Shigesato M, et al. - Among 74,481 participants at risk for breast cancer, researchers assessed this risk in relation to sleep duration at cohort entry as well as in relation to the interaction of sleep duration with body mass index (BMI). Although sleep duration was not significantly related to breast cancer risk, they found higher risk estimates for short and long sleep vs normal sleep. Across categories of sleep duration (≤ 6, 7-8, ≥ 9 hours), similar risk estimates were reported for underweight, overweight, and obesity vs normal BMI-normal sleep group; this was observed when the combined sleep duration and BMI interaction impact was assessed. Lower breast cancer incidence was reported in the underweight-normal sleep group; raised breast cancer incidence was observed in the overweight-short sleep group, overweight-normal sleep group, and all obese women. Among obese women, 1.35, 1.27, and 1.46 were the estimated respective HRs for short, normal, and long sleep.