The term ‘social isolation’ was first proposed by Berkman et al.,(2017).1 in their study on social relations and death relationships, where it was defined as an irreversible loss of social attachment and community hubs. Subsequently, Nicholson expanded on this definition. Social isolation is now generally defined as a phenomenon of shrinking social networks, a lack of social participation, and diminished social belonging due to unsatisfactory social relationships, characterized by a deficiency or limitation in the number of social interactions.2,3 Long-term development of social isolation reduces the individual's ability to participate in and maintain healthy behaviors, leading to compromising their physiological and immune function over time.4

According to the World Health Organization, the global population of individuals aged 60 and above is projected to rise from 900 million to 2 billion between 2015 and 2050, showing a rising trend.5 As the worldwide aging population continues to grow, the risk of experiencing social isolation with age also increases.6 The elderly are the most vulnerable to social isolation. The decline in physical and cognitive functions often associated with older age tends to limit participation in outdoor activities and hinder interpersonal communication. Consequently, retirees may easily experience loneliness, becoming disconnected from evolving society and facing social isolation.7 According to a study of elderly Americans, one in four older individuals has experienced social isolation.8 Furthermore, research indicates that the severity of social isolation has increased since 2010. Specifically, between 2010 and 2016, the proportion of elderly individuals lacking interaction with their loved ones increased by 5 %, reaching 15 %.9 Currently, the phenomenon of social isolation among the elderly has become a social and public health problem worldwide. In addition, there is increasing evidence that social isolation seriously threatens the psychological and physical health of the elderly.10 According to a meta-analysis of prospective cohort studies, social isolation was associated with a 32 % increased risk of death compared with non-socially isolated individuals.11 Meanwhile, a longitudinal study in 2017 by Berkman and Syme in Alameda County found that, after 9 years of follow-up, patients experiencing social isolation had a mortality rate twice that of non-socially isolated patients.1 A secondary analysis of 11,486 older Australian adults revealed that, over a mean follow-up period of 4.5 years, socially isolated individuals were 42 % more likely to develop cardiovascular disease.12 In addition, social isolation also leads to a range of health problems such as depression,13 stroke,14 and cognitive impairment15 in the elderly. The medical and economic costs of social isolation are also substantial. Studies have revealed that individuals experiencing social isolation are more inclined to seek medical assistance to fulfill their need for interaction and interpersonal stimulation. This observation has been supported by Swedish researchers who discovered that socially isolated older individuals used healthcare services more extensively compared to their non-socially isolated counterparts.16,17 Meanwhile, a study by the AARP reveals that the U.S. government allocates an additional $6.7 billion in federal spending each year for socially isolated seniors, contributing to an economic burden.18 As a global issue that significantly impacts both physical and mental health, and represents an excessive financial burden, social isolation demands more attention.

Although many studies have been undertaken to determine the level of social isolation of the elderly, the reported incidence varies significantly, ranging from 17.0 % to 54.8 %. Furthermore, these studies differed in sample sizes and screening tools, and lacked a standardized representation, with a predominant focus on defensive measures against social isolation.19, 20, 21 In a systematic scoping review of interventions addressing social isolation among seniors, a UK intervention study reported a prevalence twice that of Japan.22 This study aims to assess the epidemiological characteristics of social isolation among the elderly, considering the study area, sample size, and assessment tools. The aim is to provide insights for the early identification and prevention of social isolation development.