Tai Yoshiaki, Obayashi Kenji, Yamagami Yuki, Saeki Keigo
Department of Epidemiology, Nara Medical University School of Medicine.
Environ Health Prev Med. 2025;30:55. doi: 10.1265/ehpm.25-00116.
Older adults in Japan have the highest drowning mortality rate globally due to frequent bathing practices. Low outdoor temperatures have been linked to bath-related deaths; however, previous studies employed limited statistical models and focused on a single prefecture. Given Japan's aging population, preventing bath-related deaths is a public health priority. This study aimed to analyze the association between outdoor temperature and bath-related drowning deaths across Japan from 1995 to 2020 (n = 110,938), examining regional variations and identifying contributing prefectural characteristics.
Daily counts of bath-related drowning deaths per prefecture were matched with daily mean temperature data from the Japan Meteorological Agency. Prefecture-level demographic and environmental data were obtained from Japan's Official Statistics. We applied a generalized additive mixed model to examine the association between daily mean temperature and bath-related drowning death risk. Meta-regression was used to identify prefecture-level modifiers.
Bath-related drowning death risk peaked at a daily mean temperature of 1.8 °C (relative risk [RR] 9.7, 95% confidence interval [CI]: 9.5-9.9), compared with the lowest risk at 30.3 °C. The association was stronger at mid-range temperatures, particularly among males and individuals aged ≥65 years. Among prefectures, Kagoshima-the southernmost prefecture on Japan's main islands-had the highest maximum RR at 19.6 (95% CI: 16.2-23.6), while Hokkaido-the northernmost prefecture-had the lowest at 3.8 (95% CI: 3.4-4.3). Prefecture-level factors that strengthened this relationship included a lower prevalence of double-pane windows as a proxy of housing insulation and higher annual mean temperatures with ratio of RR change per one standard deviation increase of 0.76 (95% CI: 0.69-0.83) and 1.27 (95% CI: 1.18-1.37), respectively.
Warmer prefectures in southern regions exhibited greater maximum-to-minimum risk ratios compared to cooler northern prefectures. This paradoxical finding underscores the importance of region-specific interventions to reduce bath-related deaths.
由于频繁的沐浴习惯，日本老年人的溺水死亡率在全球最高。室外低温与与沐浴相关的死亡有关；然而，以往的研究采用的统计模型有限，且仅聚焦于一个县。鉴于日本的人口老龄化，预防与沐浴相关的死亡是一项公共卫生重点工作。本研究旨在分析1995年至2020年日本全国范围内室外温度与与沐浴相关的溺水死亡之间的关联（n = 110,938），研究区域差异并确定相关县的特征。
各县与沐浴相关的溺水死亡每日计数与日本气象厅的每日平均温度数据相匹配。县级人口和环境数据来自日本官方统计。我们应用广义相加混合模型来研究每日平均温度与与沐浴相关的溺水死亡风险之间的关联。采用Meta回归来确定县级修饰因素。
与沐浴相关的溺水死亡风险在每日平均温度为1.8°C时达到峰值（相对风险[RR] 9.7，95%置信区间[CI]：9.5 - 9.9），而在30.3°C时风险最低。这种关联在中等温度范围内更强，尤其是在男性和年龄≥65岁的个体中。在各县中，日本主岛最南端的鹿儿岛县的最大RR最高，为19.6（95% CI：16.2 - 23.6），而最北端的北海道县最低，为3.8（95% CI：3.4 - 4.3）。加强这种关系的县级因素包括作为房屋隔热指标的双层玻璃窗普及率较低，以及年平均温度较高，每增加一个标准差，RR变化率分别为0.76（95% CI：0.69 - 0.83）和1.27（95% CI：1.18 - 1.37）。
与较凉爽的北部各县相比，南部较温暖的县的最大风险与最小风险之比更高。这一矛盾的发现凸显了针对不同地区采取干预措施以减少与沐浴相关死亡的重要性。
