At a dialysis center in Atlanta, Lauren Kasper tended to patients resting in hospital beds, some too sick to be transferred to a chair. Many arrived in wheelchairs or walked with canes, their bodies weakened from kidney disease.

As she hooked them up to dialysis machines, Kasper, a nurse practitioner, was struck by how young many of her patients were.

“The majority of the patients that you would see in a typical outpatient center are 60-plus,” she said. “With these patients, some of them were in their 20s and their 30s, 40s. The fact that they were a really significant portion of the population was really startling.”

In 2022, Kasper co-authored a study on the work histories of these patients. Many had labored in landscaping, roofing or agriculture, where they were exposed to harsh chemicals and extreme heat. The study suggested that, in a warming climate, people working in heat-stressed environments may be at even greater risk of kidney disease.

Older man in foreground, huge industrial facility in background, with a map to the side showing chemical concentrations from a toxic plume of smoke.

“It’s not just the heat, it’s that humidity too – that combo is so hard on the body and can be so dehydrating for people,” Kasper said.

This summer much of the US baked under deadly, record-breaking heat. While extreme heat exposure is commonly associated with acute emergencies like heat stroke, researchers are finding it can also contribute to longer-term health problems, like heart disease, cognitive impairment and kidney failure.

When the body is exposed to extreme heat, the cardiovascular system goes into overdrive to keep the body at a safe temperature. Over time, experts say, these functions take a toll on organs like the heart and kidneys – especially for people who exert themselves outdoors.

“There are definitely risks for outdoor workers in terms of chronic disease, the main one being chronic kidney disease of unknown origin,” said Kristie Ebi, professor at the Center for Health and the Global Environment at the University of Washington. “With more research, it’s likely that others will arise.”

In recent decades, young people have been showing up in dialysis centers in Sri Lanka, Central America, India, Saudi Arabia, Taiwan and the US with severe kidney damage and none of the typical risk factors, such as diabetes, autoimmune disease or severe high blood pressure.

It’s still unclear whether heat is the primary cause of the illness in otherwise healthy young people, or if other factors like pesticides, contaminated drinking water or the use of painkillers are also contributing, researchers say.

“This is probably multifactorial, multiple things coming together, merging and making the perfect storm for farm workers to suffer kidney dysfunction,” said Roxana Chicas, a registered nurse and professor at Emory University. “But I do think that dehydration is one of the biggest players along with heat exposure – the high, ambient heat that they’re exposed to, and working really hard.”

Kidneys filter the blood, removing waste and excess fluids from the body. But heat exposure and dehydration can decrease blood flow to the kidneys, depriving them of oxygen; cause them to become inflamed and break down muscle tissue, releasing certain enzymes that can injure the kidneys.

“We are thinking of heat as an accelerator” to kidney injuries that accumulate over time, said Shuchi Anand, a nephrologist at Stanford University.

Though workers in several sectors are vulnerable to extreme heat, researchers said farmworkers – many immigrants with few labor protections – face specific risk-factors, such as payment systems that disincentivize water breaks.

In May, Chicas published a study that found workers who are paid a piece rate for the amount of food picked rather than hours worked had higher rates of acute kidney injury. She said workers drenched in sweat often push themselves to pick fruits and vegetables as quickly as possible. “It’s almost suffocating to breathe because it’s so hot and humid. They describe it as working inside an oven,” Chicas said.

They know they need to drink water and take breaks to stay safe, she said. “But that’s really hard when there’s such a demand and wages are so low that they have to push themselves to meet their quotas.”

She said some workers with kidney disease ultimately return to their home countries because they can’t access healthcare in the US, and they have family to care for them at home.

Heat protections for workers in the US are currently a patchwork. Only a handful of states have heat exposure standards, whereas some states, notably Florida and Texas, prohibit local governments from enacting protections. In July, the Biden administration proposed a national heat standard that could go into effect next year, affecting some 36 million workers. Experts said such a standard could help prevent an onslaught of heat-related illnesses.

Researchers are still figuring out what longer term exposure to higher temperatures means for the general population. Ebi, the University of Washington professor, noted that humans have long lived in a range of temperatures and that the body acclimatizes over time.

But Chicas said what’s happening to farmworkers is a warning to people who might not currently feel they’re in danger. “Farmworkers, being at the frontline of climate change, are already giving us a glimpse into this kidney dysfunction associated with rising temperatures,” she said. “In a warming climate, we could all be at risk for this.”