Preexisting multimorbidity predicts greater mortality risks related to long-term PM_2.5 exposure

Area of Science:

• Environmental Health
• Epidemiology
• Public Health

Background:

• Ambient fine particulate matter (PM2.5) exposure is a known health risk, but its impact on individuals with multimorbidity is understudied.
• Both PM2.5 exposure and multimorbidity are independently associated with increased mortality.
• The combined effects and interactions between PM2.5 and multimorbidity require further investigation.

Purpose of the Study:

• To assess the associations between long-term PM2.5 exposure and all-cause, cardiovascular, and respiratory mortality in individuals with and without multimorbidity.
• To examine the joint effects and interactions between PM2.5 exposure and multimorbidity on mortality risk.
• To quantify the excess risks and attributable proportions of PM2.5-induced mortality in relation to multimorbidity status.

Main Methods:

• A cross-cohort analysis of 3 prospective cohorts, enrolling 869,038 adults (aged ≥18 years) from 2005-2022.
• Multimorbidity identified at baseline using nine common chronic conditions.
• Cox proportional hazards models used to analyze associations, joint effects, and interactions, with stratified analyses by number of chronic conditions.

Main Results:

• Among 713,119 eligible participants, 65,490 had prevalent multimorbidity.
• PM2.5 exposure showed stronger associations with all-cause and cardiovascular mortality in individuals with multimorbidity compared to those without (P < 0.05 for heterogeneity).
• Significant additive interaction observed: PM2.5 and multimorbidity synergistically increased mortality, with risks escalating with higher PM2.5 levels and more chronic conditions.

Conclusions:

• Long-term PM2.5 exposure poses a significantly greater mortality risk to individuals with pre-existing multimorbidity.
• Synergistic effects between PM2.5 exposure and multimorbidity intensify mortality risks, particularly in those with multiple chronic conditions.
• Public health strategies should consider the heightened vulnerability of multimorbidity populations to air pollution.