Table 2.

Night-shift work duration and colorectal cancer risk according to tumor IRS1 and IRS2 expression status in the NHS.

Night-shift work duration
Never1–14 years≥15 yearsPtrendaPheterogeneityb
Total colorectal cancer in the full cohorts
 No. cases (N = 1,397)536718143
 Age-adjusted HR (95% CI)1 (ref)1.01 (0.90–1.13)1.28 (1.06–1.54)0.008
 Multivariable HR (95% CI)c1 (ref)1.01 (0.90–1.13)1.20 (0.99–1.45)0.06
Total colorectal cancer among women with IRS1 data
 No. cases (N = 304)12214636
 Age-adjusted HR (95% CI)1 (ref)0.91 (0.71–1.16)1.42 (0.97–2.06)0.05
 Multivariable HR (95% CI)c1 (ref)0.90 (0.70–1.14)1.31 (0.89–1.91)0.13
IRS1
 Negative/weak
  No. cases (N = 218)9010523
  Age-adjusted HR (95% CI)1 (ref)0.88 (0.66–1.17)1.23 (0.77–1.94)0.360.02
  Multivariable HR (95% CI)c1 (ref)0.87 (0.65–1.15)1.13 (0.71–1.80)0.560.02
 Moderate/intense
  No. cases (N = 86)324113
  Age-adjusted HR (95% CI)1 (ref)0.98 (0.62–1.56)1.96 (1.02–3.77)0.03
  Multivariable HR (95% CI)c1 (ref)0.97 (0.61–1.54)1.81 (0.94–3.48)0.06
Total colorectal cancer among women with IRS2 data
 No. cases (N = 308)11915336
 Age-adjusted HR (95% CI)1 (ref)0.98 (0.77–1.25)1.46 (1.00–2.13)0.04
 Multivariable HR (95% CI)c1 (ref)0.97 (0.76–1.23)1.35 (0.92–1.97)0.11
IRS2
 Negative/weak
  No. cases (N = 206)909818
  Age-adjusted HR (95% CI)1 (ref)0.83 (0.62–1.11)0.98 (0.59–1.63)0.950.008
  Multivariable HR (95% CI)c1 (ref)0.83 (0.62–1.10)0.90 (0.54–1.51)0.720.008
 Moderate/intense
  No. cases (N = 102)295518
  Age-adjusted HR (95% CI)1 (ref)1.46 (0.93–2.29)2.92 (1.61–5.30)0.0004
  Multivariable HR (95% CI)c1 (ref)1.42 (0.90–2.22)2.69 (1.48–4.89)0.001
  • Note: Duplication-method Cox proportional cause-specific hazards regression for competing risks data was used to compute HRs and 95% CIs. All analyses were stratified by age (in month) and year of questionnaire return.

  • Abbreviation: No., number.

  • aLinear trend test using the median years of each category.

  • bThe likelihood ratio test was used to test for the heterogeneity of the associations between night-shift work duration (median) and colorectal cancer risk according to the expression of IRS1 and IRS2 (ordinal).

  • cMultivariable HRs were adjusted for age (in month), adult BMI (<25, 25–<27.5, 27.5–<30, or ≥30 kg/m2), smoking (0, 1–10, or >10 pack-years), history of colorectal cancer in a parent or sibling (yes or no), history of sigmoidoscopy/colonoscopy (yes or no), postmenopausal status and hormone use (premenopause, postmenopause and never use hormone, postmenopause and current use hormone, postmenopause and past use hormone), physical activity (<3, 3–<27, ≥27 METs—hours/week), regular aspirin use (yes or no), alcohol consumption (0 –<5, 5–<15, or ≥15 g/day), total intake of vitamin D, folate, calcium, red meat and processed meat (all in tertiles), sleep duration (<6 h, 6–<7 h, 7–<8 h, 8–<9 h, or ≥9 h), and history of type II diabetes (yes or no).