Key 1999.

Study characteristics
Methods	Cohort study in Japan
Participants	Participants: 34,759 women from Hiroshima and Nagasaki Inclusion criteria: women (93,741) present in Hiroshima and Nagasaki at the time of the bombings and city residents on 1 October 1950 and residents (23,580) not present at the time of the bombings but present between 1950 and 1953. Data of women recruited in the 1st and 2nd mail surveys, alive on 1 September 1969 (survey 1) and alive in September 1979 (Hiroshima) and July 1979 (Nagasaki) Parental cohort: Radiation Effects Research Fundation's Life Span Study: final population of 34,765 women Recruitment: 1969‐1970 (survey 1) and 1979 (survey 2)
Interventions	N/A
Outcomes	Number of cases Outcome assessment: 31 December 1993 Breast cancer: 405/427 eligible cases (22 cases excluded due to missing data on green tea intake)
Green tea in exposure categories	Exposure assessment: hot green tea intake Lowest exposure: ≤ 1 time/d Intermediate exposure: 2‐4 times/d Highest exposure: ≥ 5 times/d
Notes	Funding: research performed at the Radiation Effects Research Foundation (RERF), Hiroshima and Nagasaki, Japan. RERF is funded equally by the Japanese Ministry of Health and Welfare and the USA Department of Energy (DOE) Department of Energy through the National Academy of Sciences, Japan Statistical methods: Poisson regression Variables controlled in analysis: age, calendar period, city, age at the time of the bombing and radiation dose Variables controlled by matching: ‐