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Green tea and risk of gastric cancer

 

Some, but not all studies have found a reduced risk of gastric cancer in association with green tea consumption. This study examines whether green tea protects against gastric cancer among a large number of the Japanese population.

Message

Green tea consumption is not associated with the risk of gastric cancer in Japanese men and women.

Reference

Y Tsubono et al. Green tea and the risk of gastric cancer in Japan. The New England Journal of Medicine 2001 344: 632-636.

Study

Participants were 26,311 Japanese (11,902 men and 14,409 women), aged at least 40 years, residents of three municipalities from a region in northern Japan (chosen for its high incidence of gastric cancer). In 1984 participants completed questionnaires, which were delivered to and collected from their homes, on their health habits (e.g. diet, alcohol consumption, smoking), frequency of green tea consumption and family history of disease. They were followed for nine years.

Green tea consumption was divided into four categories: less than one cup a day; one or two cups a day; three or four cups a day; and five or more cups a day. In the region studied, a typical cup contains 100 ml of tea.

The incidence of cancer was obtained from the local cancer registry. A total of 419 cases of gastric cancer (296 in men and 123 in women) were reported.

Results

Nineteen per cent of participants drank less than one cup of green tea a day, 17% drank one or two cups, 22% drank three or four cups and 42% drank five or more cups a day.

There was no association between green tea consumption and risk of gastric cancer for men or for women (or men and women combined). These results (shown in Table 1) were adjusted for gender, age, history of peptic ulcer, smoking status, alcohol intake, daily consumption of rice, black tea, coffee, meat, green/yellow, pickled and other vegetables, fruit, bean-paste soup and socio-economic status.

Table 1. Relative risk of gastric cancer according to green tea consumption for men and women.

 

Green tea consumption (cups/day)

Less than 1

1 or 2

3 or 4

5 or more

No. of gastric cancer cases

66

68

79

206

Relative risk (95% CI)

1

1.1 (0.8 to 1.6)

1.0 (0.7 to 1.4)

1.2 (0.9 to 1.6)

Comment

Most of the studies which have found a reduced risk of gastric cancer in association with green tea consumption are case-control studies which are subject to many forms of bias, e.g. errors in recall, as information is collected after cases have developed the disease. In contrast, this study was prospective (i.e. participants were followed for a number of years) with a large sample of over 26,000 men and women (recruited from the population). However, its results were not adjusted for participants' history of cancer. This information was not collected because at the time of the survey the majority of cancer patients were not told their true diagnosis.

Given the inconsistent findings between studies it would be useful to perform a meta-analysis to provide a summary of results. In the meantime, on balance, this study has several methodological advantages over the case-control studies and it appears that green tea consumption is not associated with the risk of gastric cancer.