Epidemiologist Anna Wu is trying to close in on another key to reducing breast cancer risk.

After studying dietary habits of Asian-American women in the mid-1990s and finding that soy played a significant role in reducing breast cancer risk when consumed from adolescence onward, Wu turned her attention to another common comestible: green tea.

Wu, professor of preventive medicine at the Keck School of Medicine of USC, and her co-researchers at the USC/Norris Comprehensive Cancer Center had given Asian-American women a diet questionnaire and looked for trends in the women who developed breast cancer and those who did not.

“We saw such a strong finding on green tea that we decided to follow up,” she said.

Previous research into tea’s anti-cancer properties did not have strong findings, making some researchers lose interest in it.

Wu hypothesized that the weak results may have been because the previous studies were conducted in Western populations, who primarily drink black tea, and that few studies were conducted in populations who consumed green tea, as her study did.

Both green and black tea are made from the leaves of the Camellia sinensis plant; the difference is that green tea is dried, which preserves their natural polyphenols, while black tea is fermented, a process that destroys certain tea polyphenols.

Recent research from Wu and colleagues suggested an explanation for the mixed effects on breast cancer rates: It seems that green tea lowers estrogen levels in women’s blood, while black tea elevates it. Estrogen has been found to promote the growth of some breast cancers.

Wu’s next study is designed to determine whether green tea does lower estrogen levels.

She plans to give capsules with either a medium or high dose of green tea polyphenols or a placebo pill with no green tea extracts to 150 healthy postmenopausal women who don’t have a history of drinking tea.

The two active pills are equal to the polyphenols from an average of four to five cups of green tea for the medium dose, or eight to 10 cups for the higher dose. The study will be double-blinded, meaning neither the researchers nor the participants will know what type of pills they are receiving.

Researchers will track the women’s estrogen levels during the two-month study by taking blood and urine samples before and after taking the pills and at the one-month mark.

If the green tea pills are found to have no effect on estrogen levels, that will give Wu and the other researchers incentive to keep looking for another mechanism. However green tea works, the positive data from her earlier study was enough to make Wu, a lifelong black tea drinker, start drinking green tea for part of the day.

Wu is now recruiting women over 50 who have been postmenopausal for at least one year and who do not currently drink any type of tea to participate in the study. For more information, call (323) 226-8256 or (323) 865-0476.