Table 2

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

Reference. Country, state	Study design	Breast cancer cases	Study population	Primary exposure	Sources of primary exposure information	Non-day time exposure definition	Reference group	Reported exposed categories
Tynes et al,⁸ Norway	Nested case-control	50	Female naval radio-telegraph operators	Light at night, radio frequency fields, low frequency fields	Database 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 researcher	Frequent present in radio room both at night and during the day	No shift work	Age <50, < 3.1 yrs Age <50, ≥ 3.1 yrs Age ≥50,< 3.1 yrs Age ≥50,≥ 3.1 yrs
Hansen,¹⁰ Denmark	Population based nested case-control	7035	Female employees	Night work	Job 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 schedules	Working in trades where less than 40% of survey responders had nighttime schedules	Overall > 6 years
Davis et al,⁶ USA	Case-control	763	Females	Light at night: sleep habits, bedroom lightning, shift work	In-person interview of all jobs held for 6 months or longer	Graveyard shift: beginning work after 19:00 and leaving work before 9:00	Never 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 USA	Prospective cohort	2441	Nurses participating in Nurses Health Study I	Night work as a surrogate of light at night	Postal questionnaire in 1988	Rotating 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 USA	Prospective cohort	1352	Nurses participating in Nurses Health Study II	Rotating night shift work	Postal 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 Norway	Nested case-control	537	Nurses	Night work	Job exposure matrix based on information from the Norwegian board of Health's registry on nurses and censuses from 1960, 1970 and 1980	Nurses 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 Sweden	Retrospectiv cohort	70	Female participants from censuses in 1960 and 1970	Shift workers	Job exposure matrix based on survey (1977–1981) and occupational information from census	Occupation-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 week	Occupation- 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 Germany	Population based case-control	892	Gene Environment Interaction and Breast Cancer (GENICA) participants	Night shift work	Personal interview of occupational history. Subsequent telephone interviews on shift work	Working the full-time period between 24.00 and 05:00 h (ILO definition) for at least 1 year	Ever 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 USA	Case-control	487	Long Island Breast Cancer Study Project participants, who had lived in the same residence for 15 years or longer	Light-at-night exposure from shift work and at home	In-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