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REVIEW ARTICLE
Herbal Teas and their Health Benefits: A Scoping Review
Fatima S. Poswal
1
&Grace Russell
1
&Marion Mackonochie
2
&Euan MacLennan
2
&Emmanuel C. Adukwu
3
&
Vivien Rolfe
2
#Springer Science+Business Media, LLC, part of Springer Nature 2019
Abstract
Herbal teas are used as therapeutic vehicles in many forms of traditional medicine and are a popular global beverage. The purpose
of this scoping review was to examine the evidence relating to the clinical efficacy and safety of herbal teas, and to identify the
main research themes and gaps in knowledge to inform further work. A scoping review methodology was followed that set out
the research question and described the sourcing, selection and analysis of studies. Overall, a total of 145 research publications
were retrieved from global bibliographic databases, and after applying exclusion criteria, 21 remained. These studies looked at
herbal tea use in female health, diabetes, heart disease and weight loss, with plant species including lavender, chamomile,
fenugreek,stinging nettle, spearmint, hibiscus, yerba maté, echinacea and combinations of herbs. Observational studies explored
associations between herbal tea consumption and cancer risk, liver health, and the risks linked to the consumption of environ-
mental contaminants in the plant material. Despite plant materials being the basis for drug discovery, and the popularity ofherbal
teas, the number of articles exploring clinical efficacy and safety is small. In this review we discuss how herbal teas may be
beneficial in some areas of clinical and preventative health, and what further research is required to understand whether regular
consumption can contribute to healthy living more generally.
Keywords Infusions .Plant medicine .Phytochemicals .Plant biodiversity .Herbal tea
Introduction
In recent years, global mortality arising from non-
communicable diseases has overtaken infectious diseases,
with ischemic heart disease the most prevalent, and dementia
and diabetes now placed within the top 10 causes [1]. As
global life expectancy increases, research suggests that diet
and lifestyle changes at any time in life can improve vascular,
metabolic and cognitive health, therefore reducing the burden
of non-communicable disease [2]. Further clinical evidence
indicates that individuals need to prioritise plant materials like
fruit, vegetables, grain, nuts and oils, alongside lowering the
intake of red and processed meat and sugary drinks to achieve
a healthy diet [3]. However, these ambitions are compounded
by factors including the increased consumption of processed
foods and the dwindling availability of plant species, along-
side major global, socioeconomic and political challenges that
reduce access to a nourishing diet for many [4].
One possible solution to address these major challenges is
perhaps the consumption of valuable plant materials from other
dietary sources. The Government of the Netherlands, in their
national dietary guidelines, recommend people drink three cups
of green or black tea per day based on a body of evidence linking
tea consumption to the reduced risk of stroke and high blood
pressure [5]. The habitual consumption of black and green tea
derived from the plant Camellia sinensis dates back several thou-
sand years, and the medical benefits of the main polyphenolic
catechins and teaflavin compounds are well defined [6,7].
Alongside the ever-popular green and black varieties, tea can
be made with water infusions of the roots, leaves, flowers and
other component parts of a hugely diverse range of plant species.
These ‘herbal teas’contain a wealth of compounds and could
play a significant role in delivering nutrients and chemicals to
compensate for low quality diets.
Herbal teas have long-since been used as therapeutic vehi-
cles in Chinese, Indian and other indigenous medical systems
*Vivien Rolfe
vivien.rolfe@pukkaherbs.com
1
Department of Applied Sciences, University of the West of England,
Frenchay Campus, Bristol BS16 1QY, UK
2
Pukka Herbs, The Chocolate Factory, Bristol BS31 2GN, UK
3
Centre for Research in Biosciences, University of the West of
England, Frenchay Campus, Bristol BS16 1QY, UK
Plant Foods for Human Nutrition
https://doi.org/10.1007/s11130-019-00750-w
[8–10]. Chamomile and peppermint are the basis of some of
the most popular herbal teas, with the anti-inflammatory and
anti-mutagenic responses to chamomile, and relaxation effects
of peppermint oil on the gastrointestinal tract being
characterised [11,12]. Due to the low costs associated with
in vitro research, there is a wealth of preclinical information
about phytoconstituents and their pharmacology. However,
there is a need for more human research into observable ben-
efits in the short and long-term from herbal tea consumption,
including the efficacy of manufacturing techniques like fer-
mentation of the tea that creates a unique flavour and may
increase the biological activity.
