Traffic air pollution and mortality from cardiovascular disease and all causes: a Danish cohort study

BACKGROUND: Traffic air pollution has been linked to cardiovascular mortality, which might be due to co-exposure to road traffic noise. Further, personal and lifestyle characteristics might modify any association. METHODS: We followed up 52 061 participants in a Danish cohort for mortality in the nationwide Register of Causes of Death, from enrollment in 1993-1997 through 2009, and traced their residential addresses from 1971 onwards in the Central Population Registry. We used dispersion-modelled concentration of nitrogen dioxide (NO₂) since 1971 as indicator of traffic air pollution and used Cox regression models to estimate mortality rate ratios (MRRs) with adjustment for potential confounders. RESULTS: Mean levels of NO₂ at the residence since 1971 were significantly associated with mortality from cardiovascular disease (MRR, 1.26; 95% confidence interval CI, 1.06-1.51, per doubling of NO₂ concentration) and all causes (MRR, 1.13; 95% CI, 1.04-1.23, per doubling of NO₂ concentration) after adjustment for potential confounders. For participants who ate < 200 g of fruit and vegetables per day, the MRR was 1.45 (95% CI, 1.13-1.87) for mortality from cardiovascular disease and 1.25 (95% CI, 1.11-1.42) for mortality from all causes. CONCLUSIONS: Traffic air pollution is associated with mortality from cardiovascular diseases and all causes, after adjustment for traffic noise. The association was strongest for people with a low fruit and vegetable intake.