Is there an association between severe job strain, transient rise in blood pressure and increased mortality?

BACKGROUND

Job strain may be associated with various diseases and increased mortality but there is little data available from prospective studies with long-term follow-up.

OBJECTIVE

To assess the effect of heat exposure followed by severe job strain on blood pressure, heart rate and mortality.

DESIGN

Prospective 19-year observational study (1982-2000) of a cohort of employees in a ferry alloy plant undergoing two economical crises. The participants were 218 healthy males aged 30-59 years.

MEASUREMENTS

Annual standardized measurements of blood pressure, heart rate, serum cholesterol and registration of morbidity and mortality.

RESULTS

Heat-exposed men (n = 25) and non-heat-exposed men (n = 193) had unchanged blood pressure from 1982 to 1984. Thereafter the plant underwent two serious economic crises, in 1985-87 and 1990-91, respectively. The first one was handled by decisions exclusively taken by the head office and included a gradual lay-off of 25% of the workers, and the second one was handled jointly between the local management, union leaders and employees and included a modest, voluntary lay-off. Thus, the two crises differed markedly in low vs high job control. Blood pressures gradually increased from 1985 to 1988 in the whole cohort until systolic blood pressure reached 15 mmHg and diastolic blood pressure 12 mmHg above baseline levels (p < 0.001). Thereafter blood pressures decreased to slightly above baseline levels and then remained unchanged for the next 5 years. However, heart rate increased from 62 +/- 12 beats/min in 1982-83 to 69 +/- 10 beats/min in 1988 (p < 0.01) and did not return to baseline. Total mortality by 31 December 2000 in the study cohort was significantly higher over the 19 years of follow-up than among age-matched, Norwegian men (p < 0.01).

CONCLUSIONS

If a cause-effect relationship exists between the first economical crisis in the ferry alloy plant and the concomitant rise in blood pressure, job strain had a powerful but time-limited effect on blood pressure. Since the same phenomenon was not reproduced 5 years later, the marked difference in job control (high vs low) may constitute the difference. Alternatively, age-related effects or adaptive coping mechanisms may have prevented a similar second blood pressure rise despite exposure to a job strain of similar severity. However, there was also a high 19-year total mortality in the study population, which could be related to long-term health consequences of the first or both economic crises. This study provides some support for the notion that increased job strain elevates blood pressure and deteriorates outcome.