31.
Nobre AC, Rao A, Owen GN. Asia Pac J Clin Nutr. 2008;17(Suppl. 1):167–8.
Nurk E, Refsum H, Drevon CA, Tell GS, Nygaard HA, Engedal K, Smith AD. J Nutr. 2009;139:120–7.
Owen GN, Parnell H, De Bruin EA, Rycroft JA. Nutr Neurosci. 2008;11:193–8.
Pardo de Santayana M, Blanco E, Morales R. J Ethnopharmacol. 200598:1–19.
Ramadan G, El-Beih NM, El-Ghffar EAA. Br J Nutr. 2009;102:1611–9.
Rao DN, Ganesh B, Dinshaw KA, Mohandas KM. Int J Cancer. 2002;99:727–31.
Rogers PJ, Heatherley SV, Hayward RC, Seers HE, Hill J, Kane M. Psychopharmacol. 2005;179:742–52.
Rogers PJ, Smith JE, Heatherley SV, Pleydell-Pearce CW. Psychopharmacol. 2008;195:569–77.
Setiawan VW, Zhang ZF, Yu GP, Lu QY, Li YL, Lu ML, Wang MR, Guo CH, Yu SZ, Kurtz RC, Hsieh CC. Int J
Cancer. 2001;92:600–4.
Simons CCJM, Hughes LAE, Arts ICW, Goldbohm RA, van den Brandt PA, Weijenberg MP. Int J Cancer
2009;125:2945–52.
Steptoe A, Gibson EL, Vuononvirta R, Hamer M, Wardle J, Rycroft JA, Martin JF, Erusalimsky JD. Atheroscler.
2007a;193:277–82.
Steptoe A, Gibson EL, Vuononvirta R, Williams ED, Hamer M, Rycroft JA, Erusalimsky JD, Wardle J. Psychopharmacol.
2007b;190:81–9.
Sun CL, Yuan JM, Lee MJ, Yang CS, Gao YT, Ross RK, Yu MC. Carcinogen. 2002;23:1497–503.
Tanabe N, Suzuki H, Aizawa Y, Seki N. Int J Epidemiol. 2008;37:1030–40.
Tsubono Y, Nishino Y, Komatsu S, Hsieh CC, Kanemura S, Tsuji I, Nakatsuka H, Fukao A, Satoh H, Hisamichi S. N
Engl J Med. 2001;344:632–6.
Venables MC, Hulston CJ, Cox HR, Jeukendrup AE. Am J Clin Nutr. 2008;87:778–84.
Vignes M, Maurice T, Lante F, Nedjar M, Thethi K, Guiramand J, Recasens M. Brain Res. 2006;1110:102–15.
Vita JA. Am J Clin Nutr. 2005;81:292s–7s.
Wang H, Wen Y, Du Y, Yan X, Guo H, Rycroft JA, Boon N, Kovacs EM, Mela DJ. Obesity (Silver Spring). 2009a.
Wang L, Lee IM, Zhang SM, Blumberg JB, Buring JE, Sesso HD. Am J Clin Nutr. 2009b;89:905–12.
Weber P. Agro Food Ind Hi-Tech. 2004;15:20–2.
... In the cortical neurons of the hippocampus, it can bind to the three glutamate receptor subtypes. Two of them are AMPA (a-amino-3-hydroxy-5-methylisoxazole-4-propionicacid) and kainite [12,38,87,101,103]. Several studies provided evidence that L-theanine induces neuroprotective effects in cortical neurons due to its antagonistic action with the two named receptors by blocking the binding of L-glutamic acid to glutamate receptors, thereby positively affecting mood and memory abilities [103,114]. ...
Article
Background: Green tea is traditionally known to induce mental clarity, cognitive function, physical activation and relaxation. Recently, a special green tea, matcha tea, is rapidly gaining popularity throughout the world and is frequently referred to as a mood- and brain food. Matcha tea consumption leads to much higher intake of green tea phytochemicals compared to regular green tea. Previous research on tea constituents caffeine, L-theanine, and epigallocatechin gallate (EGCG) repeatedly demonstrated benefits on mood and cognitive performance. These effects were observed when these phytochemicals were consumed separately and in combination. Methods: A review was conducted on 49 human intervention studies to summarize the research on acute psychoactive effects of caffeine, L-theanine, and EGCG on different dimensions of mood and cognitive performance. Conclusions: Caffeine was found to mainly improve performance on demanding long-duration cognitive tasks and self-reported alertness, arousal, and vigor. Significant effects already occurred at low doses of 40 mg. L-theanine alone improved self-reported relaxation, tension, and calmness starting at 200 mg. L-theanine and caffeine combined were found to particularly improve performance in attention-switching tasks and alertness, but to a lesser extent than caffeine alone. No conclusive evidence relating to effects induced by EGCG could be given since the amount of intervention studies was limited. These studies provided reliable evidence showing that L-theanine and caffeine have clear beneficial effects on sustained attention, memory, and suppression of distraction. Moreover, L-theanine was found to lead to relaxation by reducing caffeine induced arousal.
