Table 1. Selected characteristics of the study population of pre- and postmenopausal women by system of work
Characteristics Premenopausal women N = 388 Postmenopausal women N = 269
Day shifts N = 170
Rotating night shifts N = 218
p-diff Day shifts N = 160 Rotating night shifts N = 109 p-diff Parity (%) Yes No 92 8 91 9 0.846 94 6 94 6 1.000 Breastfeeding (%) Yes No 73 27 71 29 0.704 63 37 65 35 0.806
Age at menarche (years), mean (SD) 14.8 (4.0) 14.5 (4.3) 0.484 14.1 (3.2) 14.9 (4.7) 0.103
Age at menopause (years), mean (SD) 49.5 (4.1) 48.7 (3.9) 0.083
Age at first full-term birth, mean (SD) 24.5 (3.1) 24.7 (3.9) 0.632 25.0 (3.4) 25.1 (4.2) 0.902 Current use of steroid medications
or oral contraceptives (%) Yes No 12 88 13 87 0.869 7 93 5 95 0.602
Menstrual cycle stage (%) Follicular phase Other phase 40 60 41 59 0.880
Family history of breast cancer (%) Yes No 5 95 8 92 0.425 9 91 10 90 1.000 BMI (kg/m2), mean (SD) 26.7 (4.4) 26.1 (4.1) 0.157 27.8 (5.1) 28.9 (5.0) 0.080
Smoking 24 h before blood sample collection (%) Yes No 22 78 31 69 0.068 32 68 43 57 0.084 Smoking status (%) Current Past Non-smoker 22 31 47 31 23 46 0.112 32 31 37 40 24 36 0.333
Average alcohol consumption (drinks per week),
mean (SD) 0.7 (0.9) 0.6 (0.8) 0.189 0.5 (0.6) 0.5 (0.5) 0.810
Alcohol consumption 24 h before blood sample collection (%) Yes No 21 79 3 97 <0.001 16 84 1 99 <0.001 Coffee consumption (%) < 1per week 1-6 per week daily 17 9 74 13 4 83 0.049 20 9 71 13 8 79 0.274
Quality of sleep, PSQI (score), mean (SD) 6.0 (3.3) 6.1 (2.9) 0.861 7.5 (3.7) 6.8 (3.0) 0.104
Age (years), mean (SD) 46.4 (3.8) 45.6 (3.9) 0.050 54.1 (3.5) 53.1 (3.5) 0.027
Season when blood sample was collected (%) October-June July-September 90 10 89 11 0.993 86 14 77 23 0.076
