Low back pain among industrial workers : occupational health studies on prevalence, incidence, and associations with work and lifestyle in I.R. Iran

Abstract

This thesis presents the results from a prospective industrial population cohort study on epidemiology and risk factors for low back pain (LBP) in Iran. The four papers in the thesis were based on a cross-sectional survey and one-year follow-up of 18,000 employees in the car industry. The main goals of this thesis were: 1) to identify prevalence and incidence of LBP, and 2) to identify work-related exposures and lifestyle factors related to LBP.

In paper I, the study group consisted of all 18,000 employees working in the automotive industry. In this cross-sectional study, the majority of the study population were young males (<30 years), and the one-year prevalence of self-reported LBP was 21 % (20 % in males and 27 % in females). The self-reported prevalence rate of absence due to LBP was 5 % per annum.

In paper II, the study population was the same as in study 1, and we followed them for one year. All new episodes of disabling LBP lead to medically certified sickness absence being registered. During the one-year follow-up, the incidence of disabling LBP was 2.1 % and the recurrence rate was 2.9 %. The incidence rate of disabling LBP among employees who rejected our invitation to participate at baseline was 3.9 %. A history of previous low back pain significantly increased the risk of a new episode of disabling low back pain. In our study, there was a higher prevalence of LBP in women than in men. However, LBP incidence and recurrence were more frequent in male employees. Men in this study were mostly unskilled workers with physically demanding tasks, while women were office workers with more sedentary tasks.

In paper III, the study population was a cohort of 4500 randomly and strategically selected employees from the automotive industry. The aim was to study the effect of psychosocial exposures on disabling LBP. The results showed that high demands, low control, job strain, low job satisfaction and low job appreciation were associated with both LBP prevalence and incidence of disabling LBP. This prospective study suggests the aetiological role of job strain for LBP. From the prevention point of view, our findings suggest that a reduction in exposure to adverse psychosocial workplace factors may lower the risk of LBP.

In paper IV, the study group was the same as in study III (n=4500), and the aim was to study the effect of cigarette smoking as one important lifestyle factor on the occurrence of disabling LBP. With increasing age and work experience, the number of employees who smoked increased. The results showed that there was a positive significant association between LBP and current smoking. Current smoking increased both LBP prevalence and the incidence of disabling LBP. Smokers experienced three times the number of new episodes of disabling LBP compared with non-smokers.

In conclusion, incidence of LBP differs considerably between developed countries and developing countries. Psychosocial risk factors at the workplace are associated with LBP. Lifestyle factors such as cigarette smoking will increase the risk of getting LBP. A better understanding of such key issues as the exposure panorama, causal pathway and dimension of the selected health problem is paramount for interventional health promotion programmes in the workplace. Our study results generate knowledge and open up possibilities for evidence-based intervention programmes.