Catechins are a type of antioxidant found in the greatest abundance in the leaves of the tea plant Camellia sinensis. In smaller amounts, they are found in other foods such as red wine, chocolate, berries, and apples. Their health benefits of have been under close examination since the 1990s, due to the strong association of tea with long life and health in many ancient cultures.
The varieties found in the leaves of the tea plant are also known as catechin polyphenols. They are part of a molecular family called flavonoids, which are plant secondary metabolites. This means they are not essential for the growth of the plant, but are important for its good health.
Medical research has uncovered evidence that catechins are beneficial for the good health of humans as well as plants. In laboratory tests, those present in tea leaves have been shown to inhibit the growth of cancer cells. In addition to this, they are able to prevent the activity of free radicals, the molecules that cause cellular damage that can lead to cancer.
Unfortunately, results of catechin-related studies in humans have not been conclusive. Some studies show that tea drinkers have a reduced risk of certain types of cancer, but other studies have shown no evidence that drinking tea has beneficial health effects. This means it is difficult to say for sure how helpful the antioxidants in tea really are.
For example, a study of 18,000 Chinese men found that men who drank tea frequently had a 50% lower risk of developing stomach cancer as compared to men who did not drink tea frequently. On the other hand, a study conducted with approximately 120,000 men and women in the Netherlands investigated the link between tea drinking and the frequency of stomach cancer and found no evidence that tea provided any protection.
One important fact that has been uncovered about catechins is that there are more in green tea than in black tea. All types of tea leaves, whether green or black, undergo the same initial preparation processes, but black tea leaves are also allowed to ferment and oxidize. It is thought that these extra preparation steps reduce the amount of antioxidants, making green tea leaves a better source.
This may be one explanation for the differences in the studies in China and the Netherlands; green tea is a dietary mainstay in China, but is perhaps less so in most other parts of the world. This means it is possible the people in the Netherlands study drank mostly black tea, which contains fewer catechins and may therefore provide less protection.