Social isolation was associated with lower volume in areas of the brain related to cognition, increasing the risk of subsequent dementia by over 20%, according to a new longitudinal study published in Neurology.

Home- and community-based memory care models

Study details and key findings

For the study, researchers analyzed data from 462,619 people in the U.K. Biobank study. Enrollment in the study began in 2006, and data on the participants was collected through Jan. 31, 2021. Of the participants, 45.4% were men, 95.3% were Caucasian, and the mean baseline age was 57.

The 12 risk factors tied to 40% of dementia cases

At the start of the study, 41,886 (9%) participants reported being socially isolated, and 29,036 (6%) reported being lonely. Participants who were socially isolated or lonely had worse cognitive function compared to controls, even after adjusting for age, sex, ethnicity, education, and income. Depressive symptoms were also linked to cognitive function after controlling for the same variables.

In addition, a subset of 32,263 participants also underwent neuroimaging an average of 8.8 years after baseline. In total, 2,371 of these participants (7%) said they were socially isolated, and 1,503 participants (5%) said they were lonely.

Overall, participants were followed up for a mean of 11.7 years, and 4,998 people in total developed all-cause dementia. The researchers found that dementia incidence was 26% higher in socially isolated participants. Among participants with neuroimaging results, those who said they were socially isolated also had lower gray matter volume in brain regions associated with learning and memory, which was positively correlated with the reduced cognitive functioning seen in dementia.

Dementia incidence was also roughly 4% higher in lonely participants, but researchers found that this association was not significant, since 75% of the relationship was attributable to depressive symptoms.

When analyzing subgroups, the researchers found that the association between social isolation and dementia was consistent for both men and women. However, when analyzing by age, only older people who were socially isolated (mean age: 64.6) had a significant association with dementia.

The researchers also noted limitations to the study, including the fact that participants in the U.K. Biobank were less likely to live alone than the general population and reported fewer health conditions.

Commentary

According to Edmund Rolls, one of the study's authors from the University of Warwick, "[t]here is a difference between social isolation, which is an objective state of low social connections, and loneliness, which is subjectively perceived social isolation."

"Both have risks to health, but using the extensive multi-modal data set from the U.K. Biobank and working in a multidisciplinary way linking computational sciences and neuroscience, we have been able to show that it is social isolation, rather than the feeling of loneliness, which is an independent risk factor for later dementia," Rolls said.

"With the growing prevalence of social isolation and loneliness over the past decades, this has been a serious yet underappreciated public health problem," he added. "Now, in the shadow of the COVID-19 pandemic there are implications for social relationship interventions and care, particularly in the older population."

In an accompanying editorial, Lawrence Whalley, from the University of Aberdeen in Scotland, noted that much of the clinical research in Alzheimer's disease focuses on how to prevent age-related neurodegeneration and that the study opens up new areas of research for dementia prevention.

"The first is to show where social isolation appears as a primary agent leading to dementia and is not a consequence of cognitive impairment," Whalley wrote. "What follows becomes an intellectual challenge to reveal the substructure of social isolation and to identify those elements most relevant to dementia risk." (George, MedPage Today, 6/9; Lopez, Neurology Advisor, 7/13; Shen et al., Neurology, 7/12)