Iwasaki 2010a.

Study characteristics
Methods	Cohort studies in Japan (Iwasaki 2010a) and case‐cohort nested study (Iwasaki 2010b)
Participants	Participants: 140,420 (male/female: 68,722/71,698) from cohort 1 and cohort 2. From the available 67,422 women Inclusion criteria: incident breast cancer cases in women at baseline aged 40‐59 years in cohort 1 and 40‐69 years in cohort 2, with no history of breast cancer, respondent to baseline questionnaire, not moved out of study area In Iwasaki 2010b: included data with available plasma tea polyphenol levels. Final population of 144 cases and 288 controls Parent cohorts Japan Public Health Center‐based Prospective Study (JPHC)‐I Japan Public Health Center‐based Prospective Study (JPHC)‐II Recruitment JPHC‐I: 1990 JPHC‐II: from 1993‐1994
Interventions	N/A
Outcomes	Number of cases Outcome assessment: 31 December 2006 in Iwasaki 2010a and 31 December 2002 in Iwasaki 2010b Breast cancer: 581 cases, based on baseline questionnaire data
Green tea in exposure categories	Exposure assessment: green tea intake at baseline Iwasaki 2010a Lowest exposure: < 1 cup/week Intermediate exposure 1: 1‐2 cups/week Intermediate exposure 2: 3‐4 cups/week Intermediate exposure 3: 1‐2 cups/d Intermediate exposure 4: 3‐4 cups/d Highest exposure: ≥ 5 cups/d Iwasaki 2010b Lowest exposure: < 1 cup/week Highest exposure: ≥ 5 cups/d
Notes	Iwasaki 2010a Funding: Grant‐in‐Aid for Scientific Research from Monbusho, the Japanese Ministry of Education, Science and Culture (N.11181101) Statistical methods: Cox proportional hazard regression Variables controlled in analysis: age, area (10 Public Health Centres), age at menarche, menopausal status at baseline, number of births, age at first birth, height, BMI, alcohol intake, smoking status, leisure time physical activity, exogenous hormone use, family history of breast cancer, oolong tea intake, black tea intake and coffee intake Variables controlled by matching: ‐ Iwasaki 2010b Funding: Grants‐in‐Aid for Cancer Research and for the Third Term Comprehensive Ten‐Year Strategy for Cancer Control from the Ministry of Health, Labour and Welfare of Japan and Grants‐in‐Aid for Scientific Research on Priority Areas (17015049) from the Ministry of Education, Culture, Sports, Science and Technology of Japan. Statistical methods: crude data analysis Variables controlled in analysis: crude data Variables controlled by matching: ‐ Data of parent study Iwasaki 2010a were used for breast cancer analysis including a larger population.