Air pollution vs. tobacco smoking

Extract

This commentary refers to ‘Cardiovascular disease burden from ambient air pollution in Europe reassessed using novel hazard ratio functions’, by J. Lelieveld et al., 2019;40:1590–1596.

Lelieveld et al.¹ suggest that air pollution is a health risk factor that may exceed that of tobacco smoking, a finding widely covered by the media. However, owing in part to the complexity of the mathematical model, candid clinicians have difficulties to reconcile this claim with some hard facts.

Small particles PM_2.5 produced by the combustion of fossil fuels and tobacco penetrate deep into the lungs, are carcinogenic, and increase cardiovascular risk.¹ However, consistent with the differences in PM_2.5 concentrations, the negative health effects of tobacco smoke appear much larger than those of air pollution (Table 1). Hence, if air pollution is now rated as the larger risk factor,¹ how can we explain this discrepancy?

The first obvious answer could lie in the numbers of exposed subjects. However, in countries like France, 32% of adults (18–75 years) were still self-declared current smokers in 2017, not counting former smokers and second-hand smoke exposure.⁴ Was Lelieveld et al.’s model applied only to non-smoking populations? Also, the prevalence of smoking is higher in low- than in high-income populations (34 and 19.5% in France in the lower and upper tertiles, respectively⁴) As low-income populations are less likely to live in ‘clean air’ areas, was this potential confounder also taken into account when computing and interpreting the correlations between traffic pollution and health risks? In other words, could Lelieveld et al. comment on how many, if any, of the deaths attributed to air pollution in their model may have been already counted in the excess death rate from tobacco smoking (of) 7.2 million per year  ¹?