The World Health Organisation seeks to capitalize on the use
of traditional medicines including herbal medicines in its 2014–
2023 strategy, with the aim of keeping populations healthy
through providing access to effective and affordable alternatives
to medicine, and to provide healthcare choices coherent with
people’s cultural practices [13]. As these strategies become more
integrated into global and national healthcare policies, so has
grown the need to examine the important issues of efficacy,
safety and quality assurance through establishing evidence-
based approaches [14]. For example, there are safety concerns
regarding the levels of fluoride following black, green and herbal
teas consumption highlighting the need for robust quality assur-
ance and standards [15]. Also an area of concern is growing
availability of adulterated herbs and spices with dyes and bulking
agents, with individuals motivated by the economic advantages
of participating in a billion dollar industry [16].
What do we know of the health benefits of herbal tea, and
to what extent has research explored their clinical effective-
ness and safety? The main aim was to carry out a scoping
review to follow a precise methodology “to examine the ex-
tent, range and nature of research activity around a particular
topic”[17]. The implications for further research are discussed
along with the dominant research themes and gaps therein.
Methods
This scoping review utilised a six-step process (setting the
research question; sourcing studies; selecting studies; record-
ing data; summarising results; consulting on the findings) [17,
18]. The search strategy was informed by the PRISMA check-
list for reporting systematic reviews [19], and further en-
hanced by the recommendations of Narahari et al. [20]; these
approaches include the utilisation of relevant regional data-
bases and broadening the range of study types to gain a com-
prehensive and inclusive view of available research.
Article Eligibility Criteria
Articles were selected on the efficacy and safety of hu-
man herbal tea consumption, and excluded animal and
in vitro studies. Articles were included regardless of par-
ticipant age or health status. As defined by the World
Health Organisation (WHO), health included “complete
physical, mental and social well-being and not merely
the absence of disease or infirmity”[21], so studies were
included if they were interventions for clinical disease or
as part of preventative measures, including both physical
and mental health.
Herbal tea was defined as an aqueous infusion in hot or
cold water for an unspecified amount of time to extract the
phytochemical constituents of the plant materials. Studies
where herbs were administered as supplements, injected, or
delivered in other ways were excluded. Herbs that were either
administered individually or part of a blend in the tea were
included. Hot and cold teas were included.
BasedonNaraharietal’s[20] recommendations to
include a broad catchment of articles, both experimental
and observational studies were included: controlled trials
(randomised, non-randomised), controlled before and af-
ter studies, and observation studies (cohort or case con-
trol) with a comparison across two or more population
groups. Studies were included if they had measurable
health or clinical outcomes or used qualitative techniques
or self-reporting through questionnaires or interviews.
Case studies and review articles were excluded. Studies
were not excluded on the basis of language or if a full
text article was not available.
Search Strategy
A number of global electronic databases were searched with
no date restrictions: PubMed, Science Direct, MEDLINE
via EBSCO, AYUSH Research Portal and DHARA
Online. The search terms included (Humans) and (“herbal
infusion”or “herbal tea”or “tisane”)aswellas(“health”or
“clinical”or “heath benefits”or “health risks”or “well-be-
ing”). The search was limited to the title and abstract, and
more simple search strategies were applied to some data-
bases. Further articles were retrieved through hand
searching reference lists, using Google Scholar and consult-
ing with experts in this field of work. The search terms and
process were developed iteratively.
Study Selection
The full references of articles retrieved or added from grey
literature were downloaded from the individual databases or
added manually into Microsoft Excel. An initial screening of
article titles and abstracts for inclusion or exclusion was car-
ried out in the database and results entered into Excel. Articles
were screened a further time by reading the full-text. Two
reviewers screened articles for inclusion with discrepancies
resolved with a third reviewer.
Plant Foods Hum Nutr
Data Collection
The details ofthe inclusion and exclusions were recorded. For
included articles that passed the two rounds of screening the
following data was gathered: Full reference; URL; Study iden-
tifier (authors and year of publication); methodologies; abbre-
viations and terminology used; participant details; location
details; herbal intervention details (botanical/Ayurvedic/tradi-
tional name; doses; duration of study); outcome measures;
concluding remarks. The datawas extracted by two reviewers.
Results were discussed by consultation between all of the
authors. A separate consultation took place with experts in
the field of herbal science.
Synthesis
The methodological quality or risk of bias of the included
articles was not critiqued as appropriate for a scoping
review [18]. The synthesis of evidence included a fre-
quency analysis of key research themes and depiction of
included and excluded studies. The characteristics of in-
cluded studies were reported in tables and clustered into
research themes within the discussion.
Results and Discussion
A total of 21 human studies examining the health benefits
of herbal tea consumption were identified (Fig. 1).
Sixteen clinical studies of varying methodological design
and quality evaluated the health benefits of drinking tea,
from the immediate effects of drinking lavender or cham-
omile to the benefits of longer-term consumption. Most
studies identified were randomised controlled studies that
utilized a placebo and some degree of blinding. Five stud-
ies were large-scale cohort studies or case controls,
reporting on health outcomes in relation to the frequency
of herbal or non-herbal tea consumption (with consump-
tion usually defined as one or more cups per day).
