Can Drinking Green Tea Prevent Cancer?

Can Drinking Green Tea Prevent Cancer?

Tea has been regarded as an aid to good health for centuries, particularly in the Chinese and Indian cultures. In China, green tea is a mainstay of the diet. All varieties of tea are derived from the leaves of the evergreen plant Camellia sinensis. Tea leaves are picked, rolled, dried, and heated. An additional process of allowing the leaves to ferment and oxidize produces black tea. Green tea is produced when tea leaves undergo less processing than black tea. Tea contains antioxidants called catechins. Possibly because it is less processed, green tea contains higher levels of antioxidants or catechins than black tea. Steeping either green or black tea for about 5 minutes releases 80% of its antioxidant catechins. Instant ice tea, however, contains negligible amounts of these antioxidants (Dufresne & Farnworth, 2001).

The environment contains multiple sources of oxidizing agents called free radicals. Body cells also naturally produce free radicals. Free radicals or oxidants are unstable molecules which steal electrons from other molecules, damaging cell proteins and genetic material in the process. This type of damage leaves cells at risk for changes which can lead to cancer. Free radicals injure cell membranes and leave DNA vulnerable to damage. Tea antioxidants are very effective at scavenging free radicals before cell injury can occur. Tea antioxidants are also believed to target and repair DNA changes caused by the oxidizing free radicals. Laboratory studies show that tea antioxidants inhibit cancer growth in animals in three ways:
Scavenge free radicals.

Reduce the incidence and size of chemically induced tumors.
Inhibit growth of tumor cells.

Animal research has shown that liver, stomach, and skin cancer growth diminished in mice that were fed green and black tea (Hakim & Harris, 2001). However, human research studies show ambiguity. A substantial number of human intervention studies with green and black tea demonstrate a significant increase in plasma antioxidant capacity 1 hour after consumption of moderate amounts of tea (1-6 cups/day) (Rietveld & Wiseman, 2003). In China, 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 diet factors (Sun et al., 2002). However, an earlier study in the Netherlands did not have similar findings. A study of 58,000 men and 62,000 women ages 55 to 69 found no link between tea consumption and protection against cancer (Goldbohm, Hertog, Brants, van Poppel, & van den Brandt, 1996). Currently, green tea is under investigation for its beneficial effects in different types of cancer as well as in cardiovascular disease. There is no specific quantity of green tea which is known to confer health benefits. Studies have shown health benefits from drinking amounts of 1 to 6 cups of green tea daily, a very broad range. Investigators have focused on steeped hot tea rather than iced tea. In sum, green tea may have antioxidants which can benefit health, and no significant side effects have been reported.


Consumers should not confuse black or green tea with "dieter's teas" advertised for weight loss. Those products contain senna, aloe, rhubarb root, buckthorn, cascara, or castor oil additives. Dieter's teas can exert a potent diuretic and/or laxative effect on the body that can lead to serious adverse effects. Diarrhea, electrolyte disturbances, dehydration, cardiac arrhythmias, and hypotension can result from ingesting these teas. Dieter's teas are considered potentially harmful by the Food and Drug Administration (FDA) (National Cancer Institute, 2002).