January 23, 2008
Stressful Job Raises Heart Disease Risk
Workers under age 50 who experience job-related stress are over two-thirds more likely to develop coronary heart disease than their non-stressed counterparts, according to study results reported today by European researchers.
The research is the first large-scale study to look at the cardiovascular mechanisms of work stress and provides the strongest evidence yet of how it can lead to coronary heart disease (CHD), either directly, by activating stress pathways controlled by the interaction between the nervous system and hormones (neuroendocrine mechanisms), or indirectly through its association with unhealthy lifestyles.
The research is part of the long-running Whitehall II study, which has been monitoring over 10,000 British civil servants since 1985.
Heart disease is the leading cause of death worldwide, and can be caused by high blood pressure, blocked arteries and other factors.
"Stress at work is associated with an increased risk of coronary heart disease, but the mechanisms underlying this association have remained unclear until now," said Dr Tarani Chandola, the study's first author and a senior lecturer at University College London's Department of Epidemiology and Public Health.
"This study addressed three questions: 1) Is the accumulation of work stress associated with higher risks of incident CHD and risk factors? 2) Is this association stronger among working-age populations? 3) Does work stress affect CHD directly through neuroendocrine mechanisms, or indirectly through behavioral risk factors for CHD, or both?"
The researchers measured stress among the workers by asking questions about their jobs and work environments, such as the degree of control they had at work, how pressed for time the workers felt throughout the day, and whether or not they took breaks.
The researchers then collected evidence on the incidence of CHD, deaths from CHD, non-fatal myocardial infarctions, angina, heart rate variability, morning rises in the levels of the "stress" hormone cortisol, metabolic syndrome and behavioral risk factors such as diet, exercise, smoking and drinking.
"During 12 years of follow-up, we found that chronic work stress was associated with CHD and this association was stronger among both men and women aged under 50 "“ their risk of CHD was an average of 68% more than for people who reported no stress at work. Among people of retirement age (and therefore less likely to be exposed to work stress), the effect on CHD was less strong."
Dr Chandola said the most important new finding was the evidence linking work stress with the biological mechanisms underlying CHD.
"If you're constantly stressed out, these biological systems become abnormal," he said.
The autonomic nervous system (ANS) regulates involuntary actions, such as the action of the heart, and plays a central role in the neuroendocrine stress responses. The signals that are sent to the heart by the vagus nerve, telling it how to work and controlling the variability of the heart rate, are mediated by the ANS.
The researchers found that workers who suffered from greater stress were more likely to have lowered heart rate variability and poor vagal tone. They also found that the hypothalamic-pituitary-adrenal axis (HPA) "“ a major part of the neuroendocrine system "“ was disturbed by greater stress, and this was shown by the fact that stressed workers had higher than normal morning levels of cortisol. These results were independent of the workers' health behaviors.
"Adjusting for health behaviors did not change the association between work stress and low heart rate variability, suggesting a direct effect on the ANS and neuroendocrine function, rather than indirect effects through health behaviors," said Dr Chandola. "The effect on the ANS and neuroendocrine function in turn affects the signals to the heart, leading to cardiac instability."
The researchers also found work stress was associated with poor health behaviors that could lead indirectly to CHD. "There have been relatively few studies that have found an association between work stress and unhealthy behaviors."
Work stress is associated with a poorer diet in terms of eating less fruit and vegetables, and less exercise. It has also been linked to problem drinking. In this study, around 32% of the effect of work stress on CHD could be explained by its effect on health behaviors and the metabolic syndrome," he said.
"This study demonstrates that cumulative stress at work can lead to CHD through direct activation of neuroendocrine stress pathways and indirectly through unhealthy behaviors," he concluded.
The study was published in today's European Heart Journal.
The full study report can be viewed at http://www.oxfordjournals.org/our_journals/eurheartj/press_releases/freepdf/ehm584.pdf.
The European Society of Cardiology (ESC) press release about the study can be viewed here.
Additional information about the Whitehall II study, led by Sir Michael Marmot, professor of epidemiology and public health at University College London (UCL), can be viewed at http://www.ucl.ac.uk/whitehallII.