Table 2.

Age and age-standardized characteristics of 132 participants from the NHS2 stratified by work schedule and compared with full cohort of n = 90,051 women participating in NHS2 (2005)

Characteristics/lifestyle covariatesValidation subgroup (n = 132)Full NHS2 cohort (n = 90,051)
Day worker (n = 47)Night worker (n = 85)Never or past night workerCurrent night worker
(n = 68,350)(n = 21,701)
Age, mean (SD), y48.3 (4.4)47.0 (5.0)c48.5 (4.7)48.2 (4.7)d
BMI, mean (SD), kg/m225.8 (5.3)28.2 (7.1)d26.3 (7.0)27.5 (7.2)d
Alcohol consumption, mean (SD), g6.6 (11.2)3.3 (5.6)d5.7 (9.6)4.7 (8.5)d
Current smokers, %1.82.5c7.315.9d
Premenopausal, %54.560.3c45.343.0
Number of years worked rotating night shifts, mean (SD)6.9 (6.7)c10.7 (6.0)c, d4.1 (3.7)5.8 (5.0)d
Paritya, mean (SD)2.0 (0.9)2.0 (0.9)2.1 (0.9)2.1 (0.9)
Exercise, mean (SD), METsa23.9 (20.9)25.7 (30.6)23.2 (29.5)22.7 (30.5)
Chronotypeb
 Definite morning type, %21.321.2NANA
 Probable morning type, %46.832.9NANA
 Probable evening type, %21.327.1NANA
 Definite evening type, %10.617.7NANA
 HO scores, mean (SD)53.2 (12.8)55.2 (9.7)NANA

Abbreviation: MET, metabolic equivalents.

  • aAmong parous women only.

  • bHorne–Ostberg (HO) scores only available from a subgroup of women (11 day workers, 71 night workers).

  • cDifference in frequency (χ2 test) or mean (t test) statistically significant between day and night workers, respectively, comparing the validation subgroup with the full cohort, P < 0.05.

  • dDifference in frequency (χ2 test) or mean (t test) statistically significant between day and night worker groups, P < 0.05.