Prospective study of breast cancer in relation to coffee, tea and caffeine in Sweden

Studies of coffee and tea consumption and caffeine intake as risk factors for breast cancer are inconclusive. We assessed coffee and tea consumption, caffeine intake, and possible confounding factors among 42,099 women from the Swedish Women's Lifestyle and Health study, the participants of which were aged 30–49 years at enrollment in 1991–1992. Complete follow‐up for breast cancer incidence was performed through 2012 via linkage to national registries. Poisson regression models were used to estimate relative risks (RRs) and 95% confidence intervals (CIs) for breast cancer. During follow‐up 1,395 breast cancers were diagnosed. The RR was 0.97 (95% CI 0.94–0.99) for a 1‐unit increase in cups of coffee/day, 1.14 (95% CI 1.05–1.24) for a 1‐unit increase in cups of tea/day, and 0.97 (95% CI 0.95–1.00) for a 100 mg/day increase in caffeine intake. Although the RR for no consumption (RR = 0.86, 95% CI 0.69–1.08), a group with a relatively small number of women, was not statistically significant, women with higher consumption had a decreased breast cancer risk (3–4 cups/day: RR = 0.87, 95% CI 0.76–1.00; ≥5 cups/day: RR = 0.81, 95% CI 0.70–0.94) compared to women consuming 1–2 cups of coffee/day. Compared to no consumption, women consuming >1 cups tea/day showed an increased breast cancer risk (RR = 1.19, 95% CI 1.00–1.42). Similar patterns of estimates were observed for breast cancer risk overall, during pre‐ and postmenopausal years, and for ER+ or PR+ breast cancer, but not for ER− and PR− breast cancer. Our findings suggest that coffee consumption and caffeine intake is negatively associated with the risk of overall and ER+/PR− breast cancer, and tea consumption is positively associated with the risk of overall and ER+/PR+ breast cancer. What's new? Coffee and tea are surpassed in global consumption only by water, suggesting that any association they might have with cancer is potentially of great magnitude. The present investigation assessed the relationship between coffee and tea consumption and breast cancer risk using data from the Swedish Women's Lifestyle and Health study. Analyses show that women who consumed ≥3 cups of coffee daily were at decreased risk of breast cancer, whereas women who consumed ≥1 cups of tea per day were at increased risk. Coffee may play a role in breast cancer prevention.