Association between exposure to indoor PM2.5 constituents and mortality risk among chinese older adults: a nationwide prospective cohort study

Abstract

With global population aging, investigating the health impacts of PM2.5 and its chemical components in older adults has become increasingly important. Due to age-related limitations in mobility and activity patterns, older adults spend the majority of their time indoors. The chemical composition of PM2.5 is complex, and its various components may adversely affect the health of older adults by inducing systemic inflammatory responses. This study examines the association between indoor PM2.5 and its components and all-cause mortality, and explores the potential intermediate pathway of systemic inflammatory factors. We analyzed 12,607 elderly participants (mean age 86.81 ± 11.34) followed from 2008 to 2018. Over a median follow-up of 4.14 years, 8,643 deaths were recorded. Indoor concentrations of PM2.5, black carbon (BC), organic matter (OM), sulfate (SO42−), ammonium (NH4+), and nitrate (NO3−) were estimated using high-resolution ambient data and infiltration factors. Time-varying Cox proportional hazards models were used to assess the associations between PM2.5 and its major components and all-cause mortality. Dose-response relationships were characterized using restricted cubic splines (RCS), and sensitivity analysis with a one-year lag exposure window was also conducted. Additionally, fixed-effects models were used to explore the relationship between PM2.5 and the neutrophil-to-lymphocyte ratio. Time-varying Cox models identified PM2.5, BC, OM, and SO42− as significantly associated with increased all-cause mortality. Specifically, a 1 µg/m³ increase in PM2.5 was associated with a 0.3% higher risk (HR = 1.003, 95% CI: 1.001–1.005). Regarding the constituents, each 1 µg/m³ increase in BC corresponded to a 7.2% higher risk (HR = 1.072, 95% CI: 1.035–1.111); the HRs for OM and SO42− were 1.009 (95% CI: 1.002–1.016) and 1.010 (95% CI: 1.001–1.019), respectively. These associations remained robust in sensitivity analyses after excluding participants with hypertension or diabetes. Furthermore, the mortality risk was more pronounced among rural residents, and the concentration–risk relationships exhibited a nonlinear pattern. Notably, significant associations were observed between PM2.5 and the neutrophil-to-lymphocyte ratio. This study underscores the need to prioritize control of BC, OM, and SO42− in indoor environments. Stricter emission controls and component-specific standards are needed to reduce health risks.