Acute kidney injury, often abbreviated AKI, is a abrupt deterioration in kidney function that develops over hours to days. It is marked by a rapid rise in serum creatinine, a fall in urine output, and a cascade of metabolic disturbances that can become life-threatening without prompt treatment. Unlike chronic kidney disease, which unfolds over years, AKI is frequently reversible if caught early, which makes identifying its triggers a public health priority. Dehydration, reduced blood volume, inflammatory stress, and certain medications all contribute, and clinicians have long suspected that heat plays a role. What has been missing is a rigorous, population-wide quantification of that role, particularly for people experiencing their very first episode rather than recurrent events in patients with established kidney disease.

Researchers Hsi-Yun Chang and Hsiao-Yu Yang of National Taiwan University addressed this gap using a time-stratified case-crossover design, a method well suited to studying transient triggers of acute events. In this framework, each patient serves as their own control: the temperature on the day of hospitalization is compared with the temperature on nearby days when the same individual was not hospitalized. Because factors that remain constant for a given person, such as genetics, baseline health, and long-term lifestyle, are held fixed, the design isolates the effect of short-term exposure with unusual precision. The team analyzed 474,949 first recorded AKI hospitalizations in Taiwan between 2008 and 2019, drawing on the National Health Insurance Research Database, which covers virtually the entire population of the island.

To capture the nonlinear and delayed ways that temperature can act on the body, the investigators paired conditional logistic regression with distributed lag non-linear models, a statistical framework that simultaneously estimates how risk varies with the intensity of exposure and how that risk is distributed across the days that follow. The main model examined temperature alone over a lag window of zero to six days, while sensitivity analyses added relative humidity and major air pollutants, including fine particulate matter, nitrogen dioxide, and ozone, to test whether the temperature signal persisted after accounting for other environmental hazards. The result was a J-shaped exposure-response curve: risk remained relatively flat across cool and moderate temperatures, then rose steeply as daily mean temperatures climbed into the upper range.

The numbers are striking. Using a minimum morbidity temperature of 3.9 degrees Celsius as the reference point, the odds of a first AKI hospitalization at 33 degrees Celsius were 1.530 times higher, with a 95 percent confidence interval of 1.313 to 1.783. Above the 90th percentile of daily mean temperature, which sits at 29.98 degrees Celsius in Taiwan, every additional degree was associated with a 14.2 percent increase in the odds of hospitalization. The authors also calculated an attributable fraction: roughly 5.5 percent of first AKI hospitalizations could be attributed to temperatures above the minimum morbidity threshold. In a country with tens of thousands of such admissions each year, that fraction translates into a substantial burden of preventable illness.

Perhaps the most clinically important finding concerns timing. The temperature-associated risk was greatest on the very day of exposure and attenuated rapidly at later lags, indicating a predominantly acute effect. This pattern fits the known physiology of heat-related kidney injury. During intense heat exposure, sweating and insufficient fluid replacement reduce blood volume, the kidneys concentrate urine to conserve water, and the combination of dehydration, increased blood viscosity, and possible inflammatory and endothelial stress can compromise renal perfusion. In patients already taking diuretics, blood pressure medications, or other drugs that affect kidney hemodynamics, these stresses can tip renal function into overt injury within a single hot afternoon. The short lag structure suggests that same-day protective measures, rather than long-term preparation alone, could meaningfully reduce risk.

The study also probed who is most susceptible, and the answers carry direct implications for heat action plans. Effect modification was statistically significant for age, hypertension, and diabetes status, meaning the temperature-AKI association was stronger in certain subgroups defined by these characteristics. Older adults, whose kidneys have diminished reserve and whose thirst perception often blunts with age, are physiologically less able to defend blood volume during heat stress. Patients with hypertension frequently take medications that alter kidney blood flow, and diabetes damages the small vessels that sustain renal filtration. By contrast, the analysis did not find statistically significant differences in heat-related risk by sex, chronic kidney disease status, occupation, or socioeconomic status, a result that may reflect the granularity of the available data and the way occupational exposure was classified at the population level.

Taiwan offers an instructive setting for this kind of research. Its subtropical climate produces long, humid summers with frequent days above 30 degrees Celsius, and its dense urban environment amplifies heat through the urban heat island effect. At the same time, its single-payer National Health Insurance system generates comprehensive, longitudinal records that make it possible to identify first hospitalizations with confidence and to stratify risk across the entire population rather than in selected cohorts. That combination of intense heat exposure and complete data coverage is rare, and it is part of what makes the new findings relevant far beyond the island’s shores. As climate change pushes more regions into sustained extreme heat, the mechanisms and susceptibility patterns identified in Taiwan are likely to generalize to many other populations.

The authors argue that their results support a concrete policy shift: kidney health should be explicitly incorporated into heat action plans, which have traditionally focused on heatstroke, cardiovascular events, and respiratory illness. Practically, that means warning systems that flag dangerously hot days for people with hypertension or diabetes, guidance for patients on heat-sensitive medications to discuss hydration strategies with their clinicians, and workplace protections that account for the acute, same-day nature of the risk. It also means ensuring that emergency services anticipate surges in kidney-related admissions during heat waves, so that early recognition and fluid resuscitation can prevent progression to dialysis or death.

For the public, the takeaway is deceptively simple but backed by nearly half a million hospitalizations of evidence: the kidneys are an underappreciated casualty of extreme heat, and the danger window is measured in hours, not weeks. A hot day is not just uncomfortable; for millions of people with hypertension, diabetes, or advanced age, it can be the event that initiates a first kidney crisis. As global temperatures continue to rise, protecting renal health during heat waves is emerging as a core component of climate adaptation, and this Taiwanese study provides both the epidemiological justification and the vulnerability map needed to act on it.

Subject of Research: Short-term effects of ambient temperature on first acute kidney injury hospitalizations in Taiwan

Article Title: Association between ambient temperature and first recorded hospitalizations for acute kidney injury in Taiwan: a nationwide case-crossover study

Article References: Chang, H.-Y., & Yang, H.-Y. (2026). Association between ambient temperature and first recorded hospitalizations for acute kidney injury in Taiwan: a nationwide case-crossover study. Environmental Health. https://doi.org/10.1186/s12940-026-01344-1

Image Credits: AI Generated

DOI: 10.1186/s12940-026-01344-1

Keywords: acute kidney injury, ambient temperature, heat stress, case-crossover study, Taiwan, nephrology, climate change, hypertension, diabetes, vulnerable populations, hospitalization, environmental health