Associations Between Extreme Temperatures and Cardiovascular Cause-Specific Mortality: Results From 27 Countries.

BACKGROUND: Cardiovascular disease is the leading cause of death worldwide. Existing studies on the association between temperatures and cardiovascular deaths have been limited in geographic zones and have generally considered associations with total cardiovascular deaths rather than cause-specific cardiovascular deaths. METHODS: We used unified data collection protocols within the Multi-Country Multi-City Collaborative Network to assemble a database of daily counts of specific cardiovascular causes of death from 567 cities in 27 countries across 5 continents in overlapping periods ranging from 1979 to 2019. City-specific daily ambient temperatures were obtained from weather stations and climate reanalysis models. To investigate cardiovascular mortality associations with extreme hot and cold temperatures, we fit case-crossover models in each city and then used a mixed-effects meta-analytic framework to pool individual city estimates. Extreme temperature percentiles were compared with the minimum mortality temperature in each location. Excess deaths were calculated for a range of extreme temperature days. RESULTS: The analyses included deaths from any cardiovascular cause (32 154 935), ischemic heart disease (11 745 880), stroke (9 351 312), heart failure (3 673 723), and arrhythmia (670 859). At extreme temperature percentiles, heat (99th percentile) and cold (1st percentile) were associated with higher risk of dying from any cardiovascular cause, ischemic heart disease, stroke, and heart failure as compared to the minimum mortality temperature, which is the temperature associated with least mortality. Across a range of extreme temperatures, hot days (above 97.5th percentile) and cold days (below 2.5th percentile) accounted for 2.2 (95% empirical CI [eCI], 2.1-2.3) and 9.1 (95% eCI, 8.9-9.2) excess deaths for every 1000 cardiovascular deaths, respectively. Heart failure was associated with the highest excess deaths proportion from extreme hot and cold days with 2.6 (95% eCI, 2.4-2.8) and 12.8 (95% eCI, 12.2-13.1) for every 1000 heart failure deaths, respectively. CONCLUSIONS: Across a large, multinational sample, exposure to extreme hot and cold temperatures was associated with a greater risk of mortality from multiple common cardiovascular conditions. The intersections between extreme temperatures and cardiovascular health need to be thoroughly characterized in the present day-and especially under a changing climate.

Relationship between short-term ozone exposure, cause-specific mortality, and high-risk populations: a nationwide, time-stratified, case-crossover study.

BACKGROUND: Previous studies reported that short-term exposure to ground-level ozone is associated with mortality risk. However, due to the limited monitored areas, existing studies were limited in assessing the nationwide risk and suggesting specific vulnerable populations to the ozone-mortality risk. METHODS: We performed a nationwide time-stratified case-crossover study to evaluate the association between short-term ozone and cause-specific mortality in South Korea (2015- 2019). A machine learning-ensemble prediction model (a test R2>0.96) was used to assess the short-term ozone exposure. Stratification analysis was conducted to examine the high-risk populations, and the excess mortality due to non-compliance with the WHO guideline was also assessed. RESULTS: For all-cause mortality (1,343,077 cases), the risk associated with ozone (lag0- 1) was weakly identified (odd ratio: 1.005 with 95% CI: 0.997-1.014), and the risk was prominent in mortality with circulatory system diseases. In addition, based on the point estimates, the ozone-mortality risk was higher in people aged less than 65y, and this pattern was also observed in circulatory system disease deaths and urban areas. CONCLUSIONS: This study provides national estimates of mortality risks associated with short-term ozone. Results showed that the benefits of stricter air quality standards could be greater in vulnerable populations.

Association between long-term PM2.5 exposure and risk of Kawasaki disease in children: A nationwide longitudinal cohort study.