Article
Full-text available
Background/Objectives Ingestion of the non-proteinic amino acid l-theanine (γ-glutamylethylamide) has been shown to influence oscillatory brain activity in the alpha band (8–14 Hz) in humans during resting electroencephalographic (EEG) recordings and also during cognitive task performance. We have previously shown that ingestion of a 250-mg dose of l-theanine significantly reduced tonic (background) alpha power during a demanding intersensory (auditory-visual) attentional cueing task. Further, cue-related phasic changes in alpha power, indexing the shorter-term anticipatory biasing of attention between modalities, were stronger on l-theanine compared to placebo. This form of cue-contingent phasic alpha activity is also known to index attentional biasing within visual space. Specifically, when a relevant location is pre-cued, anticipatory alpha power increases contralateral to the location to be ignored. Here we investigate whether the effects of l-theanine on tonic and phasic alpha activity, found previously during intersensory attentional deployment, occur also during a visuospatial task. Subjects/Methods 168-channel EEG data were recorded from thirteen neurologically normal individuals while engaged in a highly demanding visuo-spatial attention task. Participants underwent testing on two separate days, ingesting either a 250-mg colorless and tasteless solution of l-theanine mixed with water, or a water-based solution placebo on each day in counterbalanced order. We compared the alpha-band activity when subjects ingested l-Theanine vs. Placebo. Results We found a significant reduction in tonic alpha for the l-theanine treatment compared to placebo, which was accompanied by a shift in scalp topography, indicative of treatment-related changes in the neural generators of oscillatory alpha activity. However, l-theanine did not measurably affect cue-related anticipatory alpha effects. Conclusions This pattern of results implies that l-theanine plays a more general role in attentional processing, facilitating longer-lasting processes responsible for sustaining attention across the timeframe of a difficult task, rather than affecting specific moment-to-moment phasic deployment processes.
Article
Full-text available
We investigated the effect of consumption of a catechin-containing drink on body fat level and its safety in healthy adults. The beverage (250 ml/bottle) contained 215.3 mg of tea catechins mostly possessing a galloyl moiety, which included (-)-epigallocatechin gallate 74.6 mg, (-)-epicatechin gallate 34.1 mg, (-)-gallocatechin gallate 77.8 mg, (-)-catechin gallate 24.5 mg. We conducted a double-blind study with three parallel groups. Healthy subjects (98 men and 97 women) aged from 20 to 65 years old with 22.5 < body mass index (BMI) < 30 kg/m2 were assigned to consume 3 bottles of placebo drink (control group), 2 bottles of catechin-containing drink and 1 bottle of placebo drink (low-dose group), or 3 bottles of catechin-containing drink (high-dose group), per day at mealtimes for 12 week (daily consumption of catechins was 41.1, 444.3 or 665.9 mg respectively). Compared to the value at 0 week, consumption of two or three bottles of catechin-containing drink results in significant decrease in body weight and BMI at 8 and 12 or 4, 8 and 12 week, respectively. Body weight and BMI was significantly decreased in both catechin groups compared with the control group from 4 to 12 week. The measurements of abdominal fat areas indicated significant reduction of total fat area and visceral fat area in both catechin groups compared with the control group at 12 week. Thus our present observations suggest that consumption of a catechin-containing drink may be useful for the prevention of obesity-related disorders.
Article
Full-text available
Although considerable experimental and animal evidence shows that green tea may possess potent activities of neuroprotection, neurorescue, and amyloid precursor protein processing that may lead to cognitive enhancement, no human data are available. The objective was to examine the association between green tea consumption and cognitive function in humans. We analyzed cross-sectional data from a community-based Comprehensive Geriatric Assessment (CGA) conducted in 2002. The subjects were 1003 Japanese subjects aged > or =70 y. They completed a self-administered questionnaire that included questions about the frequency of green tea consumption. We evaluated cognitive function by using the Mini-Mental State Examination with cutoffs of <28, <26, and <24 and calculated multivariate-adjusted odds ratios (ORs) of cognitive impairment. Higher consumption of green tea was associated with a lower prevalence of cognitive impairment. At the <26 cutoff, after adjustment for potential confounders, the ORs for the cognitive impairment associated with different frequencies of green tea consumption were 1.00 (reference) for < or =3 cups/wk, 0.62 (95% CI: 0.33, 1.19) for 4-6 cups/wk or 1 cup/d, and 0.46 (95% CI: 0.30, 0.72) for > or =2 cups/d (P for trend = 0.0006). Corresponding ORs were 1.00 (reference), 0.60 (95% CI: 0.35, 1.02), and 0.87 (95% CI: 0.55, 1.38) (P for trend = 0.33) for black or oolong tea and 1.00 (reference), 1.16 (95% CI: 0.78, 1.73), and 1.03 (95% CI: 0.59, 1.80) (P for trend = 0.70) for coffee. The results were essentially the same at cutoffs of <28 and <24. A higher consumption of green tea is associated with a lower prevalence of cognitive impairment in humans.
