Fritschi L, et al. – This research inspected the proposition that women working during their biological night would be at increased risk of breast cancer. There was no variation between the new and old classifications of exposure. The total number of chronodisrupted shifts could not be estimated over a lifetime in order to assess dose. The number of women exposed to circadian disruption (CD) when doing shifts which began before midnight, could not be determined. Its practical application underscored the challenges for prospective chronobiology–based research.

Methods

• Data was cumulated from the case-control study of breast cancer to explore the correlations between shift work involving CD and breast cancer risks.
• Previously, the assumption was that everyone working in jobs which involved work for two or more shifts between midnight and 05:00 hours was equally exposed to CD.
• In the present analyses, reclassification was conducted as unexposed, those who had a late chronotype in which their preferred bedtime was 2 hours after the end of their shift.

Results

• 30 out of the 1385 night jobs changed the classification.
• The overall finding (OR 1.17, 95% CI 0.98 to 1.41) did not vary from the original finding when chronotype was not taken into account.