title: Work at night and breast cancer--report on evidence-based options for preventive actions.
abstract: In 2007, the International Agency for Research on Cancer classified shift work involving circadian disruption         as probably carcinogenic to humans (group 2A), primarily based on experimental and epidemiologic evidence for breast         cancer. In order to examine options for evidence-based preventive actions, 16 researchers in basic, epidemiological and         applied sciences convened at a workshop in Copenhagen 26-27 October 2011. This paper summarizes the evidence from         epidemiological and experimental studies and presents possible recommendations for prevention of the effects of night         work on breast cancer. Among those studies that quantified duration of shift work, there were statistically significant         elevations in risk only after about 20 years working night shift. It is unclear from these studies whether or not there         is a modest but real elevated risk for shorter durations. Hence, restriction of the total number of years working night         shift could be one future preventive recommendation for shift workers. The diurnal secretion of melatonin by the pineal         gland with peak in secretory activity during the night is a good biochemical marker of the circadian rhythm. Disruption         of the diurnal melatonin secretion pattern can be diminished by restricting the number of consecutive night shifts.         Reddish light and reduced light intensity during work at night could potentially help diminish the inhibitory activity         of light with strong intensity on the melatonin secretion, but further mechanistic insight is needed before definite         recommendations can be made. Earlier or more intensive mammography screening among female night shift worker is not         recommended because the harm-benefit ratio in this age group may not be beneficial. Preventive effects of         melatonin supplementation on breast cancer risk have not been clearly documented, but may be a promising avenue if a         lack of side effects can be shown even after long-term ingestion. Women with previous or current breast cancer should         be advised not to work night shifts because of strong experimental evidence demonstrating accelerated tumor growth by         suppression of melatonin secretion. Work during the night is widespread worldwide. To provide additional evidence-based         recommendations on prevention of diseases related to night shift work, large studies on the impact of various shift         schedules and type of light on circadian rhythms need to be conducted in real work environments.
authors.affiliation: Department of Occupational and Environmental Medicine, Bispebjerg University Hospital, Bispebjerg Bakke 23, DK-2400 Copenhagen NV, Denmark. jpb@bbh.regionh.dk
authors.forename: Jens Peter
authors.initials: JP
authors.lastname: Bonde
authors.forename: Johnni
authors.initials: J
authors.lastname: Hansen
authors.forename: Henrik Albert
authors.initials: HA
authors.lastname: Kolstad
authors.forename: Sigurd
authors.initials: S
authors.lastname: Mikkelsen
authors.forename: Jørgen H
authors.initials: JH
authors.lastname: Olsen
authors.forename: David E
authors.initials: DE
authors.lastname: Blask
authors.forename: Mikko
authors.initials: M
authors.lastname: Härmä
authors.forename: Helge
authors.initials: H
authors.lastname: Kjuus
authors.forename: Harry J
authors.initials: HJ
authors.lastname: de Koning
authors.forename: Jørn
authors.initials: J
authors.lastname: Olsen
authors.forename: Morten
authors.initials: M
authors.lastname: Møller
authors.forename: Eva S
authors.initials: ES
authors.lastname: Schernhammer
authors.forename: Richard G
authors.initials: RG
authors.lastname: Stevens
authors.forename: Torbjörn
authors.initials: T
authors.lastname: Åkerstedt
mesh_terms: D001943:Breast Neoplasms / Q000517:prevention & control*; D019317:Evidence-Based Medicine; D005260:Female; D006801:Humans