Long-term exposure to particulate matter with an aerodynamic diameter ≤2.5 μm (PM_2.5) was associated with increased risk of coronary heart disease (CHD) and acute myocardial infarction (AMI), according to a nationwide cohort study published July 15 in JACC. The findings emphasize the need for constituent-specific air pollution control beyond PM_2.5 mass.

The prospective study included nearly 102,000 adults from the China-PAR Project, which enrolled nearly 128,000 participants from diverse demographic and geographic backgrounds across 15 provinces of China. Participants had a mean age of 51 years, were 40% men, and were followed from Jan. 1, 2003, to Dec. 31, 2019. All were free of cardiovascular disease at baseline. Notably, 92% of participants resided in rural areas at initial assessment.

Wenhao Wang, PhD, et al., estimated annual residential exposures to PM_2.5 constituents, including elemental carbon (EC), organic carbon (OC), nitrate and sulfate, using validated satellite-based machine learning models. Cox proportional hazards models with time-varying exposures were used to estimate hazard ratios (HRs) and 95% CIs per interquartile range (IQR) increase, adjusted for major demographic, behavioral and clinical covariates. Primary outcomes were incidence and mortality of CHD and AMI.

Over a median follow-up of 11 years, there were 3,500 incident cases of CHD. This included 1,771 AMI events and 1,321 CHD deaths, of which 808 were due to AMI. For each IQR increase in EC, OC, nitrate and sulfate exposure, HRs for the incidence of CHD were 1.10, 1.60, 1.43 and 0.93, respectively. Additionally, positive associations for EC, OC and nitrate were observed, while sulfate health impacts were weaker and less consistent.

Based on concentration-response curves, the risk of CHD generally increased with exposure to OC, EC and nitrate, although the increase plateaued at higher levels of EC and OC exposure. In contrast, sulfate showed a less consistent pattern and was not associated with a sustained risk increase.

"A key strength [of the study] was the ability to evaluate adjudicated [CHD] and AMI outcomes in a large national cohort with long-term follow-up and annual time-varying exposures," write the authors. "Building on existing broad air pollution controls, our study suggests that greater attention to the sources and emissions of PM_2.5 constituents may help reduce the burden of [cardiovascular disease] in China."

"…the study from Wang et al. provides compelling evidence that the cardiovascular risks of PM_2.5 are highly constituent dependent, driven primarily by OC, EC and nitrate but not sulfate," write Huihuan Luo, PhD; Renjie Chen, PhD; and Haidong Kan, PhD. "Future efforts on advanced multi-pollutant modeling, source apportionment and mechanistic explorations are warranted to further mitigate cardiovascular disease burden attributable to PM_2.5 exposure."