Table 1 Cohort studies of night work and breast cancer

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)