Physical workload and exit from the labour market : epidemiological studies with a focus on employees with musculoskeletal disorders

Sammanfattning: Background: The length of working life is expanding in the light of the ageing population. In response, countries including Sweden are increasing the retirement age. However, many workers, especially workers with heavy physical workload, exit the labour market prematurely often because of poor health. Musculoskeletal disorders (MSDs) are a leading cause of premature exit from work and are expected to become more prevalent among the workforce as the average age of the working population increases. More knowledge is needed on how occupational exposures, specifically heavy physical workload, can impact on worsening MSDs, work ability and early health-related exit from work. Aims: The aim of this thesis is to investigate the effect of exposure to a heavy physical workload and changes to lower exposure levels for the prognosis of employees with MSDs with regards to worsening pain, reduced self-reported work ability and disability pension. This thesis also aims to identify how the co-occurrence of high physical workload and low job control impact on disability pension. Methods: This thesis is comprised of four cohort studies. The first two studies used the Stockholm Public Health Cohort (SPHC), a population-based cohort that comprises of participants aged 18–84-year-old from Stockholm County. Study I used a sample of 5715 employees with baseline occasional musculoskeletal pain (MSP) to investigate the impact of exposure to heavy physical workload (eight specific ergonomic exposures) on more frequent musculoskeletal pain. Study II used a sample of 9419 employees with good baseline work ability to investigate the separate and combined effects of strenuous work (heavy physical workload/low job control) and MSP on later reduced physical work ability. The last two studies used the Swedish Work, Illness, and labour-market Participation (SWIP) cohort. The SWIP cohort is a population-based cohort created through the linkage of registers. Study III used a sample of 1,804,242 workers to investigate the separate and combined associations between heavy physical work and low job control on the risk of disability pension. Study IV used a sample of 359 453 workers who were exposed to heavy physical workload to investigate if a change to an occupation with a lower exposure to physical work was associated with a reduced risk of disability pension. In all studies, Job Exposure Matrices (JEMs) were used to estimate exposure to heavy physical workload and/or job control. Results: Heavy physical workload was associated with an increased risk of more frequent MSP (e.g., men and heavy lifting OR 1.57 95%CI 1.13 to 2.20 and women and strenuous work OR 1.76 95%CI 1.35 to 2.29) (study I). After adjustment, small changes in the OR were found for both sexes and, among men, many of the ORs for PWL were no longer statistically significant. Male and female workers with a combination of exposure to MSP and strenuous work often had higher risks of poor physical workability (e.g., MSP and overall heavy physical workload, men: OR 4.04 95% CI 2.00–8.15 and women: OR 3.25 95% CI 1.81–5.83) than when summing the risks of the single exposures (study II). However, the results of the synergy index (SI) for additive interaction were not statistically significant. Workers with combined exposure to overall heavy physical workload and low decision authority often had higher risks of all-cause disability pension (men: HR 3.23 95%CI 3.07-3.39 and women: 2.46 95%CI 2.37-2.57) and MSD disability pension (men: HR 7.61 95%CI 6.48-8.94 and women: 4.21 95%CI 3.82–4.64) than when adding the effects of the separate exposures (study III). The results for the SI were above 1 for all-cause disability pension for both sexes, and MSD disability pension for men. After adjustment, the estimates for SI remained above 1 but were not statistically significant. A change from a high to a lower level of physical workload was associated with a reduced risk of all-cause (men: HR 0.59, 95% CI 0.46–0.77, women: HR 0.63, 95% CI 0.52–0.76) and musculoskeletal (men: HR 0.52, 95% CI 0.31–0.89, women: HR 0.61, 95% CI 0.44–0.84) disability pension (study IV). The reduction in risk of musculoskeletal disability pension appeared greater among older workers than middle-aged workers. Furthermore, a change to low physical workload was associated with a greater reduced risk of disability pension than a change to medium-high physical workload. Conclusion: The results of this thesis contribute to the state of art by indicating that heavy physical workload is associated with an increased risk of later worsening musculoskeletal pain, reduced work ability and disability pension. The results also suggest that workers with combined MSP and strenuous work may be a more vulnerable group regarding reduced work ability than workers with only one of the exposures. In addition, to some extent, the results suggest that job control exacerbates the effect of heavy physical on disability pension. Last, compared to staying in an occupation with heavy physical workload, changing to an occupation with a lower level of physical workload was associated with a reduced risk of disability pension.