LOS ANGELES, CALIFORNIA. Green tea and black tea are derived from the leaves of the same plant, Camillia sinensis, with the manufacture of black tea requiring an additional fermentation step. Both teas contain polyphenols, antioxidant compounds that block the action of enzymes that cancers need for growth and deactivate substances that promote the growth of cancers. Because of the widespread popularity and availability of tea, this makes it an excellent candidate for dietary cancer prevention.
Although several laboratory (in vitro) studies have documented anti-cancer activity in polyphenols, additional trials in living subjects (in vivo) are needed. In a study of 30 healthy adult men and women, researchers affiliated with the David Geffen School of Medicine at the University of California compared the absorption and antioxidant activity of polyphenols in green tea, black tea or a green tea extract supplement.
Subjects were randomly assigned to 3 different sequences of green tea, black tea, or the green tea extract supplement, and changing sequences (a 3 x 3 crossover design) after abstaining from tea consumption for a period of one week in between sequences. Blood samples were collected from subjects at 1, 2, 4, 6, and 8 hours after tea or supplement consumption.
The results showed that all 3 interventions provided similar amounts of (-)-epigallocatechin-3- gallate, the polyphenol most strongly associated with cancer prevention. However, absorption was enhanced when tea polyphenols were administered as a green tea extract supplement compared with tea polyphenols consumed as black tea or green tea, and led to a small but significant increase in antioxidant activity in the blood. Based on these observations, the investigators concluded that green tea extract supplements retain the beneficial effects of green and black tea and deserve further study. Of particular interest is the fact that the use of a green tea extract, rather than regular tea prepared from tea bags, would allow the use of much larger doses of tea polyphenols without incurring the side effects of a large caffeine "jolt".
NOTE: The study received support from National Institute of Health (NIH). The test substances
by Pharmanex (green tea extract), Uncle Lee's Tea (green tea), and R.C. Bigelow, Inc. (black