Abstract
With global temperatures rising due to climate change, heatstroke is emerging as a public health concern, particularly among older adults. The population of Japan is aging, with heatstroke causing frequent hospitalizations and deaths. This study investigated the impact of symptomatic comorbidities, including cardiovascular, pulmonary, and renal disorders, on prognosis of heatstroke. Data were collected from 2,373 adult patients diagnosed with heat-related illnesses during 2017–2021 across multiple centers in Japan. Among them, 608 patients (25.6%) had at least one comorbidity. Patients were compared based on the presence and number of comorbidities. Statistical analyses, including logistic regression and Kaplan–Meier survival curves after propensity-score matching, were performed to evaluate the relationship between comorbidities and in-hospital mortality. The results showed significantly higher in-hospital mortality among patients with comorbidities compared to those without (15.3% vs. 10.9%, p = 0.005). Although mortality was higher in those with multiple comorbidities, the difference was not statistically significant. Respiratory comorbidities emerged as a significant risk factor for heatstroke-related mortality (odds ratio = 2.93, 95% CI = 1.53 – 5.61). Survival analysis further demonstrated a lower survival probability in patients with comorbidities, suggesting that symptomatic comorbidities, particularly respiratory diseases, notably influenced heatstroke outcomes and require focused preventive strategies.
Data availability
The datasets used and/or analyzed during the current study available from the corresponding author on reasonable request.
References
Atwoli, L. et al. Call for emergency action to limit global temperature increases, restore biodiversity, and protect health. N. Engl. J. Med. 385, 1134–1137 (2021).
IPCC. Climate Change: Impacts, Adaptation and Vulnerability. Contribution of Working Group II to the Sixth Assessment Report of the Intergovernmental Panel on Climate Change [Pörtner HO, Roberts DC, Tignor M, Poloczanska ES, Mintenbeck K, Alegría A, Craig M, Langsdorf S, Löschke S, Möller V, Okem A, Rama B (eds.)]. https://doi.org/10.1017/9781009325844. (2022).
Robine, J. M. et al. Death toll exceeded 70,000 in Europe during the summer of 2003. C. R. Biol. 331, 171–178 (2008).
Fouillet, A. et al. Excess mortality related to the August 2003 heat wave in France. Int. Arch. Occup. Environ. Health 80, 16–24 (2006).
The BC Coroners Service, Extreme Heat and Human Mortality: A Review of Heat-Related Deaths in B.C. in Summer 2021. https://www2.gov.bc.ca/assets/gov/birth-adoption-death-marriage-and-divorce/deaths/coroners-service/death-review-panel/extreme_heat_death_review_panel_report.pdf. Accessed 3 Sept 2024. (2022).
Bouchama, A. & Knochel, J. P. Heat stroke. N. Engl. J. Med. 346, 1978–1988 (2002).
Hayashida, K., Shimizu, K. & Yokota, H. Severe heatwave in Japan. Acute Med. Surg. 6, 206–207 (2019).
Kanda, J. et al. Current status of active cooling, deep body temperature measurement, and face mask wearing in heat stroke and heat exhaustion patients in Japan: A nationwide observational study based on the Heatstroke STUDY 2020 and 2021. Acute Med. Surg. 10, e820 (2023).
Basagaña, X. et al. Heat waves and cause-specific mortality at all ages. Epidemiology 22, 765–772 (2011).
Kovats, R. S., Hajat, S. & Wilkinson, P. Contrasting patterns of mortality and hospital admissions during hot weather and heat waves in Greater London, UK. Occup. Environ. Med. 61, 893–898 (2004).
Kim, S. H., Jo, S. N., Myung, H. N. & Jang, J. Y. The effect of pre-existing medical conditions on heat stroke during hot weather in South Korea. Environ. Res. 133, 246–252 (2014).
Monteiro, A., Carvalho, V., Oliveira, T. & Sousa, C. Excess mortality and morbidity during the July 2006 heat wave in Porto. Portugal. Int. J. Biometeorol. 57, 155–567 (2013).
