Kidney Health in a Warming World: Heat, Climate Change, and Implications for Care

Introduction

The decision of the World Health Assembly to recognize kidney disease as a global public health priority¹ marks an important inflection point for nephrology. It reflects not only the accelerating global burden of chronic kidney disease (CKD)—now affecting nearly 1 in 10 people worldwide—but also the scale and urgency of the challenge: without coordinated global action, CKD is projected to become the fifth leading cause of death by 2050.¹

Importantly, the resolution acknowledges that kidney health is shaped across the life course by a complex interplay of social, economic, and environmental determinants. It explicitly elevates climate change as a major risk to kidney health, particularly for resource-constrained populations with limited capacity to adapt.

Among climate-related exposures, heat has emerged as one of the most significant threats to kidney health. Global mean temperature has risen by approximately 1.3 °C since preindustrial times, with recent years repeatedly approaching or temporarily exceeding 1.5 °C, a threshold widely associated with increased climate-related harms.² Rising baseline temperatures and increasingly frequent and intense heatwaves have transformed heat exposure from an episodic stressor into a routine environmental condition for much of the global population.²

Pathophysiological Pathways Linking Heat and Kidney Injury

The kidneys are uniquely vulnerable to heat-related injury owing to their distinctive physiology and high metabolic demands. During heat exposure, thermoregulatory responses increase cutaneous blood flow to promote heat dissipation.^3,S1 This may be accompanied by reduced renal perfusion, particularly in the setting of volume depletion. Concurrent increases in sweating and insensible fluid losses further reduce effective circulating volume and activate vasoconstrictive neurohormonal pathways, compounding reductions in renal blood flow and, when sufficiently severe, in glomerular filtration.

In addition, heat stress may contribute to kidney injury via hyperuricemia and urate crystalluria, clinical or subclinical rhabdomyolysis, and through hyperosmolality-driven vasopressin release and activation of renal aldose reductase.^4,S2 Activation of vasopressin and the polyol pathways during dehydration is adaptive in the short term by promoting urinary concentration and osmoprotection; however, recurrent or excessive activation may become maladaptive, promoting oxidative stress, inflammation, hypertension, and profibrotic signalling.S2 Over time, repeated or prolonged episodes of injury, even if subclinical, may accumulate and contribute to tubulointerstitial fibrosis and glomerulosclerosis.³

Clinical and Epidemiological Evidence Across the Kidney Disease Spectrum

Heat Exposure and Acute Kidney Injury

Multiple studies across diverse settings have shown increased hospital admissions for acute kidney injury on days of high ambient temperature and during heatwaves.S3–S8 Particularly susceptible groups include the very young, the older population, individuals using medications that impair physiological adaptation to heat and dehydration, and those with pre-existing kidney disease.³ Occupational and environmental factors are also important; for example, outdoor work and residence in urbanized areas, where exposure to the urban heat island effect—higher local temperatures driven by dense built environments and limited vegetation—can further amplify heat-related kidney risk.S9

Heat Exposure and the Development of CKD

Beyond acute injury, accumulating evidence also links heat exposure to the development of CKD and kidney failure. CKD of unknown etiology (CKDu) describes clusters of CKD that share a tubulointerstitial pattern of injury, occurring in populations without the usual drivers, such as diabetes or long-standing hypertension.⁴ CKDu has been described most prominently in hot, economically disadvantaged settings across the Global South, including South Asia (e.g., India and Sri Lanka), parts of Africa, and Central and South America.S10 It disproportionately affects working-age adults engaged in manual or agricultural labor, although demographic and contextual characteristics differ between regions. Concentrated in resource-poor settings, CKDu is associated with high rates of progression to kidney failure and substantial premature mortality; while precise estimates are lacking, tens of thousands of deaths have occurred in recent decades, many in early and midadulthood, with profound social and economic consequences.S11^,S12

A leading hypothesis proposes that CKDu arises from repetitive heat exposure combined with heavy physical workload and dehydration, resulting in recurrent subclinical or overt acute kidney injury with incomplete recovery—often conceptualized as “heat-stress nephropathy.”⁵ Increasingly, however, CKDu is viewed as a multifactorial condition, in which heat stress interacts with a constellation of occupational, environmental, and individual factors.S13^,S14 Work practices such as limited rest breaks, inadequate access to water and shade, and sustained high physical workload likely shape risk and help explain disease clustering within particular industries and communities. Additional contributors under investigation include water quality, agrochemicals and pesticides, heavy metals, recurrent infections, and genetic susceptibility, although evidence remains mixed and is often highly context-specific.S13^,S14 This heterogeneity suggests that CKDu may represent a spectrum of overlapping disease pathways that share a common phenotype.