BACKGROUND: Based on previous studies suggesting air pollution as a potential risk factor for Kawasaki Disease (KD), we examined the association of long-term exposure to childhood fine particulate matter (PM2.5) with the risk of KD. METHODS: We used National Health Insurance Service-National Sample Cohort data from 2002 to 2019, which included beneficiaries aged 0 years at enrollment and followed-up until the onset of KD or age 5 years. The onset of KD was defined as the first hospital visit record with a primary diagnostic code of M30.3, based on the 10th revision of the International Classification of Diseases, and with an intravenous immunoglobulin (IVIG) prescription. We assigned PM2.5 concentrations to 226 districts, based on mean annual predictions from a machine learning-based ensemble prediction model. We performed Cox proportional-hazards modeling with time-varying exposures and confounders. RESULTS: We identified 134,634 individuals aged five or less at enrollment and, of these, 1220 individuals who had a KD onset and an IVIG prescription during study period. The average annual concentration of PM2.5 exposed to the entire cohort was 28.2 µg/m³ (Standard Deviation 2.9). For each 5 µg/m³ increase in annual PM2.5 concentration, the hazard ratio of KD was 1.21 (95% CI 1.05-1.39). CONCLUSIONS: In this nationwide, population-based, cohort study, long-term childhood exposure to PM2.5 was associated with an increased incidence of KD in children. The study highlights plausible mechanisms for the association between PM2.5 and KD, but further studies are needed to confirm our findings.

Air pollution and acute kidney injury with comorbid disease: A nationwide case-crossover study in South Korea.

Emerging evidence suggests that air pollution is a significant contributor to the global burden of kidney disease. Although acute kidney injury (AKI) is a common secondary event in ill patients, evidence regarding the association between air pollution and AKI accompanied by specific comorbidities is limited. This study aimed to estimate the association between short-term exposure to air pollution (fine particulate matter ≤2.5 µm [PM2.5] and ozone [O3]) and incident AKI by comorbid diseases using the Korea National Health Information Database (NHID). Total of 160,390 incident AKI cases, defined as an emergency department (ED) visit due to AKI, were observed within the period 2015-2021 in inland South Korea. A time-stratified case-crossover design was applied for PM2.5 and O3 individually, using a conditional logistic regression model within each case and its own control (three or four days of the same day of the week in the same month) to estimate the association between short-term air pollution exposure and ED visits due to AKI. Short-term exposure to PM2.5 and O3 was associated with ED visits due to AKI with ORs of 1.008 (95% confidence interval [CI]: 0.999, 1.017) and 1.019 (95% CI: 1.005, 1.033) for an interquartile range (IQR) increase in lag 0-1 day PM2.5 and O3 respectively, although OR for PM2.5 was marginally significant. The odds of incident AKI associated with PM2.5 was evident in conjunction with ischemic heart disease, cerebrovascular disease, gastrointestinal bleeding, and pneumonia. For O3, the estimated odds was prominent for AKI with ischemic heart disease. In addition, the comorbid disease-specific odds of AKI attributed to air pollution varied by sex and age. Our findings provide epidemiological evidence of a plausible mechanism between air pollution and incident AKI and suggest the need for personalized AKI prevention strategies attributed to air pollution.

Surviving the cold: Assessing long-term outcomes among Korean CKD patients exposed to low perceived temperature during winter.

Perceived temperature (PT), which encompasses meteorological factors such as wind speed, cloud cover, and humidity, reflects the actual effect of temperature on the human body. However, limited data exist on the health implications of prolonged exposure to low temperatures during winter in individuals with chronic kidney disease (CKD). We investigated the association between winter PT and long-term outcomes among CKD patients. A total of 32,870 CKD patients from three tertiary hospitals in Seoul were enrolled in this retrospective study (2001-2018). PT was calculated using Staiger's equation, integrating temperature data from 29 automated weather stations across Seoul, along with dew point temperature, wind velocity, and cloud cover data. Kriging interpolation was utilized to estimate PT values at the patients' locations. Overall mortality and major adverse cardiovascular events (MACEs) were assessed using a time-varying Cox proportional hazards model. Additionally, the Cox regression model evaluated PT corresponding to temperature thresholds for cold surge watches or warnings. Over a median follow-up of 6.14 ± 3.96 years, 6147 deaths (18.7%) were recorded. We found that as the average or minimum PT and Ta decreased by 1 °C, the risk of overall mortality significantly increased. In multivariable analyses, the hazard ratio (HR) for the average PT was 1.049 (95% confidence interval [CI] 1.028-1.071), and that for the minimum PT was 1.038 (CI 1.027-1.052). Furthermore, a cold surge warning at a PT of -25.63 °C indicated an HR of 1.837 (CI 1.764-1.914) and a C-index of 0.792. The increased risk of mortality was more pronounced in patients with low or middle socioeconomic statuses. For MACEs, lower average and minimum PT and Ta were associated with an increased risk, following a similar trend to overall mortality, although not all results reached statistical significance. These findings emphasize the importance of targeted public health policies to mitigate risks among vulnerable CKD patients.

