Long-term effects of traffic exposures on mortality in a Chinese cohort

A large proportion of the population living in close proximity to roads are continuously exposed to vehicle traffic and vulnerable to its ill effect in everyday life. However, only a limited number of epidemiological studies have examined effects of long-term road vehicle traffic exposures on mortality. We investigated long-term associations between road vehicle traffic exposures measured by vehicle-kilometres travelled (VKT) and mortality in a cohort of Chinese elderly in Hong Kong, where road vehicle traffic is generally high. The Elderly Health Service cohort consisted of 66,820 adults aged 65 years or older enrolled at 18 Elderly Health Centres of the Department of Health from 1998 to 2001. Deaths were followed-up until 2011. All cohort members had medical, socio-demographic, lifestyle, anthropometric data and place of residence recorded at baseline. The residential addresses of cohort members were geo-coded and aggregated by geographic areas, Tertiary Planning Units (TPU). The annual total VKT was used as traffic exposure at the TPU level. We used Cox proportional hazards regression to estimate hazard ratios (HR) for one million km increase in the annual total VKT for natural-cause and cardiopulmonary mortality, adjusted for individual demographic and socio-economic variables, lifestyle, and medication, as well as environmental covariates. There were 17,422 deaths in 197 TPUs, with the median age at death of 75.3 years. The mean annual total VKT was 26 million kilometres. A 1 million increase in the annual total VKT was associated with excess risk [100 × (HR - 1)] of 0.45% (95% confidence interval [CI]: 0.17, 0.74) for natural-cause mortality and 0.81% (95% CI: 0.30, 1.32) for cardiovascular mortality. No significant association was found for respiratory mortality. These findings suggest that vehicle traffic exposure is associated with raised risks of natural-cause and cardiovascular mortality in the older population.