The impact of social isolation on functional disability in older people: A multi-cohort study

Objectives: We assessed the relationship between social isolation and functional disability in older people.

Design: Comparison of longitudinal cohort studies.

Setting and participants: Harmonised longitudinal datasets from the United States, England, European countries, Japan, Korea, China and Hong Kong.

Methods: Social isolation was operationalised as a composite score with five domains, such as marital status, living alone, and social contact with others. Functional disability was defined as whether the cohort participant had any difficulty in activities of daily living (ADL). In each dataset, we used robust Poisson regression models to obtain the relative risks (RRs) and the corresponding 95 % confidence intervals (CI). We combined the RRs to synthesize a pooled estimate using meta-analysis with random-effects models.

Results: Overall, the social isolation composite score was not associated with ADL disability (pooled RR = 1.05, 95 % CI [0.97-1.14], n = 40,119). Subgroup analysis suggested social isolation composite score was associated with ADL disability in Asian regions (pooled RR = 1.09, 95 % CI [1.02, 1.16], but not in Western regions (pooled RR = 1.01, 95 % CI [0.96, 1.07]). The relationships between different domains of social isolation and ADL disability were heterogeneous, except that no participation in any social clubs or religious groups was consistently associated with ADL disability (pooled RR = 1.12, 95 % CI [1.04, 1.21]).

Conclusion: Targeting social isolation may prevent decline in functional abilities in older adults, providing an avenue to active and healthy ageing. Nonetheless, interventions tackling social isolation should tailor to the unique cultural and social underpinnings. A limitation of the study is that reverse causality could not be ruled out definitively.