Association between ambient temperature and first-time hospitalizations for acute kidney injury in Taiwan: A nationwide case-crossover study

Background Although substantial epidemiological evidence has demonstrated associations between high temperatures and acute kidney injury (AKI), few studies have focused on initial AKI events or examined differential vulnerability across populations, particularly with respect to occupational groups. This study aimed to examine the short-term effects of temperature on first-time AKI hospitalizations and to identify vulnerable subpopulations. Methods We conducted a time-stratified case-crossover study of 141,934 first-time AKI hospitalizations in Taiwan between 2008 and 2019 using data from the National Health Insurance Research Database. Patients with pre-existing chronic kidney disease were excluded. Associations between ambient temperature and AKI hospitalization were estimated using conditional logistic regression with distributed lag non-linear models, adjusting for relative humidity and major ambient air pollutants. Effect heterogeneity was examined across demographic, comorbidity, occupational, and socioeconomic subgroups. Results A J-shaped exposure–response relationship was observed, with a minimum morbidity temperature of 10°C. Compared with this reference, the odds ratio (OR) of AKI hospitalization was more than doubled at 34°C (OR = 2.058; 95% CI: 1.68–2.51). Each 1°C increase above the minimum morbidity temperature was associated with a 2.3% increase in AKI risk, and approximately 8% of AKI hospitalizations were attributable to high-temperature exposure. The heat effect was strongest on the same day of exposure. Stronger associations were observed among older adults, women, low-income groups, and particularly fishermen, who exhibited the highest heat-related risk. Conclusions Elevated ambient temperature is an important trigger of AKI, with disproportionately higher risks among occupational and socially vulnerable populations. These findings underscore the need to integrate kidney health into heat action plans and to develop targeted, occupation-specific adaptation strategies under ongoing climate change.