Disparities in the association between ambient temperature and preterm birth according to individual and regional characteristics: a nationwide time-stratified case-crossover study.

BACKGROUND: Several studies have reported that climate change elevates heat exposure in pregnant women and high temperatures during pregnancy are associated with preterm births (PTBs). Although the association might be disproportionate, related evidence remains sparse. We evaluated the disproportionate risk of PTB associated with ambient temperature during pregnancy by individual and regional characteristics in South Korea. METHODS: We collected data on birth certificates and daily mean temperatures during the period from 2011 to 2019. A time-stratified case-crossover design was used to investigate the association between temperature and PTB and stratified analyses were conducted to examine the effect modification of individual and regional characteristics. RESULTS: A total of 160,067 singleton PTBs were recorded in Korea from 2011 to 2019. A 5℃ increase in the mean temperature during the last four weeks before delivery was associated with an increased risk of PTB with an odds ratio (OR) of 1.03 (95% confidence interval [CI]: 1.02, 1.05), and the association was more evident in mothers aged ≥35 years (OR: 1.06 [95% CI: 1.03, 1.10]) and with low education levels (OR: 1.04 [95% CI: 1.02, 1.05]). Additionally, the estimated risk was evident in districts with lower medical resources and more prominent disparities were shown by individual and regional characteristics in rural areas than in urban areas. CONCLUSIONS: This study provides evidence that the risk of PTB related to ambient temperature is disproportionate by individual and regional characteristics and suggests the need for public health policies to alleviate the disparities, especially in rural areas.

Association of long-term exposure to air pollution with chronic sleep deprivation in South Korea: A community-level longitudinal study, 2008-2018.

BACKGROUND AND OBJECTIVE: Although there are many findings about the effects of fine particulate matter (PM2.5) and sleep deprivation on health respectively, the association between PM2.5 and chronic sleep deprivation has rarely been investigated. Thus, we aimed to investigate this association using a nationwide survey in South Korea. METHOD: We examined the association between long-term exposure to PM2.5 and chronic sleep deprivation using a national cross-sectional health survey covering the entire 226 districts in inland South Korea from 2008 to 2018, with a machine learning-based national air pollution prediction model with 1 km2 spatial resolution. RESULTS: Chronic sleep deprivation was positively associated with PM2.5 in the total population (odds ratio (OR): 1.09, 95% confidence interval (CI): 1.05-1.13) and sub-population (low, middle, high population density areas with OR: 1.127, 1.09, and 1.059, respectively). The association was consistently observed in both sexes (males with OR: 1.09, females with OR: 1.09)) and was more pronounced in the elderly population (OR: 1.12) than in the middle-aged (OR: 1.07) and young (OR: 1.09) populations. CONCLUSIONS: Our results are consistent with the hypothesis regarding the relationship between long-term PM2.5 exposure and chronic sleep deprivation, and the study provides quantitative evidence for public health interventions to improve air quality that can affect chronic sleep conditions.

Hospital admission risks and excess costs for neurological symptoms attributable to long-term exposure to fine particulate matter in New York State, USA.

