Synergistic effects of air pollution and cold spells on ischemic heart disease hospitalization risk: a case-crossover study in Xinxiang, China.

Air pollution and extreme weather events pose a serious threat to human health. We collected atmospheric pollution, meteorological factors, and hospitalisation data for ischemic heart disease (IHD) in Xinxiang, Henan Province, from 2016 to 2021. Using a time-stratified case-crossover design and conditional Poisson regression analysis, we explored the association between atmospheric pollutants (particulate matter with diameter ≤ 2.5 μm [PM_2.5], particulate matter with diameter ≤ 10 μm [PM₁₀], nitrogen dioxide [NO₂], carbon monoxide [CO]), meteorological factors, and IHD hospitalizations. We evaluated synergistic effects using relative excess risk due to interaction (RERI), attribute proportion (AP), and synergy index (S). PM_2.5, PM₁₀, NO₂, CO, relative humidity, and cold spells were significantly associated with IHD hospitalization risk. Significant interaction effects (RERI > 0, AP > 0, S > 1) were found in PM_2.5-PM₁₀-NO₂ combinations. The attributable fractions were 3.4-7.3% for pollutant combinations and 8-17% during cold spells with different PM_2.5 levels. Males and individuals aged ≥ 65 were more susceptible to pollutants, while females and elderly individuals showed higher sensitivity to cold spells. These findings provide evidence for optimizing extreme weather warning systems and reducing air pollution exposure to protect public health.