Details of Included Studies
Sixteen clinical studies (Table 1) and five observational stud-
ies (Table 2) were examined. Of the clinical studies, three were
small-scale clinical studies and the remainder were
randomised controlled trials (Table 1). In two studies of ma-
ternal health, lavender and chamomile herbal tea improved
sleep quality and remedied feelings of low mood in new
mothers [30,31]. Two studies explored whether nettle and
fenugreek teas improved lactation [32,33]. In a further study,
fenugreek tea consumption did not boost the levels of antiox-
idants in milk, which had been hypothesised to account for its
beneficial effects [34]. In a final study of maternal health, the
aroma characteristics of a fennel-based herbal tea were tested,
and there was no transfer of odiferous compounds into the
milk, which was initially a concern [35].
In other areas of women’s health, spearmint tea was
perceived to be effective as anti-androgen therapy by fe-
male participants with poly-cystic ovary syndrome
(PCOS) who reported improvements in their symptoms
of hirsutism, although there were no changes to the ob-
jective clinical scores [28]. In a second spearmint study,
anti-androgenic effects were observed in a PCOS patient
group but not those with idiopathic hirsutism, indicating a
possible selective mode of action [29].
In hypertensive patients, and diabetic patients with hyper-
tension, hibiscus tea was shown to reduce blood pressure [24,
25]. In a study exploring the effects of beverage temperature
on physiological responses, a cold yerba maté tea (a South
American drink) altered the sensitivity of the cardiac barore-
flex, fat oxidation and energy expenditure when tested, al-
though there was no change in blood pressure or cardiac out-
put between the hot or cold teas [36].
For herbal tea as an intervention for weight loss and diabe-
tes, in an uncontrolled study, weight reductions were observed
in a group of volunteers drinking a combination of Garcinia
cambogia, Commiphora mukul and Cyperus scariosus [22].
For type 2 diabetes, a tea made with Populus tremuloides was
not effective in reducing markers of the disease, although was
well tolerated during the 10-day trial [26]. In 32 patients drink-
ing chamomile tea for 8 weeks, there were reductions in gly-
cosylated haemoglobin (HbA1c) and other serum markers of
diabetes, and these were accompanied by increases in total
serum antioxidant capacity and oxidative activity [27]. In a
Fig. 1 PRISMA flow diagram of the article selection process
Plant Foods Hum Nutr
Table 1 Characteristics of clinical studies evaluating herbal tea and health outcomes
Design Population Intervention Outcomes Reference
Non-controlled clinical study,
pre- and post- test surveys
35 male and female volunteers, 4–6kg
overweight
A slimming tea with Garcinia cambogia,
Commiphora mukul and Cyperus scariosus.2cups
daily for 2 months.
Tea reduced group weight on average by 1.5-2 kg.
Volunteers reported improvements - less oedema and
less feeling of bloating. No side effects.
[22]
RCT, placebo controlled, double
blind, cross-over
51 male and female patients with type 2
diabetes
Salacia reticulata tea (n= 51) versus placebo (n = 51)
in cross-over design; 3 months.
Tea reduced HbA1C; reduced dose of anti-diabetic
drug glibenclamide but not metformin. Safe and
effective.
[23]
RCT, placebo controlled, double
blind
65 pre- and mildly hypertensive male
and female adults not yet on
medication
3 cups of brewed hibiscus tea (n= 35) versus placebo
beverage (hibiscus flavoured) (n= 30) for 6 weeks.
Hibiscus tea lowered SP compared to placebo at
6 weeks, and reduced mean arterial blood pressure
(p< 0.06). DP was lower for both at 6 weeks.
[24]
RCT, double blind 60 male and female diabetic patients
with mild hypertension not yet on
medication
2 cups of hibiscus tea (n= 30) versus black tea
(n= 30) daily for 1 month.
3 patients in hibiscus group and 4 in black tea group
withdrew from study. Hibiscus reduced SP versus
increases in black tea group. No change to DP.
Hibiscus reduced mean pulse pressure.
[25]
RCT, placebo controlled, single
blind
40 male and female patients with type 2
diabetes
Herbal tea (Populus tremuloides and Heracleum
lanatum,n= 20) versus placebo (Chinese green
tea, mint and fennel, n= 20). 2 cups daily for
10 days.
No differences to a responder challenge, or HbA1c
between groups. Reduction in blood glucose for high
HbA1c subgroup. No toxic effects or adverse events
reported.
