Faculty of Health and Sport Sciences, University of Tsukuba, Tsukuba, Japan.
Department of Global Health Policy, Graduate School of Medicine, The University of Tokyo, Tokyo, Japan.
Environ Health Perspect. 2023 May;131(5):57005. doi: 10.1289/EHP11444. Epub 2023 May 12.
The health effects of heat are well documented; however, limited information is available regarding the health risks of hot nights. Hot nights have become more common, increasing at a faster rate than hot days, making it urgent to understand the characteristics of the hot night risk.
We estimated the effects of hot nights on the cause- and location-specific mortality in a nationwide assessment over 43 y (1973-2015) using a unified analytical framework in the 47 prefectures of Japan.
Hot nights were defined as days with ) minimum temperature () and ) minimum temperature percentile () for the prefecture. We conducted a time-series analysis using a two-stage approach during the hot night occurrence season (April-November). For each prefecture, we estimated associations between hot nights and mortality controlling for potential confounders including daily mean temperature. We then used a random-effects meta-analytic model to estimate the pooled cumulative association.
Overall, 24,721,226 deaths were included in this study. Nationally, all-cause mortality increased by 9%-10% [ relative risk , 95% confidence interval (CI): 1.08, 1.10; , 95% CI: 1.09, 1.11] during hot nights in comparison with nonhot nights. All 11 cause-specific mortalities were strongly associated with hot nights, and the corresponding associations appeared to be acute and lasted a few weeks, depending on the cause of death. The strength of the association between hot nights and mortality varied among prefectures. We found a higher mortality risk from hot nights in early summer in comparison with the late summer in all regions.
Our findings support the evidence of mortality impacts from hot nights in excess of that explicable by daily mean temperature and have implications useful for establishing public health policy and research efforts estimating the health effects of climate change. https://doi.org/10.1289/EHP11444.
热对健康的影响已有充分记录；然而，关于热夜对健康的风险的信息有限。热夜变得越来越普遍，其增加速度超过了热天，因此迫切需要了解热夜风险的特征。
我们使用统一的分析框架，在日本 47 个县进行了一项全国性评估，在 43 年（1973-2015 年）的时间跨度内，估计了热夜对特定原因和特定地点死亡率的影响。
热夜被定义为日最低温度（）和该地区日最低温度百分位数（）的日子。我们在热夜发生季节（4 月至 11 月）使用两阶段方法进行时间序列分析。对于每个县，我们估计了热夜与死亡率之间的关联，控制了包括日平均温度在内的潜在混杂因素。然后，我们使用随机效应荟萃分析模型来估计累积关联的汇总结果。
总体而言，本研究共纳入 24721226 例死亡。与非热夜相比，全国范围内所有原因的死亡率在热夜增加了 9%-10%[相对风险，95%置信区间（CI）：1.08，1.10；，95%CI：1.09，1.11]。所有 11 种死因特异性死亡率与热夜密切相关，并且这种关联似乎是急性的，持续数周，具体取决于死因。热夜与死亡率之间的关联强度因县而异。我们发现，在所有地区，初夏的热夜死亡率风险高于夏末。
我们的研究结果支持热夜对死亡率的影响超出日平均温度解释范围的证据，这对于制定公共卫生政策和开展估计气候变化对健康影响的研究工作具有重要意义。https://doi.org/10.1289/EHP11444.
