ObjectivesIn Japan, frailty is a major risk factor for requiring long-term care, especially among older adults aged 75 years or older (ie, late-stage older adults). Both physical and social factors (eg, social activities, social support and community trust) are protective factors against frailty. However, few longitudinal studies have examined reversible change or stage improvement in frailty. This study investigated social activity participation and trust in the community that may affect the transition of late-stage older adults’ frailty status.DesignA mail-based survey was used to analyse the improvement or deterioration of frailty status (categorised as frailty, pre-frailty and robust) over a 4-year period. Binomial and multinomial logistic regression analyses were conducted; the transition in frailty classification was the dependent variable, while a change in social activity participation and the degree of trust in the community were the independent variables.SettingIkoma City, Nara Prefecture, Japan.Participants4249 community-dwelling older adults, aged ≥75 years, not requiring long-term care who completed a follow-up questionnaire from April to May 2016.ResultsAdjusting for confounding factors, no significant social factors were detected regarding improvement in frailty. However, an increase in exercise-based social participation was an improvement factor in the pre-frailty group (OR 2.43 (95% CI 1.08 to 5.45)). Conversely, a decrease in community-based social activity was a risk factor in the deterioration from pre-frailty to frailty (OR 0.46 (95% CI 0.22 to 0.93)). In the robust group, increased community-based social activity (OR 1.38 (95% CI 1.00 to 1.90)) was a protective factor against frailty, whereas decreased community trust was a risk factor (OR 1.87 (95% CI 1.38 to 2.52)).ConclusionsNo social factors had a significant influence on the improvement of frailty in late-stage older adults. However, the promotion of exercise-based social participation was found to be important for improvement in the pre-frailty state.Trial registration numberUMIN000025621.