Rotating Night Shift Work and CHD Risk in Women
Is rotating night shift work associated with increased coronary heart disease (CHD) risk?
Data from the Nurses’ Health Studies (NHS) (both ongoing perspective cohort studies) including NHS conducted between 1988 and 2012 (n = 73,623) and NHS2, conducted between 1989 and 2013 (n = 115,535), were used for the present analysis. NHS began in 1976 with 121,701 female US nurses, ages 30-55 years at baseline. NHS2 began in 1989 with 116,430 female US nurses, ages 25-42 years. In the NHS, lifetime years of exposure to rotating night shift work (defined as ≥3 night shifts per month, in addition to day and evening shifts) was assessed in1988. In the NHS2, women indicated in 1989 how many years of rotating night shift work they had worked, with updates in 1991, 1993, 1997, 2001, 2005, and 2007; retrospective assessments for shift work in 1995, 1999, and 2003 were included on the 2001 and 2005 questionnaires. The outcomes of interest included incident CHD (nonfatal myocardial infarction, CHD death, angiogram-confirmed angina, and revascularization [coronary artery bypass grafting and percutaneous coronary intervention]).
A total of 7,303 incident CHD cases occurred in the NHS cohort (mean age at baseline was 54.5 years) and 3,519 incident CHD cases occurred in the NHS2 cohort (mean age 34.8 years). Number of years of rotating night shift work was associated with increased risk for CHD in both cohorts. For the NHS cohort, those who reported 10 or more years of rotating shift work at a hazard ratio of 1.27 (95% confidence interval, 1.13-1.42) for the first half of follow-up compared to participants who reported no rotating shift work. A similar pattern was noted for participants of NHS2. Longer time since quitting shift work was also associated with a decrease in CHD risk among participants of NHS2 (p < 0.001 for trend).
The investigators concluded that among women who worked as registered nurses, longer duration of rotating night shift work was associated with a statistically significant but small absolute increase in CHD risk. Further research is needed to explore whether the association is related to specific work hours and individual characteristics.
These data suggest that rotating shift work, which includes night shifts, increases a woman’s risk for CHD when the duration of rotating shift work is >5 years. CHD risk decreases with elimination of rotating shift work.
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