Evidence suggests that firefighters represent an occupational group at high risk for cardiovascular events. However, few studies have examined the association between psychosocial work factors and cardiovascular disease risk factors (e.g., hypertension) in firefighters. This study aims to investigate whether the interaction between psychological demands and job control (job strain) has a significant effect on firefighters’ blood pressure (BP) levels.
277 non-randomly selected firefighters (63% of the total population) were drawn from the Bogota Fire Department. Psychological demands (α= 0,74) and job control (α= 0,64) were measured using the standard 27-item version of Job Content Questionnaire (JCQ). BP was taken in the workplace every 15 minutes for 4 hours while answering an institutional questionnaire. BP was measured by the investigators with Omron HEM-670 wrist devices. The measurements were averaged to obtain an estimate of systolic and diastolic BP at work. Age, weight and height were taken from the latest firefighters’ annual medical examination record, and were controlled using hierarchical multiple linear regressions.
Demands and control separately were not associated with BP, nor was job strain when added to the model. However, after controlling for age, BMI, seniority and the main effects of demands and control, job strain was significantly associated with systolic (p=0,047) and diastolic BP (p=0,023), but the effect sizes of the models were low (f2=0.156 for systolic and f2=0.157 for diastolic BP). A further graphical exploration of Demands/Control interaction showed that positive extreme values of demands and negative extreme values of control are associated with higher levels of diastolic and systolic BP.
Although demands and control by themselves apparently do not influence BP, after controlling for known confounders – age, BMI and seniority– the interaction effect between high-demands and low-control (i.e. job strain) was found to have a low but significant effect on firefighters’ systolic and diastolic BP.