Role of Life’s Essential 8 in the association of night shift work with cardiovascular disease and mortality: a prospective cohort study of UK Biobank participants

Background: Night shift work is linked to higher risks of cardiovascular disease (CVD) and mortality, but mechanisms remain unclear. Lifestyle, captured by the American Heart Association's Life's Essential 8 (LE8), may act as a modifiable mediator. We aimed to examine the associations of night shift work with CVD and mortality and quantify the mediating role of LE8. Methods: We analysed 131,844 employed participants without baseline CVD from the UK Biobank (2006-2010). We categorised night shift work as day workers, shift but never/rarely night shifts, some night shifts, and usual/permanent night shifts. LE8 scores included diet, physical activity, nicotine exposure, sleep, body mass index, blood pressure, lipids, and blood glucose. Primary outcomes were incident CVD and all-cause mortality, and secondary outcomes included myocardial infarction (MI), stroke, and atrial fibrillation (AF). We used Cox models to estimate associations and counterfactual mediation analysis to quantify the proportion mediated by LE8. Results: Over a median follow-up of 13.78 years (interquartile range = 13.09-14.42), 39,115 (29.7%) developed CVD and 5474 (4.2%) died. Compared with day workers, usual/permanent night shifts had higher risks of CVD (hazard ratio (HR) = 1.24; 95% confidence interval (CI) = 1.18-1.31), all-cause mortality (HR = 1.23; 95% CI = 1.07-1.41), AF (HR = 1.31; 95% CI = 1.13-1.51), and MI (HR = 1.29; 95% CI = 1.09-1.51), but not cardiovascular mortality. LE8 mediated 39.2% of the CVD association, 33.1% of all-cause mortality, and 40.8% of MI. Counterfactual analyses suggested that improving cardiovascular health (CVH) could prevent 35.1% of CVD events and 30.2% of deaths among night shift workers. Conclusions: Night shift work is associated with higher risks of CVD, AF, MI, and all-cause mortality. A substantial proportion of this burden may be preventable through improved CVH. Further studies are needed to evaluate integrated lifestyle interventions in night shift workers.