Association Between Rotating Night Shift Work and Risk of Coronary Heart Disease Among Women

IMPORTANCE: Prospective studies linking shift work to coronary heart disease (CHD) have been inconsistent and limited by short follow-up. OBJECTIVE: To determine whether rotating night shift work is associated with CHD risk. DESIGN, SETTING, AND PARTICIPANTS: Prospective cohort study of 189 158 initially healthy women followed up over 24 years in the Nurses’ Health Studies (NHS [1988-2012]: N = 73 623 and NHS2 [1989-2013]: N = 115 535). EXPOSURES: Lifetime history of rotating night shift work (≥3 night shifts per month in addition to day and evening shifts) at baseline (updated every 2 to 4 years in the NHS2). MAIN OUTCOMES AND MEASURES: Incident CHD; ie, nonfatal myocardial infarction, CHD death, angiogram-confirmed angina pectoris, coronary artery bypass graft surgery, stents, and angioplasty. RESULTS: During follow-up, 7303 incident CHD cases occurred in the NHS (mean age at baseline, 54.5 years) and 3519 cases in the NHS2 (mean age, 34.8 years). In multivariable-adjusted Cox proportional hazards models, increasing years of baseline rotating night shift work were associated with a significantly higher CHD risk in both cohorts. In the NHS, the age-standardized incidence rate (IR) for less than 5 years of rotating night shift work per 100 000 person-years was 435.1 (hazard ratio [HR], 1.02; 95% CI, 0.97-1.08); the IR for 5 to 9 years of rotating night shift work was 525.7 (HR, 1.12; 95% CI, 1.02-1.22); and the IR for 10 years or more of rotating night shift work was 596.9 (HR, 1.18; 95% CI, 1.10-1.26; P