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Carcinogenesis Advance Access published online on April 30, 2008
Carcinogenesis, doi:10.1093/carcin/bgn100
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© The Author 2008. Published by Oxford University Press. All rights reserved. For Permissions, please email: journals.permissions@oxfordjournals.org

Sleep duration, melatonin and breast cancer among Chinese women in Singapore

Anna H. Wu, Renwei Wang, Woon-Puay Koh, Frank C. Stanczyk, Hin-Peng Lee and Mimi C. Yu

Affiliations of authors: A.H.Wu, Department of Preventive Medicine; F.Z. Stanczyk, Department of Obstetrics and Gynecology, University of Southern California Keck School of Medicine, Los Angeles, California 90089. R.Wang, M.C. Yu, The Cancer Center, University of Minnesota, Minneapolis, MN 55455 W.P. Koh, H.P. Lee, National University of Singapore, Singapore

Correspondence: Dr. Anna H. Wu, Department of Preventive Medicine, University of Southern California, 1441 Eastlake Ave, Los Angeles, CA 90089. Ph: 323 865 0484 Fax: 323 865 0139. Email: annawu{at}usc.edu

Background: Sleep duration has been hypothesized to be inversely associated with breast cancer risk, possibly due to greater overall melatonin production in longer sleepers. However, data are inconclusive from the three studies conducted in Western populations on sleep duration and breast cancer risk.

Methods: We investigated the relationship between self-reported usual sleep duration determined at baseline and subsequent risk of breast cancer in the prospective, population-based cohort of the Singapore Chinese Health Study. We excluded from the study women with less than 2 years of follow up due to possible change in sleep pattern among breast cancer cases close to the time of diagnosis. Five hundred and twenty-five incident cases of breast cancer were identified among the remaining 33,528 women after up to 11 years of follow-up.

Results: Among women postmenopausal at baseline, breast cancer risk decreased with increasing sleep duration (P trend = 0.047); those who reported 9+ hours of sleep showed a RR of 0.67 (95% CI = 0.4-1.1) compared to women who reported <=6 hours of sleep. This inverse association was observed primarily in lean women (i.e., body mass index below the median value (23.2 kg/m2)) (P = 0.024). In this study population, irrespective of gender, urinary 6-sulfatoxymelatonin levels increased with increasing self-reported hours of sleep (P trend = 0.035) after adjustment for age and time of day of urine collection. Melatonin levels were 42% higher in those with 9+ vs those with 6 or fewer hours of sleep.

Conclusions: Sleep duration may influence breast cancer risk, possibly via its effect on melatonin levels.

Received December 17, 2007; revised April 18, 2008; accepted April 19, 2008.


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