The Heat Is On

How climate change is affecting kidney health

Due to the increasing effects of climate change, hot weather poses a greater threat to public health than ever before. Exposure to rising temperatures speeds deterioration of kidney function that can culminate with CKD.

“As extreme heat events become more frequent and intense, the scale of heat-related kidney disease is likely to grow,” Katherine Barraclough, MD, told Nephrology Times. Dr. Barraclough is a nephrologist at the Royal Melbourne Hospital in Australia and associate professor in the School of Medicine at the University of Melbourne.

“In terms of the magnitude of the problem, reliable global prevalence estimates are difficult to obtain because heat-related kidney injury often goes unrecognized and surveillance is limited in many of the regions most affected,” she said. However, although estimates suggest that hundreds of thousands of people worldwide may be affected, the true number is likely much higher, Dr. Barraclough added.

Statistics suggest a strong association between acute kidney injury (AKI) and heat-related illnesses. A UK study shows that a 7-day heatwave in 2021 was linked to a 28.6% rise in AKI. Other research indicates that AKI is present in 91% of exertional heatstroke cases and suggests that less severe maladies, such as heat exhaustion, also may lead to AKI. Another investigation shows that the likelihood of having an AKI episode is higher at a temperature of 89.6 °F compared with 62.6 °F. 1

Aside from being associated with AKI, heat is related to the formation of kidney stones, Dr. Barraclough said. She cited an analysis that predicts the US could see an additional 1.6 to 2.2 million lifetime cases of nephrolithiasis by 2050.2

Certain segments of the population are especially vulnerable to heat-related illnesses, including older adults, young children, those lacking access to air conditioning, and those with chronic illnesses. Even people who are healthy but engage in sustained or vigorous activity outdoors—such as construction workers, farmers, athletes, and members of the military—are at a higher risk.

“Repeated exposure to very hot temperatures can absolutely cause AKI in someone without any other risk factors or previous kidney problems,” Karen Papez, MD, director of Pediatric Critical Care Nephrology at Phoenix Children’s Hospital in Arizona, explained in an interview. “When episodes of AKI happen close together, before the kidneys have fully recovered at a cellular level, it can cause chronic inflammation. This can progress to chronic kidney disease and even permanent kidney failure.”

As evidence mounts on the broad scope and serious nature of the effects of global warming on kidney health, nephrologists are examining the underlying mechanisms involved and proposing means of mitigation. Addressing the problem requires a multifaceted approach, including clinical practice interventions, hospital preparations for heatwaves, and advocacy.

Underlying Mechanisms

The kidneys are uniquely susceptible to the effects of heat for several reasons. Dehydration causes the urine to become concentrated, an effect that decreases the glomerular filtration rate (GFR), with the most rapid declines correlating with the highest heat exposure. In fact, even among patients with modest CKD, hot weather can impair this function. One analysis shows that an additional annual GFR loss of 3.7 mL/min/1.73 m² occurs in hot temperatures.1

Moreover, when body temperatures rise, more blood flows away from internal organs to the skin to promote cooling, resulting in reduced perfusion to the kidneys and resulting in tissue hypoxia injury.3 Also, hyperthermia and dehydration boost energy demands, increasing the body’s efforts to conserve electrolytes and fluids. This puts additional strain on the kidneys and may lead to kidney damage.3

Interventions for Clinical Practice

“Extreme heat should be considered a modifiable risk factor for kidney injury,” Pranav Garimella, MBBS, MPH, chief medical officer at the American Kidney Fund, told Nephrology Times. “As temperatures continue to rise, both clinicians and patients need to treat heat exposure with the same seriousness as other established stressors for the kidneys. The encouraging message I can provide is that many heat-related kidney injuries are preventable.”

The following interventions can help protect patients and optimize outcomes.

Patient Counseling

Counseling about the effects of high temperatures on CKD progression should focus on the following areas4:

Hydration: Replacing fluids lost through perspiration can help prevent some of the harmful effects of heat by reducing sodium reabsorption in the kidneys. It can also preserve kidney perfusion by helping to maintain plasma volume and lowering core temperature. “For individuals with established CKD, avoiding heat-related volume depletion may be as important as pharmacologic therapies in slowing disease progression,” said Dr. Barraclough.

Rest and Shade: Rest lowers metabolic heat production, and shade decreases exposure to the sun and fosters heat dissipation in the environment. Outdoor workers should be advised to avoid payment systems involving piece-rate compensation, which incentivizes overwork. Cooling approaches—such as ice slurry or cold-water ingestion, cooling vests, and wind/skin wetting techniques—may help prevent hyperthermia in athletes, but these approaches are not always feasible for outdoor workers.

Heat Acclimation: To some extent, outdoor workers may adapt to a hot environment over time. Repeated heat exposure can lead to physiologic adaptations for improving temperature regulation, such as a lower core body temperature and a higher perspiration rate. However, these adaptations may not be sustainable over the long term because they can increase the risk for AKI.

