Article Figures & Data
Tables
- 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) Characteristics n (%) Mean (SD) n (%) Mean (SD) n (%) Mean (SD) Age,a y 49.0 (5.4) 48.1 (5.2) 50.0 (5.4) Menopausal status Pre 368 (57.5) 206 (64.0) 162 (51.0) Post 272 (42.5) 115 (36.0) 157 (49.0) Age at menopause (in postmenopausal),b y 49.3 (3.9) 48.8 (3.9) 49.6 (4.1) Age at menarche,b y 13.2 (1.5) 13.3 (1.4) 13.0 (1.6) Number of full-term births 0 76 (11.9) 39 (12.1) 37 (11.6) 1 215 (33.6) 101 (31.5) 114 (35.7) 2 313 (48.9) 156 (48.6) 157 (49.2) 3–4 36 (5.6) 25 (7.8) 11 (3.5) Age at first full-term birth (≥37 wk), y ≤24 319 (56.6) 159 (56.4) 160 (56.7) >24–<30 188 (33.3) 91 (32.3) 97 (34.4) ≥30 57 (10.1) 32 (11.3) 25 (8.9) Family history of breast cancerb No 587 (91.7) 292 (91.0) 295 (92.5) Yes 51 (8.0) 27 (8.4) 24 (7.5) BMI, kg/m2 27.2 (4.7) 27.1 (4.7) 27.2 (4.7) Smoking Current 188 (29.4) 106 (33.0) 82 (25.7) Past 173 (27.0) 77 (24.0) 96 (30.1) Nonsmokers 279 (43.6) 138 (43.0) 141 (44.2) Ever oral contraceptives or sex hormones use Yes 153 (23.9) 74 (23.0) 79 (24.8) No 487 (76.1) 247 (77.0) 240 (75.2) Calendar season of mammography Summer 135 (21.1) 63 (19.6) 72 (22.6) Autumn 251 (39.2) 129 (40.2) 122 (38.2) Winter 101 (15.8) 47 (14.6) 54 (16.9) Spring 153 (23.9) 82 (25.6) 71 (22.3) Total duration of the night shift work,a y ≤5 77 (12.0) 3 (0.9) 74 (23.2) >5–≤15 163 (25.5) 26 (8.1) 137 (43.0) >15–≤25 234 (36.6) 145 (45.2) 89 (27.9) >25 166 (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.
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↵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.
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- Table 2.
Percentage and absolute mammographic density by selected characteristics of the rotating night shift work
Night shift work characteristics n Percentage of mammographic density Adjusteda mean (95%CI) Absolute density, cm2 Adjusteda mean (95%CI) Current rotating night shift No 319 22.5 (20.8–24.3) 21.8 (19.4–24.3) Yes 321 23.6 (21.9–25.4) 23.9 (21.4–26.4) P 0.62 0.25 Total duration of night shift work, y ≤5 64 22.5 (18.8–26.1) 23.3 (17.8–28.8) >5–≤15 165 24.5 (22.1–27.0) 23.8 (20.3–27.2) >15–≤25 206 21.5 (19.4–23.7) 21.9 (18.8–24.9) >25 205 23.7 (21.4–26.0) 23.1 (20.0–26.2) Ptrend 0.93 0.78 Total number of hours of night shift work by tertilesb I 214 24.0 (21.8–26.1) 23.8 (20.7–26.9) II 214 22.3 (20.2–24.5) 22.5 (19.5–25.5) III 212 23.0 (20.7–25.2) 22.3 (19.3–25.4) Ptrend 0.49 0.49 Cumulative number of night shifts ≤999 185 23.8 (21.5–26.1) 23.6 (20.3–26.9) 1,000–1,999 225 22.5 (20.5–24.6) 22.9 (19.9–25.8) 2,000+ 230 23.1 (20.9–25.2) 22.3 (19.4–25.2) Ptrend 0.66 0.56 Average frequency (weighted by duration); no. of night shifts/mo ≤2 214 24.2 (22.0–26.3) 24.4 (21.3–27.5) >2–≤3.9 213 22.3 (20.3–24.4) 22.8 (19.8–25.8) >3.9 213 22.7 (20.6–24.8) 21.5 (18.6–24.4) Ptrend 0.33 0.18 Total duration of reported exposure to surgical lamp, y Day shifts (reference) 550 23.3 (21.9–24.6) 23.0 (21.1–24.9) >0–≤10 39 21.3 (16.8–25.9) 21.1 (14.3–27.8) >10 51 22.7 (18.4–26.9) 23.2 (17.1–29.4) Ptrend 0.61 0.92 - Table 3.
Percentage of mammographic density and absolute density by selected characteristics of the rotating night shift work
Current rotating night shift work characteristics n Percentage of density Adjusteda mean (95%CI) Absolute density, cm2 Adjusteda mean (95%CI) Current night shift work frequency per month Day shifts (reference) 319 22.5 (20.8–24.3) 21.8 (19.4–24.3) 2–7 nights 285 23.6 (21.8–25.5) 23.9 (21.2–26.5) 8+ nights 36 23.7 (18.4–29.0) 24.2 (16.7–31.7) P 0.40 0.27 Night shifts working hours,c h Day shifts (reference) 319 22.5 (20.7–24.2) 21.8 (19.4–24.2) <10 84 23.2 (19.9–26.5) 22.7 (18.0–27.4) ≥10–14 230 23.8 (21.7–25.9) 24.3 (21.3–27.3) P 0.34 0.20 Light at workc Day shifts (reference) 319 22.5 (20.7–24.2) 21.8 (19.4–24.2) Dim 139 23.0 (20.4–25.6) 23.0 (19.3–26.7) Full light 140 24.4 (21.8–27.1) 25.1 (21.2–28.9) Surgical lamp 35 22.8 (17.7–28.0) 22.8 (15.3–30.2) Ptrend 0.34 0.24 Activities at work during the night shiftc Day shifts (reference) 319 22.5 (20.7–24.2) 21.8 (19.4–24.2) 1b 23 26.8 (19.9–33.7) 25.4 (15.9–35.0) 1 and 2 or 2 221 23.1 (21.1–25.2) 23.3 (20.4–26.3) Any combination with 3 70 24.1 (20.4–27.8) 25.1 (19.6–30.6) Ptrend 0.43 0.24 -
↵aAdjustment for age, BMI, menopausal status, age at menopause, age at menarche, smoking, and season of the year.
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↵bCategories of the activities: 1, taking care of patients, injections, administering pills; 2, small interventions; and 3, assistance in operations (deliveries).
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↵cMissing information for 7 women.
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- Table 4.
Percentage and absolute mammographic density by morning MT6s levels
Morning MT6sb Q1 (n = 160) Q2 (n = 160) Q3 (n = 160) Q4 (n = 160) P Percent mammographic density [adjusteda mean (95%CI)] 22.6 (20.1–25.1) 23.1 (20.7–25.6) 23.2 (20.8–25.5) 23.4 (21.0–25.9) 0.65 Absolute density [adjusteda mean (95%CI)] 21.8 (18.3–25.2) 22.8 (19.3–26.2) 23.0 (19.6–26.4) 23.9 (20.3–27.4) 0.42
Additional Files
Supplementary Data
Files in this Data Supplement:
- Supplementary Tables 1 - 3 - PDF file, 86KB, Supplemental table 1. Percent mammographic density and absolute density by selected characteristics of rotating night shift work by menopausal status. Supplemental table 2. Percent mammographic density and absolute density by selected characteristics of current rotating night shift work by menopausal status. Supplemental table 3. Adjusted means of percent density and absolute density according to the quartiles of urinary MT6s levels.