Social isolation in relation to the incidence and dynamic progression of frailty in the oldest old: a trajectory analysis of a nationwide cohort.

Background: There is still a lack of evidence examining the association of behavioral and social factors with frailty transitions and mortality. We investigated whether social isolation is associated with different progressions and outcomes of frailty among community-dwelling older adults.

Methods: This community-based cohort study assessed the frailty index and objective social isolation of 31,168 participants (58.3% female; average age: 88.1 ± 11.1 years) from the Chinese Longitudinal Healthy Longevity Survey (CLHLS) from 1998 to 2018. Four Markov state-transition models were constructed to examine the associations between social isolation and the seven transitions of the frailty trajectory.

Results: According to the Markov state-transition model, for every one-point increase in the social isolation score of non-frail participants, the risk of developing prefrailty increased by 4.2% [hazard ratio (HR) = 1.042, 95% confidence interval (CI): 1.007-1.079], whereas for prefrail participants, the risk of developing frailty and death increased by 3.9% (HR = 1.039, 95% CI: 1.007-1.073) and 16.1% (HR = 1.161, 95% CI: 1.099-1.226), respectively. For each increase in the social isolation score in the frail population, the risk of death increased by 2.9% (HR = 1.029, 95% CI: 1.004-1.054). Socially isolated persons had a greater cumulative transition probability to prefrailty and frailty. Socially isolated women were more likely to experience prefrailty and frailty than socially isolated men, whereas the latter were more likely to die from prefrailty and frailty than the former.

Conclusions: This study indicates that social isolation may contribute to an increased risk of both the incidence and progression of frailty, elevating deterioration risks in initially non-frail and prefrail populations, while primarily exacerbating mortality risks in those already experiencing prefrailty or frailty.