Older adults are particularly susceptible to heat-related morbidity, including kidney complications, according to a recent study.
The study, published in JAMA, assessed the impact of extreme heat exposure on kidney function biomarkers in 20 young (18-39 years, mean age, 27.5 years) and 18 older (≥65 years, mean age, 70.2 years) adults. Following institutional review board approval from the University of Texas Southwestern Medical Center, participants provided written informed consent. Data collection occurred between March 2021 and March 2023. Participants were exposed to two heat conditions: a dry setting (47°C at 15% relative humidity) and a humid setting (41°C at 40% relative humidity), simulating historical heat waves. They engaged in seven, five-minute bouts of light physical activity during the three-hour exposure and consumed 3 mL/kg water per hour.
Blood samples were collected at baseline, end-heating, and two hours post-exposure. The primary outcome was plasma creatinine, with changes ≥0.3 mg/dL was considered clinically meaningful, researchers noted. Cystatin C was the secondary outcome.
In the dry setting, older adults experienced a mean core temperature increase of 1.4°C and a mean body mass loss of 1.1%. Plasma creatinine increased significantly from baseline to end-heating by 0.10 mg/dL and by 0.17 mg/dL two hours post-exposure; two older adults had increases ≥0.3 mg/dL. Researchers also reported cystatin C levels also increased significantly. In young adults, the mean core temperature increased by 0.7°C, with a mean body mass loss of 1.2%. Plasma creatinine increased by 0.06 mg/dL two hours post-exposure.
In the humid setting, older adults showed a mean core temperature increase of 1.1°C and a mean body mass loss of 0.6%. Plasma creatinine did not change significantly from baseline to end-heating but increased by 0.06 mg/dL two hours post-exposure; one older adult had an increase ≥0.3 mg/dL. In young adults, the mean core temperature increased by 0.6°C, with a mean body mass loss of 0.5%. Plasma creatinine decreased by −0.05 mg/dL from baseline to end-heating and did not change significantly two hours post-exposure. Cystatin C levels did not show significant interaction by group.
“These findings provide limited evidence that the heightened thermal strain in older adults during extreme heat may contribute to reduced kidney function,” stated researchers. “Older adults had increases in plasma creatinine and cystatin C after exposure to the dry setting, but there were only minor changes in young or older adults following exposure to the humid setting.”
The study’s limitations included using plasma-based kidney function markers, a short lab-based exposure, and a small, generally healthy participant pool.
This study was funded by the NIH and the American Heart Association. Full list of author disclosures can be found in the original study.