Social isolation and functional impairment trajectories in a diverse cohort of middle-aged and older adults in Northern California

BACKGROUND: Social isolation is a key social determinant of health, yet research on its relationship with functional impairment is limited. We compared functional impairment score trajectories of older adults who experienced social isolation versus those who did not, using 2 different statistical approaches to handle attrition due to dropout and death. METHODS: Data were from 2 Northern California observational cohorts of people aged 50+ (n = 2476): Kaiser Healthy Aging and Different Life Experiences (KHANDLE) and Study of Healthy Aging in African Americans (STAR). We fit linear mixed effects models for functional impairment scores (sum of 12 items measuring basic activities of daily living [ADLs], instrumental ADLs, and mobility; range: 0-36) by baseline social isolation status (yes/no; 3-5 positive answers on 5 social contact items), adjusted for age and sex/gender. We estimated average marginal wave-specific differences in functional impairment scores, comparing approaches to address attrition. RESULTS: At baseline, 30% of participants reported social isolation; the median functional impairment score was 2 (Q1, Q3 = 0, 5). Baseline functional impairment scores were 1.03 points (95% CI, 0.84-1.20) higher among participants experiencing social isolation versus not. At wave 4, this difference decreased to 0.80 (95% CI, 0.52-1.07) among those remaining in the study and increased to 1.16 (95% CI, 0.83-1.42) assuming attrition was eliminated. Dropout and death were higher among participants experiencing social isolation. CONCLUSION: In a diverse cohort of older adults, those experiencing social isolation tend to experience greater functional impairment, but differences in trajectories depend on how attrition is handled.