[26]
RCT, placebo controlled,
single-blind study
64 patients with type 2 diabetes (male
and female)
Chamomile tea (n= 32) versus control (water,
n= 32); 3 x day after meals for 8 weeks.
Chamomile significantly reduced HbA1c, HOMA-IR,
serum insulin and serum blood glucose levels
(adjusted for baseline variables); total AOX,
superoxide dismutase, glutathione peroxidase, and
catalase activity significantly increased.
[27]
RCT, placebo controlled, 2 centres 42 female volunteers with hirsutism in
PCOS
Spearmint tea (n= 21) 2 x per day versus placebo
(n=21) for30 days.
At 30 days, 1 patient from spearmint group withdrew
(due to taste of tea). Spearmint significantly changed
hormone levels (reduced testosterone, elevated FSH,
LH), self-reported improvements in hirsutism but
not clinically rated scores.
[28]
Clinical study, 1 centre 12 female hirsute patients (with PCOS)
versus 9 with ideopathic hirsutism
Spearmint tea 2 x day for 5 days. Spearmint decreased free testosterone and increased
LH, FSH and oestradiol in PCOS.
[29]
RCT, pre- and post-test surveys 80 Taiwanese postnatal women with
poor sleep quality
1 x lavender tea daily (spending time to appreciate
and smell the aroma) (n= 40) for 2 weeks plus post
atal care versus control postnatal care only (n= 40).
Lavender tea reduced fatigue, reduced depressive
feelings and improved infant bonding at 2 weeks but
not at 4 weeks.
[30]
RCT, pre- and post-test surveys 80 Taiwanese postnatal women with
poor sleep quality
1x chamomile tea daily plus postnatal care (n= 40)
versus controls with postnatal care only (n= 40).
Reduced sleep deficiency and feelings of depression at
time of drinking but not after.
[31]
RCT, placebo controlled 95 mothers with infants born before
37 weeks gestation and < 2 kg birth
weight
Stinging nettle tea (n= 32) versus fruit tea (n= 21)
versus placebo (n= 32); all had postnatal care.
Herbal increased milk production but induced no
change in serum prolactin levels. No changes in
infant weight gain between groups. No adverse
effects. Volunteers withdrew - 4 in nettle group; 4 in
fruit group and 2 in placebo group.
[32]
RCT, placebo controlled, double
blind
66 mothers in early postnatal period Fenugreek (n= 22) versus placebo (apple, n=22)
versus placebo (no tea, n= 22). All had same care.
Fenugreek increased mean breast milk volume;
increased weight gain and babies regained their birth
weight faster than placebo and controls.
[33]
RCT, placebo controlled 80 healthy mothers in early postnatal
period
3 cups fenugreek tea daily (n= 40) versus water
placebo (n= 40) for 10 days.
No change in AOX levels in human milk from
fenugreek. OSI of breast milk samples taken in the
[34]
Plant Foods Hum Nutr
Tab l e 1 (continued)
Design Population Intervention Outcomes Reference
1st day and 7–10 d increased for both groups during
lactation.
Non-controlled clinical study 5 volunteer new mothers Fennel-anise-caraway tea versus control tea in block
design 1 day sampling.
No influence of fennel tea on milk odour profiles. [35]
RCT, cross-over design 23 healthy male and female subjects Yerba maté tea hot (55o, n= 23) versus cold (3d,
n= 23) ingested over a 5 min period.
At 90 mins cold tea decreased heart rate, baroreflex
sensitivity, fat oxidation and energy expenditure. No
change in cardiac output or BP.
[36]
RCT, placebo controlled, double
blind, post test survey
95 people with early cold or flu
symptoms (males plus
predominantly females)
5 cups of echinacea tea daily (starting with 1 per day
and increasing; n= 48) for 2 weeks versus placebo
herbal tea (n= 47).
Echinacea relieved cold and flu symptoms and
shortened duration after 2 weeks via self-scoring
survey.
[37]
AOX, total antioxidant status or capacity, or oxidative stress index; BP, blood pressure; DS, diastolic pressure; FSH, follicle stimulating hormone; HbA1c, glycated haemoglobin; HOMA, homeostatic
model assessment for insulin resistance quantification; LH, lutenising hormone; OSI, oxidative stress index; PCOS, poly-cystic ovary syndrome; RCT, randomised controlled trial; SP, systolic pressure
Table 2 Characteristics of characteristics and outcomes of observational studies on herbal tea
Design Population Investigation / exposure Outcomes Reference
Cohort study 222 male and female Chinese student
volunteers Questionnaires on attitudes toward herbal tea
consumption, reporting of somatization and
alexithymia. Explored association with herbal tea
consumption.
