Social isolation increases risk for dementia and correlates with structural gray matter volume loss. Depressive symptoms might factor into the relationship between loneliness and dementia, but loneliness overall did not contribute to dementia risk. These are the findings of a study published in Neurology.
Common public health problems with old age include social isolation and loneliness. Among older adults, dementia is a major cause of disability, the researchers explained. Yet, the effect of social isolation and loneliness on the risk of developing dementia is unknown.
The objective of the current study was to independently evaluate how social isolation and loneliness impact the likelihood of developing dementia in older adults.
The researchers analyzed data from 462,619 patients with a mean baseline age of 57; 45.4% were men; 95.3% were White, using the UK Biobank cohort covering 22 centers across the UK from time of patient enrollment between 2006 and 2010 until January 31, 2021.
Three questions determined the level of social isolation by assessing social activity participation, social contact, and living alone. Two questions modeled from the revised ULCA loneliness scale assessed the extent of loneliness. Pairs matching and reaction time tests with predictive value for dementia assessed cognitive function.
At baseline, 41,886 people (9%) said they were socially isolated and 26,036 people (6%) said they were feeling lonely.
Structural magnetic resonance imaging (MRI) of the cortical and subcortical regions allowed for calculation of gray matter volumes of these brain regions for 32,263 (mean age 63.5; 52% female) participants. This was conducted on an average of 8.8 years after baseline. The researchers also compared gene expression in adults with neurotypical brains to those with gray matter volume loss using the Allen Human Brain Atlas.
Of this subset, 2371 people (7%) reported being socially isolated and 1503 people (5%) reported feeling lonely.
All-cause dementia occurred in 4998 patients. The incidence of dementia was 26% higher among patients who reported being socially isolated (adjusted HR, 1.26; 95% CI, 1.15-1.37). Overall, loneliness did not elevate risk for developing dementia, although depressive symptoms related to loneliness were associated with worse cognitive function (P <.001).
Of the patients with neuroimaging results, those who classified as socially isolated demonstrated lower gray matter volumes of brain regions responsible for learning and memory, including the temporal, frontal, and hippocampal regions. This correlated positively with reduced cognitive functioning indicative of dementia.
Lower gray matter volume which associated with social isolation correlated with decreased cortical expression of genes that are typically downregulated in Alzheimer disease (AD) as well as genes related to mitochondrial dysfunction and oxidative phosphorylation.
The researchers acknowledged there are several issues that should be considered when interpreting their findings. These range from fewer self-reported health conditions from the participants in UK Biobank — who were also less likely to live alone compared with the general population — to the potential of cultural factors influencing the social relationship-health association. Furthermore, they noted the cognitive tests used in the study were brief, and in the future, it would be “important to include episodic memory tests, which have been shown to be valid, sensitive tests for the early detection of amnestic mild cognitive impairment and the early stage of AD.”
“We revealed that social isolation was associated with an increased incidence of dementia independent of loneliness and many potential risk factors,” the authors stated. “In the context of the COVID-19 pandemic, which critically exacerbates social isolation, these findings have implications for social relationship interventions.”
Disclosure: A study author declared affiliations with biotech, pharmaceutical, and/or device companies. Please see the original reference for a full list of authors’ disclosures.
Shen C, Rolls E, Cheng W, et al. Associations of social isolation and loneliness with later dementia. Neurology. Published online June 8, 2022. doi:10.1212/WNL.0000000000200583