A quick look at two papers and an editorial on the effects on lung function of exposure to levels of air pollution below current EPA standards, published in this week’s New England Journal of Medicine.
Epidemiologic studies of the health effects of air pollution keep improving, with scientists designing studies able to measure small but important effects of relatively low levels of exposure. There are implications for policy: our pollution current standards are not sufficiently protective, especially for individuals who already have lung disease or are otherwise more sensitive or susceptible to environmental exposures.
The first study, “Reduced Exposure to PM10 and Attenuated Age-Related Decline in Lung Function” by Sara H. Downs and a multinational group of investigators, reports on the decline of lung function among 9600 Swiss adults over an 11-year period. Exposure to fine dust or particulates in the outdoor air (fairly low to begin with) decreased over the 11 years. As individuals in the study aged, their lung function declined (it happens to all of us). But those with lower PM exposure had less decrease in lung function than those with higher exposures. The authors conclude that “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 the second study, the investigators compared the lung function of volunteers with mild or moderate asthma immediately after they were exposed to diesel exhaust while walking on busy Oxford Street or in Hyde Park, London. In “Respiratory Effects of Exposure to Diesel Traffic in Persons with Asthma,” James McCreanor and his colleagues reported that both groups, but especially the volunteers with moderate asthma, showed small but measurable decreases in lung function after walking near traffic, concluding
Our observations serve as a direct demonstration and explanation of the epidemiologic evidence that associates exposure to diesel traffic with the severity of asthma and of the symptoms that many patients with asthma report after exposure to diesel exhaust. The changes in our primary end point (FEV1) were small and unaccompanied by clinically significant symptoms but would be more important in patients with more compromised lung function.
What do these two studies mean? The Journal astutely asked Mort Lippman, one of the giants in the study of the health effects of air pollution, to pen an editorial. So in interpreting the policy implications, I’ll give him the final word:
Both groups of researchers were able to produce statistically significant group-level effects at particulate-matter concentrations below current WHO guidelines and EPA standards because of their ability to limit exposure error by assigning personal exposure levels to each subject. The magnitude of the effects was relatively small and of limited clinical relevance to individual patients, but it does have public health relevance. Standards and guidelines are needed to protect sensitive subpopulations such as those with preexisting lung disease. For nominally healthy people, there is a wide degree of susceptibility to reduced longevity from exposure to particulate matter (for reasons not yet established), and a small increase in the annual mortality rate related to particulate matter would correspond to thousands of excess deaths. These studies provide additional biologic data indicating that relatively low levels of airborne particles have adverse effects on human health. Are our standards too high?
Downs SH, Schindler C, Liu LJ, Keidel D, Bayer-Oglesby L, Brutsche MH, Gerbase MW, Keller R, Künzli N, Leuenberger P, Probst-Hensch NM, Tschopp JM, Zellweger JP, Rochat T, Schwartz J, Ackermann-Liebrich U; the SAPALDIA Team. Reduced Exposure to PM10 and Attenuated Age-Related Decline in Lung Function. N Engl J Med. 2007 Dec 6;357(23):2338-2347.
McCreanor J, Cullinan P, Nieuwenhuijsen MJ, Stewart-Evans J, Malliarou E, Jarup L, Harrington R, Svartengren M, Han IK, Ohman-Strickland P, Chung KF, Zhang J. Respiratory Effects of Exposure to Diesel Traffic in Persons with Asthma. N Engl J Med. 2007 Dec 6;357(23):2348-2358.
Lippmann M. Health effects of airborne particulate matter.N Engl J Med. 2007 Dec 6;357(23):2395-7.