Attitudes toward herbal tea consumption significantly
correlated with somatosensory amplification (somatic
presentations of distress).
[38]
Case-control study 113 Greek patients with thyroid cancer;
286 benign thyroid disease, 138 healthy
controls. Males and females
Lifestyle interviews and questionnaires. Explored
association between chamomile tea consumption
and thyroid disease risk.
Chamomile tea (2–6 times per week) consumption
associated with reduced risk of thyroid cancer (i.e.,
drinking for 30 years reduced risk of thyroid cancer and
disease by 80%).
[39]
MIREC Study, Canada 1954 1st trimester, singleton, pregnant
females with available biological data Clinical, biological and questionnaire data.
Measures included heavy metals at 1st and 3rd
trimester, maternal and cord blood. Associations
for herbal tea versus non-tea drinkers.
Levels of arsenic, cadmium, mercury, manganese were
within normal ranges for consumption of herbal and all
teas. Lead levels at 3rd trimester were within normal
ranges but higher for herbal tea than non-herbal tea
drinkers.
[40]
MIREC Study, Canada 1898 1st trimester, singleton, pregnant
females with available biological data Clinical, biological and questionnaire data. Tests for
OC and OP at 1st and 3rd trimester in maternal
urine. Associations between pesticides and
drinking herbal tea.
Levels of OC and OP within normal ranges for herbal and
non-herbal tea drinkers. No adverse birth outcomes in
either group.
[41]
Rotterdam population study,
prospective cohort
2424 male and females over 45 years of
age with diagnosed liver stiffness
(fibrosis or sterosis)
Clinical, biological and questionnaire data as part of
larger Rotterdam study. Associations between
liver stiffness and herbal tea consumption (plus
other beverages).
Lower liver stiffness in herbal tea group compared to
non-herbal, whereas black and green tea conferred no
benefit. This was independent of a number of lifestyle
factors.
[42]
MIREC, Maternal-Infant Research on Environmental Chemicals; OG, organochlorine; OP, organophosphate
Plant Foods Hum Nutr
clinical study of three month duration, a tea made from
Salacia reticulata, a flowering plant from Sri Lanka, reduced
HbA1c and reduced the levels of one anti-diabetic drug re-
quired by patients to treat their disorder, but had no effect on
the dose of a second drug [23].
Only one study considered tea for infectious disease,
reporting benefits from echinacea tea for cold and flu
symptoms [37].
The effects of herbal tea consumption on health has been
the subject of a number of observational studies that looked at
associations with risk during pregnancy, risk of chronic dis-
ease and also mental health (Table 2). In a Canadian study,
herbal tea consumption was not associated with raising levels
of heavy metals and pesticides, and although levels of lead in
maternal blood were slightly elevated in herbal tea drinkers
compared to non-drinkers, these were low and well within
acceptable national standards [40,41].
In Chinese students vulnerable to stress, there was an asso-
ciation with somatosensory amplification and herbal tea con-
sumption, with the students reported benefits to drinking tea if
they were particularly emotionally withdrawn in times of
stress [38]. In a Greek population study, people who regularly
drank chamomile tea had a lower associated risk of thyroid
cancer and thyroid diseases, and there was a positive relation-
ship between the duration of drinking tea and reduction in
disease risk [39]. In Netherlands cohort study, herbal tea con-
sumption was associated with a lower risk of liver stiffness
compared to green or black teas, a clinical measure of fibrosis
or fatty liver disease determined by ultrasound [42].
Details of Excluded Studies
Figure 2illustrates the characteristics of studies that were
excluded after analysis of the full text. This provides an
indicator of the range of publications in this field of re-
search. A number were excluded for being the incorrect
article type i.e., wereacasestudyorareviewofherbal
tea, articles that were clinical studies of herbs delivered in
capsule or injected forms, or research into the phytochem-
ical profiles or herbs and their biological activity deter-
mined by in vitro testing or animal research. Some of
these articles are highlighted in the discussion.
Given the popularity of herbal teas and the desire to capi-
talize on traditional medicines like herbal products to keep
populations healthy [13], this review sought to provide a cri-
tique on the available literature relating to the health benefits
of herbal tea. Evidence suggests that diverse plant material
forms a vital component of the diet and could help combat
the significant burden of non-communicable disease [2], and
the use of herbals is postulated to have evolved alongside
advances in farming and food production as the nutritional
characteristics of our native diets became depleted of plant
phytochemicals [43]. Despite the level of global interest in
herbal teas and the recognised growing importance of plant-
rich diets, this review identified only 21 clinical and observa-
tional studies that looked at herbal tea and human health.
