Using Additional Information on Working Hours to Predict Coronary Heart Disease: A Cohort Study
Does information on long working hours improve the ability of the Framingham risk model to predict coronary heart disease (CHD) in a low-risk, employed population?
This cohort study was conducted using the civil service departments in London participating in the Whitehall II study. Baseline medical exams were performed between 1991 and 1993, and prospective follow-up for incident CHD was performed until 2004. Working hours and the Framingham risk score (FRS) were measured at baseline. Coronary death and nonfatal myocardial infarction were ascertained from medical screenings every 5 years, hospital data, and registry linkage.
Participants included 7,095 adults (2,109 women and 4,986 men) ages 39-62 years, working full-time without CHD at baseline. A total of 192 participants had incident CHD during a median 12.3-year follow-up. After adjustment for their FRS, participants working 11 hours or more per day had a 1.67-fold (95% CI, 1.10- to 2.55-fold) increased risk for CHD compared with participants working 7-8 hours per day. Adding working hours to the FRS led to a net reclassification improvement of 4.7% (p = 0.034) due to better identification of persons who later developed CHD (sensitivity gain).
The authors concluded that information on working hours may improve risk prediction of CHD on the basis of the FRS in low-risk, working populations.
Increasing CHD events associated with long working hours is likely related to other classic risk factors including stress, socioeconomic, hypertension, and decreased locus of control. It is easy to discuss the implications with patients and spouses.
Keywords: Registries, Coronary Artery Disease, Myocardial Infarction, Internal-External Control, Follow-Up Studies, London
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