title: Characteristics of the Million Women Study participants who have and have not worked at         night.
abstract: OBJECTIVE
  The aim of this study was to compare the characteristics of women who had and had not worked at         night in terms of their risk factors for common disease, indicators of general health, social activities, employment,         and sleep behavior.
  
  
  METHODS
  The Million Women Study is a large prospective cohort study of women's health in the         United Kingdom with 1.3 million women recruited during 1996-2001 (aged 50-64 years) through 66 National         Health Service breast screening centers. We analyzed the data from a random sample of 41 652 participants who, in         2009-2010, reported their history of night work.
  
  
  RESULTS
  Of the participants, 1 in 8 women (13%) reported that         they had ever worked at night and 1 in 50 (2%) reported working at night for ≥20 years. For 33 sociodemographic,         behavioral, reproductive, and hormonal factors examined, 20 showed highly significant differences between         "ever" and "never" night workers (P<0.0001); 12 showed significant trends by duration of         night work (P<0.01). In particular, compared to women who had never worked at night, women who had worked at night         were more likely to (i) be of lower socioeconomic status [the odds ratio (OR) for ever versus never night workers of         being in the lowest third of socioeconomic status was 1.15, 99% confidence interval (95% CI) 1.06-1.25]; (ii)         have ever used hormone replacement therapy (HRT) for the menopause (OR 1.43, 99% CI 1.33-1.55); (iii) be current         smokers (OR 1.37, 99% CI 1.19-1.58); and (iv) be obese (OR 1.26, 99% CI 1.15-1.37). Compared to women who         had never worked at night, women who had worked at night for ≥20 years were more likely to be (i) of lower         socioeconomic status (OR 1.28, 99% CI 1.04-1.57); (ii) nulliparous (OR 1.47, 99% CI 1.12-1.91); (iii)         current smokers (OR 1.63, 99% CI 1.18-2.25); and (iv) obese (OR 1.55, 99% CI 1.25-1.93). Former night         workers were more likely than never night workers to report a range of sleep disturbances, including poor quality of         sleep (OR 1.15, 99% CI 1.01-1.31) and having to take medication to sleep (OR 1.35, 99% CI 1.15-1.60).
  
  
  CONCLUSIONS
  Women who reported having worked at night were substantially different from those who reporting never         having worked at night and many of the differences would put "ever night workers" at increased risks of         cancer, vascular disease, and many other common conditions.
authors: Cancer Epidemiology Unit, University of Oxford, Oxford OX3 7L, United Kingdom.
authors: Xiao-Si
authors: XS
authors: Wang
authors: Ruth C
authors: RC
authors: Travis
authors: Gillian
authors: G
authors: Reeves
authors: Jane
authors: J
authors: Green
authors: Naomi E
authors: NE
authors: Allen
authors: Tim J
authors: TJ
authors: Key
authors: Andrew W
authors: AW
authors: Roddam
authors: Valerie
authors: V
authors: Beral
mesh_terms: D000886:Anthropometry; D005260:Female; D006801:Humans; D008019:Life Style; D008875:Middle Aged; D011446:Prospective Studies; D006113:United Kingdom; D014940:Work Schedule Tolerance