Association of improved air quality with lung development in children

Abstract

Background: Air-pollution levels have been trending downward progressively over the past several decades in southern California, as a result of the implementation of air quality-control policies. We assessed whether long-term reductions in pollution were associated with improvements in respiratory health among children.

Methods: As part of the Children's Health Study, we measured lung function annually in 2120 children from three separate cohorts corresponding to three separate calendar periods: 1994-1998, 1997-2001, and 2007-2011. Mean ages of the children within each cohort were 11 years at the beginning of the period and 15 years at the end. Linear-regression models were used to examine the relationship between declining pollution levels over time and lung-function development from 11 to 15 years of age, measured as the increases in forced expiratory volume in 1 second (FEV1) and forced vital capacity (FVC) during that period (referred to as 4-year growth in FEV1 and FVC).

Results: Over the 13 years spanned by the three cohorts, improvements in 4-year growth of both FEV1 and FVC were associated with declining levels of nitrogen dioxide (P<0.001 for FEV1 and FVC) and of particulate matter with an aerodynamic diameter of less than 2.5 μm (P= 0.008 for FEV1 and P<0.001 for FVC) and less than 10 μm (P<0.001 for FEV1 and FVC). These associations persisted after adjustment for several potential confounders. Significant improvements in lung-function development were observed in both boys and girls and in children with asthma and children without asthma. The proportions of children with clinically low FEV1 (defined as <80% of the predicted value) at 15 years of age declined significantly, from 7.9% to 6.3% to 3.6% across the three periods, as the air quality improved (P = 0.001).

Conclusions: We found that long-term improvements in air quality were associated with statistically and clinically significant positive effects on lung-function growth in children. (Funded by the Health Effects Institute and others.).

Figure 1. Levels of Four Air Pollutants from 1994 to 2011 in Five Southern California Communities

Colored bands represent the relevant 4-year averaging period for the analysis of lung-function growth in each of the three cohorts, C, D, and E. PM_2.5 denotes particulate matter with an aerodynamic diameter of less than 2.5 μm, and PM₁₀ particulate matter with an aerodynamic diameter of less than 10 μm.

Figure 2. Mean 4-Year Lung-Function Growth versus the Mean Levels of Four Pollutants

The mean growth in forced expiratory volume in 1 second (FEV₁) (Panel A) and the mean growth in forced vital capacity (FVC) (Panel B) from 11 to 15 years of age are plotted against the corresponding levels of nitrogen dioxide, ozone, PM_2.5, and PM₁₀ for each community and cohort.

Figure 3. Proportions of Children with Low Lung Function in Each Cohort

The proportions of children with lung function below 90%, 85%, or 80% of the predicted value at 15 years of age in cohorts C, D, and E are shown for FEV₁ (Panel A) and FVC (Panel B).