Tea drinking is an ancient tradition dating back 5,000 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—called catechins—found in tea. Despite promising early research in the laboratory, however, studies involving humans so far have been inconclusive.

1. What are antioxidants?

   The human body constantly produces unstable molecules called oxidants, also commonly referred to as free radicals. 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 scavenge and seize oxidants. Like other antioxidants, the catechins found in tea selectively inhibit specific enzyme activities that lead to cancer. They may also target and repair DNA aberrations caused by oxidants (1).

2. What is the level of antioxidants found in tea?

   All varieties of tea come from the leaves of a single evergreen plant, Camellia sinensis. All 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 that steeping either green or black tea for about 5 minutes released over 80 percent of its catechins. Instant iced tea, on the other hand, contains negligible amounts of catechins (1).

3. What are the laboratory findings?

   In the laboratory, studies have shown that tea catechins act as powerful inhibitors of cancer growth in several ways: They scavenge oxidants before cell injuries occur, reduce the incidence and size of chemically induced tumors, and inhibit 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 (1, 2).

4. What are the results of human studies?

   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 in China, where green tea is a mainstay of the diet, resulted in promising findings. One study involving over 18,000 men found that 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 (3). A second study at the Beijing Dental Hospital found that consuming 3 grams of tea a day, or about 2 cups, along with the application of a tea extract, reduced the size and proliferation of leukoplakia, a precancerous oral plaque (1).

   However, a study 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 58,279 men and 62,573 women ages 55 to 69. The study took into account such factors as smoking and overall diet. It found no link between tea consumption and protection against cancer (4).

5. Is the National Cancer Institute (NCI) evaluating tea?

   NCI researchers are also investigating the therapeutic use of green tea. One recently completed but unpublished NCI trial studied the antitumor effect of green tea among prostate cancer patients. The 42 patients drank 6 grams of green tea, or about 4 cups, daily for 4 months. However, only one patient experienced a short-lived improvement, and nearly 70 percent of the group experienced unpleasant side effects such as nausea and diarrhea. The study concluded that drinking green tea has limited antitumor benefit for prostate cancer patients (5).

   Other ongoing NCI studies are testing green tea as a preventive agent against skin cancer. For example, one is investigating the protective effects of a pill form of green tea against sun-induced skin damage, while another explores the topical application of green tea in shrinking precancerous skin changes. For more information about NCI-sponsored studies on green tea, go to http://www.cancer.gov/clinicaltrials/ on the Internet.

References:

1. Dufresne CJ, Farnworth ER. A review of latest research findings on the health promotion properties of tea. J. Nutri Biochem 2001; 12(7):404–421.
2. Hakim IA, Harris RB. Joint effects of citrus peel use and black tea intake on risk of squamous cell carcinoma of the skin. BMC Derm 2001; 1(3).
   

3. Sun CL, Yuan JM, Lee MJ, Yang CS, Gao YT, Ross RK, Yu MC. Urinary tea polyphenols in relation to gastric and esophageal cancers: A prospective study of men in Shanghai, China. Carcin 2002; 23(9):1497–1503.
   

4. Goldbohm RA, Hertog MG, Brants HA, van Poppel G, van den Brandt PA. Consumption of black tea and cancer risk: A prospective cohort study. JNCI 1996; 88(2):93–100.
   

5. Phase II Study of Green Tea Extract in Patients With Androgen-Independent Metastatic Prostate Cancer. Protocol Ids: NCCTG-N9951. NCI Clinical Trials http://www.cancer.gov/clinicaltrials/.

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Glossary Terms

A substance that protects cells from the damage caused by free radicals (unstable molecules made by the process of oxidation during normal metabolism). Free radicals may play a part in cancer, heart disease, stroke, and other diseases of aging. Antioxidants include beta-carotene, lycopene, vitamins A, C, and E, and other natural and manufactured substances.

Having to do with stopping abnormal cell growth.

Cancer that forms in tissues of the breast, usually the ducts (tubes that carry milk to the nipple) and lobules (glands that make milk). It occurs in both men and women, although male breast cancer is rare.

