Antioxidants found in tea may slow down the growth of certain cancers. Recent studies conducted in animals show that tea actually reduces the number and size of certain tumors, while reducing the growth of cancer cells.
How do these findings translate to human beings? So far, results are inconclusive; limited research done using green tea (four daily cups during four months) show no changes with prostate cancer, although there were some unpleasant side effects such as nausea and diarrhea in about two-thirds of the participants in the study.
Drinking tea is an ancient tradition dating back five thousand years in China and India; long regarded in those cultures as an aid to good health, researchers now are studying tea for possible use in the prevention and treatment of a variety of cancers. Investigators are especially interested in the antioxidants found in tea.
Oxidants, also known as free radicals, are unstable molecules produced by our metabolism; to become stable, oxidants steal electrons from other molecules and in the process damage cell proteins and genetic material. This damage may leave the cell vulnerable to cancer. Antioxidants are substances that allow the human body to get rid of oxidants. The antioxidants found in tea are called catechins; they selectively inhibit specific enzyme activities that lead to cancer. They may also target and repair genetic changes caused by oxidants.
All varieties of tea come from the leaves of “Camellia sinensis,” a single evergreen plant; tea leaves are picked, rolled, dried, and heated. With the additional process of allowing the leaves to ferment and oxidize, black tea is produced. Possibly because it is less processed, green tea contains higher levels of antioxidants than black tea.
Although tea is consumed in a variety of ways and varies in its chemical makeup, one study showed steeping either green or black tea for about five minutes released over 80 percent of its antioxidants. Instant iced tea, on the other hand, contains very low amounts of antioxidants.
Laboratory studies show that tea antioxidants are powerful inhibitors of cancer growth in several ways. They eliminate oxidants before cell injuries occur, reduce the incidence and size of chemically induced tumors, and slow down the growth of tumor cells. In studies of liver, skin, and stomach cancer, chemically induced tumors were shown to decrease in size in mice that were fed green and black tea.
Although tea has long been identified as an antioxidant in the laboratory, study results involving humans have been contradictory. Some epidemiological studies comparing tea drinkers to non-tea drinkers support the claim that drinking tea prevents cancer; others do not. Dietary, environmental, and population differences may account for these inconsistencies.
Two studies done in China, where green tea is a mainstay of the diet, resulted in promising findings. One study involving over 18,000 men found tea drinkers were about half as likely to develop stomach or esophageal cancer as men who drank little tea, even after adjusting for smoking and other health and diet factors. A second study found consuming three grams of tea a day (about two cups) along with the application of a tea extract reduced the size and proliferation of leukoplakia, a precancerous oral plaque.
However, a study done in the Netherlands did not support these findings. It investigated the link between black tea consumption and the subsequent risk of stomach, colorectal, lung, and breast cancers among 60,000 men and 62,000 women ages fifty five to seventy. The study took into account such factors as smoking and overall diet. It found no link between tea consumption and protection against these cancers.
By Patricia L. Elswick, MD