Abstract
BACKGROUND: The risk of long-term sickness absence due to musculoskeletal (MSK) disorders could be driven by sleep problems and physical inactivity. However, it is not well explored if these associations differ across the lifespan. The aim of this study was to describe the annual risk of long-term sickness absence due to MSK disorders throughout working life, according to insomnia symptoms and physical activity, in people with and without MSK pain. METHODS: A total of 38,253 working-age individuals (20-62 years) with information on self-reported chronic MSK pain, physical activity, and insomnia symptoms in the third (2006-08) and/or fourth (2017-19) survey of the Norwegian HUNT Study were included. Annual sickness absence up to 5 years after participation was obtained from national registry data. Annual risk of long-term sickness absence due to MSK disorders were estimated as the proportion receiving medical benefits for ≥ 31 consecutive days each calendar year using a Poisson regression model. The model was fitted via generalized estimating equations to account for dependencies in observations and presented according to categories of chronic MSK pain combined with insomnia symptoms (yes, no) or physical activity level (inactive/low, moderate, high). RESULTS: The average annual proportion with long-term sickness absence due to MSK disorders increased from 3.7% in women < 30 years to 11.3% in women ≥ 50 years, and from 2.7 to 7.1% among men in the same age groups. Annual risk of long-term sickness absence due to MSK disorders was greater among those reporting chronic MSK pain and who also suffered from insomnia symptoms compared to those without any of these conditions. This was particularly evident in age 30-39 and 40-49 years, where the co-occurrence of chronic MSK pain and insomnia symptoms was associated with a 4-fold increased risk of long-term sickness absence due to MSK disorders in women, and an almost 5-fold increased risk in men. The risk of sickness absence did not differ according to physical activity levels. CONCLUSION: The annual risk of long-term sickness absence due to MSK disorders in working-age individuals was related to insomnia symptoms, especially among those aged 40 to 60 years, but not to physical activity.