The Smog Blog: Long-term Improvement in Air Quality Benefits Lung Function

Cessation of smoking has a beneficial effect on lung function, but the effect of reductions in air pollution on lung function has not been studied in adults until recently. It is normal for lung function to decline with age. A study published in the New England Journal of Medicine is the first to explore whether a decline in air pollution over time can attenuate this decline.

A prospective study of 9,600 Swiss adults 18 to 60 years old included measurements of several measures of lung function at baseline and 11 years later.  PM₁₀ concentrations declined over this same period. 

“Our data show that improvement in air quality may slow the annual rate of decline in lung function in adulthood.  The finding suggests that important changes in the rate of decline in pulmonary function occur across the range of exposures seen in Switzerland, where particle concentrations are relatively low.” 

The strongest beneficial effects of a reduction in PM₁₀ were in the small airways. Intervention studies such as this are important because the demonstrate the health benefits ofair pollution control programs. In its 2006 revisions to the National Air Quality Standards, EPA revoked the annual average PM₁₀ standard of 50 µg/m³.  The study authors suggest that “further reductions in these standards are likely to improve pulmonary health.” 

“Our findings provide further support for a causal role of exposure to air pollution in respiratory health,” conclude the researchers. “Relatively small reductions in exposure to PM₁₀ have measurable benefits for lung function, suggesting that a decline in air pollution, even from low levels, may have positive consequences for public health.”

In an accompanying editorial, New York University School of Medicine Professor Morton Lippmann, notes that the rate of lung function decline with age is a well-established predictor of longevity.  He finds that this study is significant because the decline in lung function was linear even at quite low concentrations, suggesting that the current EPA and World Health Organization annual average standards are not protective against such losses in lung function.

EPA is in the process of reviewing its National Ambient Air Quality Standards for particulate matter.  This study provides important evidence of the need to control long term exposures to particles in the air. 

Downs SH, Schindler C, Liu L-J S, Keidel D, Bayer-Oglesby L, Brutsche MH, Gerbase MW, Keller R, Künzli N, Leuenberger P, Probst-Hensch NM, Tschopp J-M, Zellweger J-P, Rochat T, Schwartz J, Ackermann-Liebrich U, SAPALDIA Team. Reduced Exposure to PM₁₀ and Attenuated Age-Related Decline in Lung Function. N Engl J Med 2007; 357:2338-2347. 

Lippmann, M. Health Effects of Airborne Particulate Matter. NEJM 2007; 357: 2395-2397.

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