1. ¹Division of Epidemiology, Department of Public Health and Forensic Medicine, Tohoku University Graduate School of Medicine, Sendai, Japan
2. ²Division of Behavioral Medicine, Department of Functional Medical Science, Tohoku University Graduate School of Medicine, Sendai, Japan

Correspondence: M Kakizaki, Division of Epidemiology, Department of Public Health and Forensic Medicine, Tohoku University Graduate School of Medicine, 2-1 Seiryo-machi, Aoba-ku, Sendai, Miyagi 980-8575, Japan. E-mail: m-kaki@umin.ac.jp

Received 7 July 2008; Revised 29 August 2008; Accepted 1 September 2008; Published online 23 September 2008.

Abstract

In a prospective study of 23 995 Japanese women, short sleep duration was associated with higher risk of breast cancer (143 cases), compared with women who slept 7 h per day, the multivariate hazard ratio of those who slept 6 h per day was 1.62 (95% confidence interval: 1.05–2.50; P for trend=0.03).