Green tea

When treatment is really all a matter of taste

The Irish Times
Health Supplement, p. 13
September 2, 2008


DOES IT WORK? Tea is often seen as a universal panacea – and sometimes it helps, writes Dónal Ó Mathúna

APART FROM water, tea is the most widely consumed beverage on the planet. In some countries, tea is a safer drink because the water is boiled first.

Different types of tea are consumed in different parts of the world, with green tea being the traditional tea in China, Japan, India and parts of the Middle East. The black tea more traditionally used in Ireland is made from the same plant as green tea, Camellia sinensis, as is oolong tea.

This evergreen plant is native to east Asia, but is now cultivated in many parts of the world.

After the leaves of the tea plant are picked, they begin to wilt and dry out. Enzymes in the leaves cause the production of tannins, which bring a darker colour and bitter taste. For black tea, this process is allowed to go to completion giving black tea its darker colour and stronger flavour. This stage is shortened in making green tea by steaming or heating the leaves. The resulting tea has a milder flavour, due to its lower tannin content.

This processing does not affect the caffeine level, so green and black tea have roughly the same amount of caffeine. Both are also available in decaffeinated forms.

In Asian cultures, green tea has long been reported to have health benefits. Most commonly, it has been said to be helpful in preventing or treating heart disease, cancer, diabetes, various skin conditions, bladder problems and tiredness.

Evidence from studies

Epidemiological studies are used to identify differences in people’s lifestyles that might be connected with their health. Such studies revealed that in Asian countries where green tea consumption is higher, the incidence of some cancers is lower.

While these studies point to possible connections, they don’t prove what might cause the connection. Several controlled studies carried out in Japan did not find that drinking green tea reduced the risk of cancer.

Fresh tea contains high concentrations of compounds called catechins. The process of making black tea destroys most of these, while green tea still contains relatively high levels of catechins. These stop the growth of cancer cells in laboratory experiments.

They also act as antioxidants, which are important in reducing the risk of cancer and heart disease. In this way, green tea provides antioxidants important for general health.

Epidemiological studies have found that green tea drinkers tend to have better lipid and cholesterol levels. However, in studies where people are monitored after adding green tea to their diets, no changes in lipid levels or heart disease were found.

Interestingly, while black tea contains very few catechins, it contains other antioxidants. There is growing evidence that black tea may be as beneficial as green tea, although even less research has been conducted with black tea.

Problematic aspects

People can be allergic to tea and react similarly to black or green tea. People sensitive to caffeine should also be cautious with green tea.

Milk can neutralise the effects of catechins and thus should not be added to green tea. Green tea contains vitamin K which counteracts the effects of warfarin, a common “blood thinning” drug.


Green tea is a source of antioxidants which are important components of a healthy diet. Green tea can provide additional antioxidants to those in fruits and vegetables. The connection between green tea and cancer or heart disease is intriguing, but it is too early to know if green tea has a role in preventing or treating any disease. Given the lack of controlled studies, green tea should not be used in place of medical check-ups or advice.

For those who enjoy green tea, it may have some general health benefits. However, ordinary black tea may be just as beneficial. It may all be a matter of taste.

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