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 40-69 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 (Cl) 1.101.27]. In contrast, no association was observed when OPA was classified at the occupational-group level using Standard Occupational Classification groupings (HR 1.00, 95% Cl 0.94-1.06). 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.

What is already known on this topic?

• The “physical activity paradox” suggests that high occupational physical activity may increase cardiovascular disease risk, in contrast to the established benefits of leisure-time physical activity.

• Evidence on the health effects of occupational physical activity is inconsistent, with heterogeneity in how occupational physical activity is operationalised potentially contributing to divergent findings.

• No previous UK Biobank study has examined the association between occupational physical activity and incident cardiovascular disease while comparing alternative approaches to occupational physical activity operationalisation.

What this study adds?

• This study provides the first evidence from the UK Biobank on the association between occupational physical activity and incident cardiovascular disease, showing increased risk at higher levels of individual-level self-reported occupational physical activity.

• Findings differed substantially according to how occupational physical activity was classified: individual-level self-reported occupational physical activity was associated with increased cardiovascular disease risk, whereas a group-based Standard Occupational Classification approach showed no association, demonstrating that exposure classification meaningfully influences conclusions about the occupational physical activity-cardiovascular disease association.

• Socioeconomic and health factors accounted for the greatest attenuation across both approaches, while psychosocial factors contributed primarily to associations based on individual-level self-reported occupational physical activity, highlighting that the explanatory factors most apparent in occupational physical activity - cardiovascular disease associations may also depend on how occupational physical activity is classified.

How this study might affect research, practice and policy

• The findings suggest that future research should explicitly consider how occupational physical activity is operationalised and avoid assuming that individual-level and group-level classifications are interchangeable. Occupational health research and guidance should interpret occupational physical activity-related cardiovascular risk in the context of the exposure classification used and consider the broader social and health characteristics of workers.