NCPA - National Center for Policy Analysis

Is Asthma Linked To Air Pollution?

March 21, 2002

Self-reported asthma cases have doubled in the United States over the past 20 years, and pediatric cases rose from 3.7 percent of children to 6.9 percent between 1980 and 1996. Pre-existing lung ailments can be aggravated by exposure to air pollutants, but does air pollution cause asthma?

A study in the medical journal Lancet (Feb. 3, 2002) compared asthma rates among children in 12 southern California communities from 1993 to 1998 with measured levels of ozone, airborne particulates, nitrogen dioxide and other pollutants.

  • The only pollutant for which it found a correlation with asthma was ozone.
  • In the four communities with the highest ozone levels, the 8 percent of children in three or more team sports were 3.1 times as likely as less-active children to become asthmatic.
  • But in the eight communities with lower ozone levels, asthma was unrelated to sports participation.
  • And overall asthma rates did not differ between the high- and low-pollution areas.

During the study period, four "high-ozone" study areas exceeded federal standards by about 50 days per year. However, such high pollution levels no longer occur anywhere in the United States. In fact:

  • The four "high-ozone" communities now average 11 ozone exceedances per year, a reduction of almost 80 percent; Crestline, Calif., with the worst ozone in the nation, exceeds the standard 23 days annually (see figure).
  • Ozone levels in America's next most polluted metro areas -- Fresno, Houston and Atlanta -- are much lower than the levels associated with increased asthma risk.
  • Overall, ozone levels dropped 24 percent nationwide between 1980 and 1999, and other pollutants declined substantially.

It's hard to see how decreasing pollution could cause increasing asthma. Yet in media reports, regulators and public health advocates insisted the study proves the need for stricter ozone regulations.

Source: Joel Schwartz (Reason Public Policy Institute), "Breathe Easier on Asthma-Air Pollution Link," Brief Analysis No. 390, March 21, 2002, National Center for Policy Analysis.

For text

See also "New Asthma Estimates: Tracking Prevalence, Health Care, and Mortality," National Center for Health Statistics, Centers for Disease Control, 2002.


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