Clinically "small" effects of air pollution on FVC have a large public health impact

Epidemiological studies have repeatedly established adverse health effects due to long-term exposure to ambient air pollution, The Swiss Study on Air Pollution and Lung Disease in Adults (SAPALDIA) published a -3.14% decrease in forced vital capacity (FVC) per 10 mu g.m(-3) increment in particulate matter (particles with a 50% cut-off aerodynamic diameter of 10 mu m (PM10) , Compared to the within-subject variability of FVC, the effect may be cons idered small. This individual (or clinical) perspective is, however, mislea ding. The purpose of this study was to demonstrate the public health releva nce of apparently "small" effects, using the impact of PM10 on FVC as an ex ample. The scenario compares a population A, exposed to an annual mean PM10 of 20 mu g.m(-3) , with a population B exposed to 30 mu g.m(-3) mean PM10. A shift of -3.14% in the population distribution of FVC increases the numbe r of subjects in the lower tail of the distribution. In population B a rela tive increase was expected of 47% (16-91%) in the prevalence of "FVC <80% p redicted", (i.e., from 5.17 to 7.59% and 5.88 to 8.65% among males and fema les, respectively), The relative increase in the prevalence of "FVC <70% pr edicted" (similar to 1% of population) was 63% (30-98%, males) and 57% (21- 86%, females). An epidemiological estimate of a change in the mean value of the population distribution should not be misinterpreted as an effect on the individual l evel. However, the impact of a 10 mu g.m(-3) increase in particles with a 5 0% cut-off aerodynamic diameter of 10 mu m (PM10) on the number of subjects with a clinically relevant reduction in lung function is quantitatively im portant.