Association of summer temperatures and acute kidney injury in South Korea: a case-crossover study

Ambient heat exposure and kidney function in patients with chronic kidney disease: a post-hoc analysis of the DAPA-CKD trial

BACKGROUND

Higher temperatures are associated with higher rates of hospital admissions for nephrolithiasis and acute kidney injury. Occupational heat stress is also a risk factor for kidney dysfunction in resource-poor settings. It is unclear whether ambient heat exposure is associated with loss of kidney function in patients with established chronic kidney disease. We assessed the association between heat index and change in estimated glomerular filtration rate (eGFR) in participants from the DAPA-CKD trial in a post-hoc analysis.

METHODS

DAPA-CKD was a randomised controlled trial of oral dapagliflozin 10 mg once daily or placebo that enrolled participants aged 18 years or older, with or without type 2 diabetes, with a urinary albumin-to-creatinine ratio of 200-5000 mg/g, and an eGFR of 25-75 mL/min per 1·73 m2. In this post-hoc analysis, we explored the association between time-varying daily centre-level heat index (ERA5 dataset) and individual-level change in eGFR in trial participants using linear mixed effect models and case-time series. The DAPA-CKD trial is registered with ClinicalTrials.gov, NCT03036150.

FINDINGS

Climate and eGFR data were available for 4017 (93·3%) of 4304 participants in 21 countries (mean age: 61·9 years; mean eGFR: 43·3 mL per 1·73 m2; median 28 months follow-up). Across centres, a heat index of more than 30°C occurred on a median of 0·6% of days. In adjusted linear mixed effect models, within each 120-day window, each 30 days' heat index of more than 30°C was associated with a -0·6% (95% CI -0·9% to -0·3%) change in eGFR. Similar estimates were obtained using case-time series. Additional analyses over longer time-windows showed associations consistent with haemodynamic or seasonal variability, or both, but overall estimates corresponded to an additional 3·7 mL per 1·73 m2 (95% CI 0·1 to 7·0) loss of eGFR per year in a patient with an eGFR of 45 mL per 1·73 m2 located in a very hot versus a temperate environment.

INTERPRETATION

Higher ambient heat exposure is associated with more rapid eGFR decline in those with established chronic kidney disease. Efforts to mitigate heat exposure should be tested as part of strategies to attenuate chronic kidney disease progression.

FUNDING

None.

Bidirectional modification effects on nonlinear associations of summer temperature and air pollution with first-ever stroke morbidity

High temperature and air pollution may induce stroke morbidity. However, whether associations between high temperature and air pollution with stroke morbidity are modified by each other is still unclear. Data on 23,578 first-ever stroke patients in Shenzhen, China, during the summers of 2014-2018 were collected. Distributed lag nonlinear models were used to assess the modifying effects of air pollution stratified by the median for the associations between summer temperature and stroke morbidity at 0-3 lag days; modifying effects of temperature stratified by the minimum morbidity temperature on the associations between air pollution and stroke morbidity at the same lags were also estimated. The attributable risks of high temperature and high pollution on stroke morbidity were quantified. Stratified analyses of gender, age, migration type, and complication type were conducted to assess vulnerable population characteristics. Summer high temperature may induce stroke morbidity at high-level PM2.5, PM10, O3, SO2, and NO2 conditions, with attributable fraction (AF) of 2.982% (95% empirical confidence interval [eCI]: 0.943, 4.929), 3.113% (0.948, 5.200), 2.841% (0.943, 4.620), 3.617% (1.539, 5.470), and 2.048% (0.279, 3.637), respectively. High-temperature effects were statistically insignificant at corresponding low-level air pollution conditions. High-level PM2.5, PM10, and O3 may induce stroke morbidity at high-temperature conditions, with AF of 3.664% (0.036, 7.196), 4.129% (0.076, 7.963), and 4.574% (1.009, 7.762), respectively. High-level PM2.5, PM10, and O3 were not associated with stroke morbidity at low-temperature conditions. The effects of high temperature and high pollution on stroke morbidity were statistically significant among immigrants and patients with hypertension, dyslipidemia, or diabetes but insignificant among natives and patients without complications. The associations of summer temperature and air pollution with first-ever stroke morbidity may be enhanced bidirectionally. Publicity on the health risks of combined high temperature and high pollution events should be strengthened to raise protection awareness of relevant vulnerable populations.