BACKGROUND: Although emerging evidence suggests that PM2.5 is linked to neurological symptoms (NSs) via neuroinflammation, relevant studies are scarce. This study aimed to investigate the risks and excess costs of hospital admission for five NSs-fatigue, headache, dizziness, convulsion, and paralysis-attributable to long-term exposure to PM2.5 in New York State, USA. METHODS: We analyzed the New York Statewide Planning and Research Cooperative System (SPARCS) from 2010 to 2016. A Bayesian hierarchical model with integrated nested Laplace approximations was performed to estimate the risks and excess costs of hospital admission for NSs due to long-term exposure to PM2.5 at the county level. RESULTS: A 1 µg/m3 increase in lag 0-1 years PM2.5 was associated with an increased risk of headache and convulsion by 1.06 (1.01, 1.11) and 1.04 (1.01, 1.06), respectively. The excess hospital admission cost for five NSs attributable to lag 0-1 years PM2.5 above the new World Health Organization guideline (annual standard: 5 µg/m3) was $200.24 (95% CI: 6.00, 376.96) million during 2011-2016, recording the highest for convulsion ($153.73 [95% CI: 63.61, 244.19] million). CONCLUSIONS: This study provides quantitative estimates of risks and excess costs for NSs attributable to long-term PM2.5 and suggests that policies that reduce long-term PM2.5 concentration in accordance with the new WHO air quality guidelines can yield substantial health and economic benefits related to NSs in the New York State population.

Short-term Exposure to Air Pollution and Attributable Risk of Kidney Diseases: A Nationwide Time-series Study.

BACKGROUND: Several studies have shown that long-term exposure to air pollution is associated with reduced kidney function. However, less is known about effects of short-term exposure to air pollution on kidney disease aggravation and resultant emergency room (ER) burden. This study aimed to estimate excess ER visits attributable to short-term air pollution and to provide evidence relevant to air pollution standards to protect kidney patients. METHODS: We conducted time-series analysis using National Health Insurance data covering all persons in South Korea (2003-2013). We collected daily data for air pollutants (particulate matter ≤10 µm [PM10], ozone [O3], carbon monoxide [CO], and sulfur dioxide [SO2]) and ER visits for total kidney and urinary system disease, acute kidney injury (AKI), and chronic kidney disease (CKD). We performed a two-stage time-series analysis to estimate excess ER visits attributable to air pollution by first calculating estimates for each of 16 regions, and then generating an overall estimate. RESULTS: For all kidney and urinary disease (902,043 cases), excess ER visits attributable to air pollution existed for all pollutants studied. For AKI (76,330 cases), we estimated the highest impact on excess ER visits from O3, while for CKD (210,929 cases), the impacts of CO and SO2 were the highest. The associations between air pollution and kidney ER visits existed for days with air pollution concentrations below current World Health Organization guidelines. CONCLUSION: This study provides quantitative estimates of ER burdens attributable to air pollution. Results are consistent with the hypothesis that stricter air quality standards benefit kidney patients.

Excess out-of-hospital cardiac arrests due to ambient temperatures in South Korea from 2008 to 2018.

Out-of-hospital cardiac arrest (OHCA) is a notable public health issue with negative outcomes, such as high mortality and aftereffects. Additionally, the adverse effects of extreme temperatures on health have become more important under climate change; however, few studies have investigated the relationship between temperature and OHCA. In this study, we examined the association between temperature and OHCA and its underlying risk factors. We conducted a two-stage time-series analysis using a Poisson regression model with a distributed lag non-linear model (DLNM) and meta-analysis, based on a nationwide dataset from South Korea (2008-2018). We found that 17.4% of excess OHCA was attributed to cold, while 0.9% was attributed to heat. Based on central estimates, excess OHCA attributed to cold were more prominent in the population with hypertension comorbidity (31.0%) than the populations with diabetes (24.3%) and heart disease (17.4%). Excess OHCA attributed to heat were larger in the populations with diabetes (2.7%) and heart disease comorbidity (2.7%) than the population with hypertension (1.2%) based on central estimates. Furthermore, the time-varying excess OHCA attributed to cold have decreased over time, and although those of heat did not show a certain pattern during the study period, there was a weak increasing tendency since 2011. In conclusion, we found that OHCAs were associated with temperature, and cold temperatures showed a greater impact than that of hot temperatures. The effects of cold and hot temperatures on OHCA were more evident in the populations with hypertension, diabetes, and heart diseases, compared to the general population. In addition, the impacts of heat on OHCA increased in recent years, while those of cold temperatures decreased. Our results provide scientific evidence for policymakers to mitigate the OHCA burden attributed to temperature.

