Purpose: Coffee, caffeinated tea, and caffeine have been suggested to play a role in breast carcinogenesis or in the promotion or inhibition of tumor growth. Prior epidemiologic evidence has not supported an overall association between consumption of caffeinated beverages and risk of breast cancer, but consumption in some studies was low.
Methods: We studied this relation in the Swedish Mammography Screening Cohort, a large population-based prospective cohort study in Sweden comprising 59,036 women aged 40-76 years. Sweden has the highest coffee consumption per capita in the world.
Results: During 508,267 person-years of follow-up, 1271 cases of invasive breast cancer were diagnosed. Women who reported drinking 4 or more cups of coffee per day had a covariate-adjusted hazard ratio of breast cancer of 0.94 [95% confidence interval (CI) 0.75-1.28] compared to women who reported drinking 1 cup a week or less. The corresponding hazard ratio for tea consumption was 1.13 (95% CI 0.91-1.40). Similarly, women in the highest quintile of self-reported caffeine intake had a hazard ratio of beast cancer of 1.04 (95% CI 0.87-1.24) compared to women in the lowest quintile.
Conclusions: In this large cohort of Swedish women, consumption of coffee, tea, and caffeine was not associated with breast cancer incidence.