Social Isolation and Cognitive Health: Does Physical Activity Protect Against Cognitive Decline in Socially Isolated Older Adults?

Background and Purpose

The rising prevalence of cognitive decline among older adults presents a major public health challenge. A growing body of research focuses on the negative impact of social isolation on cognitive function. However, the mechanisms underlying this relationship remain underexplored—particularly the role of potentially modifiable protective factors. While physical activity has been highlighted as an additional contributor to cognitive reserve within recent research applying the cognitive reserve framework, little is known about the mitigating role of physical activity on the adverse effect of social isolation on cognitive function among older adults. To fill this gap, this study investigated the longitudinal association between social isolation and cognitive function over 12 years and the moderating role of physical activity in the relationship.

Methods

Data was obtained from the longitudinal Health and Retirement Study 2006-2020, a nationally representative sample of middle aged and older adults (N=11,485). Cognitive function was measured using the Langa-Weir 27-point scale. Social isolation was assessed using six items related to relationships with family, friends, and communities, with scores of ≥ 3 indicating isolation and < 3 indicating not isolated. Physical activity was measured using self-reported engagement in light, moderate, and vigorous activities. Responses were converted into Metabolic Equivalent of Task scores to categorize activity levels as sedentary, light, moderate, or vigorous. Sociodemographic characteristics included as covariates were age, gender, race/ethnicity, education at baseline, and time-varying annual household income. Generalized linear mixed models, accounting for repeated observations of cognitive function within individuals, were estimated with cognitive function as the outcome, social isolation as the exposure, and physical activity levels as the moderator.

Results

Approximately 28% of respondents reported being socially isolated. Our analysis showed that social isolation was associated with lower cognitive function, even after adjusting for sociodemographic characteristics and physical activity (b= -0.59, 95% CI=-0.96, -0.21). Additionally, the interaction terms of moderate and vigorous physical activity were statistically significant (moderate: b=0.52, 95% CI=0.12, 0.92; vigorous: b=0.54, 95% CI=0.11, 0.97), whereas the interaction term between light physical activity and social isolation was not significant (b=0.26, 95% CI= -0.11, 0.64). In other words, the negative association between social isolation and cognitive function was weakened for those who engaged in moderate and vigorous physical activity, compared to those who were sedentary.

Conclusions and Implications

Our findings confirmed that social isolation is significantly associated with lower cognitive function over time among older adults. Moreover, we observed that moderate to vigorous physical activity served as a protective factor against the negative effect of social isolation on cognitive health. These results align with the Physical Activity Guidelines for Americans, highlighting the protective role of physical activity. Our study suggests that promoting moderate to vigorous physical activity in older adults could be an effective strategy for supporting cognitive health. Given that older adults are particularly vulnerable to the adverse impact of social isolation, our findings emphasize the importance of integrating physical activity promotion into community-based interventions, targeting to address both social isolation and cognitive decline.