Those living in Asia have a lower risk of virtually all forms of cancer. This has interested scientist who have tried to understand why this is so. One line of reasoning suggest that the miso and tofu Asians eat may be protective of cancer because of the phytoestrogens it contains. However, another line of reasoning suggests the low rates of cancer in Asian countries may be a result of extensive tea drinking.
Tea is a decoction. This means it is made by simply adding it to water and allowing the contents to dissolve into the water. In this process a number of constituent within the leave enter the water and are drunk. The most well known substance in tea is caffeine, and this is responsible for some of the energising effects of tea. However, another component, the polyphenols may be the component responsible for the anti-cancer effects of tea.
Green Versus Black Tea
Green tea is made by a simple steaming process that maintains the green colour of the leaves from the Camellia sinensis plant. In contrast, black tea is made by fermenting the tea leave. This is an important distinction because in the fermentation process of black tea, the polyphenols thought to be responsible for the anti-cancer effect of green tea are converted to less beneficial substances called theaflavins.
Catechins Are Anti-Cancer Compounds
The polyphenols in green tea thought to be responsible for its anti-cancer effect are called flavan-3-ols. These are more commonly called the green tea catechins. They represent their own subclass of a group of well known plant compounds called the flavonoids. Of the catechins, epigallocatechin gallate is the catechin with the highest anti-cancer activity. However, other catechins may also play a role.
How Does Tea Prevent Cancer?
Epidemiological studies show that high intakes of green tea are associated with a lower risk risk of cancer, This is especially true for cancers of the gastrointestinal tract. It is unknown how tea prevent cancer, but a number of theories have been suggested and tested in studies. Most convincing is the evidence that the catechins in green tea is particularly epigallocatechin gallate, are able to inhibit the formation of blood vessels required to sustain a tumour.
Green Tea Practicalities
Not all green teas are the same. T an extent the way,the tea is grown, how it is prepared and how long it is stored can all affect the catechin content. These factors are generally outside the control of the individual. However, one thing that can increase the catechin content of tea, and which is under the control of the individual, is the brewing time. Brewing green tea for longer than 10 minutes significantly increases the catechin content of the tea.