Nutritional Supplementation: Decreased blood flow to the kidneys due to physical exertion in heat can result in kidney hypoxia and ischemia, which generate reactive oxygen species that can harm tubal cells. Adding antioxidants to beverages may help prevent AKI worsening from this cause, but more research is necessary to verify the benefit.

Recognize Signs of Heat Illness: If patients with AKI or CKD know the signs and symptoms of heat-related illness, they are more likely to engage in remediation measures when they become overheated and seek prompt medical attention.

Risk Stratification

Despite expanding evidence of the link between heat exposure and kidney health, the nephrology community has not fully incorporated environmental stressors into guidelines and risk models. Yet more endeavors in this area can help. Just as pulmonary physicians consider exposure to environmental allergens when making patient care plans, nephrologists can incorporate heat stress into risk stratification to optimize kidney disease treatment.

Factors that increase risk include older age, dehydration, and comorbidities that tax the kidneys, making them less able to tolerate high temperatures.5 Estimating heat stress also involves consideration of indoor and outdoor temperatures and humidity in addition to direct sunlight exposure and contact with hot surfaces. Other relevant factors include fluid access, work intensity, and type of clothing worn because some garments can trap heat.

Medication Review

The widespread use of medications including nonsteroidal anti-inflammatory drugs, metformin, antibiotics, diuretics, and sodium-glucose cotransporter 2 inhibitors can contribute to drug-induced nephropathy. The repeated use of medications with harmful effects on the kidneys accounts for 20% of all causes of kidney toxicity.5 Their use can cause direct tubular injury, resulting in cellular damage, acute tubular necrosis, and obstruction due to crystalline precipitation. In addition, chemotherapeutic agents, quinine, antiangiogenic agents, and gemcitabine can compromise renal perfusion, impair glomerular filtration, and induce thrombotic microangiopathy, leading to kidney injury.

Such adverse effects highlight the need to review a patient’s medication regimen more frequently during hot conditions to determine the need for dosage adjustments or changes to alternative drugs that do not impair thermoregulation.

Comorbidity Management

Management of comorbidities that affect kidney health—including diabetes, hypertension, and obesity—is vital. Diabetes interferes with the body’s ability to maintain an optimal temperature because it compromises the main mechanisms of heat loss and affects the nerves that facilitate involuntary function, including thermoregulation. Hypertension constricts blood vessels throughout the body, including the kidneys, reducing blood flow. Obesity lowers the body’s capacity to dissipate heat, an effect that raises the risk for heat-related illnesses and their consequences, such as kidney disease.

Close Oversight

Patients with AKI face dangers from hot weather that necessitate closer clinical oversight during heatwaves. This involves updating care plans, using telehealth check-ins, and having tighter monitoring windows.

Hospital Preparation Strategies

The Texas Hospital Association provides the following recommendations for hospitals to take when preparing for heatwaves6:

Devise plans to address heat-related illness during power outages and conduct regular drills to promote efficient response in a crisis.

Establish infrastructure in facilities to ensure staff and patient comfort, including power generators, alternate cooling systems, and temperature-monitoring tools.

Educate staff on the dangers of extreme heat and train them to recognize symptoms of heat-related illness.

Use innovative technology to monitor the vital signs and temperatures of patients to foster prompt intervention when needed.

For high-risk patients, designate cool zones within the hospital, equipped with water dispensers, air conditioning, and fans.

Launch public awareness campaigns to spread information on heat safety.

Advocacy

Dr. Barraclough believes the kidney community has an important role to play in advocacy for occupational safety and climate safeguards.

Occupational Safety Advocacy

Advocacy for occupational safety includes promoting improved access to cooling, water, and shaded rest for outdoor workers. An example reported by the International Labor Organization offers some evidence that such measures can make a significant difference.

A program founded in Central America in 2017 provides safer conditions for sugarcane workers who face very high temperatures and their consequences. It involves mandated access to water and restrooms and the provision of work breaks in mobile tents for shaded rest throughout the day. In its first 3 years, the program resulted in a 94% drop in AKI due to exposure to excessive heat, along with a 10% to 20% increase in productivity.7

Advocacy for Climate Safeguards

Advocacy must extend to the root cause of the problem, global warming. Worldwide temperatures are rising at a rate of approximately 0.27 °C per 10 years, which greatly surpasses warming rates in the past.8 While this is concerning, the rate is expected to increase even more in the coming years.

Dr. Barraclough recommends that clinicians support policies that reduce greenhouse gas emissions, strengthen urban design, and reduce the environmental footprint of healthcare, including dialysis and transplant services.

However, as Dr. Barraclough explained in a recent editorial, addressing environmental stressors that affect kidney disease requires more than advocacy from nephrologists. Instead, a fundamental change in how the natural world and society intersect is needed.9 She suggested that the kidney health community work with oversight agencies, such as the WHO, to engage with structural and economic drivers of environmental degradation to advocate for interventions, such as decarbonization.

A key takeaway of Dr. Barraclough’s editorial is to adopt environmental stewardship as a key part of kidney care, while continuing to ensure safety and quality of treatment. “Kidney health and planetary health are closely interconnected, and progress in one will increasingly depend on advances in the other,” she wrote.