The New Nation - Internet Edition

Jamayet Ali

Tea is a variable evergreen bushy shrub or small tree with leathery deep green leaves and fragrant white flowers, cultivated commercially for the production of tea in Sylhet, Moulvibazar, Chittagong and Chittagong Hill Tracts of Bangladesh. The main tea growing countries of the world namely China, India and Srilanka lie within a restricted geographical region in Asia. Indonesia, Turkey, Bangladesh, Kenya and Russia also produce sizeable quantities of tea. It is also cultivated in Malawi, Argentina, Iran, Japan and in some other countries. The harvestable area under tea in the world in 1986 was 2537 thousand hectares, 93.9 percent of which exists in the developing countries. Within Asia, the maxium area under tea is in China with about 1,174 thousand hectares which accounts for 532 % of Asia's harvestable tea area and 46.2 % of the world's. India ranks second with about 400 thousand hectares (18.1 % of harvest able tea area in Asia and 15.7 % of the world's area under tea), whereas Sri Lanka harvested from about 252 thousand hectares (11.4 % of share of tea area in Asia and 9.9 % of world's tea are) in 1986.

Tea is today the most widely used and popular non alcoholic beverage and large quantities are consumed daily by millions of people in all parts of the world. About half the world's population drinks tea regularly and it is the commonest beverage in Asia and the Far East. The word tea comes from a Chinese indiogram pronounced 'Tay' in Amoy dialect and came into English with the pronunciation changing to its present form in the 18th century. In Cantonese it is known as ehah a name which came into use in India and Russia. China was the first country to cultivate tea. Tea as a beverage, produced by steeping processed top leaves and buds of the tea plants in freshly boiled water originated in China c2700 BC; but the tea leaf has probably been in use as a medicine much longer than that Tea cultivation of the tea plant in Japan began about 200 AD. The use of tea later spread to the other Asian countries. Tea cultivation in sub-continent began as early as 1778. The tea plants growing wild in Upper Assam was discovered in 1823. In Java, commercial production of tea began in 1824. Extensive planting began in Srilanka in the 1870's. Tea as a beverage was introduced to Europe in 1610 AD by the Dutch and by the first half of 18th century tea was a popular beverage in Holland, England and the American continent. Several types of commercial teas are known such" as black, green, oolong, brick and let-pet teas. Each of these teas has its own characteristic aroma and taste.

Medicinal Properties: Tea is a stimulating drink. It relieves muscular and mental fatigue and is taken for fever. The stimulating action is attributed to the purine base alkaloid, caffeine present to an extent of 1-5 per cent in black tea, 80 per cent of which is extracted during normal brewing. An average consumption of 5-6 cups per day represents a caffeine intake of about 0.3g, which is less than half the daily 'tolerable limit' of 0.65g for the medical administration of pure caffeine. Caffeine has a diuretic effect on the kidneys and stimulates gastric secretion. Hence, tea is thought to aid digestion and relieve post prandial distress. Excessive doses of caffeine, however, can lead to anxiety and unpleasant gastric sensation. Tea has also been claimed to have beneficial effect on numerous other diseases and conditions. Tea may be of value in treatment of gout and restoration fluid balance following vomiting and diarrhoea.

The diuretic property of tea is useful in therapy of cardiac odema. It seems to reduce serum lipid, induce synthesis and secretion of catecholamines and to prevent atherosclerosis. Tea polyphenols may inhibit the absorption of dietary cholesterol and prevent the degradation of catecholamines. There is indication that successive administration of tea could stimulate the degradation of triglycerides in the adipose tissue, thereby reducing the weight. Tea may be used in relieving bronchial asthma and difficulty in breathing due to the smooth muscle relaxant effect of caffeine. Tea polyphenols strengthen the walls of blood vessels and regulate their permeability, an activity associated with o-dihydroxybenzene group collectively termed vitamin P or biflavonoids.

Tea polyphenols protect ascoroic acid from oxidation in rat tissue homogenates because of their antioxidant properties. Tea extracts increase the accumulation of ascorbic acid in rat and guinea-pig tissues and reduce the level of ascoroic acid through urinary excretion. It indicates an important role of green tea in human nutrition in preventing symptoms of ascorbic acid deficiency. Green tea polyphenols have been found to normalise thyroid hyperfunction which induces thyrotoxicosis; this has been attributed to flavanols, especially galocatechins. Flavonol glycosides exihibit a similar action. tea was used extensively in combating plague in Japan. Green tea infusion shows anti-bacterial activity against a number of bacteria and is an effective cure against dysentery. Without milk and sugar the tea liquor is beneficial in diarrhoea but with milk and sugar it acts as a laxative.

Green tea inhibits the growth of cancer tumours. Tea affords protection against the development of leukemia after exposure to radiation in mice. Epigallocatech in gallate (EGCG) from green tea changes the properties of the receptor on the surface of mouse eland blocks the section of tumour promoter and thus prevents the formation of ur cells. EGCG might also prevent the growth of tumours in humans especially cancers of oesophagus, stomach and intestines. High selenium content in teas has been correlated with low incidence of cancer in Japan. Green tea is best in preventing the synthesis of the carcinogen, followed by black and jasmine teas.

Green tea extract has been reported to be more effective in preventing tooth decay than fluoride compounds. An extract of Japanese green tea inhibited the growth of streptococcus mutans Clarke, the cariogenic bacterium responsible for causing dental caries. Tea is considered a cure for cold and removes phlezm. It prevents the formation of stones in bladder, liver and kidney. Tea can be used as a base for the extraction of catechin, the preparations of which are useful in treating nephritis and chronic hepatitis. The bitter leaf juice is taken for abortion. Dried leaves are chewed to remove foul smell. The leaf juice is also applied to cuts and injuries as haemostatic. Tea has also been successfully used in treating severe abdominal , intestinal and cerebral haemorrhages. Green tea tannin or its active constituents may be used in treating toxic goiter.

The extract of Japanese Green tea shows anti-hepatoxic effects. Tea has been found to aid liver, lessen tissue waste, promote cerebration, aid mental arid physical work, preserve mental equilibrium, induce tranquility and promote slenderness. Tea inhibits absorption of iron and leads to iron deficiency. Polyphenolic compounds in tea which forms strong complexes with iron are believed to be partly responsible. Tannase, a polyphenol degrading enzyme, and lemon juice solubilise iron and also calsium in some teas and, therefore, might reduce detrimental effect of tea on mineral availability. On the other hand, these observations have promoted research into a possible therapeutic use of tea for individuals who suffer from iron over load from excessive absorption (Wealth of India, Raw Materials, Vo 1. III ).

Medicine: Tea is useful in treating infections of the digestive tract. Leaves are excellent CNS stuimulant, diuretic and astringent. They possess antimicrobial activity against microorganisms causing intestinal disorders. Lyophilised aqueous extract of leaf, stem and twigs is useful in cosmetic and dermo-pharmaceutical beauty products. Pharmaceuticals containing tea extract and other ingredients are useful against tumours, diabetes and arthritis. Caffeine is extensively used in modem medicine in the treatment of migraine, hemicrania, neuralgia and other nervous affection and as a stimulating hot drink. Theaflavin extracted from leaves is an effective antibacterial agent. The saponins of tea leaves produce anti-hypertensive rats (Medicinal Plants of Bangladesh, Second Edition, 143-44).