Article
Full-text available
Cardiovascular complications are a major cause of morbidity and mortality in patients with diabetes, obesity and the metabolic syndrome. Recently, there has been an increasing interest in tea as a protective agent against CVD. Here, we compared the modulatory effects of two different doses (50 and 100 mg/kg body weight given orally for 28 consecutive days) of black tea aqueous extract (BTE, rich in theaflavins and thearubigins) and green tea aqueous extract (GTE, rich in catechins) on experimentally induced hyperglycaemia, hyperlipidaemia and liver dysfunction by alloxan (which destroys pancreatic beta-cells and induces type 1 diabetes) and a cholesterol-rich diet (which induces obesity and type 2 diabetes) in male Wistar albino rats. Both tea extracts significantly alleviated most signs of the metabolic syndrome including hyperglycaemia (resulting from type 1 and 2 diabetes), dyslipidaemia and impairment of liver functions induced by alloxan or the cholesterol-rich diet in the animals. Also, the tea extracts significantly modulated both the severe decrease and increase in body weight induced by alloxan and the high-cholesterol diet, respectively. The modulatory effects obtained here were partial or complete, but significant and dose dependent, and slightly more in GTE in most cases. No harmful effects were detected for tea consumption on all parameters measured, except that the high dose of both tea extracts significantly decreased the spleen weight:body weight ratio and induced lymphopenia. The present study supports the hypothesis that both black and green teas may have beneficial effects against the risks of the metabolic syndrome and CVD as shown in rat models of human obesity and diabetes.
Article
Full-text available
Although green tea or its constituents might reduce psychological stress, the relation between green tea consumption and psychological distress has not been investigated in a large-scale study. Our aim was to clarify whether green tea consumption is associated with lower psychological distress. We analyzed cross-sectional data for 42,093 Japanese individuals aged > or =40 y from the general population. Information on daily green tea consumption, psychological distress as assessed by the Kessler 6-item psychological distress scale, and other lifestyle factors was collected by using a questionnaire. We used multiple logistic regression analyses adjusted for age, sex, history of disease, body mass index, cigarette smoking, alcohol consumption, time spent walking, dietary factors, social support, and participation in community activities to investigate the relation between green tea consumption and psychological distress. We classified 2774 (6.6%) of the respondents as having psychological distress (Kessler 6-item psychological distress scale > or =13/24). There was an inverse association between green tea consumption and psychological distress in a model adjusted for age and sex. Although the relation was largely attenuated when possible confounding factors were adjusted for, a statistically significant inverse association remained. The odds ratio (with 95% CI) of developing psychological distress among respondents who consumed >/=5 cups of green tea/d was 0.80 (0.70, 0.91) compared with those who consumed <1 cup/d. These relations persisted when respondents were stratified by social support subgroups or by activities in communities. Green tea consumption was inversely associated with psychological distress even after adjustment for possible confounding factors.
Article
Full-text available
Evidence in support of the neuroprotective effects of flavonoids has increased significantly in recent years, although to date much of this evidence has emerged from animal rather than human studies. Nonetheless, with a view to making recommendations for future good practice, we review 15 existing human dietary intervention studies that have examined the effects of particular types of flavonoid on cognitive performance. The studies employed a total of 55 different cognitive tests covering a broad range of cognitive domains. Most studies incorporated at least one measure of executive function/working memory, with nine reporting significant improvements in performance as a function of flavonoid supplementation compared to a control group. However, some domains were overlooked completely (e.g. implicit memory, prospective memory), and for the most part there was little consistency in terms of the particular cognitive tests used making across study comparisons difficult. Furthermore, there was some confusion concerning what aspects of cognitive function particular tests were actually measuring. Overall, while initial results are encouraging, future studies need to pay careful attention when selecting cognitive measures, especially in terms of ensuring that tasks are actually sensitive enough to detect treatment effects.
