Caffeine intake from coffee and tea and invasive breast cancer incidence among postmenopausal women in the Women's Health Initiative

Research findings remain inconsistent whether caffeine consumption is associated with invasive breast cancer. We aimed to examine the association between caffeine intake from coffee and tea and incident invasive breast cancer among postmenopausal women. We included 79 871 participants in the Women's Health Initiative Observational Study in the current analysis. Incident invasive breast cancers were identified through September 30, 2015. Caffeine intake (mg/day) from caffeinated and decaffeinated coffee and tea was estimated based on self-reported frequency (cups/day) and average caffeine amount in each beverage. Cox proportional hazards regression models were used to estimate hazard ratios (HRs) and 95% confidence intervals (CIs). Subgroup analyses were conducted to explore whether associations of caffeine intake from coffee and tea with invasive breast cancer were different by age, race and ethnicity, smoking status, body mass index, history of hormone therapy use, alcohol intake and subtypes of breast cancer. During a median follow-up of 16.0 years, 4719 incident invasive breast cancers were identified. No significant association was found between caffeine intake from coffee and tea and invasive breast cancer incidence after adjusting for demographic, lifestyle and reproductive factors: HRs (95% CIs) for increasing quartiles of caffeine intake compared to the lowest were 1.03 (0.94, 1.12), 1.04 (0.95, 1.13) and 1.03 (0.94, 1.13), respectively (P-for-trend =.54). No significant associations of coffee and tea intake (cups/day) with overall breast cancer risk were found. Our findings are consistent with others showing no clear association of caffeine consumption with invasive breast cancer among postmenopausal women.