Impact assessment of the mortality effects of longer-term exposure to air pollution: exploring cause-specific mortality and susceptibility

In previous work, we have developed the use of actuarial life-table methods, using PC spreadsheets, for predicting the impacts of changes in pollution levels on long- term patterns of mortality. This approach is flexible, and allows the simulation of impacts that affect only some causes of death; to date, we have focused on effects on the group of non-malignant cardio-respiratory causes as well as on all-cause mortality. Because recent work has suggested that risks of air pollution may be greater for cardiovascular than for respiratory causes, we present and compare new predictions for cardiovascular impacts. In addition, we have for the first time modelled differences in mortality risk in different notional strata of the population, to represent differences in individual frailty or susceptibility to pollution effects. Previous results showed that the impact of 1.8% reduction in cardio-respiratory risk was of the order of 10% smaller than that of a 1% reduction in the all-cause effect, and our results show that a purely cardiovascular 2% reduction produces an impact almost 30% smaller than the all-cause. Similar results were obtained when the population was stratified to simulate a frailty distribution; however, when the sensitivity to the effects of pollution was allowed to differ by stratum, with the sensitivity increasing with increasing frailty, then the differences across cause groups were much reduced. These results are interpreted as being due to the different age distributions for different causes of death, and particularly to the tendency for cardiovascular deaths to be predominantly in older persons, which limits their cumulative effects on life expectancy. The revised spreadsheets offer great flexibility for further predictions under complex assumptions.