A current study suggests long-term exposure to combustion-related air pollutants, nitrogen dioxide (NO2), and black carbon (BC) may be mortal risk factors for patients with pneumonia, influenza, and acute lower respiratory infections (ALRI), according to findings published recently in the American Journal of Respiratory and Critical Care Medicine. Participants in the study who were overweight, current smokers, or employed presented higher risks.

Mortality from chronic cardiorespiratory diseases has been linked to ambient air pollution exposure, but few studies examine ambient air pollution and respiratory infections. Researchers sought to examine the association between pneumonia-related mortality and long-term exposure to air pollution.

To accomplish this, they pooled data from the multicenter ‘Effects of Low-Level Air Pollution: A Study in Europe’ (ELAPSE) that included 8 cohorts in 6 European countries, 325,367 participants (mean age 48.7 years; 66% female, as 3 cohorts/sub-cohorts were female-only by design; proportion of current smokers in each cohort ranged from 13% to 37%; overweight participants in each cohort ranged from 21% to 74%). During a mean follow-up of 19.5 years, 712 participants died from pneumonia and influenza combined, 682 died from pneumonia, and 695 died from ALRI. The 3 primary study outcomes were mortality from pneumonia and influenza combined, pneumonia only, and ALRI.

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Increases in combined mortality from pneumonia and influenza of 10 to 12% were associated with NO2 and BC (95% CIs included unity [which implies no difference between arms of the study]; hazard ratios [HRs]: 1.12 (0.99-1.26) per 10 µg/m3 for NO2; 1.10 (0.97-1.24) per 0.5 10-5m-1 for BC). Pneumonia and ALRI mortality associations were almost identical, and, stronger associations with NO2 or BC were suggested in participants who were currently smoking, employed, or overweight compared to participants who were non-smoking, unemployed, or not overweight.

Researchers concluded that even at low levels, “combustion-related air pollutants NO2 and BC…may be risk factors for pneumonia related mortality.” They added that long-term exposure “may be associated with mortality from lower respiratory infections, but larger studies are needed to estimate these associations more precisely.” Study researchers further suggested that overweight, current smoking, employed participants are especially susceptible.

Study limitations included the use of exposure data for the year 2010 as the baseline of cohorts recruited in 1990s and early 2000s and a lack of data on influenza vaccinations.


Liu S, Lim YH, Chen J, et al. Long-term air pollution exposure and pneumonia related mortality in a large pooled European cohort. Am J Respir Crit Care Med. Published online March 8, 2022. doi:10.1164/rccm.202106-1484OC