A large US study using causal modeling shows that lowering social isolation, not just addressing loneliness, could play a key role in preserving cognitive health as people age.
Study: Disentangling social isolation, loneliness, and later-life cognitive function for older adults in the United States: Evidence from causal inference modeling. Image Credit: Troyan / Shutterstock
In a recent study published in The Journals of Gerontology: Series B, researchers investigated the effects of loneliness and social isolation on cognitive function in later life.
Research on loneliness and social isolation has substantially increased in recent years, especially among older adults and adolescents. About one-fourth of older adults in the United States (US) were socially isolated even before the coronavirus disease 2019 (COVID-19) pandemic, raising concerns about the impacts of isolation. Moreover, loneliness is recognized as a major public health concern in several countries.
Population aging has triggered interest in pathological cognitive decline as a possible consequence of loneliness and social isolation. Evidence suggests that greater loneliness and social isolation are associated with poorer cognitive function. However, the interdependent nature of loneliness, cognitive function, and social isolation presents a significant challenge, as it can lead to a dynamic relationship that unfolds across the later-life age trajectory.
Study Data and Population Design
In the present study, researchers explored the effects of loneliness and social isolation on later-life cognitive function. They relied on the Health and Retirement Study (HRS), an ongoing, nationally representative, longitudinal, biennial survey of US residents aged 50 and older and their spouses. The team used data from all survey waves but focused on waves between 2004 and 2018 in which social isolation, loneliness, and cognitive measures were consistently assessed.
Respondents who participated in two consecutive waves were included, while those who required a proxy respondent were excluded. The study’s outcome was cognitive function. From the HRS telephone interview for cognitive status, a subset of questions reflecting neurophysiological health was extracted. These included immediate and delayed word recall, counting backward from 20, and serial 7s, counting backward from 100 by sevens.
Measuring Social Isolation and Loneliness
The primary exposure was the social isolation index, constructed as an eight-item score that captures partnership status, social helping and caregiving ties, communication and functional barriers such as email use, mobility limitations, and hearing impairment, and participation in religious and volunteer activities, rather than solely sociability or organizational membership.
Loneliness was assessed using a single binary item from the Center for Epidemiological Studies Depression (CES-D) scale asking whether respondents felt lonely in the past week. A counterfactual framework based on the g-formula was used to simulate the effect of decreasing social isolation on cognitive function averaged across later adulthood, relative to the natural course. A mediation analysis evaluated the extent to which the association between social isolation and cognitive function was mediated by loneliness. The effect of a targeted simulated intervention among individuals living alone was also estimated.
Sample Characteristics and Social Patterns
The analytical sample included 30,421 respondents with 137,653 observations. The correlation between loneliness and social isolation was modest. Among respondents who reported being lonely, only 55% were more isolated, while 26% reported no loneliness despite being more isolated. Differences in social isolation were observed across sociodemographic factors, with older, Black, and Latinx individuals reporting greater social isolation.
Individuals with lower childhood socioeconomic status, lower education, and those in the lowest wealth quintile were also more isolated. In contrast, people who worked, lived with others, had fewer comorbidities, or were not depressed were less isolated.
Effects of Isolation Reduction on Cognition
The simulated intervention was associated with a 0.19-point increase in cognitive function on a 0 to 27 cognitive scale, based on the confidence intervals reported in the original analysis. This finding indicates that reducing social isolation was protective against cognitive decline, despite the modest absolute magnitude relative to typical age-related decline.
Mediation analysis showed that loneliness accounted for 6% of the effect of social isolation on cognitive function. The intervention targeting only individuals living alone accounted for approximately half of the effect observed when reducing social isolation across the entire population.
Interpretation and Policy Implications
The findings reveal a protective effect of reduced social isolation on later-life cognitive decline, which was generally similar across males and females, across Black, White, and Latinx individuals, and across levels of educational attainment. The authors note that this effect may be particularly insulative for structurally disadvantaged groups, given lower baseline cognitive scores and greater exposure to social risk factors. Loneliness mediated only a small proportion of the total effect.
Because social isolation has an independent effect on cognitive decline, focusing solely on loneliness management is unlikely to be sufficient. Instead, loneliness and social isolation should be treated as distinct targets for intervention. Policy-relevant interventions that address structural and functional drivers of isolation, particularly those tailored to living conditions such as living alone, may yield meaningful benefits.
Lentilactobacillus kefiri can prevent and even reverse aging-related immune alterations