Report: What is it about green tea and tomatoes? Investigator: Can-Lan Sun; Susan Mayne Sunday Apr 7th, 2002 by Apoorva Mandavilli Antioxidants in green tea can decrease the risk of gastric and esophageal cancers, results from the first biomarker-based prospective study of green tea reveal. The results confirm previous observations from a retrospective study. "We found approximately a 50% risk reduction in relative risk," said Can-Lan Sun, the lead author of the study and a researcher at the University of Southern California/Norris Comprehensive Cancer Center in Los Angeles. Researchers at the center, in collaboration with scientists at the Shanghai Institute, measured levels of two polyphenol markers, epigallocatechin and epicatechin, in urine samples from middle-aged and older Chinese men. The presence of epigallocatechin in the urine is associated with a protective effect, the researchers found, while epicatechin had no effect. The protective effect of the tea polyphenols is also limited to those with low serum levels of other antioxidants. Most foods can have 2000 or more chemical constituents, and each of those may act by a variety of internal pathways. The results from a biomarker-based study are therefore more reliable than those that correlate dietary intake with an observed effect, says Susan Mayne, associate professor of epidemiology at Yale. With an observational study, it is "extremely difficult to untangle correlated behaviors and know what in fact is causal," she said. For example, several studies over the last decade have documented that eating tomato-based foods can decrease the risk of prostate cancer. But researchers are just beginning trials to pinpoint whether the effect is due to lycopene, or to some other chemical found in tomatoes. To determine whether the effects are due to antioxidant activity, researchers will measure markers of oxidative stress like oxidation of DNA, lipid, or protein. Microarray studies can also assess the effect of antioxidant nutrients on free-radical response genes. As with the green tea trial, researchers generally infer a positive association as evidence of causal effect. But trials with negative results are much more difficult to interpret, says Alan Kristal, professor of epidemiology at the Fred Hutchinson Cancer Center in Seattle. The lack of results could be from incorrect dosing, poor adherence, missing risk factors, or simply because the nutrient was not given for long enough, Kristal says. At the same time, the costs of running such trials are enormous. The trials are long and expensive, difficult to evaluate, raise questions of compliance, and expose healthy people to treatments of unknown efficacy. "Given the high likelihood of false negatives, random clinical trials should proceed with caution," Kristal suggested. Still, long-term prevention of cancers with dietary changes is critical, says John Potter, Kristal's colleague at Hutchinson. Between 30-40% of cancers can be prevented by dietary changes, Potter says. In the developing world, where cancer rates are expected to increase, that could help save millions of lives. Potter acknowledges the obstacles of preventive research, saying that dietary observations are replete with seeming contradictions. For example, he says, the Japanese eat very little fat and the French eat a lot of fat, while Saudis drink very little red wine and the Italians drink a lot of red wine. All of those groups, however, "suffer fewer heart attacks than Brits, Americans or Australians." The moral of the story, Potter said joking, is to "eat and drink what you like. It's speaking English that kills you." AACR, 4/08/02 Reuters Health Remember we are NOT Doctors and have NO medical training. This site is like an Encylopedia - there are many pages, many links on many topics. Support our work with any size DONATION - see left side of any page - for how to donate. You can help raise awareness of CAM.