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
CVD Cardiovascular disease
EGCG Epigallocatechin gallate
LDL Low-density lipoprotein (cholesterol)
DNA Deoxyribonucleic acid
GABA Gamma-aminobutyric acid
CFF Critical ﬂicker fusion test
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
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
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
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
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)
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
wikimedia.org/ – public
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)
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.
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
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.)
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
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.
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.
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.
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 •
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.
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