Long-term exposure to outdoor air pollutants may spur emphysema progression
Exposure to outdoor air pollutants, in particular ozone, was associated with increased emphysema progression and lung function decline among city dwellers, according to the MESA* study.
“Because percent emphysema is related to respiratory symptoms, hospitalizations, and mortality even among individuals without airflow obstruction, these associations in a community-based population demonstrate novel evidence that air pollution contributes to worsening lung health,” said the researchers.
The MESA cohort included 7,071 participants (mean age 60 years, 47.1 percent men) whose long-term exposure to outdoor air pollutants were estimated using each participant’s residential address across six metropolitan regions in the US. [JAMA 2019;322:546-556]
Over a median follow-up of 10 years, percent emphysema (calculated based on full-lung CT scans) increased by an average of 0.58 percentage points per 10 years (95 percent confidence interval [CI], 0.38–0.78), from a median percent emphysema of 3 percent at baseline.
An increase of 3 parts per billion (ppb) of long-term ozone exposure was significantly associated with increased progression of percent emphysema during follow-up (by 0.18 percentage point, 95 percent CI, 0.08–0.28) as well as at baseline (by 0.13 percentage point, 95 percent CI, 0.03–0.24).
“This increase is equal to the association of 29 pack-years of smoking ... or 3 years of ageing in this cohort,” the researchers said.
In addition, ambient ozone concentrations were also significantly associated with a greater decline in lung function, in terms of FEV1** per 10 years during follow-up (18.15 mL per 3 ppb, 95 percent CI, 1.59-34.71) and FVC (40.19 mL per 3 ppb, 95 percent CI, 17.88–62.49) over 10 years.
Long-term exposure to oxides of nitrogen was similarly associated with a significantly faster progression of percent emphysema during follow-up (by 0.12 percentage-point per 10 ppb, 95 percent CI, 0.04–0.19) and at baseline (0.06 per 10 ppb, 95 percent CI, 0.01-0.12).
There were no significant associations between concentrations of other pollutants such as PM2.5***, oxides of nitrogen, or black carbon and changes in lung function.
“Long-term exposure to ambient air pollutants was significantly associated with increasing emphysema assessed quantitatively using CT imaging and lung function,” said the researchers. “Findings were most robust and of greatest magnitude for ozone.”
Interestingly, the researchers found that while the annual mean concentrations of oxides of nitrogen and PM2.5 declined over the 18 years of observation (from 2000–2018), ozone concentration did not.
“Long-term average concentrations of ozone levels did not decline during the years of observation … despite existing regulations to prevent short-term excursions,” the researchers pointed out. In the absence of new control strategies, they believed that the levels are not expected to drop as climate change advances.
“Because long-term concentrations of ozone at current levels were strongly and consistently associated with both progression of emphysema and decline in lung function in this study, more effective control strategies to reduce ozone concentrations may be needed to protect lung health,’ they urged.
Nonetheless, the researchers also acknowledged that most people spend a large part of their time indoor, and thus, outdoor air pollution concentrations may not fully reflect individual exposures to air pollution.