After water, tea is the most common drink in the world. Current research presents a compelling case for the health benefits of tea, thanks to its abundant supply of antioxidants. At the recent International Symposium on Tea and Health held in Sydney, Australia in May 1998, the findings of the latest research on tea were presented.

Did you know?
The original Chinese word for tea was t'e (pronounced 'tay').

The Health Benefits of Tea
Legend has it that tea was discovered in a forest by Chinese emperor Sheng Nung in the year 2,737BC when leaves from a nearby bush fell into a pot of boiling water. Whatever its origins, it is certain that by the 8th century AD, tea drinking was widespread throughout the Orient, both as a refreshing beverage and for its medicinal value.

There is a reliable and well-documented history of using tea as a medicinal potion in China from the 4th century AD onwards. Research today is finding that tea's long-held reputation as a medicinal - said to treat a range of digestive and nervous ailments - may well be proving true.

Both green and black teas are essentially plant foods and are derived solely from the leaves of the Camellia sinensis. Their health benefits are thought to be due to certain polyphenols (classed as flavonoids) which are potent anti-oxidants and free radical scavengers.

Tea anti-oxidants show great promise as cardio- protective and anti-cancer agents in both animal and human studies. However, well-designed intervention studies are needed to provide more specific information.

Although there's been more research on green tea (it's less complex and easier to analyse), both green and black teas have comparable effects and benefits, even though they differ in the type of anti-oxidants they contain.

The flavonoids of tea
Tea flavonoids are potent anti-oxidants and free radical scavengers. They consist of a number of compounds including four catechins:

• epicatechin (EC)
• epigallocatechin (EGC)
• epicatechin gallate (ECG)
• epigallocatechin gallate (EGCG)

Green tea contains these four catechins, of which EGCG predominates, plus the flavonol quercetin. These five compounds account for approximately 30% of the dry weight of green tea leaves.

Black tea contains these four catechins plus the more complex polyphenols theaflavins and thearubigins, which are created during tea maufacture from the simpler catechins and are responsible for tea's astringency, flavour and rich brown-red colours. Theaflavins and thearubigins account for approximately 20% of the dry weight of black tea leaves. In the past, they were often (and incorrectly) called 'tannins'. Catechins have been shown to be powerful anti-oxidants - anywhere from 2 to 6 times more powerful than the well-known vitamin C and vitamin E.

In a 1997 study conducted at the National Defence Medical College in Japan(1), catechins were shown to prolong the lag time before initiation of LDL oxidation in the test tube. In this study, EGCG exerted the most marked effect, prolonging lag time more than vitamin E. Theaflavins from black tea displayed even stronger inhibitory effects than catechins.

In the same 1997 study, 14 volunteers consumed 5 cups of black tea per day for 4 weeks. At the end, they showed a significantly increased lag time before LDL-cholesterol became oxidised (from 54 to 62 minutes), compared to the control group that consumed water.

Milk and lemon.
Other studies have shown that adding milk or lemon has no effect on tea's anti-oxidant capacity. The catechins are absorbed and detected in the bloodstream, peaking two hours after consumption (2).  Brewing time affects the amount of flavonoids released from the tea leaves into the tea. The majority of flavonoids are released within the first minute of brewing, although the longer the brewing time, the greater the flavonoid content. Major tea brands are blended to give consistent flavour, colour and flavonoids, although individual tea types will vary in their flavonoid content, depending on which type of tea leaf and where it is grown.

Tea and heart disease
Tea came to the attention of nutritionists in 1993 after a number of epidemiological studies (but not all) turned up positive correlations between tea and heart disease.   For example, one of the earliest reports was a Dutch study of 805 elderly men published in The Lancet in 1993. It found that those men who had the highest intake of flavonoids had the lowest incidence of heart disease and myocardial infarction. Tea accounted for 61% of the flavonoids (specifically quercetin), followed by apples and onions (3).

A similar study in 1900 coalminers in Caerphilly in Wales men showed no protective effect and in fact an increase in mortality with tea drinking. However, in this Caerphilly study, tea drinking was associated with an unhealthy lifestyle including heavy smoking, inactivity and high alcohol intake.

At this point, there is no single explanation as to how tea may be cardio protective. One mechanism suggested is that tea prevents the oxidation of LDL-cholesterol. Another suggests an improvement in platelet aggregation or an increase in clotting time or improvement in blood vessel relaxation because tea flavonoids are water soluble.

Scientists in Japan, China and USA have been conducting studies to examine if tea or tea flavonoids might help prevent cancer. To date, over 50 animal studies have been published, suggesting tea is beneficial, especially for cancers of the skin, stomach and lung.

In Australia, Dr Ian Record of the CSIRO studied the effects of green and black tea, with or without milk, on hairless mice whose skins were damaged by exposure to UVB and UVA+B light. Both green and black tea reduced the number of skin papillomas (30 per cent less) and tumours (50 per cent less) induced by UVA+B light, but black tea provided greater protection against UVB tumours compared to green tea.

The CSIRO data is supported by similar research conducted at the Saitama Cancer Centre in Japan, which reported that tumour growth in mice was inhibited when the mice were given repeated applications of EGCG, the main anti-oxidant in green tea.

At the Saitama Cancer Centre, a 10-year follow up study identified 175 female and 244 male cancer patients from a prospective cohort study involving 8522 people. Using this data, they found the first evidence that the onset of cancer in patients who had consumed over 10 cups of green tea a day was 7.3 years later among females and 3.2 years later among males, compared with patients who consumed under three cups a day.

Tea tips
For good health, eat a varied low-fat diet with plenty of vegetables and fruit and enjoy a few cups of tea a day to top up your anti-oxidants. The flavonoids in both green and black tea are powerful anti-oxidants, more potent in the test tube than the vitamins C and E.   Tea is an extract of leaves, so think of it as 'plant food', just like vegetables and fruit.

What Tea is that?

Green
Green tea is the 'simplest' form of tea. Tea leaves are simply steamed soon after harvesting to prevent oxidation. The leaves remain green and the flavour is light and refreshing. Green tea comprises around 20 per cent of all tea consumed in the world.

Black
Rolling or breaking the withered tea leaves mixes the enzyme polyphenol oxidase with the tea polyphenols and starts an oxidation reaction (once called 'fermentation') before heating. This turns the leaves from green to copper; they then turn black in the final firing.

In this process, some of the simpler catechins of green tea are combined and converted into polymerised forms called theaflavins and thearubigens, which give tea its astringency and rich dark colour. Black tea is the major form of tea in the world, accounting for 78 per cent of all tea drunk.

Oolong
Has been partially oxidised, resulting in a delicate light fruity flavour. Nutritionally oolong is halfway between green and black. Not a common type; only 2 per cent of the world's tea is oolong.

Did you know?
During the Ming dynasty (1368-1644), black and oolong teas were developed as was the tradition of brewing tea in a teapot.