Article
Experimental studies have shown that tea and tea polyphenols have anticarcinogenic properties. There have been no prospective investigations examining the relationship between tea polyphenols and cancer risk using validated biomarkers. In the present study, a nested case–control study design was used to investigate the association between prediagnostic urinary tea polyphenol markers and subsequent risk of gastric and esophageal cancers. One hundred and ninety incident cases of gastric cancer and 42 cases of esophageal cancer occurring in members of the Shanghai Cohort (18 244 men aged 45–64 years at recruitment with up to 12 years of follow-up) were compared with 772 cohort control subjects. The control subjects were individually matched to the index cases by age, month and year of sample collection, and neighborhood of residence (case–control ratio 1:3 for gastric cancer, 1:5 for esophageal cancer). Urinary tea polyphenols, including epigallocatechin (EGC) and epicatechin (EC), and their respective metabolites 5-(3,4,5-trihydroxyphenyl)-γvalerolactone (M4) and 5-(3,4-dihydroxyphenyl)-γ-valerolactone (M6), were measured in all study subjects by means of a validated assay. Odds ratios (ORs) and 95% confidence intervals (CIs) were calculated from logistic regression models. After exclusion of cases diagnosed under 4 years follow-up, urinary EGC positivity showed a statistically significant inverse association with gastric cancer (OR 0.52, 95% CI 0.28–0.97) after adjustment for Helicobactor pylori seropositivity, smoking, alcohol drinking, and level of serum carotenes. The protective effect was primarily seen among subjects with low (below population median) serum carotenes. The odds ratio for EGC positivity was 0.49 (95% CI 0.26–0.94) among subjects with low serum carotenes while the corresponding odds ratio among subjects with higher levels of serum carotenes was 1.02 (95% CI 0.46–2.28). Similar tea polyphenol–cancer risk associations were observed when the gastric cancer and esophageal cancer sites were combined. The present study provides direct evidence that tea polyphenols may act as chemopreventive agents against gastric and esophageal cancer development.
Article
Tea is one of the most widely consumed beverages worldwide. Several studies have suggested that catechins and theaflavins found in tea may reduce the risk of various types of cancers. Major advances have been made to understand the molecular events leading to cancer prevention; however, the evidence is not conclusive. Evidence from pre-clinical and clinical studies also suggests that persistent inflammation can progress to cancer. Several possible mechanisms of action may explain the cancer preventive aspects of tea components specifically anti-inflammatory effects. In regards to brain health, green tea catechins have been recognized as multifunctional compounds for neuroprotection with beneficial effects on vascular function and mental performance. Theanine, a unique amino acid in tea, enhances cognition in humans and has neuroprotective effects. Human interventional studies with well characterized tea products are needed.
Article
Amyloid beta (Abeta)-induced neurotoxicity is a major pathological mechanism of Alzheimer disease (AD). In this study, we investigated the inhibitory effect of l-theanine, a component of green tea (Camellia sinensis), on Abeta(1-42)-induced neuronal cell death and memory impairment. Oral treatment of l-theanine (2 and 4 mg/kg) for 5 weeks in the drinking water of mice, followed by injection of Abeta(1-42) (2 microg/mouse, icv), significantly attenuated Abeta(1-42)-induced memory impairment. Furthermore, l-theanine reduced Abeta(1-42) levels and the accompanying Abeta(1-42)-induced neuronal cell death in the cortex and hippocampus of the brain. Moreover, l-theanine inhibited Abeta(1-42)-induced extracellular signal-regulated kinase (ERK) and p38 mitogen-activated protein kinase as well as the activity of nuclear factor kappaB (NF-kappaB). l-Theanine also significantly reduced oxidative protein and lipid damage and the elevation of glutathione levels in the brain. These data suggest that the positive effects of l-theanine on memory may be mediated by suppression of ERK/p38 and NF-kappaB as well as the reduction of macromolecular oxidative damage. Thus, l-theanine may be useful in the prevention and treatment of AD.
Article
The aim of this study is to investigate the effects of theanine, a tea characteristic amino acid, on human lung cancer and leukemia cells. In the present study, we have demonstrated that theanine suppressed the in vitro and ex vivo growth of human non-small cell lung cancer A549 and leukemia K562 cell lines in dose- and time-dependant manners. In addition, theanine displayed the inhibitory effect on the migration of A549 cells. More importantly, theanine enhanced the anticancer activity of anticancer agents such as trichostatin A (the histone deacetylase inhibitor), berbamine and norcantharidin (the anticancer drugs in China) by strongly reducing the viability and/or migration rate in A549 cells. In addition, theanine significantly suppressed A549 cell invasion. Suppression of A549 cell migration may be one of the important mechanisms of action of theanine against the A549 cell invasion. Our present results suggest that theanine may have the wide therapeutic and/or adjuvant therapeutic application in the treatment of human lung cancer and leukemia.