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Tea - western medicine
Tea's stimulant effects are caused by xanthines such as caffeine. Caffeine is included in small doses in some over-the-counter medicines for its stimulant effect, and is often combined with medicines that treat pain such as aspirin.
Active compounds
A related compound found in tea is theophylline, which is a licensed medicine for the treatment of respiratory diseases such as asthma.
Tea also contains flavonoids, compounds reported to have anti-oxidant properties. These effects may be beneficial to health such as in the prevention of heart disease and cancer. Tea flavonoids are also reported to reduce inflammation and to have antimicrobial effects. Some studies suggest that tea may help prevent tooth decay. Consumption of tea may have diuretic effects, which is largely due to the caffeine, and tea may also inhibit the absorption of iron in the gut. Tea is also used in some cosmetic products for an astringent effect.
The chemical composition of tea may vary depending on a number of factors, such as the conditions in which the plant is grown and how the leaves are processed. Tea consists of over 2000 different substances and many of these are compounds called polyphenols. Green tea, which is unfermented, contains various polyphenols, which are mainly types of compounds called catechins. Catechins are responsible for the bitterness and astringency of green tea. Tender shoots from tea plants generally contain higher levels of catechins than older shoots that contain more fibre. Good quality tea is produced from the tender shoots that contain higher amounts of catechins.
Unlike green tea, a fermentation process is included in the production of black tea. During fermentation complex chemical reactions occur, which are promoted by the action of enzymes present in the tea leaves. This action converts some of the catechins into other compounds, including compounds called theaflavins and thearubigens. Oolong tea is semi-fermented and contains a mixture of catechins, theaflavins and thearubigens. Tea also contains some compounds called purine alkaloids such as caffeine. The type of tea and the method of tea preparation may affect the caffeine content. Fresh, unprocessed tea shoots typically contains 2-5% caffeine. Many volatile compounds (e.g. monoterpenes) have been identified in tea, which contribute to the characteristic aroma and flavour of tea
Tea also contains flavonoids, compounds reported to have anti-oxidant properties. These effects may be beneficial to health such as in the prevention of heart disease and cancer. Tea flavonoids are also reported to reduce inflammation and to have antimicrobial effects. Some studies suggest that tea may help prevent tooth decay. Consumption of tea may have diuretic effects, which is largely due to the caffeine, and tea may also inhibit the absorption of iron in the gut. Tea is also used in some cosmetic products for an astringent effect.
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| After rolling and leaving the leaves to ferment, the leaves must be dried in order to stop the fermentation process. (1930's) |
Unlike green tea, a fermentation process is included in the production of black tea. During fermentation complex chemical reactions occur, which are promoted by the action of enzymes present in the tea leaves. This action converts some of the catechins into other compounds, including compounds called theaflavins and thearubigens. Oolong tea is semi-fermented and contains a mixture of catechins, theaflavins and thearubigens. Tea also contains some compounds called purine alkaloids such as caffeine. The type of tea and the method of tea preparation may affect the caffeine content. Fresh, unprocessed tea shoots typically contains 2-5% caffeine. Many volatile compounds (e.g. monoterpenes) have been identified in tea, which contribute to the characteristic aroma and flavour of tea
Safety
Tea has been consumed for thousands of years, so has a long safety record for use. However, excessive doses of caffeine may cause headaches and anxiety. Regular intake of large amounts of caffeine, aminophylline or theophylline by breastfeeding mothers may affect the infant. A number of side-effects may occur from large amounts of theophylline and aminophylline. These include heart problems such as palpitations, sickness, insomnia and convulsions. Toxic effects are more likely to occur when theophylline and aminophylline are given at high doses or if given with certain other medicines. It has been reported that there may be some link between the occurrence of cancer of the oesophagus and excessive consumption of tea that contains high amounts of condensed tannin compounds.This information is provided for general interest only. It is not intended as guidance for medicinal use. Further information on using herbal medicines is available.
