Revisiting the ‘physical activity paradox’ in a Chinese context: Occupational physical activity and mortality in 142,302 urban working adults from the China Kadoorie Biobank study

BACKGROUND: Previous research suggests that while leisure-time physical activity (LTPA) is beneficial, occupational physical activity (OPA) may be detrimental to health, known as the ‘physical activity paradox’. However, the current evidence is primarily based on data from Western countries. We examined the association of OPA with all-cause and cardiovascular disease mortality in working adults in urban China. METHODS: This prospective longitudinal study was based on a sample of 142,302 urban working adults aged 30–79 years from the China Kadoorie Biobank study. Self-reported OPA (mainly sedentary, standing occupation, and manual work) was collected at baseline (year 2004–2008) and linked to death registries until 31st December 2016. Multivariable Cox proportional hazards models were used to examine the relationship between OPA and mortality outcomes, with further tests for effect modification by sex, educational attainment and LTPA. FINDINGS: During a median follow-up of 10·2 years, 4,077 deaths occurred, of which cardiovascular disease was the primary cause for 727 deaths. Crude modelling showed that compared with the sedentary workers, manual work was associated with increased risk of all-cause mortality. However, after adjusting for socio-demographic and lifestyle variables, the association was attenuated to null (HR=1·00, 95%CI: 0·93–1·08). In subgroup analysis, higher OPA was associated with lower risk of all-cause mortality in the least educated group (HR=0·84, 95%CI: 0·75–0·95 for manual work, and HR=0·86, 95%CI: 0·75–0·99 for standing occupation), but harmful in the most educated group (HR=1·17, 95%CI: 1·01–1·36) and in those who reported regular LTPA (HR=1·20, 95%CI: 1·01–1·43). INTERPRETATION: OPA was not associated with mortality risk in the overall sample. However, findings support the ‘physical activity paradox’ within better educated Chinese workers. FUNDING: None.