Sleep duration and breast cancer risk in the Breast Cancer Detection Demonstration Project follow-up cohort

Background: Short sleep has been hypothesised to increase the risk of breast cancer. However, little is known about the association between sleep and different subtypes of breast cancer defined by hormone receptor status. Methods: Among 40013 women in the Breast Cancer Detection Demonstration Project, including 1846 incident breast cancer cases, we prospectively examined self-reported weekday and weekend sleep duration in relation to breast cancer risk. We used multivariate Cox proportional hazards regression models to estimate relative risks (RRs) and 95% confidence intervals (CIs). Results: We found no association between sleep and overall breast cancer. However, we observed a decreased risk of ER+PR+ breast cancer (RR (<6) (vs) (8-9h) (95% CI): 0.54 (0.31, 0.93), P for trend, 0.003) with shorter sleep duration. Conclusions: Our finding does not support an association between sleep duration and overall breast cancer risk. However, the effect of sleep on different subtypes of breast cancer deserves further investigation.