Abstract: To keep pace with progressing urbanization organisms must cope with extensive habitat change. Anthropogenic light and noise have modified differences between day and night, and may thereby interfere with circadian clocks. Urbanized species, such as birds, are known to advance their activity to early morning and night hours. We hypothesized that such modified activity patterns are reflected by properties of the endogenous circadian clock. Using automatic radio-telemetry, we tested this idea by comparing activity patterns of free-living forest and city European blackbirds (Turdus merula). We then recaptured the same individuals and recorded their activity under constant conditions. City birds started their activity earlier and had faster but less robust circadian oscillation of locomotor activity than forest conspecifics. Circadian period length predicted start of activity in the field, and this relationship was mainly explained by fast-paced and early-rising city birds. Although based on only two populations, our findings point to links between city life, chronotype and circadian phenotype in songbirds, and potentially in other organisms that colonize urban habitats, and highlight that urban environments can significantly modify biologically important rhythms in wild organisms.

Abstract: BACKGROUND: Shift work causing circadian disruption is classified as a 'probable carcinogen' and may contribute to the pathogenesis of hormone-sensitive cancers. This study investigated shift work exposure in relation to epithelial ovarian cancer (EOC) risk. METHODS: In a population-based case-control study with 496 EOC cases and 906 controls, lifetime occupational histories were collected and used to calculate cumulative years of shift work exposure, average number of night shifts per month, and average number of consecutive night shifts per month. Odds ratios (ORs) and 95% confidence intervals (CIs) for associations with EOC risk were estimated using logistic regression. Associations were also examined according to chronotype and menopausal status. RESULTS: Over half of the cases (53.4%) and controls (51.7%) worked evening and/or night shifts. There was no clear pattern of increasing EOC risk with increasing years of shift work; the adjusted OR (95%CI) of EOC comparing the highest shift work category vs. never working shift work was 1.20 (0.89-1.63). This association was more pronounced among those self-identified as having a “morning” chronotype (OR=1.64, 95%CI: 1.01-2.65). Associations did not greatly differ by menopausal status. CONCLUSION: These results do not strongly demonstrate a relationship between shift work and EOC risk. IMPACT: This study collected detailed shift work information and examined shift work patterns according to shift times and schedules. The findings highlight that chronotype should be considered in studies of shift work as an exposure.