Green tea and cancer: A mixed bag By Bernadine Healy, M.D.
Green tea has been a medicinal potion for thousands of years. Laden with plant chemicals called flavonoids known for their powerful antioxidant abilities, green tea is touted to protect against two of the biggest of human scourges — coronary disease and cancer. But just how green tea works its wonders in the prevention or treatment of individual disease remains a mystery.
Thomas Gasiewicz, researcher in the Department of Environmental Medicine at the University of Rochester Medical Center, presented evidence for some of its magic at an international conference on diet and cancer held in Washington, D.C., today. His laboratory demonstrated that the prime antioxidant component of green tea, which is in the family of plant chemicals called catechins—or epigallocatechin-3-gallate (EGCG) to be precise—zooms in on a key target in the cancer cell. And the target is a big one: a normal stress protein, known as heat shock protein 90 (HSP90).
Heat shock or stress proteins are critical to survival of all cells, cancerous or otherwise. Stress proteins abound in both plants and animals. Think of them as protectors that chaperone the thousands of worker-bee proteins that interact in and on the surface of our cells in the course of any one cell's life. Growth, performance, communication, you name it, and some form of HSP is a key player. When cells are threatened by a treacherous environment such as heat (from which we get the name HSP), proteins curl up and then clump up. We now know it also happens with damaging cold, low oxygen, or poisons. Heat shock protein protectors quickly rev up and come to the rescue to both repair injured proteins and to carry the irreversibly damaged ones to a disposal dump for an out-of-the-way burial so new ones can take their place.
Cancer hijacks the stress protein network in its efforts to overtake the body. Cancer cells are fast growing and on the march wherever they set up shop—breast, prostate, colon, bone marrow. And in that superstressed state of attack, cancer cells produce abnormally high levels of HSP90 to protect their cancer-producing proteins. Even in the face of toxic radiation and chemotherapy, some cancer cells survive because of these natural potent protectors. What Gasiewicz and his colleagues have shown is that the age-old EGCG does battle with HSP90.
A few months ago, his laboratory reported for the first time that EGCG binds to this protective stress protein important to cancer growth and survival and essentially takes it out of commission. One caveat: You have to drink a lot of tea to get enough EGCG to do any good. Just how much is not known, but it is somewhere between three to 10 cups a day. Because of its bitterness and the caffeine load of that much tea, that's hard to do. No wonder that after a detailed analysis of numerous studies of green tea and cancer involving tens of thousands of patients, the Food and Drug Administration announced only two weeks ago that there is "no credible evidence" to support green tea's health claims when it comes to cancer. And for the two cancers where the studies are the most promising, namely prostate cancer and breast cancer, the FDA calls it "highly unlikely" that green tea reduces the risk of either.
However — and there's always a however in clinical medicine—studies are underway to look at cancer and concentrated green tea extract, which is rich in ECGC but free of the side effects of overdosing on the full tea brew.
Source: U.S. News & World Report online, at http://www.usnews.com/usnews/health/briefs/alternativemedicine/hb050714a.htm. Copyright © 2005 U.S. News & World Report, L.P. All rights reserved.