Suicide rate and social environment characteristics in South Korea: the roles of socioeconomic, demographic, urbanicity, general health behaviors, and other environmental factors on suicide rate.

BACKGROUND: Suicide is a serious worldwide public health concern, and South Korea has shown the highest suicide rate among Organisation for Economic Co-operation and Development (OECD) countries since 2003. Nevertheless, most previous Korean studies on suicide had limitations in investigating various social environment factors using long-term nationwide data. Thus, this study examined how various social environment characteristics are related to the suicide rate at the district-level, using nationwide longitudinal data over 11 years. METHODS: We used the district-level age-standardized suicide rate and a total of 12 annual social environment characteristics that represented socioeconomic, demographic, urbanicity, general health behaviors, and other environmental characteristics from 229 administrative districts in South Korea. A Bayesian hierarchical model with integrated Laplace approximations (INLA) was used to examine the spatiotemporal association between the rate of suicide and the social environment indicators selected for the study. RESULTS: In the total population, the indicators "% of population aged 65 and older eligible for the basic pension", "% vacant houses in the area", "% divorce", "% single elderly households", "% detached houses", "% current smokers", and "% of population with obesity" showed positive associations with the suicide rate. In contrast, "% of people who regularly participated in religious activities" showed negative associations with suicide rate. The associations between these social environment characteristics and suicide rate were generally more statistically significant in males and more urbanized areas, than in females and less urbanized areas; however, associations differed amongst age groups, depending on the social environment characteristic variable under study. CONCLUSIONS: This study investigated the complex role of social environments on suicide rate in South Korea and revealed that higher suicide rates were associated with lower values of socioeconomic status, physical exercise, and religious activities, and with higher social isolation and smoking practice. Our results can be used in the development of targeted suicide prevention policies.

Excess mortality and the COVID-19 pandemic: causes of death and social inequalities.

BACKGROUND: During the coronavirus diseases 2019 (COVID-19) pandemic, population's mortality has been affected not only by the risk of infection itself, but also through deferred care for other causes and changes in lifestyle. This study aims to investigate excess mortality by cause of death and socio-demographic context during the COVID-19 pandemic in South Korea.  METHODS: Mortality data within the period 2015-2020 were obtained from Statistics Korea, and deaths from COVID-19 were excluded. We estimated 2020 daily excess deaths for all causes, the eight leading causes of death, and according to individual characteristics, using a two-stage interrupted time series design accounting for temporal trends and variations in other risk factors. RESULTS: During the pandemic period (February 18 to December 31, 2020), an estimated 663 (95% empirical confidence interval [eCI]: -2356-3584) excess deaths occurred in South Korea. Mortality related to respiratory diseases decreased by 4371 (3452-5480), whereas deaths due to metabolic diseases and ill-defined causes increased by 808 (456-1080) and 2756 (2021-3378), respectively. The increase in all-cause deaths was prominent in those aged 65-79 years (941, 88-1795), with an elementary school education or below (1757, 371-3030), or who were single (785, 384-1174), while a decrease in deaths was pronounced in those with a college-level or higher educational attainment (1471, 589-2328). CONCLUSION: No evidence of a substantial increase in all-cause mortality was found during the 2020 pandemic period in South Korea, as a result of a large decrease in deaths related to respiratory diseases that offset increased mortality from metabolic disease and diseases of ill-defined cause. The COVID-19 pandemic has disproportionately affected those of lower socioeconomic status and has exacerbated inequalities in mortality.

Effects of Asian dust-derived particulate matter on ST-elevation myocardial infarction: retrospective, time series study.

