Long Work Hours Linked to Heart Disease

Summary
Based on the medical examination of a person, it is possible to predict the risk of coronary heart disease or the chances of heart failure in the next few years. This study examines whether the number of hours a person works affects this risk, and whether that information should be added to the parameters used when determining the risk. Between 1991 and 1993, medical examinations were performed for workers in the Civil Service Departments in England. After every five years, their cardiac history was collected. Those who worked more than 11 hours a day had a 1.67 times higher risk than those working seven or eight hours.

Introduction
It is a norm in the clinical world to determine the risk factors for coronary heart disease for the next ten years, based on medical tests, medical history and the lifestyle of an individual. This helps risk management and decision making about treatment later on. The “Framingham risk score” considers blood pressure, cholesterol levels and habits like smoking to predict the risk. Work-related stress has recently become a factor affecting cardiac health. The number of working hours is a contributor to the stress. This study, called the “Whitehall II” study, assessed whether including information about work hours, in the parameters used to develop the Framingham risk score, improves the risk predictions.

Methods

  • Between 1991 and 1993, 7095 workers answered a questionnaire about working hours. They worked full-time, had no coronary disease, and were between ages 39 and 62 years of age. Their medical history was followed until 2004.
  • Data regarding age, sex, cholesterol levels, smoking habits, blood pressure, and medicines used was collected for each participant. Their average work hours were recorded. This was taken as the baseline. Those with a history of cardiac disease were excluded.
  • Every five years, their heart functions were tested by checking some enzyme levels and electrocardiograms. Fatal and non-fatal cardiac arrests/incidents were recorded between 2002 and 2004.
  • The risk factor was determined statistically, with and without the work hour data. Predicted risks and observed risks were compared.

Results

  • It was found that 54% workers worked 7-8 hours/day, and 10.4% worked more than 11 hours/day.
  • The Framingham risk score for cardiac disease steadily increased after eight work hours.
  • People who worked more than 11 hours per day were 67% more likely to develop coronary heart disease.

Shortcomings
The population tested consisted of largely young white male and low-risk individuals. The findings cannot be generalized to hard physical/manual workers, or those with higher health risk at the baseline. The study also did not take into account medication or newer risks developed during the period of study. The study was not validated using another group.

Conclusion
Working hours have increased in the employed population in many developed countries. This study tried to test how it affects the health of the people, and whether the findings can be used to prepare for future crises. It was found that it did help to include work hour related information when calculating the risk factors for the predicting coronary heart disease. Doing so increased the accuracy of classification of individuals at risk. This marker is easy to acquire and is cost-free too. The predictions of risk improve significantly in a low-risk working population. Previous studies have shown increased risk of death from heart problems among employees working long hours; this study supports it.

For More Information:
Using Additional Information on Working Hours to Predict Coronary Heart Disease
Publication Journal: Annals of Internal Medicine, 2011
By Mika Kivimaki, PhD; G David Batty, PhD
From the University College London, London, UK

*FYI Living Lab Reports Are Summaries of the Original Research.



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