title: Night-shift work, sleep duration, daytime napping, and breast cancer risk.
abstract: OBJECTIVE
  Sleep habits vary among different countries, and sleep problems may cause various health problems. The aim of our study was to evaluate the separate and combined associations of night-shift work, sleep duration, and daytime napping with breast cancer risk among the Chinese population.
  
  
  METHODS
  This study conducted face-to-face interviews with 712 women diagnosed with incident invasive breast cancer before treatment and 742 age-matched controls. Information on sleep habits, demographic characteristics, and suspected or established risk factors of breast cancer were collected from the two groups. Multivariate logistic regression models were used to estimate the odds ratios (ORs) and 95% confidence intervals (CIs).
  
  
  RESULTS
  Night-shift work was associated with an increased risk of breast cancer [OR (95% CI): 1.34 (1.05-1.72)]. Compared to women with a sleep duration of 6.1-8.9 h/day, women who had shorter [(≤6.0 h/day) (OR (95% CI): 1.53 (1.10-2.12)] and longer (≥9.0 h/day) sleep duration [(OR (95% CI): 1.59 (1.17-2.17)] had an increased risk of breast cancer. In addition, daytime napping was associated with a reduced risk of breast cancer among night-shift workers [OR (95% CI): 0.57 (0.36-0.90)], but no association was found among women who never had night-shift work [OR (95% CI): 1.01 (0.75-1.35)] (P for interaction = 0.054). Night-shift work and longer sleep duration also synergistically increased breast cancer risk [OR (95% CI): 3.69 (1.94-7.02)] (P for interaction = 0.009).
  
  
  CONCLUSIONS
  Sleep problems, including night-shift work, and shorter and longer sleep duration, are associated with an increased breast cancer risk. In particular, the combined effects of night-shift work with no daytime napping or longer sleep duration are greater than the independent effects.
authors: The School of Public Health, Sun Yat-sen University, Guangzhou 510080, China.
authors: Pan
authors: P
authors: Wang
authors: The School of Public Health, Sun Yat-sen University, Guangzhou 510080, China.
authors: Fang-Mei
authors: FM
authors: Ren
authors: The First Affiliated Hospital, Sun Yat-sen University, Guangzhou 510080, China.
authors: Ying
authors: Y
authors: Lin
authors: The Second Affiliated Hospital, Sun Yat-sen University, Guangzhou 510120, China.
authors: Feng-Xi
authors: FX
authors: Su
authors: The Sun Yat-Sen University Cancer Center, Guangzhou 510080, China.
authors: Wei-Hua
authors: WH
authors: Jia
authors: School of Public Health and Primary Care, Faculty of Medicine, The Chinese University of Hong Kong, Hong Kong, China; CUHK Shenzhen Research Institute, Shenzhen, China.
authors: Xue-Fen
authors: XF
authors: Su
authors: The Third Affiliated Hospital, Sun Yat-sen University, Guangzhou 510630, China. Electronic address: tangly@mail.sysu.edu.cn.
authors: Lu-Ying
authors: LY
authors: Tang
authors: The School of Public Health, Sun Yat-sen University, Guangzhou 510080, China. Electronic address: renzef@mail.sysu.edu.cn.
authors: Ze-Fang
authors: ZF
authors: Ren
mesh_terms: D001943:Breast Neoplasms / Q000209:etiology*; D016022:Case-Control Studies; D005260:Female; D006801:Humans; D007407:Interviews as Topic; D016015:Logistic Models; D008875:Middle Aged; D012307:Risk Factors; D012890:Sleep / Q000502:physiology*; D013997:Time Factors; D014940:Work Schedule Tolerance
keywords: 24-h sleep duration; Breast cancer; Daytime napping; Interaction; Night-shift work