Combined association of social isolation and loneliness with frailty onset among independent older adults: A JAGES cohort study

OBJECTIVES: Social isolation and loneliness each have negatively affect various health outcomes. No studies have examined the combined association of social isolation and loneliness on frailty onset. This study aimed to investigate both the objective and subjective aspects of isolation by evaluating social isolation and loneliness and to determine their interaction effects on frailty onset. METHODS: This cohort study used data from the 2019 and 2022 Japan Gerontological Evaluation Study. The eligible participants were independent older adults aged ≥65 years without frailty in 2019. The outcome variable was frailty onset in 2022. The exposure variables were social isolation and loneliness in 2019. Risk ratios (RR) and 95 % confidence intervals (CI) were estimated using modified Poisson regression models, with potential confounders as covariates. Moreover, a multiplicative scale and relative excess risk due to interaction (RERI) was used to assess the interaction. RESULTS: The analysis included 8440 participants (mean age: 73.2 [standard deviation, 5.5] years). During the follow-up, 15.1 % of participants experienced frailty onset. After adjusting for all covariates, the "severe isolation" & "severe loneliness" group had the highest risk of frailty onset (RR = 2.09 [95 % CI: 1.60-2.73]) compared to "no isolation" & "no loneliness" group. However, there were no significant multiplicative and additive interaction between social isolation and loneliness on frailty onset (multiplicative scale: 0.75 [95 % CI: 0.50-1.11]; RERI:0.29 [95 % CI:1.02-0.44]). DISCUSSION: These findings highlight the importance of considering social factors such as interaction with others and loneliness, to prevent frailty.