Camellia sinensis (Tea)
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Tea is the second most commonly drank liquid on earth
after water. It has numerous medicinal benefits mainly due to its antibacterial
and antioxidant properties. The cafeine in tea keeps us awake, sometimes too
much so. Excessive tea drinking can cause anaemia due to inhibition of iron
Many of us would agree with the ancient Chinese saying: "
Better to be deprived of food for three days, than of tea for one" (Ody
1993). Tea has been consumed socially and habitually by people for so long
(since Ī 3000 BC), that aside from the astringent taste and boost it provides,
itís medicinal properties are often over-looked. However, traditional
healers have long believed that drinking tea is a means of prolonging life
Native to China, C. sinensis spread to India and
Japan, then to Europe and Russia, arriving in the New World in the late 17th
century (Chopra 2000). As a cultivated evergreen plant, tea is usually trimmed
to below six ft. in height. However, if left to grow wild, the bush can reach 30
ft. green, Oolong and black (Ďnormalí) tea are all made from the leaves of
the same plant species, Camellia sinensis (Ody 1993). Their chemical
content and flavours are, however, very different due to their respective
fermentation processes. Green tea leaves are allowed to wither in hot air then
pan-fried to halt the oxidation (fermentation) processes. The leaves of Oolong
tea are wilted in sunlight, bruised and allowed to partially oxidise, until
reddening of the leaf edges occurs. Black teas leaves are fermented in cool,
humid rooms, until the entire leaf is darkened (Chopra: 87).
Tea leaves contain many compounds, such as
polysaccharides, volatile oils, vitamins, minerals, purines, alkaloids
(eg.caffeine) and polyphenols (catechins and flavonoids). Although all three tea
types have antibacterial and free radical capturing (antioxidising)
activities, the efficacy decreases substantially the darker the variety of tea
is. This is due to lower contents of anti-oxidising polyphenols remaining in the
leaves (Chopra 2000).
Tea is an old home remedy for unsettled
digestive systems. All three varieties have antibacterial, antioxidant,
antiseptic and detoxifying properties that make tea effective in treating
infectious dysentery as well as easing inflammatory bowel disease.Infections. The
antiseptic properties of tea are attributed to the tannins and flavonoids
present. The former also have anti-inflammatory effects, while the latter act as
detoxifiers (van Wyk et al). Tea has been used as an age-old home remedy
for burns, wounds and swelling. A poultice of green tea eases itching and
inflammation of insect bites, while a compress stems bleeding.Guards against tooth
decay. As well as containing catechins,
green tea is known to be very rich in flouride. A study using natural toothpaste
(containing green tea bioflavonoid/zinc ascorbate) was conducted to determine
the effect on bacterial plaque accumulation. The results showed a significant
decrease in total viable plaque biomass when compared with a non-active control
toothpaste19. Another in vitro experiment, using both green
and black tea, showed the epicatechins to have properties that prevent bacterial
adherence to teeth, inhibit human and bacterial amylases and inhibit glucosyl
transferase, thereby limiting the biosynthesis of sticky glucan. The few human ex
vivo clinical trials performed, suggest that regular tea drinking may
decrease the incidence and severity of caries. If substantiated, tea could play
a very economical role in public health 6.Skin disorders. Using
different animal models, many laboratories have shown that green tea extract,
taken orally or applied to the skin, inhibits skin tumour formation induced by
chemical carcinogens or ultra-violet radiation(UVB). The extracts also possess
anti-inflammatory activity that, similarly to the anti-cancer forming activity,
is owed to the polyphenolic constituents present therein. The polyphenol mainly
responsible for the prevention of cancer formation is
epigallocatechin-3-gallate(EGCG). When applied to mouse skin, EGCG prevents
UVB-induced oxidative stress and suppression of the immune system. Mouse skin
models have illustrated extensive beneficial effects of green tea extracts and
although only a few human skin studies have been conducted, many cosmetic and
pharmaceutical companies are supplementing their skin care products with green
tea extracts10.Immune booster. This
is due to the free radical capturing (antioxidant), invigorating
(caffeine),detoxifying antibacterial properties of tea, as well as the vitamins
and minerals present therein.Combats various
forms of cancer. Green tea has a reputed
role in cancer prevention as tea catechins have been shown to inhibit tumour
cell proliferation as well as promote the destruction of leukaemia cells 17.
Laboratory studies on cultures of tumour cells and mice given carcinogenic
chemicals, showed green teas' potential to inhibit cancer cell growth.
Similarly, both black and green tea have been shown to suppress Deoxyribonucleic
acid (DNA) reproduction and promote the demise of tumour cells (Chopra: 2000).
- Flavonoids (polyphenols). Proven medicinal
properties include antioxidant, anti-inflammatory, anti-allergic,
antibacterial and antiviral effects. They also have the ability to
strengthen veins and decrease their permeability. It is widely believed that
the antioxidising effects of both black and green varieties are reduced when
taken with milk.This is thought to be due to the effective binding of
flavonoids by proteins (Chopra: 2000). However, a recent ex vivo
study concluded that flavonols are absorbed from tea and their
bioavailability is not affected by milk.7
- Tea tannins - called catechins (polyphenols).
