Health benefits of tea

Introduction

Tea is the second most consumed beverage in the world after water. Tea drinking originated in China more than four and a half thousand years ago and the habit was adopted in the UK during the 17th Century after the sea routes to China from Europe had been opened up.

The most commonly consumed type of tea, black tea, comes from an evergreen plant called Camellia sinensis. There are three main types of Camellia sinensis: China, Assam (mostly found in India) and Cambodian (mainly a cross between the other two). Even though only three types of plant exist, there are hundreds of varieties of teas available.

Types of teas

The huge number of types of tea is due to differences in soil and climate in which Camellia sinensis is grown, as well as the way the plant is harvested and processed. Oolong tea, green tea and white tea are also produced from the same plant and the difference between these and black tea involves the processing of the plant leaves. The leaves for black tea undergo a fermentation process before drying and they become fully oxidised. However, the leaves for green tea are not fermented but lightly steamed before drying; they do not become oxidised. The leaves for oolong tea are processed to a degree somewhere between black and green tea and they become partially oxidised. In producing white tea, the leaves are picked and harvested before the leaves open fully, when the buds are still covered by fine white hair, hence the name white tea. The leaves go through less processing than the leaves for black, oolong and green tea and are not oxidised. 

In addition to tea from the Camellia sinensis plant, herbal teas can be made by steeping fresh or dried herbs in hot water. There are also fruit teas, which usually consist of a blend of herbs and fruit essences, sometimes with added spices.

Health benefits

Flavonoids are a group of compounds with powerful antioxidant activity, antioxidants being protective against the damage caused by excess free radicals. They are found within all plant foods in our diet and Camellia sinensis has one of the highest flavonoid contents of all plants at 15% of the leaf by dry weight ¹.

A significant number of studies have shown that the tea flavonoids have anti-cancer properties and they are increasingly recognised as potential cancer preventative compounds. There are also suggestions that the tea flavonoids may be helpful for those already diagnosed with cancer, as highlighted by a study from Japan that found that the regular consumption of green tea (more than 3 cups a day) might be protective against recurrence of breast cancer in the early stages ².

Black, oolong, green and white teas contain similar amounts of flavonoids, however they differ in their chemical structure. The green and white teas contain more of the simple flavonoids called catechins, while the oxidation that the leaves undergo to produce oolong and black tea converts these simple flavonoids to the more complex varieties called theaflavins and thearubigins ³.

In the past a lot of the research investigating the health benefits of tea has focused on the catechins, giving green tea a glowing reputation as a health promoting drink. Recently, scientists have expanded their studies to include black tea and are concluding that black and green tea have similar beneficial attributes in lowering the risk of many human diseases ⁴.

In addition to the antioxidants, teas contain trace amounts of various nutrients such as the minerals calcium, magnesium, manganese and potassium and the vitamins C and K.

The health benefits of herbal teas will differ from those of the black, oolong, green and white teas and will depend on the properties of the particular herb. Most herbs are good sources of antioxidants and also contain trace amounts of other nutrients. They also possess a variety of other health benefits, for example peppermint aids digestion, ginger counteracts nausea and chamomile acts as a mild sedative.

A herbal tea that has recently become popular in the UK is prepared from the leaves and stems of the South African plant Aspalathus linearis (rooibos). The tea is commonly known as red bush or rooibos tea. Like the teas prepared from the Camellia sinensis plant, red bush tea has been shown to contain very high levels of antioxidants. Unlike most other herbal teas, red bush mixes well with milk (we would recommend non-dairy milk).

Caffeine in tea

All teas produced from the Camellia sinensis plant contain caffeine. Black tea contains the highest amount, then oolong, green and white tea (which has the lowest amount). Herbal teas including red bush are naturally caffeine-free.

An average size cup of black tea contains around 50mg caffeine, which is approximately half the amount present in a cup of coffee of the same size ⁵.

De-caffeinated teas are available, however some de-caffeination processes involve the use of toxic solvents, traces of which can remain in the tea. Safe removal of caffeine involves the use of carbon dioxide gas; good quality tea companies such as Clipper and Twinings use this method of de-caffeination. 

Date completed: December 2004.

References

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