BACKGROUND: Dust storms affect human health by impairing visibility and promoting interactions with microscopic organisms, such as bacteria and fungi. Although ST-elevation MI (STEMI) and non-ST-elevation MI (NSTEMI) differ mechanistically, few studies have investigated the incidence of cardiovascular diseases according to infarction type; these studies have yielded inconsistent findings. This study aimed to examine whether PM size (< 2.5 µm (PM2.5) and < 10 µm (PM10)) modifies the effect of Asian dust on acute myocardial infarction (AMI), with separate analyses for STEMI and NSTEMI. METHODS: MI-related data from 9934 emergency visits were collected from the Korea AMI Registry from 2005 to 2017. Asian dust events were defined as days with visibility of ≤10 km. Generalized linear models were used to analyze data with natural cubic splines. To examine potential modifiers, analyses were stratified by age, smoking status, and body mass index (BMI). RESULTS: No significant associations were observed between Asian dust and AMI. By adjusting for different lag structures, a significant effect was exclusively observed in STEMI. For moving average lags, the largest value at lag 5 (relative risk [RR] 1.083; 95% confidence interval [CI], 1.007-1.166) for single and lags 0-7 (RR 1.067; 95% CI: 1.002-1.136) was observed for PM2.5; for PM10, the largest significant effect was observed at lag 4 (RR 1.075; 95% CI: 1.010-1.144) for single and lags 0-7 (RR 1.067; 95% CI: 1.002-1.136). RRs were significantly higher in < 65-year-olds than in ≥65-year-olds. Additionally, RRs between the BMI < 25 and BMI ≥ 25 groups were not different; statistically significant effects were observed for concentration at lags 0-5 (RR: 1.073; 95% CI: 1.002-1.150) and lags 0-6 (RR: 1.071; 95% CI: 1.001-1.146) in the BMI < 25 group. A negative exposure-response association was observed between daily average visibility-adjusted PM and STEMI and daily average visibility-adjusted PM in < 65-year-olds. CONCLUSIONS: Reducing PM2.5 and PM10 emissions, particularly during the days of Asian dust, may be crucial and reduce STEMI and AMI incidence among < 65-year-olds. These results indicate that the Asian dust alarm system needs revision to protect vulnerable populations.

Interactive Effect of Diurnal Temperature Range and Temperature on Mortality, Northeast Asia.

BACKGROUND: The diurnal temperature range (DTR) represents temperature variability within a day and has been reported as a potential risk factor for mortality. Previous studies attempted to identify the role of temperature in the DTR-mortality association, but results are inconclusive. The aim of this study was to investigate the interactive effect of temperature and DTR on mortality using a multicountry time series analysis. METHODS: We collected time series data for mortality and weather variables for 57 communities of three countries (Taiwan, Korea, and Japan) in Northeast Asia (1972-2012). Two-stage time series regression with a distributed lag nonlinear model and meta-analysis was used to estimate the DTR-mortality association changing over temperature strata (six strata were defined based on community-specific temperature percentiles). We first investigated the whole population and then, the subpopulations defined by temperature distribution (cold and warm regions), sex, and age group (people <65 and ≥65 years of age), separately. RESULTS: The DTR-mortality association changed over temperature strata. The relative risk (RR) of mortality for 10°C increase in DTR was larger for high-temperature strata compared with cold-temperature strata (e.g., = 1.050; 95% confidence interval [CI] = 1.040, 1.060 at extreme-hot stratum and RR = 1.040; 95% CI = 1.031, 1.050 at extreme-cold stratum); extreme-hot and -cold strata were defined as the days with daily mean temperature above 90th and below 10th percentiles each community's temperature distribution. Such increasing pattern was more pronounced in cold region and in people who were 65 years or older. CONCLUSIONS: We found evidence that the DTR-related mortality may increase as temperature increases.

Short-term PM2.5 exposure and emergency hospital admissions for mental disease.

