Association between outdoor temperature and bath-related drowning deaths in Japan (1995–2020): modifying factors and the role of prefectural characteristics
Background: 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 agi...
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| Main Authors: | , , , |
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| Format: | Article |
| Language: | English |
| Published: |
Komiyama Printing Co. Ltd
2025-07-01
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| Series: | Environmental Health and Preventive Medicine |
| Subjects: | |
| Online Access: | https://www.jstage.jst.go.jp/article/ehpm/30/0/30_25-00116/_html/-char/en |
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| Summary: | Background: 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. Methods: 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. Results: 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. Conclusions: 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. |
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| ISSN: | 1342-078X 1347-4715 |