Table 2

Shift work history and breast cancer risk

Years shift work history*CasesControlsOR95% CIInteraction by menopausal status
n (%)n (%)
Overall†
 None751 (66.2)773 (65.6)
 0–14283 (25.0)312 (26.5)0.950.79 to 1.16p=0.01
 15–2972 (6.3)81 (6.9)0.930.67 to 1.30p=0.7
 ≥3028 (2.5)13 (1.1)2.211.14 to 4.31p=0.2
p-trend=0.5
Postmenopausal‡
 None531 (71.5)501 (68.3)
 0–14142 (19.1)175 (23.8)0.750.58 to 0.97
 15–2948 (6.5)46 (6.3)0.970.63 to 1.49
 ≥3022 (3.0)12 (1.6)1.630.80 to 3.35
p-trend=0.8
Premenopausal‡
 None220 (56.3)272 (61.1)
 0–9126 (32.2)119 (26.7)1.320.97 to 1.80
 10–1927 (6.9)35 (7.9)0.990.57 to 1.70
 ≥2018 (4.6)19 (4.3)1.300.66 to 2.58
p-trend=0.3
Health occupations
 None62 (44.9)94 (5.0)
 0–1438 (27.5)72 (34.4)0.800.48 to 1.33
 15–2926 (18.8)37 (17.7)1.060.58 to 1.92
 ≥3012 (8.7)6 (2.9)3.111.10 to 8.77
Non-health occupations
 None689 (69.2)679 (70.0)
 0–14245 (24.6)240 (24.7)1.040.84 to 1.29
 15–2946 (4.6)44 (4.5)1.060.69 to 1.62
 ≥3016 (1.6)7 (0.7)2.250.92 to 5.52
  • *Using 50% of time definition.

  • †Model adjusted for age and centre.

  • ‡Model adjusted for age, centre and BMI.