Epidemiologic studies regarding the relationship between short-term exposure to particulate matter with a median aerodynamic diameter < 2.5 µm (PM2.5) and mental disease are limited. This study examined the effects of short-term exposure to PM2.5 on emergency admissions to the hospital for mental disease in Seoul, Korea. Data regarding 80,634 emergency admissions for mental diseases were collected from a nationally centralized healthcare claims database in Seoul during 2003-2013. Generalized linear models with climate variables were used to examine associations between short-term PM2.5 exposure and mental disease admissions. To comprehensively assess PM2.5 effects, we used single- and two-pollutant models, which considered other pollutants in combination with PM2.5. The relative risk (RR) of emergency admissions for mental disease was 1.008 (95% confidence interval, 1.001-1.015) for each 10 µg/m3 increase in 2-day average PM2.5 concentration. This effect persisted or became slightly stronger in the two-pollutant models that included carbon monoxide, nitrogen dioxide, ozone, or sulfur dioxide (RR, 1.01-1.021), but association appeared to be limited to individuals < 65 years of age. Significant association was estimated only during the warm season (RR, 1.021-1.023) in the two-pollutant models. The exposure-response curve was steeper at lower concentrations, suggesting that the risk of mental disease at lower concentrations of pm2.5 (0-30 µg/m3). PM2.5 was associated with increased admissions even when it was below the World Health Organization's Air Quality Guidelines (25 µg/m3), but the association was not statistically significant. Thus, based on the data from a large database, exposure to PM2.5 was associated with increases in emergency admissions for mental diseases, and this association was significant during the warm season. PM2.5 may even affect mental disease at levels below the current air quality guidelines. These results provide substantial insight regarding the effects of air pollutants and have important implications for policy makers.

Synergic effect between high temperature and air pollution on mortality in Northeast Asia.

High temperature and air pollutants have been reported as potential risk factors of mortality. Previous studies investigated interaction between the two variables; however, the excess death risk due to the synergic effect (i.e. interaction on the additive scale) between the two variables has not been investigated adequately on a multi-country scale. This study aimed to assess the excess death risk due to the synergism between high temperature and air pollution on mortality using a multicity time-series analysis. We collected time-series data on mortality, weather variables, and four air pollutants (PM10, O3, NO2, and CO) for 16 metropolitan cities of three countries (Japan, Korea, and Taiwan) in Northeast Asia (1979-2015). Quasi-Poisson time-series regression and meta-analysis were used to estimate the additive interaction between high temperature and air pollution. The additive interaction was measured by relative excess risk due to interaction (RERI) index. We calculated RERI with relative risks (RR) of the 99th/10th, 90th/90th, and 99th/90th percentiles of temperature/air pollution metrics, where risk at the 90th/10th percentiles of temperature/air pollution metrics was the reference category. This study showed that there may exist positive and significant excess death risks due to the synergism between high temperature and air pollution in the total population for all pollutants (95% lower confidence intervals of all RERIs>0 or near 0). In final, we measured quantitatively the excess death risks due to synergic effect between high temperature and air pollution, and the synergism should be considered in public health interventions and a composite warning system.

Monte Carlo simulation-based estimation for the minimum mortality temperature in temperature-mortality association study.

BACKGROUND: Rich literature has reported that there exists a nonlinear association between temperature and mortality. One important feature in the temperature-mortality association is the minimum mortality temperature (MMT). The commonly used approach for estimating the MMT is to determine the MMT as the temperature at which mortality is minimized in the estimated temperature-mortality association curve. Also, an approximate bootstrap approach was proposed to calculate the standard errors and the confidence interval for the MMT. However, the statistical properties of these methods were not fully studied. METHODS: Our research assessed the statistical properties of the previously proposed methods in various types of the temperature-mortality association. We also suggested an alternative approach to provide a point and an interval estimates for the MMT, which improve upon the previous approach if some prior knowledge is available on the MMT. We compare the previous and alternative methods through a simulation study and an application. In addition, as the MMT is often used as a reference temperature to calculate the cold- and heat-related relative risk (RR), we examined how the uncertainty in the MMT affects the estimation of the RRs. RESULTS: The previously proposed method of estimating the MMT as a point (indicated as Argmin2) may increase bias or mean squared error in some types of temperature-mortality association. The approximate bootstrap method to calculate the confidence interval (indicated as Empirical1) performs properly achieving near 95% coverage but the length can be unnecessarily extremely large in some types of the association. We showed that an alternative approach (indicated as Empirical2), which can be applied if some prior knowledge is available on the MMT, works better reducing the bias and the mean squared error in point estimation and achieving near 95% coverage while shortening the length of the interval estimates. CONCLUSIONS: The Monte Carlo simulation-based approach to estimate the MMT either as a point or as an interval was shown to perform well particularly when some prior knowledge is incorporated to reduce the uncertainty. The MMT uncertainty also can affect the estimation for the MMT-referenced RR and ignoring the MMT uncertainty in the RR estimation may lead to invalid results with respect to the bias in point estimation and the coverage in interval estimation.