Rocklöv, J., Forsberg, B., Ebi, K. & Bellander, T. Susceptibility to mortality related to temperature and heat and cold wave duration in the population of Stockholm County, Sweden. Glob. Health Action 7, 22737 (2014).
Gronlund, C. J., Zanobetti, A., Wellenius, G. A., Schwartz, J. D. & O’Neill, M. S. Vulnerability to renal, heat and respiratory hospitalizations during extreme heat among U.S. elderly. Clim. Change 136, 631–645 (2016).
Martin-Latry, K. et al. Psychotropic drugs use and risk of heat-related hospitalisation. Eur. Psych. 22, 335–338 (2007).
Rai, M. et al. Heat-related cardiorespiratory mortality: Effect modification by air pollution across 482 cities from 24 countries. Environ. Int. 174, 107825 (2023).
Yamamoto, T. et al. Evaluation of a novel classification of heat-related illnesses: A multicentre observational study (heat stroke STUDY 2012). Int. J. Environ. Res. Public Health 15, 1962 (2018).
Argaud, L. et al. Short- and long-term outcomes of heatstroke following the 2003 heat wave in Lyon, France. Arch. Intern. Med. 167, 2177–2183 (2007).
Davido, A. et al. Risk factors for heat-related death during the August 2003 heat wave in Paris, France, in patients evaluated at the emergency department of the of the Hôpital Européen Georges Pompidou. Emerg. Med. J. 23, 515–518 (2006).
Hausfater, P. et al. Prognostic factors in non-exertional heatstroke. Intensive Care Med. 36, 272–280 (2010).
Misset, B. et al. Mortality of patients with heatstroke admitted to intensive care units during the 2003 heat wave in France: A national multiple-center risk-factor study. Crit. Care Med. 34, 1087–1092 (2006).
Pease, S. et al. Early organ dysfunction course, cooling time and outcome in classic heatstroke. Intensive Care Med. 35, 1454–1458 (2009).
Arbuthnott, K. G. & Hajat, S. The health effects of hotter summers and heat waves in the population of the United Kingdom: A review of the evidence. Environ. Health 16, 119 (2017).
Ma, W., Chen, R. & Kan, H. Temperature-related mortality in 17 large Chinese cities: How heat and cold affect mortality in China. Environ. Res. 134, 127–133 (2014).
Díaz, J. et al. Heat waves in Madrid 1986–1997: Effects on the health of the elderly. Int. Arch. Occup. Environ. Health 75, 163–170 (2002).
Ishigami, A. et al. An ecological time-series study of heat-related mortality in three European cities. Environ. Health 7, 5 (2008).
Stafoggia, M. et al. Factors affecting in-hospital heat-related mortality: A multi-city case-crossover analysis. J. Epidemiol. Comm. Health 62, 209–215 (2008).
Schifano, P. et al. Susceptibility to heat wave-related mortality: A follow-up study of a cohort of elderly in Rome. Environ. Health 8, 50 (2009).
Pigakis, K. M. et al. Effect of hydration on pulmonary function and development of exercise-induced bronchoconstriction among professional male cyclists. Adv. Respir. Med. 91, 239–253 (2023).
Kenny, G. P., Yardley, J., Brown, C., Sigal, R. J. & Jay, O. Heat stress in older individuals and patients with common chronic diseases. CMAJ 182, 1053–1060 (2010).
Liu, J. et al. Is there an association between hot weather and poor mental health outcomes? A systematic review and meta-analysis. Environ. Int. 153(1), 06533 (2021).
Zilbermint, M. Diabetes and climate change. J. Community Hosp. Intern. Med. Perspect. 10, 409–412 (2020).
Xu, R. et al. Association between heat exposure and hospitalization for diabetes in brazil during 2000–2015: A nationwide case-crossover study. Environ. Health Perspect. 127, 117005 (2019).
Schuman, S. H. Patterns of urban heat-wave deaths and implications for prevention: Data from New York and St. Louis during July, 1966. Environ. Res. 5, 59–75 (1972).
