The demands of a job and how it is organized can lead to stress at work. A new study shows that this can cause development of the metabolic syndrome, which in turn can be followed by cardiovascular disease.

Introduction

Previous studies have reported a link between stress at work and the metabolic syndrome ¹. This is important, as there's a known link between stress and coronary heart disease, and the metabolic syndrome is a step on the path towards coronary disease. Until now, however, such studies have been of the 'cross-sectional' type, giving a snapshot view, but not providing evidence of a cause-and-effect relationship; such evidence has to come from a prospective, or longitudinal, study, like the one we report here. It's just been published in the British Medical Journal.

What was done

British scientist studied over 10,000 government employees ('civil servants') working in central London over a 14-year period. They were between 35 and 55 at baseline, and employed in one of 20 different civil service departments.

Enrollment was between 1985 and 1988. Postal questionnaires were completed in 1989, then 2-3 years after that, then 2-3 years later, and again 2-3 years later. These stages were called phase 1, 2, etc. Physical exams were done in stages 3 and 5. The necessary exams to diagnose the metabolic syndrome were done in phase 5, at the end of the study.

Work stress was measured by a self-reported Job Strain questionnaire. Job Strain was considered present when job demands were registered as 'high' and decision latitude, or control over the job, was scored as 'low'. The accumulation of exposure to job stress over the study period was obtained by adding together the number of times the participant was exposed to Job Strain. Chronic work stress was defined as three or more instances of Job Strain in the 5 phase reports (i.e. over ¾ of the time).

Social position was also measured, using employment grades at baseline. Lifestyle measurements recorded were smoking status, daily intake of fruit and vegetables, alcohol consumption, and physical activity. A basal metabolic index (BMI) over 30 was taken as an indication of obesity (waist measurements weren't made at baseline).

What was found

1. Men and women from lower employment grades were more likely to have developed the metabolic syndrome.
2. Men with chronic work stress were nearly twice as likely to have developed the syndrome as those with no work stress; for women, the likelihood was over five times as great. When the sexes were combined, and adjusted for age and employment grade, those with chronic work stress were over twice as likely to develop the metabolic syndrome.
3. A health-damaging lifestyle (poor diet, smoking, heavy alcohol use, no exercise) was more likely to result in the metabolic syndrome in men than in women.
4. Excluding people with obesity at baseline from the analysis did not alter the results to a relevant extent.

What these findings mean

This study suggests a biological mechanism for how stress at work is linked to coronary heart disease and heart attacks. The relationship between stress and the metabolic syndrome persisted after exclusion of obese participants from the analysis, showing that pre-existing physiological changes are unlikely to explain the linkage.

The study doesn't clarify which of the remaining risk factors (insulin resistance, raised blood pressure, abnormal lipid levels) is primarily influenced by stress, but other studies indicate that all of these may be involved. And of course, it's possible that stress at work will influence any bad lifestyle habits (smoking, alcohol, no exercise) that were shown to encourage the development of the syndrome.

Other reports from this particular study indicate that those participants with the metabolic syndrome had raised cortisol and normetanephrine in their urine, which are known markers of nervous and endocrine system response to stress.

More will certainly be uncovered about the effects of stress at work. However, there's enough known to act on. While one component of Job Strain - high demand - is likely to persist in many (even most) jobs, the other component - control over the job, or decision latitude - can be addressed by organizations' managements. If people find their job is demanding without any opportunity for decision-making, they might be advised to look for alternative work.

Source

• Chandola T, Brunner E, Marmot M. Chronic stress at work and the metabolic syndrome: prospective study. BMJ online: BMJ 2006:386934353, doi:10.1136/bmj.38693.435301.80

Footnotes
1. The metabolic syndrome requires 3 of the following risk factors to be present: (a) Waist size over 40 inches (102 cm) in men, or 35 inches (88 cm) in women. (b) Serum triglyceride level over 150 mg/dL (1.7 mmol/L). (c) Serum HDL ('good') cholesterol below 40 mg/dL (1.0 mmol/L) in men, or 50 mg/dL (1.29 mmol/L) in women. (d) Blood pressure over 130/85 mm Hg (either number), or being on blood pressure medication. (e) Fasting blood sugar over 110 mg/dL (6.1 mmol/L). Take the self-test, at the link below.

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