03/01/2001 - By Anne MacLennan
Green tea has been found to have no protective effect against gastric cancer.
The beverage is widely consumed in Asia and is the most popular beverage in Japan, where it is considered to have healthful properties.
A large, prospective, cohort study in Japan provides the strongest epidemiologic evidence to date on the link between this drink and risk of gastric cancer.
Findings are in contrast to earlier laboratory experiments and case-control studies suggesting green tea provides protection against gastric cancer.
Until now, few prospective studies have been performed, although large cohort studies and intervention trials on the relationship continue in Japan, where green tea drinking is pervasive.
Indeed, the tea no longer needs to be prepared in a teapot at home; canned and bottled, it is widely available in vending machines and convenience stories across the country.
Some health-conscious people drink one litre of more per day.
Although gastric cancer was once the leading cause of cancer-related death in most countries, the incidence has steadily decreased around the world, with dramatic decreases in the West.
In Japan, however, incidence has decreased much more slowly, and the disease remains the most common type of cancer in both men and women.
In 1997, the 49,739 deaths from gastric cancer in Japan accounted for 18 percent of all cancer-related deaths.
Participants in this study were 11,902 men and 14,409 women who resided in three municipalities in a rural region of northern Japan, where the incidence of gastric cancer is relatively high.
In January 1984, all participants completed a self-administered questionnaire that included questions about frequency of consumption of green tea, with use ranked in one of four categories, ranging from none to more than five cups per day.
From enrollment through December 1992 -- 199,748 person-years of follow-up -- researchers identified 419 cases of gastric cancer, 296 in men and 123 in women.
No link between green tea consumption and risk of gastric cancer was found. In fact, there was a nonsignificant increase in risk among people who drank five or more cups per day versus those who drank less than one cup per day.
Use was, however, linked with other factors that can increase -- or decrease -- gastric cancer risk.
For example, among men who drank less than one cup of green tea per day, rates of daily consumption of pickled vegetables (a risk factor) and fruits (a protective factor) were 60.1 percent and 47.1 percent respectively. In men who consumed more than five cups of tea per day, the respective rates were 73.2 and 58.1 percent.
The higher the rate of consumption of pickled vegetables and fruits, the greater the consumption of green tea.
Smoking was another factor linked with green-tea consumption. Among men who drank less than one cup per day, 72.1 percent were current or former smokers, whereas among those who drank five or more cups per day, 81.2 percent were current or former smokers.
Contributing researchers were from the Tohoku University Graduate School of Medicine, Sendai, Japan; Harvard School of Public Health, Boston, Massachusetts, United States; Sendai College, Miyagi, Japan; University of Massachusetts Medical Center, Worcester, Massachusetts; Miyagi University School of Nursing, Sendai, and Yamagata University School of Medicine, Yamagata, Japan.
N Engl J Med 2001;344:632-6.