Non-optimum temperatures modified the associations between PM_2.5 and its components and hospitalizations for chronic kidney disease in China

Epidemiological evidence concerning whether exposure to fine particulate matter (PM_2.5) and its components was linked to an elevated risk of hospitalizations for chronic kidney disease (CKD) remains insufficient. Moreover, it remains unclear whether ambient temperatures have potential modification effects on PM_2.5's impacts. In the current study, we collected a nationwide sample of 2,259,240 hospitalization records for CKD in 260 Chinese cities. The associations between air pollutants and CKD hospitalizations were determined by the space-time-stratified case-crossover design. We further assessed the effects of PM_2.5 and its components in three temperature strata [i.e., lowest (<25th), medium (25–75th), and highest (>75th)]. The findings demonstrated the significant and monotonic associations between risk of CKD hospitalizations and exposure to PM_2.5, black carbon (BC), sulfate (SO₄²⁻), nitrate (NO₃⁻), ammonium (NH₄⁺), and organic matter (OM). For instance, along with an interquartile range increment in PM_2.5 (29.47 μg/m³), the relative risks (RR) were 1.016 (95 % confidence interval [CI]:1.012–1.019) at lag 0–4 days. Higher ambient temperature significantly exacerbated the estimated impact of PM_2.5 and its components on CKD hospitalizations, while significantly stronger associations were also observed at lower temperature for SO₄²⁻ and NO₃⁻. The modification effects of non-optimum temperatures varied among different etiologies of CKD and geographic regions. This study provides insights into the joint kidney health effects of climate change and air pollution. These findings highlight the necessity of protection measures against high concentration of PM_2.5 and non-optimum temperatures for the vulnerable populations.