If you have a weak stomach and poor digestion, do not drink green tea or jasmine tea, advised Professor Hong Hai, a registered TCM practitioner.
'You could feel slight pain in the stomach after drinking the tea even in moderate quantities,' said the Nanyang Business School professor from the Nanyang Technological University.
He recommended oolong and pu er tea instead for such people. According to the Journal Of Chinese Medicine, these invigorate the spleen, where redundant red blood cells are destroyed, clears stomach heat and counteracts alcohol toxins.
Drinking green tea on an empty stomach is also not recommended by Chinese tea specialists, especially for those with gastric problems. This is because the acid in the tea can harm the stomach, causing stomach aches and, in severe cases, stomach flu.
Tea is also not recommended for pregnant women and toddlers said MsKaren Wright, head dietitian at the Food Clinic. This is because polyphenols in tea bind with iron, making it harder for the body to absorb it.
Cutting down on tea and coffee could help to improve iron levels in the body. This is important particularly for young or pregnant women and toddlers who are most at risk of iron deficiency anaemia, she said.
Drinking too much tea can also be counter-productive.
'Supposedly one has to drink more than five cups of green tea to obtain a good level of the antioxidant...[but] I wouldn't tell people to drink that much. Probably two to three cups should be the max,' holistic nutritionist Yondi Lee of Ascension Healing said, adding that it also depends on what type of tea one is drinking.
This is because teas are diuretic, which increases the rate of urination. This in turn causes the body to lose minerals if a person passes urine too often. The tannin, a polyphenol in tea, can also reduce absorption of minerals, she said.
According to Prof Hong, too much tea can have negative effects on the body.
'You have drunk more than you need when you feel uncomfortable in the stomach, or your sleep is disturbed. You could also have loose stools the day after drinking a lot of tea,' he said.
This article was first published in Mind Your Body, The Straits Times on Jan 22, 2009.
The 3rd article below is about TCM tea:
Legend has it that more than 4,000 years ago in 2,737BC, tea was discovered by Chinese Emperor Shennong quite by chance. A dead leaf had fallen into his drinking water while it was boiling under the tree.
He unwittingly drank it and was so taken by the refreshing effect of the tea leaf that he named it "cha" (tea in Mandarin).
Tea drinking soon spread across the country and became a symbol of Chinese high culture, which later travelled to other parts of Asia, Europe, the Americas and Russia. However, beyond its social symbolism, tea was an important form of medicine used by early physicians.
Since ancient times, the Chinese have been using tea to improve their health and to cure illnesses, said Mr Chin Chew Seng, a traditional Chinese medicine (TCM) physician and senior trainer at Eu Yan Sang in Singapore.
It is not known when tea was first used for its medicinal value but the earliest records were traced back to the Han dynasty (206BC-220AD).
Today, there are about 1,500 varieties of tea according to the United Kingdom Tea Council. Only the leaves from the camellia sinensis species of plants are considered tea.
Chinese tea is also distinct from TCM tea which is prepared differently and is mixed with herbs and are often drunk for medicinal purposes rather than leisure.
There are six main grades of Chinese tea - white, green, yellow, oolong, red and black.
Indian and Ceylon tea like Darjeeling, Orange Pekoe and Earl Grey are all blends of black tea which are drunk frequently. It's the most popular type in the world.
Based on the level of fermentation, each has different health benefits.
Fermentation is the process of crushing fresh tea leaves and leaving them to ferment. This produces chemical reactions that result in different flavours and colours. The different health benefits of tea have also been attributed to the varying levels of fermentation of the leaves.
Tea contains naturally occurring chemical compounds called catechins. These are antioxidants that may boost the body's immune system, prevent infections and possibly reduce the risk and progression of cancer.
Mr Chin also said that Chinese tea helps stimulate the nervous system, aid digestion, increase metabolism and even improve one's memory.
However, it is not just Chinese physicians who recognise the medicinal value of tea.
Dr Koh Woon Puay, associate professor at the Yong Loo Lin School of Medicine at the National University of Singapore (NUS), said that laboratory research has shown that the catechins found in green and black tea may prevent the onset and/or the progression of cancer.
"Both green and black tea extracts have also demonstrated cancer preventive properties in experimental animal studies," she said, adding, however, that no human population study has been able to show that tea can cure cancer in patients.
Green and black tea may each prevent different types of diseases too said Dr Koh, who does research on the link between dietary habits and lifestyle and common diseases among adults in Singapore. This includes tea drinking.
A study of 63,000 middle-aged and elderly Chinese Singaporeans in the Singapore Chinese Health Study conducted by NUS between 1993 and 2007 showed that women who drink green tea daily had mammograms that could possibly relate to a lower risk of breast cancer. Also, men and women who drink black tea daily had a lower incidence of Parkinson's disease and possibly diabetes.
This, she said, is because of the different levels of fermentation in green and black tea, which lead to different changes to the catechins in the tea, thus altering their biological effects.
Holistic nutritionist Yondi Lee of Ascension Healing, a centre that advises on nutritional therapy, also defends the scientific basis of tea and its health benefits.
"There is definitely scientific evidence showing the benefits of tea. There is countless research on EGCG, the antioxidant touted for its anti-cancer effect," she said, adding that recent research has shown that flavonoids, chemical compounds found in black tea, help lower bad cholesterol and reduce dental decay.
Another kind of tea that is often confused with Chinese tea is TCM tea. It is a combination of medicinal herbs and tea. TCM practitioners believe that combining the two makes the medicinal quotient act better, strengthening the effect of the medicine.
"Certain tea when mixed with certain medicine would help enhance the total medicinal effect," MrChin said.
TCM tea also differs from Chinese tea in its preparation techniques. Unlike the latter which is prepared by pouring boiling water over it, TCM tea has to be brewed for 30 to 45minutes under low heat.
Unlike Western medicine, the science behind TCM is based on a compilation of traditional Chinese medicine over several thousand years and is therefore hard to pin down.
Prescriptions of TCM tea are made based on prescriptions that have been tried and tested by Chinese physicians over thousands of years.
According to Mr Chin, TCM tea helps remove "heatiness", which is due to the lack of water in the body, leading to symptoms like sore throat, red eyes and constipation.
It is also believed to purge the body of toxins and reduce inflammation and pain.
Nevertheless, Dr Koh cautioned that there is still insufficient evidence to prove the health benefits of tea and it is too early to prescribe tea drinking for its disease prevention qualities.
Not everything we consume must be for a health benefit.
"If one enjoys tea and drinks it as part of a daily diet... it adds to the simple pleasures in life," she said.
This article was first published in Mind Your Body, The Straits Times, on January 22, 2009.