Ambient Temperature and External Causes of Death in Japan from 1979 to 2015: A Time-Stratified Case-Crossover Analysis

Abstract

Background: Although substantial evidence suggests that high and low temperatures are adversely associated with nonaccidental mortality, few studies have focused on exploring the risks of temperature on external causes of death. Objectives: We investigated the short-term associations between temperature and external causes of death and four specific categories (suicide, transport, falls, and drowning) in 47 prefectures of Japan from 1979 to 2015. Methods: We conducted a two-stage meta-regression analysis. First, we performed time-stratified case-crossover analyses with a distributed lag nonlinear model to examine the association between temperature and mortality due to external causes for each prefecture. We then used a multivariate meta-regression model to combine the association estimates across all prefectures in Japan. In addition, we performed stratified analyses for the associations by sex and age. Results: A total of 2,416,707 external causes of death were included in the study. We found a J-shaped exposure–response curve for all external causes of death, in which the risks increased for mild cold temperatures [20th percentile; relative risk (95% confidence interval [CI]: 1.05,1.12)] and extreme heat [99th percentile; (95% CI: 1.20, 1.29)] compared with those for minimum mortality temperature (MMT). However, the shapes of the exposure–response curves varied according to four subcategories. The risks of suicide and transport monotonically increased as temperature increased, with RRs of 1.35 (95% CI: 1.26, 1.45) and 1.60 (95% CI: 1.35, 1.90), respectively, for heat, whereas J- and U-shaped curves were observed for falls and drowning, with RRs of 1.14 (95% CI: 1.03, 1.26) and 1.95 (95% CI: 1.70, 2.23) for heat and 1.13 (95% CI: 1.02, 1.26) and 2.33 (95% CI: 1.89, 2.88) for cold, respectively, compared with those for cause-specific MMTs. The sex- and age-specific associations varied considerably depending on the specific causes. Discussion: Both low and high temperatures may be important drivers of increased risk of external causes of death. We suggest that preventive measures against external causes of death should be considered in adaptation policies. https://doi.org/10.1289/EHP9943

Evaluating the short-term effect of ambient temperature on non-fatal outdoor falls and road traffic injuries among children and adolescents in China: a time-stratified case-crossover study

“…A conditional logistic regression was applied to analyze the short-term effect of temperature exposure on outdoor injuries. The odds ratio (OR) and 95% confidence interval (CI) were estimated after adjusting for holidays and 3-day moving averages (lag 0-2) of relative humidity, atmospheric pressure, and rainfall (Pan et al, 2022). We selected the covariates based on previous studies (Lee et al, 2020;Pan et al, 2022) and the correlations between temperature and other meteorological variables (see Tables S1 and S2).…”

“…The odds ratio (OR) and 95% confidence interval (CI) were estimated after adjusting for holidays and 3-day moving averages (lag 0-2) of relative humidity, atmospheric pressure, and rainfall (Pan et al, 2022). We selected the covariates based on previous studies (Lee et al, 2020;Pan et al, 2022) and the correlations between temperature and other meteorological variables (see Tables S1 and S2). In addition, we adjusted for the possible confounding effect of the COVID-19 pandemic by adding a dichotomous variable in the model, depending on whether a day was a lockdown day during the study period.…”

“…We calculated the OR associated with MaxRT by setting the reference value at the minimum risk temperature (MinRT) representing the lowest temperature risk. The MaxRT and MinRT were defined between the 1st and 99th percentiles of temperature (Kim et al, 2019;Lee et al, 2020;Pan et al, 2022).…”

“…The short-term effect of temperature on injuries was evaluated based on a time-stratified case-crossover design, which has been widely used to explore the environmental impact on mortality and morbidity (Lee et al, 2020;Xu et al, 2020;Pan et al, 2022). This study design compared ambient temperature exposure levels of identical students on the case day and the control day (i.e., the same day of the week in the same year and month).…”

“…Studies have revealed that non-optimal ambient temperatures may increase the risk of injury mortality (Basagaña et al, 2011;Joe et al, 2016;Pan et al, 2022) and morbidity (McInnes et al, 2017;Martínez-Solanas et al, 2018;Kim et al, 2019). A recent comprehensive study in Republic of Korea (Lee et al, 2020) found that high and low temperatures significantly increased the risk of non-fatal injury, and this correlation varied by the cause of injury.…”