Tea has been an important part of many cultures for centuries - from the green tea of Japan and China, to the black tea taken in Australia, the United Kingdom and Southeast Asia. While green tea has been the subject of research for decades, it is only recently that scientists have focussed their attention on black tea - with interesting results.

The Second International Scientific Symposium on Tea and Human Health was held in Washington DC on September 14. Scientists from around the world met to discuss new research findings on tea and health.

Tea and health

Just like fruits and vegetables, tea has been shown to contain antioxidants, naturally occurring substances which may help reduce the risk of heart disease and cancer. It is the antioxidants in tea that are believed to be responsible for the reported effects of tea in reducing the risk of heart disease and cancer.

Reduced risk of cancer

More than fifty studies have been conducted to date to look at the effect of both green and black tea on the risk of cancer. Most of these studies have been conducted in animals and suggest that tea helps to reduce the risk of cancer as well as inhibit tumour growth. Tests on rats and mice have shown that tea restricted the development of skin cancer and tumours in the lung. Studies in humans are now underway. One study in China using a mixture of green and black tea, reported a protective effect of tea on gastrointestinal cancer formation in humans.

Tea and heart disease

The risk of coronary heart disease may also be reduced by tea consumption. A Dutch study reported that a high intake of one type of antioxidant, flavonoids, was associated with a significantly reduced risk of coronary heart disease. The major source of flavonoids in the Dutch diet is tea.

Scientists are not sure why tea may reduce the risk of heart disease. Tea has no effect on blood cholesterol levels and has not been shown to affect the oxidation of low-density lipoprotein cholesterol (LDL or "bad" cholesterol). However, if animal studies are any guide, the antioxidants in tea appear to help stop platelets sticking together and therefore the tendency for the blood to clot.

Black or green?

When it comes to choosing between black and green tea, it seems to boil down to taste preferences. Both black and green tea seem to be equally effective in reducing cancer risk. And adding milk to tea doesn't appear to affect its antioxidant properties. While the total amount of antioxidants in green and black tea is similar, the type of antioxidants differs. In green tea, only catechins and flavonols are present while black tea contains both of these antioxidants, as well as theaflavin and thearubigen. These differences may help to explain differences in the observed effects of black and green tea consumption. Further studies are needed to help identify the components of tea responsible for its effects and to confirm the findings.