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Camellia sinensis (Tea) 

Life > eukaryotes > Archaeoplastida > Chloroplastida > Charophyta > Streptophytina > Plantae (land plants) > Tracheophyta (vascular plants) > Euphyllophyta > Lignophyta (woody plants) > Spermatophyta (seed plants) > Angiospermae (flowering plants) > Eudicotyledons > Core Eudicots > Asterids > Order: Ericales > Family: Theaceae > Genus: Camellia

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 uptake. 

 

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 (Chopra 2000).

Description, origin and distribution

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).

Chemical constituents

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). 

  • 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. 

Medicinal benefits

  • Digestive complaints. 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).

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: 2000).

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.

Possible health risks

  • 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.

Ecological relationships

Acetobacter diazotrophicus

Bacteria

Acid-producing, nitrogen-fixing bacteria that are found in roots of tea plants.

 

 

 

 

 

Further Reading

  • 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.

References

  1. 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 Aug;23(8):1189-93.

  2. 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.

  3. 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 14;166(1-2):63-69.

  4. 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.

  5. 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.

  6. Hamilton-Miller J.M. Anti-cariogenic properties of tea (Camellia sinensis). J. Med. Microbibiol. 2001 Apr;50(4):299-302.

  7. 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.

  8. 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.

  9. 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 23;84(6):844-850.

  10. Katiyar S.K. & Elmets C.A. Green tea polyphenolic antioxidants and skin photoprotection (Review). Int. J. Oncol. 2001 Jun; 18(6):1307-1313.

  11. 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.

  12. 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. 2001 Jun;73(6):1040-1044.

  13. Riemersma R.A., Rice-Evans C.A., Tyrell R.M., Clifford M.N. & Lean M.E. Tea flavonoids and cardiovascular health. QJM 2001 May;94(5):277-282.

  14. 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 Mar;73(3):607-612.

  15. 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.

  16. Simpson A., Shaw L. & Smith A.J. Tooth surface pH during drinking of black tea. Br. Dent. J. 2001 Apr. 14;190(7):374-376.

  17. 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.

  18. 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 Jun;131(6):1731-1737.

  19. 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.

Text by Robyn Tourle  


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