On intensely hot days, people suffering from advanced kidney disease face higher rates of hospitalization and death, according to new findings by University of Maryland School of Public Health researchers.

The study, based on an analysis of over 7,000 patients, is the first to show that race and ethnicity, geography and co-occurring illnesses affect the risk that kidney disease patients face from extreme heat.

It’s the latest study by Amir Sapkota, professor of applied environmental health—in collaboration with investigators from the Renal Research Institute and Boston University School of Public Health—to investigate links between climate change and human health. It was published today in JAMA Network Open

“Ongoing climate change is increasing the frequency of extreme heat events,” Sapkota said. Our results show that these events are particularly harmful to the most vulnerable individuals in our communities.”

The researchers analyzed 30 years of meteorological data to determine specific temperature thresholds for each location and calendar day. They used these thresholds to identify extreme heat events in Boston, New York City and Philadelphia from 2001–12. Finally, they cross-referenced the extreme heat days with patient records from local kidney disease clinics.

They found that the risk for hospitalization and death during the hottest days were consistently higher for black and white patients, but findings were less clear for Hispanic and Asian patients. Those with co-occurring conditions such as congestive heart failure, chronic obstructive pulmonary disease and diabetes also face increased risk, the study showed.

The underlying reason for the increased risk is unclear, but the researchers noted that one of the body’s responses to heat—lowered blood pressure—can be problematic for end-stage kidney disease patients.

“Hot weather can pose other challenges as well to patients who have to strictly manage fluid intake,” said Richard Remigio, a third-year doctoral student and the study’s first author.

“If it’s a hot day, we can quench our thirst, but unfortunately they don’t have that luxury,” Remigio said.

“We need to ramp up our ability to cope with these increases in extreme heat events. This is our canary in the coal mine.”

The variations shown in the current research with limited geographic coverage clearly indicate that social determinants do matter. Moving forward, the study team hopes to conduct a national level vulnerability assessment and further delve into underlying mechanisms.

With the projected increases in the number as well as duration and intensity of extreme heat events, community-specific adaptation strategies are needed to protect public health, according to the study authors.

“Climate change is not just about future scenarios and distant communities,” Sapkota said. “It is here and now, and it is adversely impacting our community’s health in more ways than we realize.”