Table 4.

Multivariate-adjusted breast cancer HRs and 95% CIs by sleep category stratifying by menopause status (premenopausal/postmenopausal) and shift work (never/ever)

≤5 h6 h7 h *8 h≥9 h
Menopause status
Premenopausal (n = 28,045)0.74 (0.39-1.41)1.05 (0.82-1.33)1.000.93 (0.73-1.19)0.92 (0.57-1.47)
Person-years (no. cases)6,205 (11)43,381 (106)79,660 (192)44,204 (102)8,574 (20)
Postmenopausal (n = 44,038)0.97 (0.82-1.14)0.97 (0.89-1.06)1.001.07 (0.99-1.16)0.96 (0.81-1.13)
Person-years (no. cases)42,425 (157)233,801 (893)371,575 (1-487)213,286 (921)42,088 (162)
Rotating night-shift work ,
Never (n = 28,066)0.83 (0.60-1.13)0.99 (0.87-1.13)1.000.96 (0.85-1.10)0.85 (0.65-1.11)
Person-years (no. cases)21,661 (65)131,891 (447)225,181 (805)131,408 (455)26,015 (84)
Ever (n = 41,308)0.98 (0.80-1.20)1.00 (0.90-1.11)1.001.13 (1.02-1.25)0.99 (0.81-1.23)
Person-years (no. cases)30,761 (109)163,840 (604)253,949 (947)140,936 (602)27,434 (105)
  • NOTE: All models adjusted for age, body mass index, height, history of benign breast disease, family history of breast cancer, parity and age at first birth, age at menarche, age at menopause, postmenopausal hormone use, physical activity, alcohol and caloric intake, and smoking.

  • * Reference category.

  • Likelihood ratio tests for interaction between menopause status and sleep duration, P = 0.72; between shift work and sleep duration, P = 0.22.

  • Models additionally adjusted for menopause status.