April 4, 2011 — In low-risk, working populations, information on working hours may improve risk prediction of coronary heart disease (CHD) on the basis of the Framingham risk score, according to results from the Whitehall II cohort study reported in the April 5 issue of the Annals of Internal Medicine.
"Long working hours are associated with increased risk for ...CHD," write Mika Kivimäki, PhD, from University College London, United Kingdom, and colleagues. "Adding information on long hours to traditional risk factors for CHD may help to improve risk prediction for this condition."
|Long working hours may predict CHD risk.|
The goal of this study was to assess whether adding information on long working hours could enhance the ability of the Framingham risk model to predict CHD in a low-risk, employed population.
Between 1991 and 1993, a total of 7095 adults (2109 women and 4986 men) aged 39 to 62 years who were working full time at civil service departments in London and who had no history of CHD underwent baseline medical examination, including measurement of working hours and the Framingham risk score. Prospective follow-up for incident CHD continued until 2004, with coronary death and nonfatal myocardial infarction determined from medical screenings every 5 years, hospital data, and registry linkage.
During median follow-up of 12.3 years, 192 participants had incident CHD. Compared with participants working 7 to 8 hours per day, those working 11 hours or more per day had a 1.67-fold increased risk for CHD (95% confidence interval [CI], 1.10 - 2.55), after adjustment for their Framingham risk score. Adding working hours to the Framingham risk score increased sensitivity, with net reclassification improvement of 4.7% (95% CI, 0.3 to 9.1; P = .034) because of better detection of persons in whom CHD later developed.
"Information on working hours may improve risk prediction of CHD on the basis of the Framingham risk score in low-risk, working populations," the study authors write. "The findings may not be generalizable to populations with a larger proportion of high-risk persons and were not validated in an independent cohort."
Additional limitations of this study include failure to account for changes in risk factors or medications during follow-up.
"Furthermore, it is important to clarify whether long working hours are a marker of CHD risk or are also a causal risk factor," the study authors conclude. "In the first case, information on working hours could contribute to risk prediction but not preventive treatment. In the second case, the clinical benefits of avoiding long working hours would need to be shown."
The Medical Research Council; British Heart Foundation; Bupa Foundation; and the National Heart, Lung, and Blood Institute and National Institute on Aging of the National Institutes of Health supported this study. Disclosures of the study authors can be viewed at the Annals of Internal Medicine Web site .
Ann Intern Med. 2011;154:457-463. Abstract
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