Herbs are rich in phytochemicals that are important constit-
uent secondary metabolities required for plant growth, natural
defence and communication, and are similar in structure to
many human biochemical compounds. Phenols are the most
abundant and widely explored for their antioxidant properties
[44], and the chemical properties of other compounds like the
steroidal components of saponins and sugar attachments of
glycosides form the basis of their biological activity [45].
Plants contain an abundance of phytochemical compounds
and these vary with the growing conditions of the plant, and
the farming and processing methods that form the ‘value
chain’through to the manufacture of products [46].
Hot, liquid-based herbal infusions provides the ideal
medium for water-soluble phytochemicals such as phenols
and flavonoids to be released and be potentially more
effective than just consuming the dried leaves of some
herbs [47]. Hot water facilitates the releaseofvolatileoils
from the herbs that enter the blood stream via the nasal or
respiratory mucosa, as demonstrated for rosemary and the
appearance of 1,8-cineole in the blood after a brief expo-
sure [48]. Tea is commonly used and simple to prepare,
and in the identified studies, teas were used for a number
of reasons. One paper explored a herbal remedy for dia-
betes based on healing practices of endogenous popula-
tions in North America that used herbal infusions [26]. In
other studies, the wide availability of herbs such as cham-
omile or lavender, which are popular herbal teas, offered a
simple therapy choice for breastfeeding women, given as
a post-natal regimen where alternatives to synthetic phar-
macological treatments were more desirable [30–33].
This review excluded many articles that analysed the phe-
nolic composition and antioxidant capacity of herbs [49,50],
or that had characterised the anti-cancer, anti-inflammatory
and anti-microbial effects of herbs in vitro [51].Despite this
wealth of literature describing anti-cancer and antioxidant ac-
tivity, there were no clinical studies looking at herbal teas in
these areas. Probably, the lower potency and complexity of
herbal preparations render them a less appropriate delivery
vehicle compared to phytochemical extracts of active ingredi-
ents given in a controlled dosage [52,53]. Further variability
can arise from the phytochemicals and volatile compounds
behaving differently within an aqueous infusion, as demon-
strated for chamomile, so producing an infusion of a standard
biological benefit would be a challenge [54]. However, think-
ing about the longer-term and preventative benefits of regular
consumption is an alternative paradigm; one study on the re-
lationship between herbal tea and cancer, showed that the
regular consumption of chamomile tea (Matricaria
chamomilla L.) over a number of years was associated with
a reduced risk of thyroid cancer amongst healthy populations
Plant Foods Hum Nutr
in Greece [39]. One theory is that chamomile phytochemicals
interact with hydrogen peroxide, a reactive oxygen species
involved in thyroid hormone biosynthesis and implicated in
thyroid cancer pathophysiology [12]. Over 120 chemical con-
stituents for chamomile have been identified, such as terpe-
noids, flavonoids, and essential oils, and further studies would
confirm any pharmacological use in relation to cancer [55]. In
a second cohort study that queried participants on their
herbal tea, black or green tea, or coffee consumption over
the previous month, the consumption of herbal tea and
also three or more cups of coffee was linked to lower liver
stiffness as measured by clinical tests, which the authors
contributed to the antioxidant-activity of the beverages
[42].
Another surprising finding was that considering traditional
herbal medicines are widely used for their antimicrobial po-
tential, and have been well researched in vitro [56,57], only
one clinical study had looked at herbal tea for the treatment of
infection. In this small-scale RCT Lindenmuth et al. [-
37]observed that echinacea tea taken for two weeks reduced
symptoms of cold and flu compared to a placebo [37].
Echinacea is used clinically for the prevention of common
cold symptoms [58] and is effective in reducing the risk of
recurrent upper respiratory tract infections in susceptible indi-
viduals [59]. It could be that echinacea delivered as a herbal
infusion may provide a more convenient remedy for the com-
mon cold and further clinical studies could compare its effica-
cy with extracts delivered in other formats.
Herbal teas were used for the benefit of female health.
Healthcare workers recommended chamomile and lavender
teas to new mothers, encouraging them to savour the taste
and aroma for a 2-week period. Both teas reduced sleep defi-
ciency and lifted feelings of depression [30,31]. The mecha-
nisms of these herbs are reasonably well delineated; the flavo-
noid and monoterpene compounds in chamomile, and linolool
in lavender oil are used clinically in aromatherapy for pain
relief and relaxation [60,61], and they are used in neurological
and psychological conditions through affecting the limbic sys-
tem, GABAergic and cholinergic neuronal transmission [62].
These teas offer a convenient and safer alternative to pharma-
ceuticals for new mothers.
