Researchers from the National Cancer Institute (NCI) and the Shanghai Cancer Institute used a cancer registry to identify 902 esophageal cancer patients from urban Shanghai, People's Republic of China. This esophageal cancer study is part of a larger, multisite study that included pancreatic, colon, and rectal cancers.
"This is the first epidemiologic study to demonstrate that green tea may protect against esophageal cancer in humans," said Joseph McLaughlin, Ph.D., the lead researcher from NCI.
Animal studies have shown that green tea infusions and extracts protect against esophageal cancer, but this study is the first investigation involving humans to support the experimental evidence, Dr. McLaughlin said.
Because 80 percent of tea consumed worldwide is black tea, there have been few studies on green tea, which is consumed mainly in Asian countries. Furthermore, large-scale studies had been nonexistent in Asia until a few years ago.
Patients ages 30 to 74 years who were diagnosed with esophageal cancer between October 1990 and January 1993 were interviewed on their residential and medical history, height and weight, diet, smoking habits, alcohol use, tea consumption, family history of cancer, occupation, physical activity, and reproductive history. There were 1,552 people without the disease (control subjects) who answered the same questions.
Information about tea consumption included types of tea consumed, frequency of consumption, and age at which tea drinking began. Researchers measured consumption in grams of tea leaves consumed per month. A tea drinker was defined as someone who drank at least one cup of tea per week for 6 months or longer.
The study found that drinking green tea was associated with a 50 percent lower risk of esophageal cancer in women. Among men, risk was also reduced, but this finding was not statistically significant. However, green tea drinking was linked to a 60 percent reduction of esophageal cancer among both men and women who did not smoke.
Individuals who drank burning-hot fluids (tea and soup) did not reap full benefits from the green tea, which lowered -- but did not eliminate -- cancer risk. These people experienced a fivefold increase in esophageal cancer risk over people who did not drink burning-hot liquids. Studies in China and other countries have shown that such repeated thermal irritation of the esophagus may be responsible for the drinkers' increased esophageal cancer risk. Subjects who drank green tea and avoided burning-hot fluids had significantly lowered cancer risk.
Scientists speculate that the protective effects of green tea arise out of polyphenol compounds in the tea. Polyphenols are a class of compounds that have strong antioxidant properties (the ability to halt enzymes that produce carcinogens) and also are able to inhibit cancer cell growth.
According to Dr. McLaughlin, additional epidemiologic studies are needed to confirm the findings from this research. Should they be confirmed, Dr. McLaughlin believes that clinical trials should be undertaken to determine the preventative effects of green tea. These trials would allow researchers to better understand the biochemical mechanisms involved in the inhibition of esophageal cancer and to determine whether green tea can truly prevent its occurrence.
This year, about 11,000 Americans will be diagnosed with esophageal cancer and 10,400 people will die of the disease.
Date Last Modified: 06/94