Anti-carcinogen properties of coffee and tea.
Leading nutritional authorities, including the highest government food agencies, have long recommended a diet high in fresh fruits and vegetables, not only for their calories, vitamin and mineral contribution; but also because they impart certain anti-cancer agents which are considered valuable in the delay or the prevention of this dread affliction.
Although they have no caloric value, coffee and green tea are included in the list of plant food products which contribute anti-carcinogenic factors to the human food intake. However, because of their caffeine content, which many nutritionists and food editors do not approve, coffee and tea, though included in technical publications, are usually deleted from vegetable groups recommended for public consumption in daily newspapers and popular weekly and monthly periodicals.
The common components in the dietary vegetable products which have anti-cancer properties is a large class of organic compounds in the category of phenols and polyphenols. In the case of coffee, the specific compound is chlorogenic acid, a soluble grayish powder with a mildly bitter flavor present in three or four times greater concentration than caffeine. In the case of green tea, the specific protective agent is epi-gallo-catechin gallate (EGCG), also a major component with a mild astringent taste.
Phenols as a class are defined as aromatic compounds with an hydroxyl (OH) group attached directly to a benzene nucleus. The simplest one is called phenol and under the synonym "carbolic acid" was once widely used as popular household disinfectant. It is a caustic, highly corrosive chemical and has long been replaced by gentler agents. More complex phenols, however, are still prevalent and are natural components of the food we eat. Some are essential to growth and health; while others are beneficial for other purposes such as components of vitamins, amino acids, anti-cancer agents, pharmaceuticals and other products.
At a recent national meeting of the American Chemical Society, held in New York in August 1991, a symposium on phenolic compounds in food and health was held under the auspices of the Division of Food and Agricultural Chemistry. In an overview lecture, John Weisburger, director emeritus of the American Health Foundation, stated a universal finding that a regular intake of vegetables and fruits along with the consumption of coffee and green tea reduces the risk of cancer in humans. "The reason is the presence of specific phenols such as chlorogenic acid and EGCG."
Pathologist Tanaka and colleagues at Japan GIFU University School of Medicine reported on the tumor inhibiting effects of chlorogenic acid. Sources included coffee beans, apples and peaches.
In tests on golden hamsters, he measured its inhibiting effect against a standard carcinogen. In these experiments, the incidence of tumors was significantly lower in the chlorogenic acid treated animals. This confirms previous reports on the anti-carcinogenic properties of this agent. Tanaka concluded, "These results suggest that chlorogenic acid is a potential chemo-preventive agent."
A chemist from the Bureau of Chemical Safety, Health and Welfare Canada noted that while there's considerable evidence that poly-phenols have a protective effect against cancer, the mechanism of this effect isn't well understood.
To demonstrate the safety of chlorogenic acid, he ran multi-generation bacterial tests (the Ames Test) with no ill effects. Other tests indicate that in some cases uptake of carcinogens are reduced by these agents as much as 20%. Overall, the data suggests that these poly-phenols may play a dual protective effect - by reducing the bioavailability of carcinogens and by interfering with their biotransformation in the liver.
Several speakers provided evidence of green tea anti-cancer properties. A biochemist with Japan's National Cancer Research Institute described experiments involving application of carcinogens to mouse skin. External application of green tea extract inhibited tumor development. They also found that a diet containing green tea reduced incidence of tumor development in mouse duodenum; and also reduced the incidence of spontaneous liver tumors in a susceptible strain of mice.
Biochemist Jeffrey Laskin of University of Medicine and Dentistry at Rutgers reported somewhat similar findings. In a two stage mouse skin carcinogenesis experiment, green tea effectively suppressed tumor development, whether applied directly to the skin or fed in the diet. Additional efforts are underway to pinpoint other active components in the beverage.
In another paper, chemist Chung, associate chief of the American Health Foundation's division of Chemical Carcinogenesis, reported there is also evidence that green tea can reduce the incidence of smoking-related lung cancer. He noted that this type of cancer mortality is much lower in Japan than in the United States, even though Japanese males on average smoke considerably more than U.S. men. Many factors could account for this difference. He ran some tests to find out if the tea or its components could be a factor.
Mice were given drinking water containing either 2% tea infusion, caffeine solution, EGCG solution or no additive. After two weeks, they received carcinogen by stomach tube three times a week for ten weeks. Mice that drank the water developed an average of 22 lung tumors per mouse. Those that drank tea or EGCG developed 30% to 45% fewer tumors. There was also a small but significant reduction for the mice that drank the caffeine solution. He concluded: "These results suggest that green tea can inhibit lung tumors in exposed mice, and the effect appears primarily due to its major poly-phenol EGCG."
How these agents serve to prevent the development of cancer has not yet been clearly established. Several laboratories report that during the tumor development process, elevated levels of reactive oxygen compounds including hydrogen peroxide have been found. These compounds are thought to be important in the carcinogenic reaction. Polyphenols such as chlorogenic acid and EGCG are anti-oxidants, preventing the formation of peroxides or destroying them as soon as they are formed. Coffee and green tea beverage often effectively suppress the formation of peroxides; and this might be a possible mechanism for their value as anti-cancer agents.
Cancer is a highly complex group of many different types of ailments, and not all have the same cause or course. It is possible that certain types may be delayed, retarded or even prevented by significant ingredients in coffee and tea. Even caffeine has been reported to have a weak effect in this direction. Much more scientific laboratory and clinical work remains to be explored before more definite statements of their value can be supported. Meanwhile, on the basis of present evidence, coffee and green tea merit serious consideration as an anti-cancer tool.