In other areas of female health, the galactagogue effects
of nettle and fenugreek teas were explored in nursing
mothers. Both herbs enhanced maternal milk production,
with fenugreek showing additional positive improvements
in infant weight gain, although the actions of fenugreek
were not linked to enhanced prolactin production [33,
34]. Stinging nettles contain phytosterols and are benefi-
cial in benign prostatic hyperplasia, and its biological ac-
tivity involves sex hormone binding globulin (SHBG), a
key regulatory molecule for testosterone and oestrogens
[63]. As SHBG also plays a role in pregnancy, birth and
lactation, it is plausible that it may be part of the mecha-
nism underlying the galactagogue effects observed, al-
though further research would confirm this. Fenugreek also
contains a number of active compounds in its seeds and
Fig. 2 Frequency and categorisation of excluded articles includingthose other than efficacy or observational studies; articles with a non-herbalor non-tea
intervention; articles relating to biological actions, herb toxicity and manufacturing methods
Plant Foods Hum Nutr
leaves, and the leaves in particular are rich in phytosterols
[64]. Since it is a widely used lactation aid, both from
traditional use and via recommendations from healthcare
professionals, there is guidance to standardise its use in
order to provide an alternative to synthetic pharmaceutical
drugs [65].
The anti-androgenic effects of plant phytochemicals was
demonstrated in two further studies, with observations that
spearmint tea (Mentha spicata) reduced blood levels of free
testosterone in females [29];the tea also improved patient self-
scoring of symptoms of hirsutism, although an absence of
change to objective clinical scores suggests that a longer du-
ration trial might be required to confirm efficacy [28]. A large
number of medical conditions utilise anti-androgen therapy
from hirsutism to cancer, and given that plant materials pro-
vide a pharmaceutical alternative and the option of fewer ad-
verse events, more clinical studies are needed to further un-
derstand these findings, and in particular, the longer-term ef-
fects associated with regulating hormonal activity [66].
In the WHO’s Traditional Medicine Strategy [13], the use
of herbal medicines is argued for the treatment of chronic
diseases, and to provide more culturally accepted and trusted
therapeutic choices. The present review found articles relating
to teas commonly used in Indian medicine to treat diabetes
and obesity. Tea made from Garcinia cambogia, Commiphora
mukul and Cyperus scariosus was consumed for two months,
and Salacia reticulata (Kothala himbutu) tea was consumed
for three months [22,23]. In the first study which was un-
controlled, there were weight reductions and self-reported im-
provements relating to weight; in the second study, Salacia
reticulata tea reduced markers of type II diabetes and also
lowered the dose required for one diabetic medication. Little
is known of the phytochemical profiles and possible mecha-
nisms of the herbs in the first study, whereas Salacia reticulata
is rich in polyphenols including mangiferin, kitalanol and
salacinol, and these are thought to contribute to the
hypoglycaemic effect [67]. A further study explored a formu-
lation indigenous to North America containing the plants
Populus tremuloides - trembling aspen, and Heracleum
lanatum - cow parsnip. There were no changes in postprandial
blood glucose in a diabetic patient group, but in a subgroup of
those with more severe diabetes, positive effects were seen
following tea consumption [26]. The mechanisms by which
herbs and their constituents may exert anti-diabetic effects
may relate to the antioxidant effects of the phenolic compo-
nents as shown for herbs such as green tea and peppermint,
and the synergistic effects of differing combinations suggest
the potential importance of the whole herb over extracts of
singular phytochemical components [68]. Further good qual-
ity research on larger groups of patients with more severe
diabetes and poorer glycaemic control is warranted. With
global diabetes increasing in prevalence and the complexity
of drug regimens and side effects of medication hampering
treatment, alternative approaches that offer better patient com-
pliance are important.
In clinical studies of herbal tea and cardiovascular disease,
studies of tea made from Hibiscus sabdariffa, which is a pop-
ular tea in the United States, resulted in an anti-hypertensive
response [24,25]. Hibiscus contains high levels of phenols
and anthocyanins, and a meta-analysis of 128 randomised
controlled trials identified a range of cardiometabolomic
events influenced by anthocyanins including reductions in
systolic and diastolic blood pressure [69]. The underlying
mechanisms are likely to be complex involving the protection
against reactive oxygen species and targeting phosopholipase
pathways to reduce pro-inflammatory prostaglandins and leu-
kotrienes; also relevant to vascular endothelial function is the
inhibition of NF-kB signalling which has been shown to be
anti-atherosclerotic [70].
