Extreme Heat Exposure and All-Cause Mortality in Chronic Kidney Disease: A Nationwide Time-Stratified Case-Crossover Study of More Than One Million Patients

Abstract

Chronic kidney disease (CKD) imposes a global public health burden and is known to be affected by environmental stress. Although extreme heat exposure is a risk factor for CKD, the short-term heat effects in patients with CKD are unclear. We examined the association between ambient heat exposure and mortality in CKD patients. From the National Health Insurance Service (NHIS) data in Korea, we constructed a cohort of approximately 1.14 million CKD patients and a matched non-CKD cohort (1:1 matched on sex and 10-year age group). Within each cohort separately, all deaths during the follow-up period (2015–2023) were identified and analyzed using a time-stratified case-crossover design. Comparing the 99th percentile temperature (extreme heat) to the 75th percentile temperature (moderate heat), associations with all-cause mortality were estimated with distributed lag nonlinear models (DLNMs; lags 0–6) within conditional logistic regression. Subgroup and sensitivity analyses assessed effect modification and robustness. During follow-up, 223,949 and 178,878 deaths occurred in the CKD group and matched non-CKD group, respectively. Extreme heat was associated with increased mortality risk in the CKD group (OR 1.041; 95% CI 1.002–1.081; p = 0.041). Between-group analysis showed no significant effect modification by CKD status (relative OR 1.048; 95% CI 0.990–1.110; interaction p = 0.107). Subgroup analyses indicated significant differences among women, elderly individuals, non-Medical Aid recipients, and those with hypertension. Short-term extreme heat exposure is associated with increased mortality in patients with CKD, with heightened vulnerability in specific subgroups. These findings highlight the need for targeted preventive strategies in the CKD population.