Introduction: Although many in-vitro and animal studies have demonstrated a protective effect of green tea against breast cancer, findings from epidemiological studies have been inconsistent, and whether high green tea intake reduces the risk of breast cancer remains unclear.
Methods: In this Japan Public Health Center-based Prospective Study, 581 cases of breast cancer were newly diagnosed in 53,793 women during 13.6 years' follow-up from the baseline survey in 1990-94. After the 5-year follow-up survey in 1995-98, 350 cases were newly diagnosed in 43,639 women during 9.5 years' follow-up. The baseline questionnaire assessed the frequency of total green tea drinking while the 5-year follow-up questionnaire assessed that of two types of green tea, Sencha and Bancha/Genmaicha, separately.
Results: Compared with women who drank less than 1 cup of green tea per week, the adjusted hazard ratio [HR] for women who drank 5 or more cups per day was 1.12 (95% confidence interval [CI] 0.81-1.56; P for trend = 0.60) in the baseline data. Similarly, compared with women who drank less than 1 cup of Sencha or Bancha/Genmaicha per week, adjusted HRs for women who drank 10 or more cups per day were 1.02 (95% CI 0.55-1.89; P for trend = 0.48) for Sencha and 0.86 (0.34-2.17; P for trend = 0.66) for Bancha/Genmaicha. No inverse association was found regardless of hormone receptor-defined subtype or menopausal status.
Conclusions: In this population-based prospective cohort study in Japan we found no association between green tea drinking and risk of breast cancer.