Appear to be the most potent therapeutic plant-derived chemicals, in that,
aside from their antiseptic and antioxidant properties, they
are able to form complexes with other molecules, thereby detoxifying
the system (van Wyk et al). Catechins include gallocatechin,
epicatechin (EC), epigallocatechin (EGC), epicatechin gallate (EGC) and
epigallocatechin gallate (EGCG). Catechins make up approximately one-quarter
of fresh dried green tea leaves, of which EGCG comprises 60 % (Chopra 2000).
- Vitamin C. A recent study by du Toit et al,
showed that Black, Green and Oolong tea are all extremely good sources of
vitamin C. They found that 1 or 2 cups a day provide the equivalent of three
glasses of orange juice or two capsules (200mg) of vitamin C.
One study involving an in vitro plasmid DNA
system and radiolytically generating reactive oxygen species (ROS) under
constant scavenging conditions, showed that all four catechins (EC; EGC; ECG
and EGCG), moderate free radical damage sustained by DNA - even when present
in low concentrations. EGCG was the most effective of the catechins, with
activity seen at micromolar concentrations. The antioxidant activity of
catechins is thought to occur by the mechanism of electron transfer from
catechins to ROS-induced radical sites on the DNA 1.
Inoue et al examined the association between
regular green tea consumption prior to diagnosis and subsequent risk of breast
cancer recurrence. The results indicated that regular intake of green tea, in
the early stages of breast cancer, may prevent the recurrence thereof.
Furthermore, the incidence of prostate cancer among Chinese men was found to
be the lowest in the world and correlated with their tea consumption (Chopra:
Stomach cancer is the second most common form of cancer
worldwide. Thus much research has gone into searching for cures and treatments
thereof. One such study, conducted in China15, aimed at
investigating the effect of green tea consumption on chronic gastritis and the
risk of stomach cancer. Their sample included 133 stomach cancer cases, 166
chronic gastritis cases and 433 healthy controls. Results showed an inverse
association between green tea drinking and both diseases. Furthermore,
dose-response relationships were observed, with years of green tea consumption
being more effective in combating both stomach cancer and chronic gastritis.
A study11 using 8552 residents,
representative of Japanís population, tested whether or not Green tea was an
effective anti-carcinogenic. Results showed a decreased relative risk of
cancer incidence for those consuming over ten cups, compared with those
consuming below three cups of green tea per day. The risks decreased by 57 %
for women, 54 % for men and 59 % for both sexes. In addition, increased
consumption was associated with a significant delay in the onset of cancer.
- Decreases risk of cardiovascular
disease. Coronary artery disease is
associated with increased oxidative stress and dysfunction of the
endothelium(cells lining the heart, blood and lymphatic vessels and various
other cavities). Some antioxidants are known to reverse endothelial
dysfunction4. Thus numerous studies have aimed at determining
whether or not the antioxidant polyphenols (flavonoids and catechins) present
in tea, can perform the same function. Although results tended to be
equivocal, several findings were quite common. Various case studies show that
tea does not decrease blood pressure, nor plasma lipids (cholesterol) ex
vivo 13 and while tea catechins do inhibit the peroxidation of
LDL (low density lipoprotein) cholesterol in vitro, the effect ex
vivo is small12,13.
Catechins are absorbed from tea but low plasma
concentrations are attained and easily excreted, unless they are rapidly
absorbed or metabolised 18. This may explain why other studies only
revealed effectiveness at high dosages. A study on 8 552 residents,
representative of Japanís population, revealed a decreased relative risk of
death from coronary disease as 82 % for women, 58 % for men, and 72 % for both
sexes consuming over ten cups of green tea per day11.
Amongst other findings, a study by Riemersma et al concluded
that although the plasma antioxidant potential increases post green tea
consumption, this is not so for black tea. However, a more recent (July 2001)
paper4 revealed increased plasma flavonoids after short- and
long-term black tea consumption and improved vasomotor functioning
(endothelium-dependant flow-mediated dilation) of the brachial artery.
While mild cholesterol lowering has been documented in
mice and green tea consumption has been shown to reduce the development of
aortic atherosclerosis (hardening, thickening and elasticity-loss of arteries)
in rabbits, it is more difficult to show in humans and results are
inconsistent. While most epidemiological studies support the suggested role of
tea in decreasing the risk of coronary artery disease, there is much debate as
to the mechanisms of benefit. However, the potential benefits of tea
consumption are worthy of confirmation by more human trials.
- Although all tea varieties possess far less caffeine
than both coffee and coke cola (with green having the least), it can induce insomnia
and nervousness in sensitive and over-indulgent individuals.
- It should also be noted that the antioxidant action of
(phenolic-rich) tea extracts has been shown to reduce the ability of
humans to utilise dietary iron. Thus excessive intake of tea should
be avoided by people who are prone to anaemia14.
Acid-producing, nitrogen-fixing bacteria that are found in roots of tea
Chopra D. & David S. 2000. The chopra
centre Herbal Handbook. Three Rivers Press, USA.
