Background
Active commuting (cycling, walking) has been linked with reduced all-cause mortality. However, active commuting in urban environments could increase intake of fine particles (PM2.5) and result in negative health effects. We aimed to evaluate the change in all-cause mortality among active commuters in London and Beijing under different commuting scenarios. Baseline scenario assumes commuters cycle to work daily while the remaining scenarios assume commuters cycle to work only when PM2.5 levels are below specific thresholds (<35 μg/m3, <50 μg/m3, <75 μg/m3).
Methods
Daily cycling time of active commuters was available from census data. City specific daily PM2.5 profiles during weekday peak hours were created for 2010-2012. Annual all-cause mortality relative risks were calculated based on published dose-response functions (DRF) (Tainio et al. Preventive Medicine 2016; 87: 233-236) and results are presented in annual averted deaths. Sensitivity analysis for the shape of the DRF and Monte Carlo simulations were performed in ANALYTICA.
Results
Mean daily PM2.5 concentration was 19 μg/m3 (min: 7 μg/m3, max: 62 μg/m3) in London and 97 μg/m3 (min: 17 μg/m3, max: 346 μg/m3) in Beijing. PM2.5 thresholds resulted in small reductions (for <35 μg/m3) or no change (for <50 μg/m3 and <75 μg/m3) in averted deaths for London but resulted in a high increase in averted deaths for all thresholds in Beijing (Table 1). Results for Beijing were sensitive to the shape of the DRF.
Conclusion
In cities with high air pollution, all-cause mortality among active commuters is expected to be reduced when cycling to work is only performed in days with low PM2.5 levels.
Table 1: Averted deaths per year in London and Beijing
| Cycling to work activity | Cycling daily |
Cycling when PM2.5 <35 μg/m3 | Cycling when PM2.5 <50 μg/m3 | Cycling when PM2.5 <75 μg/m3 |
| London | 223 (30) | 218 (31) | 223 (30) | 223 (30) |
| Beijing | 521 (131) | 614 (124) | 706 (140) | 867 (166) |