2013 Environment and Health - Basel
Nitrogen dioxide and mortality: review and meta-analysis of long-term studies
Background. Exposure to nitrogen dioxide (NO2) has been linked to increased mortality in several epidemiological studies on both short and long-term effects. The question whether NO2 is directly responsible for the health effects, or it is only an indicator for other pollutants (mainly particulate matter) remains to be assessed. Aim. We have reviewed the more recent studies evaluating the long-term effects of NO2 on mortality to provide a quantitative summary of the effects potentially useful for health impact assessment.
Methods. Original studies exploring the relationship between long-term NO2 exposure and mortality, and including also PM effects, were searched in PubMed, Web of Science and LUDOK. Twenty-seven papers published in 2004-2012 were selected. A meta-analysis was carried out on 19 studies, with different study design, estimating random effects relative risks. Results.The pooled effect on mortality was 1.05 (95% confidence intervals = 1.02-1.07) for 10µg/m3 of NO2 annual concentration. The corresponding effect for PM2.5 (10µg/m3 ) was 1.05 (95%CI=1.03-1.08). The effect on cardiovascular mortality (CV) was 1.14 (95%CI=1.10-1.19) for NO2 and 1.22 (95%CI=1.10-1.35) for PM2.5. The NO2 effect on respiratory mortality was 1.03 (95%CI1.02-1.03), whereas the effect of PM2.5 was 1.05% (95%CI 1.004-1.104). The five carried-out bi-pollutant analyses showed no changes of NO2 effects in comparison to the single-pollutant estimates. The NO2 effects were stronger in Asia and Europe than in North America.
Conclusions.There is evidence for a long-term effect of NO2 on natural mortality as high as that of PM2.5. An independent effect of NO2 emerged, though explored only in few studies. The associations of NO2 with mortality differed across the areas of the world.