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Working Hours and CVD Risk – Some new findings

An interesting article authored by Mika Kivimaki and colleagues using data from the Whitehall Study* appeared in the Annals of Internal Medicine**.

The authors report, that above and beyond the traditional Framingham Heart Risk score, that working long work days  (beyond a normal 8 hour work day) increases the risk of a coronary event. The risk increases stepwise up to 11 hours. This finding is an interesting echo of a study published by Haiou Yang, myself and several colleagues in the fall of 2006 at the University of California at Irvine. Our study found a relationship between long working hours during the week (increasing #’s of hours of work per week > 40 per week) were associated with an increase in self-reported hypertension in the CHIS (Calif Health Interview Survey) conducted by UCLA.

Readers should be aware that the Framingham risk score is derived by adding up the total risk due to exposure to the “traditional” risk factors for heart disease in particular weight, smoking, cholesterol, blood pressure and diabetes. Both of these articles are suggesting that there are other factors such as longer working hours that above and beyond traditional risk factors are contributing to the likelihood of having a heart attack.

Also I want to point out that the design of both of these studies does not rule out the possibility that even an 8 hour work day or a 40 hour work week may contribute to the development of heart disease. Both of these studies compared increased hours to either the typical work day or typical work week. Unfortunately, there were no subjects available working less than 8 hours a day in the Whitehall study or 35 or less hours in the CHIS study for comparison.

Not only are long work days and work weeks associated with heart disease but there is accumulating evidence that a number of other organizational and psychosocial work related factors are playing an important role in the development of hypertension and heart disease.  For much more on this topic stay tuned for further blogs or pick up a copy of our book “Unhealthy Work: causes, consequences and cures” published in 2009 by Baywood Publishers.

Readers should note that the Whitehall study has access to data on other work related risk factors including psychosocial variables such as job strain which were not included in the analyses done in this paper. It will be interesting to see future studies where all of these variables are included.

*The original Whitehall Study investigated social determinants of health, specifically the cardiorespiratory disease prevalenceand mortality rates among British male civil servants between the ages of 20 and 64. The initial study, the Whitehall I Study, examined over 18,000 male civil servants, and was conducted over a period of ten years, beginning in 1967. A second phase, theWhitehall II Study, examined the health of 10,308 civil servants aged 35 to 55, of whom two thirds were men and one third women. A long-term follow-up of study subjects from the first two phases is ongoing.

** Article appeared in the news this week on April 5th 2011 based on the report in the Annals of Internal Medicine.

Work Hours and Self-Reported Hypertension Among Working People in California

Haiou Yang, Peter L. Schnall, Maritza Jauregui, Ta-chen Su, Dean Baker

Abstract—Among the risk factors for hypertension, stress, especially work stress, has drawn increasing attention. Another potential work-related risk factor for hypertension identified in the past few years is work hours. This article presents an analysis of work hours and self-reported hypertension among the working population in the state of California. The data set used for this study comes from the Public Use File of the 2001 California Health Interview Survey. The logistic regression analysis shows a positive association between hours worked per week and likelihood of having self-reported hypertension. Compared with those working between 11 and 39 hours per week, individuals working 40 hours per week were 14% (95% CI: 1.01 to 1.28) more likely to report hypertension, those who worked between 41 and 51 hours per week were 17% (95% CI: 1.04 to 1.33) more likely to report hypertension, and those who worked 51 hours per week were 29% (95% CI: 1.10 to 1.52) more likely to report hypertension after controlling for various potentially confounding variables, including demographic and biological risk factors and socioeconomic status. This analysis provides evidence
of a positive association between work hours and hypertension in the California working population. (Hypertension. 2006;48:1-2.)

Key Words: occupations  risk factors  behavior

Click here for a pdf of the full article.

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