Table 2

Characteristics of studies on breast cancer regarding definitions of non-day time work

Reference. Country, stateStudy designBreast cancer casesStudy populationPrimary exposureSources of primary exposure informationNon-day time exposure definitionReference groupReported exposed categories
Tynes et al,8 NorwayNested case-control50Female naval radio-telegraph operatorsLight at night, radio frequency fields, low frequency fieldsDatabase with job history on certified telegraph operators from Norwegian Telecom. Shift work and travel through time zones was assessed from job history by a shipping journalist and a researcherFrequent present in radio room both at night and during the dayNo shift work
  • Age <50, < 3.1 yrs

  • Age <50, ≥ 3.1 yrs

  • Age ≥50,< 3.1 yrs

  • Age ≥50,≥ 3.1 yrs

Hansen,10 DenmarkPopulation based nested case-control7035Female employeesNight workJob exposure matrix based on survey (1976) on working condition, linked to population registry (job title) and pension fund registry data (duration of employment since 1964 on company and trade level)Working at least half a year at least 5 years prior to reference date in trades where at least 60% of survey responders had nighttime schedulesWorking in trades where less than 40% of survey responders had nighttime schedulesOverall > 6 years
Davis et al,6 USACase-control763FemalesLight at night: sleep habits, bedroom lightning, shift workIn-person interview of all jobs held for 6 months or longerGraveyard shift: beginning work after 19:00 and leaving work before 9:00Never worked graveyard shift
  • Ever

  • Hours/week

  • Continuous

  • Quartiles (< 1.2,1.2–2.7,2.7–5.7, ,≥5.7 h per week)

  • At least one shift/week:

  • No. of years (continuous)

  • Median (<3, ,≥3 years)

Schernhammer,11 USAProspective cohort2441Nurses participating in Nurses Health Study INight work as a surrogate of light at nightPostal questionnaire in 1988Rotating night shifts: Years in total worked at least three nights per month in addition to days or evening in that month: never, 1–2, 3–5, 6–9, 10–14, 15–19, 20–29, ≥ 30 years.Never working on rotating night shifts
  • 1–14 years

  • 15–29 years

  • ,≥30 years

Schernhammer,12 USAProspective cohort1352Nurses participating in Nurses Health Study IIRotating night shift workPostal questionnaire in 1989 (baseline), updated in 1991, 1993 and 1997. Information obtained retrospectively in 2001 for the periods 1993–1995 and 1997–1999.Rotating night shifts: total months worked for at least three nights per month in addition to days or evening in that month: none, 1–4, 5–9, 10–14, 15–19, 20–29, >=20 months. Also information on permanent night shift for ≥6 month.Never working on rotating night shifts
  • 1–9 years

  • 10–19 years

  • ,≥20 years

Lie et al,14 NorwayNested case-control537NursesNight workJob exposure matrix based on information from the Norwegian board of Health's registry on nurses and censuses from 1960, 1970 and 1980Nurses working at infirmaries (hospitals)Other work sites than infirmaries
  • >0–14 years

  • 15–29 years

  • ,≥30 years

  • (all and at age <50 and ,≥ 50 years)

  • Disregarding 20 most recent years of exposure:

  • >0–4 years

  • 5–14 years

  • ,≥15 years

  • (all and at age <50 and ,≥ 50 years)

Schwartzbaum, et al,13 SwedenRetrospectiv cohort70Female participants from censuses in 1960 and 1970Shift workersJob exposure matrix based on survey (1977–1981) and occupational information from censusOccupation-industry combinations in which at least 40% of the workers had a rotating schedule with three or more possible shifts per day or had work hours during the night (any hour between 0100 and 0400) at least 1 day during the weekOccupation- industry combinations in which < 30% of the workers had shift work (as defined to the left)
  • Census in 1970

  • Census in 1960 and 1970

Pesch et al,7 GermanyPopulation based case-control892Gene Environment Interaction and Breast Cancer (GENICA) participantsNight shift workPersonal interview of occupational history. Subsequent telephone interviews on shift workWorking the full-time period between 24.00 and 05:00 h (ILO definition) for at least 1 yearEver employed, but never in shift work
  • Ever in shift work.

  • Ever in night shift work

  • Cumulative number of nights (< 1056 nights; ,≥ 1056 nights)

  • Duration of night shift work (>0–4 ,5–9,10–19, ,≥ 20 years)

  • Age at first night shift work (<20, 20–29, 30–39, ,≥40 years)

  • Years since last night shift work (>1–9, 10–19, ,≥20 years)

O'Leary et al,9 USACase-control487Long Island Breast Cancer Study Project participants, who had lived in the same residence for 15 years or longerLight-at-night exposure from shift work and at homeIn-home interview obtaining information on all jobs held for 6 months or longer for the last 15 years.Frequency (days per week, months or years) and type of shift work for each job: Evening work (starting afternoon and ending as late as 2:00) Overnight work (starting as early as 19:00. and continue until the following morning)Participants who had never held jobs involving shift work
  • Any shift work

  • Any evening shift

  • Evening shift only

  • Any overnight shift

  • Overnight shift only

  • Duration of shift work for respectively evening and overnight shifts based on median number among controls of years working in jobs with at least one shift per week