Objective: Numerous mechanisms for the effects of coffee, tea and caffeine on the risk of breast cancer have been suggested. Caffeine intake has already been associated with high plasma levels of female hormones, but associations have not been clearly demonstrated in epidemiological studies.
Design: We examined prospectively the association of coffee, tea and caffeine consumption with breast cancer risk in a French cohort study.
Setting: Dietary information was obtained from a 208-item diet history questionnaire self-administered in 1993-1995. Multivariable Cox proportional hazards regression models were used to estimate hazards ratios and 95 % confidence intervals.
Subjects: The study was conducted on 67 703 women with available dietary information. During a median follow-up of 11 years, 2868 breast cancer cases were diagnosed.
Results: Median intake was 280 ml/d (2·2 cups/d) for coffee and 214 ml/d (1·7 cups/d) for tea. Median caffeine intake was 164 mg/d. No association was found between consumption of coffee, tea or caffeine and breast cancer risk. Sub-analyses by tumour receptor status, menopausal status, type of coffee (regular or decaffeinated) and meals at which beverages were drunk led to the same conclusion.
Conclusions: Results from this prospective study showed no relationship between coffee, tea or caffeine intake and breast cancer risk overall or by hormone receptor status.