Clinician Fact Sheet: Medicinal Foods

Reports on the ability of foods to prevent and fight cancer are reaching patients in increasing numbers. Because of their safety and availability, food and food-derived products may find widespread, long-term use in chemoprevention. This insert will examine tea and its ability to prevent and treat cancer.

Black and Green Tea (Camellia sinensis; Family: Theaceae)


Cultivated in more than 30 countries, tea, next to water, is the most commonly consumed beverage in the world. Tea contains polyphenolic antioxidants that have demonstrated anticarcinogenic properties in animal and in vitro studies.1

Historical Medicinal Use

Orally, green tea has been used for cognitive performance, stomach disorders, vomiting, diarrhea, headaches, and weight loss; to maintain Crohn’s disease remission; to reduce the risk of prostate and colon cancer; to protect against heart disease and dental caries; and to prevent kidney stones.

Topically, green tea bags are used to soothe sunburn, headache, and tired eyes, and to stop the bleeding of tooth sockets.

Orally, black tea is used as a stimulant for stomach disorders, vomiting, diarrhea, and headaches; as a diuretic; for reducing the risk of heart attack, cancer, kidney stones, and dental caries; for preventing atherosclerosis; and for weight loss.


Camellia sinensis leaves and stems are used to manufacture green tea (non-fermented), oolang tea (partially fermented), and black tea (fermented). Prepared immediately after harvest to limit enzymatic changes, green teas have six times the concentration of polyphenolic antioxidants of oolang teas or black teas.2


Green tea: The traditional Asian diet averages three cups/d with a total polyphenolic content of 240-320 mg. For medicinal purposes, dosages may be as high as 10 cups/d. More than 10 cups/d, or 300 mg caffeine, increases the risk of adverse effects.

Black tea: Dosages may range from two to three cups/d as an antidiarrheal to seven or more cups/d as a stimulant. Because of its high tannin content, higher and prolonged intake of black tea may increase the risk of rectal cancer. In cultures that drink black tea with milk, this increase is not observed.

Adverse Reactions

The caffeine in tea can cause headache, diuresis, anxiety, nervousness, insomnia, restlessness, agitation, tremor, irritability, fast heartbeat, palpitations, premature heartbeat, arrhythmias, quickened respiration, heartburn, loss of appetite, nausea, vomiting, diarrhea, dizziness, ringing in the ears, elevated blood sugar, elevated cholesterol, hepatotoxicity, delirium, and convulsions.

The caffeine in tea can aggravate gastric and duodenal ulcers, depression, anxiety disorders, and insomnia; and may induce cardiac arrhythmias.

Gastrointestinal upset, constipation

Impaired iron metabolism and microcytic anemia has been observed in infants and is theoretical in adults.

Liver dysfunction is possible with the excessive and prolonged use (65 g/d of tea leaves for five years).


Theoretically, concomitant use may inhibit the hemodynamic effects of adenosine; may precipitate anti-psychotic drugs; or may inhibit the cataleptic affects of chlorpromazine.

Because of the caffeine in tea, concomitant administration may decrease the effects of benzodiazepines.

Because of the caffeine in tea, concomitant administration may increase the effects of aspirin, acetaminophen, beta-adrenergic agonists, clozapine, theophylline, and ergotamine.

Concomitant administration with cimetidine, disulfiram, mexiletine, oral contraceptives, quinolones, or verapamil may increase the effects and adverse effects of caffeine.

Concomitant administration with phenytoin or barbiturates may decrease the effects and adverse effects of caffeine.

Concomitant administration with caffeine-containing herbs (ephedra, guarana, mate, kola) may increase the risk of agitation, tremors, and insomnia.

Abrupt caffeine withdrawal may increase serum lithium levels.

Concomitant administration with MAOIs may precipitate a hypertensive crisis.

Concomitant administration with phenylpropanol-amine may increase blood pressure and/or cause mania.

Consumption of large amounts of green tea is reported to antagonize the effects of warfarin.

Concomitant administration with grapefruit juice may increase caffeine levels and the risk of adverse effects.


Green tea should be avoided in breast-feeding mothers and in patients with unstable cardiac or psychological disease.

Clinical Research

Results of a 1999 randomized, controlled clinical trial showed that some potentially anticarcinogenic polyphenolic antioxidants in green tea enter the systemic circulation following ingestion and cause a significant increase in plasma antioxidant status.1

Two trials on green tea have been presented by the Chemoprevention Branch of the National Cancer Institute.3 In the first study, a prospective cohort of more than 8,000 individuals, daily consumption of at least 10 Japanese-size cups of green tea resulted in delayed cancer onset. The second, a follow-up study of breast cancer patients, found that stage I and II breast cancer patients who consumed more than five cups/d of green tea experienced a lower recurrence rate and longer disease-free period than those who consumed fewer than four cups/d.

This study supported the results of a 1998 trial that examined green tea consumption in 472 breast cancer patients.4 Among premenopausal women with stage I and II breast cancer, increased consumption of green tea was associated with fewer axillary lymph node metastases; postmenopausal women had increased expression of progesterone receptor and estrogen receptor. In a follow-up study, increased green tea consumption was associated with decreased recurrence of stage I and II breast cancer; no change in recurrence rates was observed for stage III breast cancer.

Less is currently known about black tea. A 1986 prospective cohort study monitored black tea consumption in 7,833 men over three years.5 Men who drank more than one cup/d of tea had a higher relative risk (RR = 4.2, P = 0.0007) of developing rectal cancer than those who almost never drank tea. However, a significant negative association was found between black tea consumption and prostate cancer incidence (P = 0.02).


1. Benzie IF, et al. Consumption of green tea causes rapid increase in plasma antioxidant power in humans. Nutr Cancer 1999;34:83-87.

2. Serafini M, et al. In vivo antioxidant effect of green and black tea in man. Eur J Clin Nutr 1996;50:28-32.

3. Fujiki H. Two stages of cancer prevention with green tea. J Cancer Res Clin Oncol 1999;125:589-597.

4. Nakachi K, et al. Influence of drinking green tea on breast cancer malignancy among Japanese women. Jpn J Cancer Res 1998;89:254-261.

5. Heilbrun LK, et al. Black tea consumption and cancer risk: A prospective study. Br J Cancer 1986;54:677-683.

Additional Resources

Natural Medicines Comprehensive Database. Stockton, CA: Therapeutic Research Center, Inc.

The Review of Natural Products. St. Louis, MO: Facts and Comparisons.