The study included a cohort of almost 80,000 participants in the Women’s Health Initiative Observational Study. This long-term national health study has followed a large group of women for decades. Women enrolled in the study complete yearly health questionnaires that scientists and clinicians across the country can access to investigate research related to health and disease.
Researchers found that 4,719 cases of invasive breast cancer were diagnosed among postmenopausal participants. Caffeine intake was based on self-reported frequency for daily caffeinated coffee and tea consumption reported in the study population.
Initial findings suggested that participants who consumed 2-3 daily cups of caffeinated coffee had a 12% higher risk of invasive breast cancer than nondrinkers. However, this analysis did not yet consider specific factors which are known to influence breast cancer risk. Demographic, lifestyle, and reproductive characteristics, including age, race, smoking status, body mass index, history of hormone therapy use, alcohol intake, and breast cancer subtype, were analysed to scrutinise this data further.
After accounting for all these factors, the research team determined no meaningful association between caffeine intake from coffee and tea and invasive breast cancer risk.