Occupational Physical Activity Paradox and Incident Cardiovascular Disease: Does Exposure Classification Matter?

Objectives The association between occupational physical activity (OPA) and cardiovascular disease (CVD) may depend on how OPA is classified. This study examined the association between OPA and incident CVD using individual level and occupational group level classifications, and assessed whether factors contributing to attenuation differed. Methods A total of 137,592 employed UK Biobank participants aged 40 to 69 years who were free of CVD at baseline were included. OPA was classified using (i) individual level self reported physical activity at work and (ii) occupational group level two digit Standard Occupational Classification. Associations with incident CVD were examined using Cox proportional hazards models. Attenuation of associations by sociodemographic, lifestyle, health, occupational and psychosocial factors was assessed using univariate adjustments and Heller's coefficient. Results During 1,656,378 person-years of follow up (median 12.6 years), 10,465 incident CVD events occurred. The association between OPA and CVD differed markedly according to exposure classification. High individual level self reported OPA was associated with increased CVD incidence after full adjustment [hazard ratio (HR) 1.19, 95% confidence interval (CI) 1.10 to 1.27]. In contrast, no association was observed when OPA was classified at the occupational-group level using Standard Occupational Classification groupings (HR 1.00, 95% CI 0.94 to 1.06). Sociodemographic and health factors accounted for the greatest attenuation across both classifications, whereas psychosocial factors contributed primarily to associations based on individual-level self-reported OPA. Conclusions The association between occupational physical activity and incident cardiovascular disease differed substantially according to how OPA was classified. These findings highlight exposure classification as a critical consideration when interpreting evidence on the physical activity paradox.