Introduction Epidemiological studies indicate that exposure to fine particulate matter air pollution mass (PM_2.5) is associated with an increased risk of premature mortality. Pope et al (2002, 2004) reported elevated mortality risks of long-term PM_2.5 exposure in the USA nationwide American Cancer Society (ACS) CP-II cohort, finding a total mortality risk of RR=1.04 per 10 ug/m³ (95% CI 1.01 to 1.08), and a cardiovascular mortality RR=1.12 per 10 ug/m³ (95% CI 1.08 to 1.15). We seek to evaluate the PM_2.5 association with these outcomes in another large US cohort.

Methods The NIH-AARP cohort is an ongoing prospective mortality study of more than a half million people from locations throughout the USA (Adams et al, 2006). Using available EPA data to interpolate exposures on a census tract level, we evaluated associations between PM_2.5 in California, the state with the largest number of cohort participants. The statistical approaches applied were similar to those used in the previously published ACS cohort research: standard Cox Proportional Hazards (CPH) modelling, including individual level covariates.

Results The CPH estimated long-term PM_2.5 risk in this NIH-AARP cohort in California was RR=1.09 per 10 ug/m³ (95% CI 1.05 to 1.12) for total mortality. The risk found for cardiovascular mortality was RR=1.18 per 10 ug/m³ (95% CI 1.11 to 1.24). These confirm excesses at least as great as observed in the ACS cohort.

Conclusion Analysis of mortality among California residents of the NIH-AARP cohort confirms excess total and cardiovascular risks from long-term exposure to PM_2.5.