Short-term effects of exposure to air pollution and mortality: are those previously diagnosed with cancer at greater risk?

摘要

Aim: It is well recognized that short-term, or daily increases, in air pollution concentrations increases the risk of mortality. A number of studies have also found that those with pre-existing disease such as diabetes, or a history of heart disease, may be particularly susceptible to these effects. To date, there have been few attempts to examine whether those previously diagnosed with cancer may be more vulnerable due to their comprised health status. Methods: We applied a time-stratified case-crossover study to investigate whether increases in NO2 and PM2.5 were associated with increased risks of mortality. These methods were applied to approximately 200,000 deaths that occurred within the Ontario Tax cohort. These deaths occurred in a follow-up of approximately 660,000 adults who lived in the province of Ontario and who were followed up between 1981 and 2004. Diagnoses of cancer were determined through record linkage to national cancer incidence data. Daily estimates of air pollution were assigned based on the reported place of death obtained from death certificates. Conditional logistic regression methods were applied to characterize the risk of death, and adjustment was made for meteorological variables including temperature, and relative humidity. Results: We found that daily increases in NO2 were associated with increased mortality during the warm season, but not during the cool season. In particular, a 5 ppb increase in NO2 was found to increase mortality by 0.9% (95% CI=0.2%-1.6%). Stratified analyses of individuals based on whether they had previously diagnosed with cancer or not revealed no substantial differences in risk. Conclusions: This study confirmed previous findings that short-term increases in air pollution are associated with increases in mortality. Importantly, our findings suggest that those diagnosed with cancer are not a susceptible population