It is well known that Indian tea is richer in all these chief ingredients than the Chinese tea. It is not the composition of leaves alone that affects the health but also the composition of infusion which is prepared by boiling tea with water. It is noted that caffeine comes out more rapidly than tannin and hence the greater the period of infusion, the more is the amount of tannin, while the amount of caffeine will remain almost the same. The use of tea is detrimental to health. Dr. P.C.Roy, the father of modern chemistry in India, equated tea drinking with the drinking of poison.
Tea is said to slow down digestion.
Its daily intake causes indigestion as it impedes the action of 'ptyalin', a digestive ferment of saliva which acts on cooked starch. The inhibition of saliva seems to be due to tannin. This effect disappears if the milk is added to it, as the protein of milk precipates the tannin. Tea is also said to delay stomach digestion. It can lead to gas formation, diarrhoea and constipation.