The world is experiencing rapid population aging. According to a report, the number of people over the age of 65 reached 723 million in 2020 worldwide, and this number will rise to 1.55 billion by 2050.1 Relatedly, frailty risk increases with advanced age.2 Frailty includes not only physical components, but also cognitive, psychological, and social aspects.3 Prior studies have pointed out that social and psychological domains of frailty have been neglected by researchers.4,5 Bunt formally defined social frailty in 2017 through integrated literature.6 Social frailty is defined as the lack of social resources, social activities, and self-management abilities that are necessary for meeting fundamental social demands.6,7 Recent studies have further shown that there was a higher prevalence of social frailty among older adults, ranging from 6.3% to 66.5% in the community.8,9 What's more, some studies have proved that demographic and sociological factors such as education level, marital status, financial burden, residence, and monthly income can deeply impact social frailty.10,11 Thus, in order to achieve successful aging and boost social engagement, it is crucial to investigate the prevalence and related factors of social frailty in older adults.

Senior citizens are more vulnerable to social frailty. In recent years, the issue of social frailty among older adults has received considerable attention because the growing evidence showed that it can lead to serious consequences for their physical, psychological, and spiritual health. For example, according to the results of a longitudinal cohort study with a four-year follow-up, people who were socially frail at the start of the study had a 3.93-fold higher risk of becoming physically frail than those who were not.12 Furthermore, a study from Japan suggested that social frailty is more closely associated with the development of depressive symptoms in older adults than physical frailty and cognitive impairment.13 Besides, social frailty can increase the risk of disability. A longitudinal cohort study found that individuals defined as socially frail and pre-frail at baseline had a 1.66-fold and 1.53-fold increased risk of disability, respectively, compared to non-frail participants.8 Additionally, some studies also showed that social frailty can predict mortality and has a strong association with older adults’ quality of life, the onset of Alzheimer's disease, cognitive decline, and moderate hearing loss.14, 15, 16, 17 Social issues faced by older adults, such as economic status, family structure, social isolation, loneliness, and social participation are equally on the rise, especially during COVID-19.18,19 Thus, social frailty caused by social problems requires more attention. Consequently, to promote healthy aging, it is imperative to take action to prevent and ameliorate social frailty among older adults in light of these findings.

Although many studies have been published on social frailty in older adults, to our knowledge, there is no summary of scientific studies to explore the prevalence of social frailty in older adults. Therefore, the primary purposes of our systematic review and meta-analysis are: (1) to explore the prevalence of social frailty among older adults; (2) to identify the associated factors such as countries, age, research sites, and years that affect the levels of social frailty in older adults.