Ody P. 1993. The Herb Societyís Complete
Medicinal Herbal. Dorling Kindersley ltd., London.
Ody P. 1995. Home Herbal. Human & Rousseau
(Pty) ltd, Cape Town..
van Wyk B., van Oudtshoorn B. and Gericke N.
1997. Medicinal Plants of South Africa. Briza Publications, Pretoria.
Anderson R.F., Fisher L.J., Hara Y., Harris
T., Mak W.B., Melton L.D., & Packer J.E. Green tea catechins partially
protect DNA from (.)OH radical-induced strand breaks and base damage through
fast chemical repair of DNA radicals. Carcinogenesis 2001
Arts I.C., Hollman P.C., Feskens E.J., Bueno
de Mesquita H.B. & Kromhout D. Catechin intake might explain the inverse
relation between tea consumption and ischemic heart desease: the Zutphen
Elderly Study. Am. J. Clin. Nutr. 2001 Aug;74(2):227-32.
du Toit R., Volsteedt Y. & Apostolides Z.
Comparison of the antioxidant content of fruits, vegetables and teas
measured as vitamin C equivalents. Toxicology 2001 Sep
Duffy S.J., Keaney J.F. Jr., Holbrook M.,
Gokce N., Swerdloff P.L., Frei B. & Vita J.A. Short- and long-term black
tea consumption reverses endothelial dysfunction in patients with coronary
artery disease. Circulation 2001 Jul 10:104(2):151-6.
Ferrara L., Montesano D. & Senatore A. The
distribution of minerals and flavonoids in the tea plant (Camellia
sinensis). Farmaco 2001 May;56(5-7): 397-401.
Hamilton-Miller J.M. Anti-cariogenic
properties of tea (Camellia sinensis). J. Med. Microbibiol.
Hollman P.C., Van Het Hof K.H., Tijburg L.B.
& Katan M.B. Addition of milk does not affect the absorption of
flavonols from tea in man. Free Radic. Res. 2001 Mar;34(3):297-300.
Inoue M., Tajima K., Mizutani M., Iwata H.,
Iwase T., Miura S., Hirose K., Hamajima N. & Tominaga S. Regular
consumption of green tea and the risk of breast cancer recurrence: follow-up
study from the Hospital-based Epidemiologic Research Program at Aichi Cancer
Centre (HERPACCO), Japan. Cancer Lett. 2001 Jun 26;167(2):175-182.
Jung Y.D., Kim M.S., Shin B.A., Chay K.O., Ahn
B.W., Liu W., Bucana C.D., Gallick G.E. & Ellis L.M. EGCG, a major
component of green tea, inhibits tumour growth by inhibiting VEGF induction
in human colon carcinoma cells. Br. J. Cancer 2001 Mar
Katiyar S.K. & Elmets C.A. Green tea
polyphenolic antioxidants and skin photoprotection (Review). Int. J. Oncol.
2001 Jun; 18(6):1307-1313.
Nakachi K., Matsuyama S., Miyake S., Suganuma
M. & Imai K. Preventive effects of drinking green tea on cancer and
cardiovascular disease: epidemiological evidence for multiple targeting
prevention. Biofactors 2000;134(1-4):49-54.
O'Reilly J.D., Mallet A.I., McAnlis G.T.,
Young I.S., Halliwell B., Sanders T.A. & Wiseman H. Consumption of
flavonoids in onions and black tea: lack of effect on F2-isoprostanes and
autoantibodies to oxidized LDL in healthy humans. Am. J. Clin. Nutr.
Riemersma R.A., Rice-Evans C.A., Tyrell R.M.,
Clifford M.N. & Lean M.E. Tea flavonoids and cardiovascular health. QJM
Samman S., Sandstrom B., Toft M.B., Bukhave
K., Jensen M., Sorensen S.S. & Hansen M. Green tea extract added to
foods reduces nonheme-iron absorption. Am. J. Clin. Nutr. 2001
Setiawan V.W., Zhang Z.F., Yu G.P., Lu Q.Y.,
Li Y.L., Lu M.L., Wang M.R., Guo C.H., Yu S.Z., Kurtz R.C. & Hsieh C.C.
Protective effect of green tea on the risks of chronic gastritis and stomach
cancer. Int. J. Cancer 2001 May 15;92(4):600-604.
Simpson A., Shaw L. & Smith A.J. Tooth
surface pH during drinking of black tea. Br. Dent. J. 2001 Apr.
Smith D.M. & Dou Q.P. Green tea polyphenol
epigallocatechin inhibits DNA replication and consequently induces leukemia
cell apoptosis. Int. J. Mol. Med. 2001 Jun;7(6):645-652.
Warden B.A., Smith L.S., Beecher G.R.,
Balentine D.A. & Clevidence B.A. Catechins are bioavailable in men and
women drinking black tea throughout the day. J. Nutr. 2001
Wolinsky LE., Cuomo J., Quesada K., Bato T.,
& Camargo P.M. A comparative study of the effects of a dentifice
containing green tea bioflavonoids, sanguinarine or triclosan on oral
bacterial biofilm formation. J. Clin. Dent. 2000;11(2):53-9.