compares the characteristics of subjects in the highest and the lowest categories of green-tea consumption. Subjects in Cohort 1 with higher intake tended to be postmenopausal, while such women in Cohort 2 tended to be slightly older, postmenopausal and have a higher body mass index. Subjects in both cohorts with a lower intake tended to drink black tea less frequently and coffee more frequently.
Characteristics of the subjects according to green-tea consumption
We found no inverse association between green-tea intake and the risk of breast cancer, whether data for Cohorts 1 and 2 were combined or separated (
). Exclusion of cases of breast cancer diagnosed in the first 3 years of follow-up did not substantially change the results and nor did further adjustment for consumption frequencies of vegetables, fruits and meat.
RR of breast cancer according to green-tea consumptiona
When we performed stratified analyses according to variables used as potential confounders in the multivariate analysis, the association between the consumption of green tea and breast cancer risk was not substantially modified. In a stratified analysis according to soybean soup intake (less than daily and daily), the pooled multivariate RRs (95% CI) of breast cancer for women who drank five or more cups per day, as compared with women who drank less than one cup per day, were 0.95 (0.29–3.10; Trend P=1.00) among those consuming soybean soup less than daily (35 cases) and 0.81 (0.54–1.24; Trend P=0.63) among those consuming soybean soup daily (185 cases).
We found no relation between breast cancer risk and the consumption of black tea and coffee. The pooled multivariate RRs (95% CI) compared with women who never drank black tea were 0.90 (0.64–1.27) for those drinking black tea occasionally and 1.44 (0.77–2.69) for those drinking one or more cups per day (Trend P=0.81). The corresponding risks for coffee were 0.78 (0.53–1.13) and 0.81 (0.55–1.18) (Trend P=0.44).