Table 1.

Descriptive characteristics of Shift Worker Study participants according to work shift status

Day shiftNight shift
CovariateN (%a)N (%a)
Age group,b y
20–2520 (13)25 (14)
26–3025 (16)31 (18)
31–3525 (16)34 (20)
36–4039 (26)37 (22)
41–4541 (27)42 (24)
46–50c1 (1)3 (2)
BMI, kg/m2
<2238 (25)34 (20)
22–2679 (52)77 (45)
26–3033 (22)59 (34)
>301 (1)2 (1)
Pregnancies
None75 (50)89 (52)
1–258 (38)55 (32)
≥318 (12)28 (16)
Alcohol consumptiond
Any45 (30)52 (30)
Number of drinks
 0108 (72)125 (73)
 124 (16)17 (10)
 212 (8)10 (6)
 ≥37 (5)20 (12)
Tobacco use (any)d
Cigarettes10 (7)16 (9)
Other tobacco or nicotine productse1 (1)1 (1)
Medication use (any)d
Psychotherapeutics20 (13)16 (9)
Sedatives2 (1)1 (1)
β-Blockers2 (1)3 (2)
Thyroid medications11 (7)11 (6)
Steroids7 (5)7 (4)
Antidiabetics1 (1)2 (1)
Narcotics3 (2)0 (0)
Ovulation
Nof26 (17)23 (13)
Yes125 (83)149 (87)
  • aPercentage calculated from 151 day shift participants and 172 night shift participants, respectively.

  • bCalculated according to date of first urine collection.

  • cThree participants were aged 46 years and one participant was aged 49 years.

  • dIn the 24 hours ending the nighttime sleep period.

  • eSuch as a nicotine skin patch or gum.

  • fAs indicated by an algorithm using the PDG assay and luteal phase length (see text).