Semenza, J. C., McCullough, J. E., Flanders, W. D., McGeehin, M. A. & Lumpkin, J. R. Excess hospital admissions during the July 1995 heat wave in Chicago. Am. J. Prev. Med. 16, 269–277 (1999).
Yardley, J. E., Stapleton, J. M., Sigal, R. J. & Kenny, G. P. Do heat events pose a greater health risk for individuals with type 2 diabetes?. Diabetes Technol. Ther. 15, 520–529 (2013).
Ichai, P. et al. Liver transplantation in patients with liver failure related to exertional heatstroke. J. Hepatol. 70, 431–439 (2019).
Semenza, J. C. et al. Heat-related deaths during the July 1995 heat wave in Chicago. N. Engl. J. Med. 335, 84–90 (1996).
Hall, D. M., Baumgardner, K. R., Oberley, T. D. & Gisolfi, C. V. Splanchnic tissues undergo hypoxic stress during whole body hyperthermia. Am. J. Physiol. 276, G1195–G1203 (1999).
Hall, D. M. et al. Mechanisms of circulatory and intestinal barrier dysfunction during whole body hyperthermia. Am. J. Physiol. Heart Circ. Physiol. 280, H509–H521 (2001).
Monzon, B., Hegarty, K. & Rech, M. A. A knack for “NAC”: Treatment for heat stroke induced acute liver injury. Am. J. Emerg. Med. 38(853), e1-853.e3 (2020).
Naughton, M. P. et al. Heat-related mortality during a 1999 heat wave in Chicago. Am. J. Prev. Med. 22, 221–227 (2002).
Acknowledgements
HsS2020-21 was supported by the Health, Labor, and Welfare Policy Research Grant to Shoji Yokobori (20CA2057) and by the Japan Society for the Promotion of Science KAKENHI grant to Jun Kanda (19K18365). HsS2019-20 was supported by the Health, Labor and Welfare Policy Research Grant to Shoji Yokobori (20CA2057) and by the Japan Society for the Promotion of Science KAKENHI grant to Jun Kanda (19K18365). HsS2017-18 was supported by Health and Labour Sciences Research Grants.
Author information
Authors and Affiliations
Contributions
KI: Writing – original draft, Visualization, Software, Methodology, Formal analysis, Data curation. RN: Writing – review & editing, Resources, Investigation, Data curation. SK: Writing – review & editing, Resources, Investigation. TT: Writing – review & editing, Investigation, Data curation. KT: Writing – review & editing, Investigation. H. Kaneko: Writing – review & editing, Investigation, Data curation. SI: Writing – review & editing, Investigation. MF: Writing – review & editing, Investigation, Data curation. JK: Writing – review & editing, Investigation. H. Kittaka: Writing – review & editing, Investigation, Data curation, Supervision. YI: Writing – review & editing, Investigation, Software. HS: Writing – review & editing, Project administration, Supervision.
Corresponding author
Ethics declarations
Competing interests
The authors declare no competing interests.
Additional information
Publisher’s note
Springer Nature remains neutral with regard to jurisdictional claims in published maps and institutional affiliations.
Supplementary Information
Rights and permissions
Open Access This article is licensed under a Creative Commons Attribution 4.0 International License, which permits use, sharing, adaptation, distribution and reproduction in any medium or format, as long as you give appropriate credit to the original author(s) and the source, provide a link to the Creative Commons licence, and indicate if changes were made. The images or other third party material in this article are included in the article’s Creative Commons licence, unless indicated otherwise in a credit line to the material. If material is not included in the article’s Creative Commons licence and your intended use is not permitted by statutory regulation or exceeds the permitted use, you will need to obtain permission directly from the copyright holder. To view a copy of this licence, visit http://creativecommons.org/licenses/by/4.0/.
About this article
Cite this article
Inukai, K., Narikawa, R., Kishitani, S. et al. Impact of symptomatic comorbidities on heatstroke outcomes: A retrospective nationwide cohort study. Sci Rep (2026). https://doi.org/10.1038/s41598-026-37133-6
Received:
Accepted:
Published:
DOI: https://doi.org/10.1038/s41598-026-37133-6
