Night shift link to small increased risk of heart disease

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Among female registered nurses, working a rotating night shift for 5 years or more was associated with a small increase in the risk of coronary heart disease, according to a new study.

The disruption of social and biological rhythms that occur during shift work have been hypothesised to increase chronic disease risk, and evidence supports an association between shift work and coronary heart disease (CHD), metabolic disorders, and cancer.

Prospective studies linking shift work to CHD have been inconsistent and limited by short follow-up. Dr Celine Vetter of Brigham and Women’s Hospital and Harvard Medical School, Boston, and colleagues examined the incidence of CHD in 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). The researchers determined the lifetime history of rotating night shift work (3 night shifts or more per month in addition to day and evening shifts) of the nurses at baseline (updated every 2 to 4 years in the NHS2).

During follow-up, 7,303 incident CHD cases (nonfatal heart attack, CHD death, angiogram-confirmed angina pectoris, coronary artery bypass graft surgery, stents, and angioplasty) occurred in the NHS and 3,519 in the NHS2.

Analysis indicated that increasing years of rotating night shift work was associated with a statistically significant but small absolute increase in CHD risk. In the NHS, the association between duration of shift work and CHD was stronger in the first half of follow-up than in the second half, suggesting waning risk after cessation of shift work. Longer time since quitting shift work was associated with decreased CHD risk among shift workers in the NHS2.

“Further research is needed to explore whether the association is related to specific work hours and individual characteristics,” the authors write.

Abstract
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 Conclusions and Relevance: 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.

JAMA material
JAMA abstract


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