Green tea extract has shown promise against cancer in numerous studies. Those findings came from animal studies and epidemiologic research, which tracks a disease's occurrence in a large population of people.
In other words, the human studies on green tea are mainly based on observation and don't prove that tea is responsible for results. But as one of the world's most popular drinks, tea is widely considered healthy, whether it's green, black, or white tea. However, green tea and green tea supplements generally contain higher amounts of disease-fighting antioxidants called polyphenols than black tea.
For instance, studies on mice showed that green tea helped prevent prostate cancer growth. Green tea extract is also reported to induce cancer cell death and starve tumors by curbing the growth of new blood vessels that feed them.
But exactly how that happens isn't clear. Tea's antioxidants may protect against some forms of cancer. They may also help prevent heart disease by relaxing blood vessels and preventing blood clots. But the precise ways green tea affects cancer aren't fully understood.
Uncovering a Clue to Green Tea's Power
University of California Los Angeles (UCLA) researchers used green tea extract on human bladder cells, some of which were cancerous. Their findings appear in the Feb. 15 issue of Clinical Cancer Research.
The green tea extract targeted the cancer cells without harming healthy cells, say the researchers. Taking a closer look, they noticed something unusual about the cancer cells.
The green tea extract apparently made the cancer cells more mature, making them bind together more closely. That made it harder for the cancer cells to become invasive and spread.
"In effect, the green tea extract may keep the cancer cells confined and localized, where they are easier to treat and the prognosis is better," says researcher JianYu Rao, MD, in a news release.
That's an important clue, but it's not the final verdict on how green tea works against cancer. More work is still needed to understand the process, say the scientists.
Meanwhile, if you're interested in trying green tea, be aware that the FDA hasn't evaluated claims about green tea's powers and that supplements are not regulated by the government. If you're watching your caffeine intake, green tea does contain some caffeine (but much less than coffee).
To get green tea's potential disease-fighting benefits, studies have suggested that you should drink four cups a day. Green tea supplements are also available, and at least one study has shown that you may actually get more powerful antioxidants from supplements than from drinking tea.
As always, let your doctor know about any over-the-counter health products you're taking.