Table 2

Risk of breast cancer in association with various aspects of night work in six separate models

Person-yearsCasesCrude HRAdjusted HR*
No night work107 20321611
Night work ever52 997830.77 (0.59–0.99)0.96 (0.74–1.23)
No night work107 20321611
1–3 years night work36 472570.78 (0.58–1.04)1.08 (0.80–1.44)
4–7 years night work15 707210.63 (0.39–0.97)0.65 (0.40–1.00)
8+ years night work81853.43 (1.18–7.95)2.80 (0.96–6.52)
No night work107 20321611
Risk per year of night work52 997830.96 (0.89–1.03)0.98 (0.92–1.05)
No night work107 20321611
Night work ever†52 997830.64 (0.40–0.98)1.04 (0.66–1.62)
Risk per year of night work1.07 (0.95–1.20)0.97 (0.86–1.09)
No night work107 20321611
Risk per 100 nights52 997831.00 (0.92–1.07)0.98 (0.91–1.05)
No night work107 20321611
Night work ever†52 997830.69 (0.50–0.93)1.01 (0.72–1.39)
Risk per 100 nights1.06 (0.97–1.15)0.98 (0.89–1.06)
  • *Adjusted for the time-dependent variables age and childbirth (up to the year of observation, yes/no) and the fixed variables profession and country of birth. Adjustment for year of follow-up is inherent in the analytical model.

  • †Adjustment for night work ever was made to disentangle the effect of working night as such and the quantity of night work, see the Methods section.