Greenness and kidney? A review of epidemiological studies on the association between green space and kidney disease.

Recent accumulating epidemiological evidence underlines the important role of environmental exposures on kidney diseases. Among environmental exposures, this study addresses "Green space," which has been recognized as one of the major environmental exposures at the population level. We review a total of seven epidemiological studies currently published on greenness and kidney disease. We also discuss knowledge gaps in the epidemiological evidence in relation to study design, greenness exposure index, emerging kidney outcomes, and inequalities. With an increase in public attention regarding environmental risks and climate change, an improved understanding of the beneficial effects of green space can play an important role in promoting kidney health.

Heat and hospital admission via the emergency department for people with intellectual disability, autism, and mental disorders in South Korea: a nationwide, time-stratified, case-crossover study.

BACKGROUND: Given the anticipated increase in ambient temperature due to climate change, the hazardous effects of heat on health have been extensively studied; however, its impact on people with intellectual disability, autism, and mental illness is largely unknown. We aimed to estimate the association between heat and hospitalisation through the emergency department (ED) among people with these mental disorders. METHODS: In this nationwide study, we used data from the National Health Insurance Database (NHID) of the National Health Insurance Service, the single universal insurer in South Korea, the claims data for which is based on the ICD-10. We included individuals with identified intellectual disability, autism, and mental disorders (including schizophrenia, bipolar disorder, recurrent depressive disorder, schizoaffective disorder and persistent obsessive-compulsive disorder, Tourette's disorder, and narcolepsy) and we established two control groups of people without these disorders: one including 1 million systematically sampled individuals, and one matched to the cohort based on sex, age, and income group. Data on hospital admission via the ED were obtained from the NHID, including the primary cause of admission and corresponding medical costs, for the warm season (June-September) of the period 2006-2021. We used the Google Earth Engine with the ERA5-Land dataset to collect data on the daily mean temperature. We applied a time-stratified case-crossover design using a distributed lag non-linear model and performed a conditional logistic regression. The risk ratio was estimated as the odds ratio (OR) with calculated odds at the 99th percentile temperature compared with that at the local 75th percentile temperature. We did not include people with lived experience of mental illness in this study. FINDINGS: Of the 456 946 people with intellectual disability, autism, or mental disorder in the NHID records, 99 845 were admitted to the ED, including 59 821 (59·9%) males and 40 024 (40·1%) females, and including 29 192 people with intellectual disability, 1428 people with autism, and 69 225 people with mental disorders. We were not able to collect data on ethnicity. The mean age at ED admission was 42·1 years (SD 17·9, range 0-102) for people with intellectual disability, 18·6 years (SD 10·4, range 1-72) for people with autism, and 50·8 years (SD 11·9, range 2-94) for people with mental disorders. The heat OR (odds at the 99th percentile vs 75th percentile of temperature) of ED admission was 1·23 (95% CI 1·11-1·36) for intellectual disability, 1·06 (0·68-1·63) for autism, and 1·20 (1·12-1·29) for mental disorders. People with intellectual disability, female individuals, people living in rural areas, or those with a low-income status were at increased risk of ED admission due to heat. The risk of ED admission due to genitourinary diseases was higher than that from other causes. Annual increase in medical costs attributable to heat among people with intellectual disability, autism, and mental disorders was US$ 224 970 per 100 000 person-years (95% empirical CI 139 784-305 770). INTERPRETATION: People with intellectual disability, autism, and mental disorders should be included in groups considered at a high-risk for heat exposure, and heat adaptation policies should be implemented with consideration of these groups and their needs. FUNDING: The National Research Foundation of Korea, Korean Ministry of Environment, and Korean Ministry of Education. TRANSLATION: For the Korean translation of the abstract see Supplementary Materials section.