In China, the proportion of the elderly has increased from 14.3 % in 2012 to 19.8 % in 2022, and approximately 1 in every 5 Chinese is aged 60 and above.1 As people age, they tend to have functional limitations, including difficulty with bathing, toileting, cooking, and managing money.2 The deterioration of functional limitation leads to adverse health outcomes, such as poor sleep quality, diminished quality of life, depression, and disability.3, 4, 5 Therefore, it is important to explore risk factors related to functional limitation and understand the mechanism through which these factors contribute to functional limitation.

Loneliness refers to a subjective negative feeling of dissatisfaction with the frequency and closeness of social relationships,6 which is considered to be a severe public health concern. Previous studies confirmed that loneliness was positively related to functional limitation and mortality among the elderly, including activities of daily living (ADL) disability and instrumental activities of daily living (IADL) disability.7,8 Socially, older adults with loneliness are more likely to have low physical activity and poor health status, which may result in functional limitation.9 Regardless of the growing interest in the association between loneliness and functional limitation, the underlying mechanisms of this relationship have not been adequately understood.

Frailty is common in older people, and the prevalence of frailty among the Chinese community was 10.1 %.10 Existing research demonstrated that loneliness was positively associated with frailty among older adults, and loneliness is one of the most important factors contributing to frailty.11 A longitudinal study using the English Longitudinal Study of Ageing dataset showed that higher levels of loneliness had a higher frailty index score.12 Improving loneliness is an essential way to reverse the frailty status. Meanwhile, a growing body of research has also suggested that elderly individuals with frailty are more likely to experience functional limitation.13,14 It is possible that frailty mediates the relationship between loneliness and functional limitation among older adults. Previous studies have found that frailty plays a significant mediating role in the relationship between some factors and functional limitation.15,16 Thus, we assume that frailty might be one of the underlying mechanisms between loneliness and functional limitation.

This study aimed to investigate the association between loneliness and functional limitation among the elderly in China, and examine the mediating role of frailty as a possible explanation for this relationship. We hypothesized that (i) there would be a significant positive association between loneliness and functional limitation, and (ii) the relationship between loneliness and functional limitation would be mediated by frailty. Identifying the association of these variables will provide a new perspective for preventing functional limitation with precise intervention strategies.