Association of shift work and smoking with new-onset hypertension-diabetes comorbidity in Chinese petroleum workers: a prospective cohort study

Hypertension-diabetes comorbidity (HDC) is a serious cardiovascular and metabolic condition. Occupational exposure and unhealthy lifestyle in the petroleum industry may increase the risk of developing HDC. This study aims to evaluate the effects of shift work and smoking on new-onset HDC among petroleum workers and to assess their potential interaction. This study is based on the prospective design of the Beijing-Tianjin-Hebei Health Effects Cohort, with a baseline survey conducted in 2017–2018 and annual follow-ups from 2019 to 2025. A total of 2,296 petroleum workers from a petroleum enterprise in Hebei Province were included in the study. The Weighted Shift Index (WSI) and Smoking Index (SI) were calculated using questionnaire data collected by trained professionals. Multivariate-adjusted modified Poisson regression, restricted cubic spline (RCS), and interaction analyses were employed to evaluate the associations. Over a 7-year follow-up period, the cumulative incidence of HDC was 8.6%. A non-linear relationship was observed between WSI and the risk of developing HDC ( P for nonlinear < 0.05). High-intensity shift work (Relative risk (RR) = 1.693, 95% Confidence interval (CI): 1.262–2.269, P < 0.001), moderate smoking (RR = 2.046, 95% CI: 1.365–3.068, P = 0.001) and heavy smoking (RR = 1.937, 95% CI: 1.300-2.886, P = 0.001) all significantly increased the risk of HDC. A significant synergistic effect was observed between high-intensity shift work and heavy smoking (Attributable proportion (AP) = 0.573, 95% CI: 0.025–1.121), whereas moderate-intensity shift work demonstrated a certain protective effect. Both high-intensity shift work and moderate to heavy smoking independently increase the risk of HDC among petroleum workers, and the synergistic effect between high-intensity shift work and heavy smoking further amplifies this risk. These findings suggest the need for targeted interventions in the occupational setting to reduce the risk of HDC in petroleum workers. Not applicable (prospective observational cohort study).