The Annual Report on the Ageing Society in Japan17 revealed that half of single-person households with ages ≥ 60 years were concerned about “death without any care that was not found for a long period.” As if to support this result, the lack of relationships, such as “greetings only” and “almost no relationships,” regarding the degree of neighborhood relationships in single-person households of aged ≥ 65 is > 60% in men and approximately 40% in women17. Similar situations have been reported in the Wakayama Prefecture18. These social situations prompted us to investigate the actual condition of solitary death cases from the viewpoint of forensic medicine.
In the past 16 years, the number of forensic autopsies has doubled from 123 in 2004 to 240–250 since 2012. In accordance with this tendency, the rates of home death and solitary death increased approximately 1.7-fold and 2.3-fold, respectively. This tendency seems to result from an increase in single-person households in Japan19. Particularly, in Wakayama Prefecture, the number of individuals in single-person households aged ≥ 65 years was 21.8%20 in 2018, with one in five living alone. Moreover, the aging rate in Wakayama Prefecture was extremely high, at 31.5 rate in 201820, while the aging rate in Japan was 28.1%21. Thus, in Wakayama Prefecture, solitary death may easily occur because of the increase in the number of households and aging of the population.
Our study demonstrated that solitary death predominantly occurred in men in their 50s to 80s, with a peak in the 70s. Solitary death cases in men and women tended to increase from the age of 40 to 60 years. As for the manner of death, natural death accounted for half of all cases, and IHD was the leading cause of death in both sexes, as previously reported6, 8, 9, 11–14, 22–26. In cases of solitary death, a large number of natural deaths are considered to reflect a large number of elderly people. Furthermore, in this study, men had a higher natural death rate than women, which tended to increase from a younger age. This may be due to lifestyle differences between men and women.
There was a difference in age distribution between accidental and suicidal death cases: accidental cases and suicidal cases were common in the 70s and 80s aged group and 30s to 60s age group, respectively. In line with a previous study9, fire-related death was the most common cause of accidental cases of solitary deaths because most fire-related deaths were usually subjects for forensic autopsy. According to a report by the Fire and Disaster Management Agency27, approximately 70% of the deaths from fires at home were from elderly persons aged ≥ 65 years, indicating that single-person households of the elderly population have a high risk of accidental death due to fire at home. In line with previous studies13, 26, our observations implied that the rate of suicide was higher in women than in men, and hanging was the most common method. Suicidal cases were more common in the younger generation than accidental death cases8, 13.
We found two peaks in PMI-f: < 1 d and 7 days to < 1 month. The PMI in male cases was significantly longer than that in female cases. There was a significant difference in PMI between natural and external death cases. The PMI of external death cases was significantly shorter that of natural death cases. In natural death cases, PMI-f cannot be found without visiting the victim’s home; therefore, the strength of the connection with their families and communities has a great effect on PMI-f. Approximately half of the cases were found more than seven days after death, suggesting that the victims were likely isolated from their families and communities. This tendency was greater in women than in men.
Several lines of accumulating evidence imply that a PMI of ≤ three days is the most common8, 11, 22, 28. In contrast, Hatake et al.13 reported that a PMI of > 7 days was the most frequent. This discrepancy depends on regional differences. In contrast, in line with our observations, PMI of solitary death cases tended to be longer in men than in women6, 13, 15, 22, 23, 29, 30. It is important that social exclusion is closely related to solitary and isolated deaths. The evaluation of PMI might be useful as an indicator of the isolated state29 − 31. Morita et al.29 reported that the PMI-f was 3 days on average in solitary death cases with social ties.
According to several previous studies8, 11, 28, the rate of discovery by family members/relatives was the highest (40–90%). In contrast, in this study, police officers were the most frequent finders, followed by family members/relatives. However, according to the sex of the victims, the rate of discovery by family members/relatives was higher in women than in men. Between PMI-f and the first finders, the rate of discovery by family members/relatives became lower in cases with long PMI-f11, 14. Thus, these observations imply that the type of first finder might be another indicator for the evaluation of the isolated state.
Hypertension was the most common, followed by DM and depression in both sexes, according to past medical history. Alcoholic liver disease, alcoholism, and schizophrenia were more frequent in men than in women. In line with this, previous studies have reported a higher prevalence of hypertension and alcohol-related disease in solitary death cases9, 12, 23, 26, 30. Our results are consistent with this finding.
Accumulating evidence has shown that solitariness or isolation from the social community increases the risk of alcohol abuse, frailty, and sarcopenia32, 33. Moreover, welfare recipients often develop alcohol-related diseases35. These observations imply that alcohol abuse, mental health, and physical health should be considered as risk factors of solitary death.
Several lines of accumulating evidence implied that there are regional characteristics and differences in the background of solitary deaths8, 11–16. Wakayama Prefecture has a long north–south terrain and consists of three areas: Kihoku, Kichu, and Kinan36 (Supplementary Fig. 1a). Population concentration in urban areas and local depopulation are serious issues. The aging rate tended to be high, particularly in depopulated areas (Supplementary Fig. 1b). In the present study, we found regional characteristics in the background of solitary deaths in the Wakayama Prefecture. The average annual number of solitary deaths per 100,000 population was 4.3 in Wakayama Prefecture. However, Kushimoto and Shingu, located in the southern part (Kinan region), had a high solitary death rate in forensic autopsy cases because of the small population and high aging rate of > 40%. Several lines of accumulating evidence suggest that low income, unemployment, and welfare are risk factors for solitary death6, 7. With focus on economic conditions, 36 participants were welfare recipients. However, few cases were welfare recipients in solitary deaths in the Kinan region (Kushimoto and Shingu). In contrast, 23 of 36 welfare recipients, who had solitary death, lived in Wakayama city, indicating that the economic state would contribute more to the occurrence of solitary death in Wakayama city. These observations indicate a difference in the background of solitary deaths between urban and non-urban areas.
Finally, the present study demonstrated several risk factors and regional characteristics of solitary death cases. However, this study has a limitation in that all data were obtained from forensic autopsy cases. Therefore, it should be noted that it does not reflect all solitary deaths in Wakayama Prefecture. Previous studies have reported that some cases had long PMI-f despite living with family12, 29, 30, 37. Therefore, in future studies, it will be necessary to conduct a survey that is not limited to living alone. However, these observations could contribute to administrative welfare measures for the prevention of solitary deaths.