Among 69,458 female nurses followed from 2009 to 2021 in the Nurses' Health Study II, each additional 5 years of rotating night shift work was associated with a 7% higher risk of incident cardiovascular disease (myocardial infarction or stroke; 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). Notably, having an evening chronotype independently raised CVD risk by 17% and mortality by 18%. Morning chronotypes appeared more vulnerable to shift-work-related CVD harm, with an 11% increased risk per 5-year increment versus essentially no increase in evening types, though the interaction did not reach statistical significance (p=0.17).
This large prospective cohort adds meaningful nuance to the well-established link between shift work and cardiovascular harm. The chronotype-by-shift-work interaction hypothesis is biologically plausible — morning types forced into night schedules experience greater circadian misalignment — but the non-significant interaction p-values urge caution against overinterpreting subgroup differences. The all-female, predominantly nurse sample limits generalizability to men and other occupations. Chronotype was self-reported only once in 2009, missing lifetime changes. Residual confounding from lifestyle, socioeconomic, and occupational factors cannot be excluded in this observational design. As a preprint not yet peer-reviewed, these findings may change after formal scrutiny. Practically, the results reinforce that minimizing rotating night shift exposure and potentially matching work schedules to individual chronotype could meaningfully reduce long-term cardiovascular and mortality risk.