Association between ambient temperature and acute kidney injury: a nationwide space-time-stratified case-crossover...

Acute kidney injury (AKI) is a severe condition characterized by a sudden decline of kidney function with a high mortality rate and healthcare costs. While extreme heat is a recognized risk factor for AKI, the effects of both heat and cold exposure across different demographics remain unclear.

To examine the association between ambient temperatures and AKI emergency hospitalizations, with a focus on age and sex differences.

Using a nationwide database, we identified 119,027 AKI emergency hospitalizations from 2011 to 2019. A space-time-stratified case-crossover study with conditional quasi-Poisson regression analysis was applied to estimate region-specific relative risk (RR) of AKI emergency hospitalization over lag days 0-13. Pooled RRs were calculated using random-effects meta-analysis. Analyses were stratified by age (younger, 15-49; middle-age, 50-64; and older, 65+ years old) and sex.

Both extreme cold (first percentile) and heat (99th percentile) were associated with an increased risk of AKI emergency hospitalizations, with cumulative RRs of 1.24 (95% CI 1.09-1.40) and 2.21 (95% CI 2.00-2.43), respectively. Heat-related susceptibility was highest in younger (RR 4.24, 95% CI 2.93-6.15) and middle-aged men (RR 4.20, 95% CI 3.46-5.10), while in women it occurred in the older group (RR 1.87, 95% CI 1.64-2.14). Cold-related susceptibility was highest among older males (RR 1.28, 95% CI 1.06-1.53) and females (RR 1.29, 95% CI 1.04-1.58).

Extreme temperatures elevate AKI risk, with distinct age- and sex-specific vulnerability patterns. These findings highlight the need for targeted prevention strategies during temperature extremes, particularly protecting younger and middle-aged men from heat and older adults from cold exposure. Understanding the biological and social mechanisms underlying these demographic differences is essential for developing effective public health interventions in a changing climate IMPACT STATEMENT: This nationwide study reveals that both extreme heat and cold significantly increase acute kidney injury (AKI) emergency hospitalizations in Japan, with distinct age- and sex-specific vulnerability patterns. Younger and middle-aged men face a fourfold higher risk during heat exposure, while older adults of both sexes are most vulnerable to cold. These findings expand beyond heat-focused research and demonstrate the need for demographically targeted prevention strategies. As climate change intensifies temperature variability, these demographic-specific patterns highlight the need for tailored public health interventions to protect kidney health and reduce preventable AKI hospitalizations.