A term for diseases in which abnormal cells divide without control and can invade nearby tissues. Cancer cells can also spread to other parts of the body through the blood and lymph systems. There are several main types of cancer. Carcinoma is a cancer that begins in the skin or in tissues that line or cover internal organs. Sarcoma is a cancer that begins in bone, cartilage, fat, muscle, blood vessels, or other connective or supportive tissue. Leukemia is a cancer that starts in blood-forming tissue such as the bone marrow, and causes large numbers of abnormal blood cells to be produced and enter the blood. Lymphoma and multiple myeloma are cancers that begin in the cells of the immune system. Central nervous system cancers are cancers that begin in the tissues of the brain and spinal cord. Also called malignancy.

The individual unit that makes up the tissues of the body. All living things are made up of one or more cells.

Having to do with the colon or the rectum.

Frequent and watery bowel movements.

The things a person eats and drinks.

The molecules inside cells that carry genetic information and pass it from one generation to the next. Also called deoxyribonucleic acid.

A protein that speeds up chemical reactions in the body.

Cancer that forms in tissues lining the esophagus (the muscular tube through which food passes from the throat to the stomach). Two types of esophageal cancer are squamous cell carcinoma (cancer that begins in flat cells lining the esophagus) and adenocarcinoma (cancer that begins in cells that make and release mucus and other fluids).

In medicine, a preparation of a substance obtained from plants, animals, or bacteria and used as a drug or in drugs.

A highly reactive chemical that often contains oxygen and is produced when molecules are split to give products that have unpaired electrons (a process called oxidation). Free radicals can damage important cellular molecules such as DNA or lipids or other parts of the cell.

Inherited; having to do with information that is passed from parents to offspring through genes in sperm and egg cells.

The number of new cases of a disease diagnosed each year.

Research done in a laboratory. These studies may use test tubes or animals to find out if a drug, procedure, or treatment is likely to be useful. Laboratory studies take place before any testing is done in humans.

An abnormal patch of white tissue that forms on mucous membranes in the mouth and other areas of the body. It may become cancer. Tobacco (smoking and chewing) and alcohol may increase the risk of leukoplakia in the mouth.

Primary liver cancer is cancer that forms in the tissues of the liver. Secondary liver cancer is cancer that spreads to the liver from another part of the body.

One of a pair of organs in the chest that supplies the body with oxygen, and removes carbon dioxide from the body.

The smallest particle of a substance that has all of the physical and chemical properties of that substance. Molecules are made up of one or more atoms. If they contain more than one atom, the atoms can be the same (an oxygen molecule has two oxygen atoms) or different (a water molecule has two hydrogen atoms and one oxygen atom). Biological molecules, such as proteins and DNA, can be made up of many thousands of atoms.

The National Cancer Institute, part of the National Institutes of Health of the United States Department of Health and Human Services, is the Federal Government's principal agency for cancer research. The National Cancer Institute conducts, coordinates, and funds cancer research, training, health information dissemination, and other programs with respect to the cause, diagnosis, prevention, and treatment of cancer. Access the National Cancer Institute Web site at http://www.cancer.gov. Also called NCI.

A feeling of sickness or discomfort in the stomach that may come with an urge to vomit. Nausea is a side effect of some types of cancer therapy.

By or having to do with the mouth.

In medicine, a small, abnormal patch of tissue on a body part or an organ. Plaques may also be a build-up of substances from a fluid, such as cholesterol in the blood vessels.

A term used to describe a condition that may (or is likely to) become cancer. Also called premalignant.

Used to prevent disease.

Cancer that forms in tissues of the prostate (a gland in the male reproductive system found below the bladder and in front of the rectum). Prostate cancer usually occurs in older men.

A molecule made up of amino acids that are needed for the body to function properly. Proteins are the basis of body structures such as skin and hair and of substances such as enzymes, cytokines, and antibodies.

A problem that occurs when treatment affects healthy tissues or organs. Some common side effects of cancer treatment are fatigue, pain, nausea, vomiting, decreased blood cell counts, hair loss, and mouth sores.

Cancer that forms in tissues lining the stomach. Also called gastric cancer.

Having to do with treating disease and helping healing take place.

On the surface of the body.

An abnormal mass of tissue that results when cells divide more than they should or do not die when they should. Tumors may be benign (not cancer), or malignant (cancer). Also called neoplasm.