Letter to the Editor, Re: Night-shift work and risk of breast cancer (Kamdar et al., doi:10.1007/s10549-013-2433-1)

摘要

The meta-analysis by Kamdar et al. [1] is misleading. The original reason for examining breast cancer in shift workers was based on the idea was that a non-day shift would increase risk of breast cancer by disruption of circadian rhythmicity, in particular diminished melatonin production which has anti-cancer properties. This is detailed in Stevens et al. [2]. Non-day shift includes any shift not confined to the time window of about 8 am to about 5 pm (i.e., day-work; mid-point of work schedule is noon), in other words, at least part of the work hours include the dark of night where the pineal melatonin secretion normally peaks. Kamdar et al. [1] purport to focus on 'night work' (apparently meaning 'graveyard' or about midnight to 8 am) yet included Schernhammer et al. [3, 4] and Hansen [5] which did not distinguish evening from graveyard shifts. Those studies that do make this distinction, however, should be included in any meta-analysis for both the evening-shift and night-shift portions of their results. Finally, the exposure, night-shift work, is defined differently in all the 15 included studies and is not defined at all in any of the included flight attendant studies. Further, duration of shift work not taking into account the number of such shifts (e.g. per week), is a poor proxy for dose.