Prevalence of and factors associated with heat-related illness in a super-aged society: a cross-sectional study of older adults in suburban Tokyo, Japan

Background The convergence of increasing extreme heat events due to climate change and rapid population aging poses a critical public health challenge. While previous studies have identified risk factors for heat-related health outcomes, most have been conducted in Western countries and have relied on indicators that require resource-intensive surveys. This study aims to identify factors associated with heat-related illness among the elderly in Japan using practical, policy-relevant indicators. Methods A cross-sectional study using a self-administered questionnaire was conducted in a suburban area of Tokyo, Japan, from September to November 2017. Elderly residents were recruited from two distinct populations: a large public housing complex and a socially active community club. The primary outcome was the self-reported history of heat-related illness within five years, defined as episodes requiring ambulance transport or hospital visits. Univariate and multivariable logistic regression analyses were performed to identify associated factors (Significance level: p < 0.10). Results Of the 743 participants included in the analysis (mean age: 73.01, SD: 10.23), 31 (4.17%, 95% CI: 2.86%–5.87%) reported having experienced heat-related illness. In the univariate analysis ( p < 0.10), heat-related illness was associated with long-term care certification (Crude OR 2.64, 90% CI 1.13–5.56), suspected dementia (Crude OR 8.24, 90% CI 2.33–24.14), and living alone (Crude OR 2.10, 90% CI 1.11–4.05). AC ownership was inversely associated with heat-related illness (Crude OR 0.30, 90% CI 0.13–0.84). In the multivariable analysis ( N = 583), factors that remained associated with heat-related illness ( p < 0.10) were advanced age (75 or above; Adjusted OR 2.49, 90% CI 1.09–5.94), living alone (Adjusted OR 2.38, 90% CI 1.03–5.69), and AC ownership (Adjusted OR 0.13, 90% CI 0.01–0.83). Conclusions Advanced age and living alone were strongly associated with heat-related illness, while air conditioning ownership was inversely associated. Utilizing easily accessible administrative data—such as age, household composition, and long-term care status—is a feasible strategy to identify vulnerable older adults and target proactive interventions in super-aged societies.