To the Editor: Ford et al. (June 7 issue)1 have developed astatistical model, called IMPACT, which explains almost 90%of the observed decrease in deaths from coronary heart diseasein the United States in the 20 years from 1980 to 2000. Thismodel, which has been validated and reproduced mainly in developedcountries, is so robust that some of its findings are similarto those of the earlier Nurses' Health Study,2 especially theproportional contributions of smoking and obesity to heart disease(13% and 8%, respectively). However, the model does not explainalmost 10% of the observed decrease in deaths. The reductionin particulate air pollution, for example, explains from 18to 76% of the decline in deaths from both coronary heart diseaseand coronary vascular disease.3,4 No doubt the U.S. outdoorair quality has improved substantially since 1980. An Irishstudy performed after the ban on burning coal showed a 10% declinein deaths from coronary vascular disease.5 Therefore, it wouldbe worth considering air pollution in the IMPACT model, datathat could be integrated into a comprehensive Chronic DiseaseRisk Model, thereby using such "gold standard" dynamic epidemiologicmodels as population-specific, evidence-based policy models.
Zubair Kabir, M.D., Ph.D. Harvard School of Public Health Boston, MA 02115 zkabir{at}hsph.harvard.edu
References
Ford ES, Ajani UA, Croft JB, et al. Explaining the decrease in U.S. deaths from coronary disease, 1980-2000. N Engl J Med 2007;356:2388-2398. [Free Full Text]
Hu FB, Stampfer MJ, Manson JE, et al. Trends in the incidence of coronary heart disease and changes in diet and lifestyle in women. N Engl J Med 2000;343:530-537. [Free Full Text]
Pope CA III, Burnett RT, Thurston GD, et al. Cardiovascular mortality and long-term exposure to particulate air pollution: epidemiological evidence of general pathophysiological pathways of disease. Circulation 2004;109:71-77. [Free Full Text]
Miller KA, Siscovick DS, Sheppard L, et al. Long-term exposure to air pollution and incidence of cardiovascular events in women. N Engl J Med 2007;356:447-458. [Free Full Text]
Clancy L, Goodman P, Sinclair H, Dockery DW. Effect of air-pollution control on death rates in Dublin, Ireland: an intervention study. Lancet 2002;360:1210-1214. [CrossRef][Web of Science][Medline]
The author and a colleague reply: With respect to Kabir's suggestionthat particulate air pollution might account for some of thedecrease in deaths from coronary heart disease that were notexplained by the risk factors in the IMPACT model: air pollutioncan have both short-term and long-term effects on outcomes inpatients with coronary heart disease.1,2,3 Strong associationsbetween peaks in air-pollution indexes and increased mortalityand admissions for cardiac and respiratory disease have longbeen recognized.2 Deaths from cardiovascular causes have alsobeen associated with cumulative long-term exposure to air pollutants.3However, quantifying the contribution of this factor remainsproblematic because of the difficulty in correcting for allpotential confounders, particularly sex and socioeconomic status.Even after adjustment, residual confounding may persist.1,3A long list of risk factors, including air pollution, couldpotentially account for the unquantified 10% of deaths in theIMPACT model. However, imprecision in the measurement and modelingof the major risk factors (cholesterol, smoking, and blood pressure)might also account for much of the gap.
David C. Taylor-Robinson, M.D., M.P.H. Simon Capewell, M.D. University of Liverpool Liverpool L69 3GB, United Kingdom capewell{at}liverpool.ac.uk
Bell ML, Davis DL. Reassessment of the lethal London fog of 1952: novel indicators of acute and chronic consequences of acute exposure to air pollution. Environ Health Perspect 2001;109:Suppl 3:389-394. [CrossRef][Web of Science][Medline]
Dockery DW, Stone PH. Cardiovascular risks from fine particulate air pollution. N Engl J Med 2007;356:511-513. [Free Full Text]
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