Impact of social isolation on change in brain volume in community-dwelling older Japanese people: The NEIGE Study

Background

Several studies have shown that social isolation is a risk factor for cognitive decline and dementia; however, its neurological mechanisms are not fully understood. Using longitudinal data, this study examined the effects of social isolation on hippocampal and total gray matter volumes in community-dwelling older Japanese individuals.

Methods

Data were obtained from the Neuron to Environmental Impact Across Generations (NEIGE) Study conducted in Tokamachi City (Niigata Prefecture, Japan), including 279 community-dwelling persons aged 65–84 years who underwent brain magnetic resonance imaging in 2017 and 2021 (male: 47.6 %; mean age: 73.0 years). We investigated two dimensions of social isolation: poor social networks and solitary living.

Results

Multiple regression analysis with inverse probability weighting showed that individuals with a social contact frequency of <1 time/week had a greater decrease in hippocampal volume than those with a contact frequency of more than or equal to 4 times/week, whereas those who lived alone tended to have a smaller decrease in hippocampal volume than those who lived with others. We found no association between the frequency of social contact, living alone, and total gray matter volume. Furthermore, there was no interaction between sex and age for any of the outcomes.

Conclusion

Our longitudinal analysis suggested that the relationship between social isolation and dementia onset may be mediated by hippocampal atrophy; however, the direction of the influence depends on the isolation type. These findings are expected to contribute to the elucidation of the social mechanisms underlying dementia onset.