Long-term exposure to specific chemical components of fine particulate matter with diameters ≤2.5 μm (PM_2.5) was associated with an increased risk of developing cardiovascular disease, according to a large cohort study published June 24 in JACC. Higher proportions of black carbon, chloride, and sulfate were found to contribute to a more hazardous exposure profile and higher rates of heart attacks and strokes.

In the largest study of its kind, researchers investigated incident cardiovascular disease among 487,037 adults from 10 regions across China participating in the China Kadoorie Biobank. Their mean age was 52 years and 59% were women.

To estimate each participants' exposure, Hongjing Shi, MSc, et al., used geocoded three-year moving average concentrations of PM_2.5 and its components at a 1 × 1 km resolution based on the location of their community recruitment clinic. Components tracked were black carbon, organic matter, chloride, nitrate, sulfate and ammonium. Data were collected from 2001 to 2021. Of note, individuals exposed to median or higher levels of PM_2.5 were more likely to live in rural areas.

Researchers used time-varying Cox proportional hazards models to evaluate the associations between PM_2.5 components and incident cardiovascular disease risk, and substitution models were used to estimate the effects of reallocating PM_2.5 component proportions while keeping total PM_2.5 mass constant to evaluate changes in cardiovascular disease risk associated with shifts in component composition.

Results showed there were 196,224 incident cases of cardiovascular disease over the median 15-year follow-up. By subtype, this included 2,747 cases of ischemic heart disease, 74,594 of ischemic stroke, 17,553 of hemorrhagic stroke and 54,306 of other cerebrovascular diseases.

Looking at the contribution of specific chemicals, the hazard ratios (HR) per interquartile range (IQR) for total cardiovascular were 1.15 for black carbon, 1.17 for organic matter, 1.28 for chloride, 1.29 for nitrate and 1.23 for sulfate. Additionally, higher levels of black carbon, chloride and sulfate were associated with an increased risk of ischemic stroke while inorganic ions were associated with a higher risk of ischemic heart disease.

"This evidence advocates for a paradigm shift in air quality management, advancing a dual approach that integrates 'mass concentration control' with 'toxicity risk control,'" write the authors. "Future studies quantifying the health effects of source-specific PM_2.5 components will be essential to further guide prioritized regulatory interventions."

"A critical feature of this new work is that it not only intercompares the relative strengths of statistical associations across constituents, but also their biological plausibility..." write George Douglas Thurston, Dsc, and Lung Chi Chen, PhD, in an accompanying editorial. "...it is important for epidemiological studies to weigh statistical associations in the context of their other comparative attributes, including their relative biological plausibility and uncertainties of exposure estimates."