In this framework, heat may operate as a primary driver of kidney injury in some contexts and as a potent risk amplifier in others. These roles are not mutually exclusive. Despite ongoing uncertainty regarding etiology, there is broad recognition of the need to reduce occupational heat exposure, including through access to hydration, rest, and shade.^4,S15 Such measures are supported by the precautionary principle and established occupational health and safety standards, although their effectiveness in reducing CKDu incidence and slowing disease progression warrants continued evaluation. Consistent with potential benefit, implementation of a water-rest-shade intervention during the harvest season in El Salvador was associated with attenuation of heat-related kidney function decline among sugarcane workers.S15

Importantly, although CKDu is the most prominent manifestation of heat-associated CKD, epidemiological evidence indicates that heat-related risk extends beyond traditional CKDu contexts. Population-based cohort studies from East Asia and the United States have linked higher ambient temperatures, extreme heat events, and heat-related illness to increased risks of incident CKD and kidney failure, including among nonoccupationally exposed groups.S16–S19

Heat Exposure and CKD Progression

Heat also represents an important and under-recognized risk factor for adverse outcomes in individuals with established CKD. In a large Chinese study, higher ambient temperatures were linked to increased CKD-related hospitalizations, particularly in subtropical cities, with additional risk during heatwaves.S20 Similarly, a post hoc analysis of the Dapagliflozin and Prevention of Adverse outcomes in CKD trial found that higher ambient heat exposure was associated with a faster rate of eGFR decline across diverse CKD etiologies, with estimates suggesting an additional ∼ 3.7 ml/min per 1.73 m² per year loss in very hot versus temperate environments—an effect similar in magnitude to the estimated glomerular filtration rate slope difference observed between treatment groups in the original trial.⁶ This suggests that attention to heat exposure may be as clinically relevant for CKD progression as pharmacological intervention.

Heat-Related Risk in Dialysis Populations

Adverse effects are also evident in dialysis populations. In nationally representative United States hemodialysis data, higher mortality and healthcare utilization were observed at moderately high temperatures (≥ 29.5 °C), with the greatest risks on extreme heat days (≥ 32.3 °C).S21 Similar associations have been reported in urban United States cohortsS22 and in Europe.S23 These excess risks may reflect a convergence of dialysis-specific vulnerabilities, including limited capacity for thermoregulation and fluid adjustment, cardiovascular instability, and the exacerbation of underlying comorbid disease during heat stress.

Studies incorporating integrated heat-stress metrics indicate heightened vulnerability under conditions of high humidity in dialysis populations, reflecting impaired evaporative cooling and greater physiological heat strain at a given temperature. Accordingly, mortality risks during extreme humid-heat events—defined using the heat-indexS24 (combining air temperature and relative humidity) or the Universal Thermal Climate IndexS25 (integrating temperature, humidity, wind speed, and radiant heat)—exceed those observed when exposure is defined by air temperature alone.

Heat Exposure and Kidney Stone Disease

Beyond acute and chronic kidney injury, a substantial body of evidence links heat exposure to an increased risk of kidney stone formation.⁷ This association is thought to arise primarily from heat-related fluid losses through sweating, which reduces urine volume and increases urinary concentration, thereby promoting supersaturation of lithogenic salts. Increased urinary calcium excretion related to sun exposure and vitamin D synthesis has also been proposed as a contributory mechanism, although supporting evidence remains limited.

Consistent with these mechanisms, the geographic distribution of kidney stone disease mirrors climatic gradients, with higher incidence observed in warmer regions,S26 and epidemiological studies consistently report seasonal peaks in stone-related emergency presentations during summer months.S27^,S28 At the individual level, short-term increases in ambient temperature have been associated with a rise in the risk of stone events.⁷

The prevalence of kidney stone disease has increased substantially over recent decades; in the United States, population-based data indicate that prevalence has nearly tripled since the 1970s, with similar upward trends reported across many other regions.S29 Although this likely reflects a complex interplay of dietary, metabolic, and behavioral factors, rising ambient temperatures and more frequent extreme heat exposure are increasingly recognized as plausible contributors.⁷ As global temperatures continue to rise, the burden of kidney stone disease is therefore expected to grow further, with important implications for individual morbidity, health-care utilization, and economic costs.

Implications for Kidney Care in a Warming World

Against this backdrop, the 2024 World Kidney Day theme—Kidney Health for All: Caring for People, Protecting the Planet⁸—is both timely and directive. It draws attention not only to the effects of heat on kidney disease, but also to a broader constellation of environmental stressors, including air pollution, extreme weather events, and the growing burden of climate-sensitive infectious diseases.

Because these stressors are largely anthropogenic, addressing them demands a fundamental rethinking of how societies interact with the natural world, including how health systems are designed and delivered. The World Kidney Day campaign explicitly highlights the substantial carbon footprint and wider environmental impacts of kidney care—particularly dialysis—underscoring a reinforcing cycle in which environmental degradation contributes to kidney disease, while kidney care delivery itself adds to environmental harm.

In response, World Kidney Day calls for renewed emphasis on prevention, early detection, and timely management of kidney disease—which necessarily includes attention to heat-related risks—alongside equitable access to transplantation, to reduce progression to dialysis. It foregrounds equity, recognizing both the unequal distribution of environmental harms and the risk that climate change will further entrench existing disparities in kidney health. Finally, it calls for environmental stewardship to be embedded as a core principle of kidney care, including accelerated innovation in lower-impact therapies, prioritization of home-based dialysis modalities, and adoption of practices such as water reuse and material recycling, while ensuring that quality and safety of care are not compromised.

More broadly, the environmental determinants of kidney health extend beyond the direct control of the health sector. The kidney health community, alongside organizations such as the World Health Organization, has an important role in engaging with upstream economic and structural drivers of environmental degradation through coordinated advocacy for decarbonization and sustainable development. Kidney health and planetary health are closely interconnected, and progress in one will increasingly depend on advances in the other.