Table 1.

Selected characteristics of the nurses and midwives with screening mammography in the cross-sectional study

Total population (n = 640)Rotating nights (n = 321)Day shifts (n = 319)
Characteristicsn (%)Mean (SD)n (%)Mean (SD)n (%)Mean (SD)
Age,a y49.0 (5.4)48.1 (5.2)50.0 (5.4)
Menopausal status
 Pre368 (57.5)206 (64.0)162 (51.0)
 Post272 (42.5)115 (36.0)157 (49.0)
Age at menopause (in postmenopausal),b y49.3 (3.9)48.8 (3.9)49.6 (4.1)
Age at menarche,b y13.2 (1.5)13.3 (1.4)13.0 (1.6)
Number of full-term births
 076 (11.9)39 (12.1)37 (11.6)
 1215 (33.6)101 (31.5)114 (35.7)
 2313 (48.9)156 (48.6)157 (49.2)
 3–436 (5.6)25 (7.8)11 (3.5)
Age at first full-term birth (≥37 wk), y
 ≤24319 (56.6)159 (56.4)160 (56.7)
 >24–<30188 (33.3)91 (32.3)97 (34.4)
 ≥3057 (10.1)32 (11.3)25 (8.9)
Family history of breast cancerb
 No587 (91.7)292 (91.0)295 (92.5)
 Yes51 (8.0)27 (8.4)24 (7.5)
BMI, kg/m227.2 (4.7)27.1 (4.7)27.2 (4.7)
Smoking
 Current188 (29.4)106 (33.0)82 (25.7)
 Past173 (27.0)77 (24.0)96 (30.1)
 Nonsmokers279 (43.6)138 (43.0)141 (44.2)
Ever oral contraceptives or sex hormones use
 Yes153 (23.9)74 (23.0)79 (24.8)
 No487 (76.1)247 (77.0)240 (75.2)
Calendar season of mammography
 Summer135 (21.1)63 (19.6)72 (22.6)
 Autumn251 (39.2)129 (40.2)122 (38.2)
 Winter101 (15.8)47 (14.6)54 (16.9)
 Spring153 (23.9)82 (25.6)71 (22.3)
Total duration of the night shift work,a y
 ≤577 (12.0)3 (0.9)74 (23.2)
 >5–≤15163 (25.5)26 (8.1)137 (43.0)
 >15–≤25234 (36.6)145 (45.2)89 (27.9)
 >25166 (25.9)147 (45.8)19 (5.9)
Arithmetic mean − percentage of mammographic density (SD)23.2 (20.0)24.5 (20.4)22.0 (19.6)
Arithmetic mean − absolute area dense, cm2 (SD)28.1 (26.9)30.0 (28.4)26.2 (25.2)
  • aP < 0.05 for the difference in means between the current rotating night shift nurses and non-shift nurses.

  • bMissing information for age at menopause in one person with rotating night shifts and one person on day shift; age at menarche, one night shift and two day shifts; family history was missing on 2 nurses working rotating night shifts.