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Table 1 Cohort studies of night work and breast cancer

From: The relationship between night work and breast cancer

Authors, (years) Country Study description Exposure assessment Exposure categories RR or HR
Schernhammer et al.
(2001) [13] USA
Prospective cohort study of 121,701 registered nurses, with
follow-up 1988–1998
Self-reported lifetime years on rotating night shifts, with
rotating night shifts defined as “at least three nights per month, in addition to evenings and afternoons in that month”
Never
1–15
15–29
≥ 30
P for trend
1.0 (ref)
1.08 (0.99–1.18)
1.08 (0.90–1.30)
1.36 (1.0–1.78)
0.02
Schernhammer et al.
(2006) [14] USA
Prospective cohort study of 116,087 registered nurses, with
follow-up 1989–2001
Self-reported lifetime years on rotating night shifts, with
rotating night shifts defined as “at least three nights per month, in addition to evenings and afternoons in that month”
Never
1–9
10–19
20+
P for trend
1.0
0.98 (0.87–1.10)
0.91 (0.72–1.16)
1.79 (1.06–3.01)
0.65
Schwartzbaum et al.
(2007) [15] Sweden
Register-based retrospective cohort study of 1,148,661 female workers, with
follow-up 1971–1989
Usual occupation and work hours (three-shift schedules and others) to define occupations with a large proportion of workers with night work; from in-person interviews in annual surveys of living conditions (1977–1981) Shift work in 1970
Shift work in both 1960 and 1970
0.94 (0.74–1.18)
0.97 (0.67–1.40)
Pronk et al. (2010) [18] China Shanghai Women’s Health Study: a population-based prospective cohort study Job exposure matrix of three categories with increasing scores for night-shift work:
0 = no night-shift work; 1 = incidental night-shift work; 2 = jobs likely to involve the night shift, 3 = jobs that probably involved all-night shifts
Never
1–5 years
6–17 years
18 years and more
1.0 (ref)
0.9 (0.6–1.3)
0.9 (0.6–1.4)
0.8 (0.5–1.2)
Knutsson et al.
(2012) [16] Sweden
WOLF (Work, Lipids, and Fibrinogen) occupational cohort study that included subjects who were employed in different public and private
companies (N = 4036), with
average follow-up time of 12.4 years
Questionnaire:
“Do you work shifts?” and “How many hours do you normally work per week, including overtime, and how are these hours distributed on average?”
Day
Shifts without nights
Shifts with nights
1.0 (ref)
1.23 (0.70–2.17)
2.02 (1.03–3.95)
Koppes et al. (2014) [19] Netherlands 14 Dutch Labor Force Surveys (1996–2009)
Record linkage with national registers on hospital admission
Current exposure to night work was assessed with the question: “Do you work at nights, meaning between midnight and 6 am?” No night work
Occasional
Regular
1.0 (ref)
1.04 (0.85–1.27)
0.87 (0.72–1.05)
Åkersted et al. (2015) [17] Sweden Cohort study of 13,656 women from the Swedish Twin Registry, with 3404 exposed to night work;
follow-up time of 12 years
Questionnaire:
“For how many years have you had working hours that meant that you worked nights at least now and then?”
Follow-up to 60 years  
No night work 1.0 (ref)
1–5 years 0.93 (0.66 to 1.31)
6–10 years 0.79 (0.45 to 1.38)
11–20 years 0.80 (0.45 to 1.42)
21–45 years 1.77 (1.03 to 3.04)
  1. RR Relative risk, HR Hazard ratio