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

BACKGROUND

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.

OBJECTIVE

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

METHODS

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.

RESULTS

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).

SIGNIFICANCE: 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.