Date Published: September 16, 2019
Publisher: Public Library of Science
Author(s): Kuan-Yu Pan, Weili Xu, Francesca Mangialasche, Rui Wang, Serhiy Dekhtyar, Amaia Calderón-Larrañaga, Laura Fratiglioni, Hui-Xin Wang, David Coggon
Abstract: BackgroundUnfavorable psychosocial working conditions have been associated with cognitive decline and chronic diseases, both of which may subsequently accelerate functional dependence. This study aimed to investigate the association between job demand–control–support combinations and trajectories of disability in later life and to further explore the role of cognitive decline and the co-occurrence of chronic diseases in mediating this association.Methods and findingsIn this cohort study, 2,937 community dwellers aged 60+ years (mean age 73 ± 10.6; 62.9% female) residing in the Kungsholmen District of Stockholm, Sweden, participated in the baseline survey (2001–2004) and were followed up to 12 years. Lifelong occupational history was obtained through a standardized interview; job demands, job control, and social support at work in the longest-held occupation were graded with a psychosocial job–exposure matrix. Job control, demands, and social support were dichotomized using the median values from the matrix, respectively, to further generate demand–control–support combinations. Disability was measured by summing the number of impaired basic and instrumental activities of daily living. Global cognitive function was assessed by Mini-Mental State Examination. Chronic conditions were ascertained by clinical examinations, medical history, and patient clinical records; the total number of chronic diseases was summed. Data were analyzed using linear mixed-effects models and mediation analysis. Age, sex, education, alcohol consumption, smoking, leisure activity engagement, early-life socioeconomic status, occupational characteristic and physical demands, and baseline cognitive function and number of chronic diseases were adjusted for in the analyses. Compared with active jobs (high control/high demands; n = 1,807), high strain (low control/high demands; n = 328), low strain (high control/low demands; n = 495), and passive jobs (low control/low demands; n = 307) were all associated with a faster rate of disability progression (β = 0.07, 95% CI 0.02–0.13, p = 0.01; β = 0.10, 95% CI 0.06–0.15, p < 0.001; β = 0.11, 95% CI 0.05–0.18, p < 0.001). The association between high strain and disability progression was only shown in people with low social support at work (β = 0.13, 95% CI 0.07–0.19, p < 0.001), but not in those with high social support (β = 0.004, 95% CI −0.09 to 0.10, p = 0.93). Moreover, we estimated that the association between demand–control status and disability trajectories was mediated 38.5% by cognitive decline and 18.4% by accumulation of chronic diseases during the follow-up period. The limitations of this study include unmeasured confounding, self-reported work experience, and the reliance on a psychosocial job–exposure matrix that does not consider variabilities in individuals’ perception on working conditions or job characteristics within occupations.ConclusionsOur findings suggest that negative psychosocial working conditions during working life may accelerate disability progression in later life. Notably, social support at work may buffer the detrimental effect of high strain on disability progression. Cognitive decline and chronic-disease accumulation, and especially the former, partially mediate the association of psychosocial working conditions with trajectories of disability. Further studies are required to explore more mechanisms that underlie the association between psychosocial working conditions and disability trajectories.
Partial Text: Adults aged 60 years or over are one of the faster growing segments of the population worldwide, and they are projected to reach 2 billion by 2050, with a major rise in the number of the oldest old (aged 85 years or over) [1,2]. Advanced age is associated with progressive increase in the occurrence of functional impairment and disability, as a result of both age-related and disease-driven mechanisms. Environmental exposures can affect the accrual rate of disability, and they could thus be modulated to prevent or delay its onset and progression.
Baseline characteristics of the study population by demand–control categories are presented in Table 2.
In this population-based cohort study, low levels of job control and demands were associated with a higher rate of disability progression among individuals aged 60+ years over 12 years of follow-up. By applying the categorization of the demand–control model, we found that in comparison with active jobs, high strain, low strain, and passive jobs were all related to an accelerated speed of disability progression. When stratified by social support, the association between high strain and disability accumulation was only shown in people with low social support at work (i.e., iso-strain), but not in those with high social support. These results remained even after taking into consideration several possible confounders including occupational characteristic and work-related physical demands. Moreover, the association between work-related psychosocial status and disability trajectories was partially mediated by both cognitive decline (38.5%) and accumulation of chronic diseases (18.4%).