Alongside evaluating the clinical benefits of herbal tea con-
sumption, the safety aspects were also considered. Only seven
of the clinical studies retrieved reported any adverse events,
with the remaining ones failing to disclose this important in-
formation. Overall, the consumption of tea was not accompa-
nied by serious adverse symptoms and were well tolerated
(Table 1). Other concerns are that tea drinking may contribute
to the exposure from environmental pollutants. In a cohort of
pregnant mothers, no association was found between herbal
tea consumption and levels of heavy metals during pregnancy
with the exception that lead was higher but well within normal
and acceptable ranges, and there were no changes in pesticide
residues in maternal urine [40,41]. Such risks will arise from
poor sourcing standards that fail to measure the quality of the
original plant material. Booker et al. [46] make strong recom-
mendations to the sector to ensure products that are a medic-
inal standard, not just ensuring good levels of phytochemicals
in the materials, but to assure quality and provide consumers
with the reassurance that they are not contaminated.
This scoping review highlights a number of clinical
scenarios where herbal teas may be beneficial, but there
are many gaps where herbs are used medicinally but have
not been explored in a tea format. Turmeric is well
recognised for its anti-inflammatory potential, and in a
meta-analysis of eight randomised controlled trials, tur-
meric extract was effective in the treatment of arthritis
as determined by pain scores and an arthritis diagnostic
index [71]. Herbs also contain cognition-enhancing prop-
erties, for example the effects of waterhyssop or Bacopa
monnieri (L.) were assessed in a meta-analysis of 9 clin-
ical studies of largely healthy volunteers, and showed im-
proved cognition and speed of attention [72]. In other
areas, given the popularity of berry teas, and considering
the rich levels of phenolic compounds and proven biolog-
ical effects of these fruits [73], the present research iden-
tified no human studies looking at fruit or berry teas and
health. In one final area, herbal tea blends that include
Plant Foods Hum Nutr
ginger have been shown to provide an enriched sensory
experience and increased beverage consumption, and this
may have important application in specific areas of
healthcare for example social enrichment and better nutri-
tional care for the elderly [74], and again there were no
studies retrieved in relation to this.
Another gap in the literature retrieved was in relation to
some evidence from traditional Chinese medicine that fer-
mentation of herbs may increase their activity and therefore,
lead to more health benefits. Camellia sinensis leaves are
fermented to produced black tea with different health and
taste properties to green tea and there is emerging evidence
that this process can enhance the biological activity of some
herbs. For example, Artemesia capillaris is from the
Asteraceae family and is traditionally used as a hepatopro-
tective herb. Solid-state fermentation of Artemesia
capillaris using Ganoderma lucidum mycelium enhanced
anti-inflammatory activity compared to unfermented herb,
possibly through the biotransformation of polyphenolic
compounds into novel materials [75]. Fermentation of
Astragalus membranicus root with Aspergillus spp. in-
creased phenolic contents and antioxidant activity, includ-
ing the generation of novel phenolic compounds [76].
The present research had some limitations. In order to
compile a comprehensive and broad scoping review, arti-
cles were not excluded based upon their methodological
quality. As a result a number of small-scale, uncontrolled
studies were included whose results should be interpreted
cautiously. Whilst every attempt was taken to develop a
search strategy that utilised a number of global databases,
extra time could have been taken to improve upon this
with more iterative steps. However, following consulta-
tion with a specialist in the field, only one additional
clinical paper was identified suggesting that the searches
were reasonably sensitive. A data file is openly available
to highlight the transparency of the research process [77].
In conclusion, is a cup of herbal tea good for you? A small
number of clinical and observational studies have explored a
wide range of herbal teas that have demonstrated potential
clinical benefits in areas of female and maternal health, and
chronic conditions including diabetes, high blood pressure
and weight loss. Observational studies suggest there may be
associations between herbal tea consumption and a reduced
risk of liver and thyroid disease, indicating further research is
warranted to understand both the clinical treatment and pre-
ventative health potential of herbal teas.
In these studies identified, herbal teas provide a cost-
effective and enjoyable therapeutic option, being an alter-
native to pharmacological treatments which might be de-
sirable for example during pregnancy, or offering a cul-
turally fitting healthcare choice.
There are many options for future research, from
optimising the brewing conditions and understanding
synergistic effects, through to much needed good quality hu-
man studies to explore a wider range of herbal teas and their
nutrient and phytochemical constituents. Could herbal teas
play a role in improving plant diversity in our diet, and offset-
ting some of the deficiencies and growing number of chronic
disorders associated with depleted diets? In all of these areas,
more high-quality clinical studies are needed to evaluate the
efficacy and safety of herbal teas. An area not to be
overlooked in future research is the development of quality
assurance processes to ensure the herbs are sourced and
manufactured to a high standard.
Acknowledgements This research was co-funded between the
University of the West of England Internship Scheme and Pukka Herbs.
Compliance with Ethical Standards
Conflict of Interest Pukka Herbs is a manufacturer of herbal teas and
supplements. The data relating to this research is shared openly for
transparency.
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