Table 1.

Description of the study population

Day workers (N = 147)Shift workers (N = 114)
Variablen (%)n (%)Pa
Age, y45.1 Embedded Image 9.640.6 Embedded Image11.9<0.01
Number of full-term births1.6 Embedded Image1.21.2 Embedded Image 1.2<0.01
Menopausal status
 Pre92 (62.6)73 (64.0)
 Post55 (37.4)41 (36.0)0.8
Age at first birth
 Nulliparous38 (25.9)49 (43.0)
 ≤2957 (38.8)32 (28.1)
 ≥2952 (35.4)33 (29.0)0.01
Chronotype (MSFb)3.29 Embedded Image0.93.6 Embedded Image 1.3
Body mass index27.0 Embedded Image 6.028.5 Embedded Image6.60.06
Current smoking status
 Smoker19 (12.9)6 (5.3)
 Non-smoker128 (87.1)108 (94.7)0.04
Current oral contraceptive use
 Yes18 (87.8)21 (18.6)
 No129 (12.2)92 (81.4)0.2
Current sleep aid use
 Yes19 (12.9)20 (17.5)
 No128 (87.1)94 (82.5)0.3
Hormone replacement therapy
 Yes14 (9.6)5 (4.5)
 No132 (90.4)107 (95.5)0.1
Employment category
 Nursing69 (46.9)98 (86.0)
 Other78 (53.1)16 (14.0)<0.01
Duration of cumulative shift
 work (years)7.9 Embedded Image 8.512.8 Embedded Image10.2<0.01
 0 Years36 (24.5)0 (0.0)
 <962 (42.2)52 (45.6)
 ≥949 (33.3)62 (54.4)<0.01
Number of consecutive night
 shifts2.7 Embedded Image 0.9
 <368 (59.6)
 ≥346 (40.4)
  • aThe P value for differences between day-only and rotating shift workers using the Wilcoxon rank-sum test for continuous variables and χ2 or Fischer's Exact tests for categorical variables.

  • bMid-sleep time using the Munich Chronotype Questionnaire.