The influence of work environment and individual factors on the risk of long-term sickness absence. An epidemiological, registry-based 5-year follow-up study

The present study was based on self-reported data on health and work-related topics from The Oslo Health Study (HUBRO), linked to several Norwegian registries based on the unique personal identification number. The study population was 10,995 respondents resident in Oslo, Norway, during 2001-2005. The overall aim of this thesis, was to identify individual and work-related predictors for longterm (> 8 weeks) sickness absence. In Norway, reducing sickness absence and disability is an important political objective. Since October 2001, these efforts have been regulated through the Inclusive working life (IW) program, a Norwegian national intervention program implemented by authorities and major labour market partners. Musculoskeletal disorders and mental health problems are two of the largest diagnostic groups in sickness absence. On this background, three papers have been worked out: In the first paper, we examined risk factors for long-term (> 8 weeks) sickness absence with psychiatric diagnoses (LSP), focusing on the influence of self-reported health, education and the psychosocial work environment. We found that lack of support from superior and selfreported poor general health seemed to have an independent and moderate adverse effect on LSP. Mental distress had a strong independent effect on LSP, somewhat stronger in men than in women. There was a strong education gradient for women, while in men, there were no statistically significant effects from education on LSP. Path and linear regression analyses indicated that the effect of support from superior on LSP was mediated through selfreported mental distress. In the second paper, we studied risk factors for long-term (> 8 weeks) sickness absence due to musculoskeletal disorders (LSM), focusing on the influence of the psychosocial and physical work environment, and a special aim was to reveal any gender differences in the associations. We found that men and women aged 40 and 45 had an LSM risk approximately 50% greater than that of subjects aged 30. There was a strong education gradient for both genders. Low job control had a strong effect, especially in men, whereas the effect of low job security was modest. Having shift/night work or rotating hours had a strong effect on the LSM risk, particularly in men. The associations with the job exposure variables were generally stronger for men; still, the LSM risk was considerably higher for women because of the high risk in women without the studied job exposures. Adding the interaction term (having both psychosocial end physical exposure) to the analysis did not significantly improve the model, and this was the case for both genders. The aim of the research in paper III was to examine the effect of the IW program by gender on long-term (>8 weeks) sickness absence (LSA), and further, to identify physical work demands and employment-sector-specific patterns on the sickness absence risk. We found that women had a higher risk than men of experiencing an LSA, but the gender-specific differences by IW groups were generally small. In a multivariate model, statistically significant risk factors for LSA were low education (stronger in men), shift work/night work or rotating hours (strongest in men in the non-IW group), and heavy physical work or work involving walking and lifting (men only and stronger in the non-IW group). Among men who engaged in shift work, the LSA risk was significantly lower in the IW group. However, this study could not demonstrate a significantly lower risk of LSA in companies signing the IW-agreement. This thesis emphasises the importance of the interplay between individual and occupational factors to achieve a deeper understanding of risk factors for long-term sickness absence. Registry data on sickness absence linked to information on diagnoses and self-reported data from health surveys, including information on both the individual and work-related level, as we have collected in this study, may contribute to increased understanding of these relationships. A broad approach that focuses on individuals as well as work-related factors is necessary for preventing sickness absence and disability pensioning and reducing the still large social in equalities in health