Rotating Night Shift Work and Risk of Incident Cardiovascular Disease and Mortality by Chronotype: A Prospective Cohort Study in Nurses' Health Study II

Introduction: Rotating night shift work is associated with chronic circadian disruption and may contribute to higher cardiovascular disease (CVD) risk and mortality. The impact of rotating night shift work may vary by chronotype, particularly when an individual's circadian preference is misaligned with work schedules. Methods: In 2009, 69,458 women (mean age 54.4 years) free of CVD in the Nurses' Health Study II reported chronotype. Duration of rotating night shift work has been assessed biennially since 1989. Participants were followed from 2009 through June 2021 for incident CVD (myocardial infarction or stroke) and all-cause mortality. We used time-varying Cox proportional hazards models to estimate hazard ratios (HRs) and 95% confidence intervals (CIs) for outcomes in relation to rotating night shift work and chronotype and to evaluate whether the associations differed by chronotype. Primary models adjusted for key demographics, CVD risk factors, and workplace factors. Results: We documented 1,005 incident CVD events over 800,630 person-years and 1,777 deaths over 806,043 person-years. Each 5-year increase in rotating night shift work was associated with a modestly higher risk of incident CVD (HR 1.07; 95% CI 1.01, 1.14) and a 13% higher risk of all-cause mortality (HR 1.13; 95% CI 1.08, 1.17). Greater eveningness was associated with higher incident CVD risk (HR 1.17; 95% CI 1.06, 1.28) and all-cause mortality (HR 1.18; 95% CI 1.10, 1.26). For incident CVD, the increased risk per 5-year increment in rotating night shift work was observed only among definite morning types (HR 1.11; 95% CI 0.99, 1.23), but not among definite evening types (HR 0.99; 95% CI 0.86, 1.15; p-interaction=0.1732). For all-cause mortality, the increased risk associated with shorter-term rotating night shift work (<5 years) was more evident among definite morning types (HR 1.39; 95% CI 1.12, 1.73) than definite evening types (HR 1.37; 95% CI 0.98, 1.91). However, this difference was not observed for longer duration of shift work ([&ge;]5 years), and the overall interaction was not statistically significant (p-interaction=0.57). Similar patterns were observed when shift work duration was modeled continuously using restricted cubic spline analyses. Conclusion: Rotating night shift work was associated with a modest increase in CVD and all-cause mortality risk. The overall pattern of associations across chronotypes suggested that nurses with a morning chronotype may be more susceptible to the adverse effects of rotating night shift work.