Table 5 Comparison of night shift work characteristics of the Nurses’ Health Study I and II to the Nightingale Study data
Study (name, country) | Participation rate baseline questionnaire (%) | N baseline | Mean age (range) at baseline | Follow-up period and identification of incident breast cancer cases | Night shift work definition and data collection | Lifetime duration of having worked night shifts (in years) among women unaffectedwith breast cancer at baseline | ||
|---|---|---|---|---|---|---|---|---|
|  | Years on rotating night shift | Nurses’ Health study | Nightingale Study dataa | |||||
Schernhammer et al. 2001 [21] (Nurses’ Health Study I, USA) | Baseline questionnaire in 1976 had 71% response rate. 85% of those responded to the 6th biennial-mailed questionnaire in 1988 which included an item on night shift work | 1988: N=103,613 of which 85,197 answered shift work question of which 78,562 were unaffected with cancer | 54.3 (43–67) years [43] | 1988-1998; every two years, cohort members receive a follow-up questionnaire with questions about diseases and health-related topics; breast cancer confirmed through medical records | Ever having worked rotating nights shifts with at least three nights per month in addition to day or evening shifts in that month (answer in 8 prespecified categories: never, 1–2, 3–5, 6–9, 10–14, 15–19, 20–29, ≥30 years); unclear whether night shift work was updated in biennial questionnaires after 1988 | Never | 31,761 (40%) | 10,480 (20%) |
Ever | 46,801 (60%) | 43,116 (80%) | ||||||
1–14 years | 40,993 (88%) | 20,440 (69%) | ||||||
15–29 years | 4,426 (9%) | 7,612 (26%) | ||||||
|  |  |  |  |  |  | ≥30 years | 1,382 (3%) | 1,312 (5%) |
Schernhammer et al. 2006 [22] (Nurses’ Health Study II, USA) | 1989: N=116,671; 116,087 (99.5%) answered night work items; 115,022 unaffected with cancer | 34.3 (25–43) years [43] | 1989-2001; every two years, cohort members receive a follow-up questionnaire with questions about diseases and health-related topics; breast cancer confirmed through medical records | Ever having worked rotating nights shifts with at least three nights per month in addition to day or evening shifts in that month (answer in 8 prespecified categories: never, 1–4, 5–9, 10–14, 15–19, ≥20 months). Shift work information was updated in 1991, 1993, 1997, and 2001. In the 2001 questionnaire the night shift work item included rotating night shifts as before and permanent night shifts for 6 or more months | Never | 35,153 (31%) | 10,480 (20%) | |
Ever | 78,063 (69%) | 43,116 (80%) | ||||||
1–9 years | 70,773 (91%) | 14,569 (50%) | ||||||
10–19 years | 6,759 (9%) | 9,338 (32%) | ||||||
|  |  |  |  |  |  | ≥20 years | 531 (<1%) | 5,457 (18%) |