What is the evidence? Many laboratory studies have shown green tea acts against cancer cells in cell cultures. Test tube studies have suggested that compounds in the tea may help stop new blood vessels from forming, thereby cutting off the supply of blood to cancer cells. It is tempting to assume that it may therefore help prevent some cancers, but results of studies in humans have been mixed. Most human studies have been epidemiologic studies in East Asia, in which researchers compared tea drinkers with non–tea drinkers while trying to account for other lifestyle differences. It is hard to draw firm conclusions from them unless there are multiple studies in which other factors are ruled out. Studies looking at large populations in East Asia generally have not found that green tea drinkers have a lower risk of breast, stomach, or colon cancer than non–tea drinkers. One study found that Asian-American women who drink green tea regularly have a lower risk of breast cancer than those who do not. A Chinese study found that green tea drinking was linked to fewer cancers of the esophagus for people who did not smoke. On the other hand, a 2006 Japanese study showed that those with cancer of the esophagus were more likely to be green tea drinkers than those who did not have the cancer. Other studies of green tea’s ability to prevent or treat lung, prostate, bladder, or other types of cancer have yielded similarly mixed results. The FDA reviewed all of the published studies and concluded in early 2011 that it is very unlikely that green tea prevents any type of cancer in humans. There are also studies looking at green tea extracts such as epigallocatechin gallate (EGCG). One such early (Phase I) study was done at Mayo Clinic to find safe dosing. They gave the extract in pill form to people with early stage chronic lymphocytic leukemia (CLL). These people had no symptoms and would not usually be treated. Some of the people who got EGCG seemed to have fewer cancer cells after taking EGCG than before they started. Eventually the researchers hope to learn if the extract can help people with early stage CLL. Further clinical trials are needed to find out if the EGCG actually changes the course and outcome of their leukemia. An Italian study published in 2006 looked at men with prostate intraepithelial neoplasi, which sometimes progresses to prostate cancer. The researchers gave half the men green tea extract and the other half sham pills. Over the next year, the men given green tea extract had fewer cases of prostate cancer than the men who got placebos. Other studies looked to see if green tea could help men who already had prostate cancer, but it didn’t seem to reduce the risk of prostate cancer continuing to grow and spread. While the results of laboratory studies have been promising, at this time the available scientific evidence does not support claims that green tea can help prevent or treat any specific type of cancer in humans. Purified extracts have shown some promise in limited areas. Controlled, randomized clinical trials are needed to learn about the effects of green tea and more about those of its extracts. Several studies are under way.
Posted on: Thu, 05 Sep 2013 13:46:20 +0000
Trending Topics
Recently Viewed Topics
© 2015