Descriptive Epidemiology of solitary death (kodokushi) in Tokyo's 23 wards, Japan, 2016-2023

Solitary death (kodokushi) has emerged as a public health and social issue in Japan with rapid population aging. However, recent epidemiological data on solitary deaths remain limited.

We conducted a population-based descriptive epidemiological study using records from the Tokyo Medical Examiner's Office from 2016 to 2023. All cases that met the study definition were selected from 110,024 records and included in the analysis. Data on demographic characteristics, postmortem interval (PMI), manner and cause of death, and underlying diseases were analyzed.

Among 46,313 solitary death cases, 32,345 were male (69.8%, median age 70 years) and 13,968 were female (30.2%, median age 80 years). Crude mortality rates per 100,000 persons increased from 69.3 to 102.5 in males and 29.7 to 41.4 in females between 2016 and 2023. Solitary deaths exhibited seasonal variation, with peaks in summer and winter. Most cases involved pensioners and welfare recipients. PMI was longer in males than females (5 days vs. 3 days). Cardiovascular diseases were the leading cause of death for both sexes. Heat stroke predominated in summer, whereas natural deaths were more frequent in winter. More than half of cases had underlying diseases, most commonly hypertension.

Solitary death in Tokyo's 23 wards increased over the study period. Seasonal, demographic, and clinical patterns highlight the need for season-specific prevention strategies and the potential role of primary care in mitigating risk.