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Background: Loneliness has been highlighted as a risk factor for dementia. However, the nature of the relationship between loneliness and cognitive function prior to onset of dementia is unclear. Objective: The aim of this systematic review and meta-analysis was to examine the relationship between loneliness and cognitive function in samples screened for dementia at study commencement. Methods: Five electronic databases (PubMed, PsycNET, Web of Science, EBSCOhost, Scopus) were searched from inception to August 31, 2021. A narrative review and random-effects meta-analysis were conducted on studies meeting search criteria. PROSPERO registration number: CRD42020155539. Results: The sixteen studies that met inclusion criteria involved 30,267 individuals, with mean age ranging from 63.0 to 84.9 years. Studies varied in dementia screening criteria, measurement of loneliness and cognitive function, and statistical modeling approach. The narrative review indicated that loneliness was associated with poorer global cognition, episodic memory, working memory, visuospatial function, processing speed, and semantic verbal fluency. Results of the meta-analysis indicated that loneliness was negatively associated with global cognitive function (overall r = –0.08; 95% CI = –0.14, –0.02; n = 6). Due to lack of sufficient data and heterogeneity between studies, we were unable to explore associations with other cognitive domains or longitudinal associations. Conclusion: Loneliness is associated with subtle impairment across multiple cognitive domains in older adults who were screened for dementia. Better characterization of this relationship will provide important information about how loneliness contributes to the clinical and pathological sequalae of AD and be informative for risk reduction and early detection strategies.

ObjectivesIn current study, we aim to extend previous research by investigating the unique impact of loneliness on health literacy and health-related factors of young adults, after controlling for social isolation, depressive symptomology, and social anxiety, as well as evaluate how social isolation and loneliness differ in their impact on health literacy, and health-related factors among young adults, after accounting for abovementioned concomitant variables.MethodsUsing a cross-sectional study design, 521 young adults completed an online survey in 2020, where they self-reported their loneliness, social isolation, health-related factors, and health literacy data.ResultsIncreased loneliness was associated with decrease in several health literacy domains (e.g., poorer social support for health, lower appraisal of health information, among others) and increase in some health-related factors (e.g., higher perceived stress, higher negative affect), among young adults, even after controlling for social anxiety, depressive symptomology, and social isolation. Contrastingly, increase in social isolation was associated with changes in some health-related factors - more somatic health complaints, higher alcohol use, poorer cognitive and physical functioning, and lower scores for only one health literacy domain (i.e., social support for health) among young adults, after adjusting for the influence of social anxiety, depressive symptomology, and loneliness.ConclusionEven after accounting for the influence of several co-occurring social and mental health symptoms, higher loneliness was associated poorer health literacy and health-related factors in young adults. We also found loneliness and social isolation may differ in the mechanisms through which they impact health literacy and health-related factors in young adults.

COVID‐19 pandemic and its associated social and physical distancing restrictions may have had a severe impact on health. In the present study, we investigate the changes in physical, social and mental health, as well as the health literacy of Australians subsequent to the onset of COVID‐19 pandemic, and examine the influence of loneliness on these health‐related factors. Using a retrospective cross‐sectional study design, 607 Australian adults completed a self‐report online survey which assessed their health‐related factors before and after onset of the COVID‐19 pandemic (data collected between June 2020 to November 2020). Australians reported statistically significant increase in a number of (poorer) health‐related factors (e.g., weight gain, sleeping difficulties, poor somatic health, higher loneliness, more issues navigating the healthcare system) post onset of COVID‐19 pandemic. Further, after adjusting for covariates, higher loneliness during pandemic predicted poorer health‐related outcomes (e.g., more somatic health complaints, poorer quality of diet, poorer social support for health). The COVID‐19 pandemic and its associated social and physical distancing restrictions may have contributed towards poorer health‐related factors among Australian adults. Further, increased loneliness during the pandemic may have further worsened physical health and health literacy outcomes among Australians.

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Loneliness has consistently been associated with dementia risk. An important precursor to dementia is cognitive decline, which can begin decades prior to clinical diagnosis of dementia. Therefore, understanding about the relationship between loneliness and cognitive function in healthy older adults may inform our understanding of how loneliness contributes to dementia risk. The aim of this systematic review was to identify the extent to which loneliness affects cognition in older adults who do not have dementia. A systematic search of five databases (PubMed, PsycNET, Web of Science, EBSCOhost, Scopus) from inception to August 31st 2021 was completed, including search terms related to loneliness, aging, and cognition. A total of 4,302 unique articles were screened for inclusion, resulting in 16 studies that met full criteria (six cross-sectional and ten longitudinal). Three of the six (50%) cross-sectional studies reported significant negative associations between loneliness and cognitive function, while six of the ten (60%) longitudinal studies reported that loneliness was associated with greater cognitive decline over time. We did not find a significant relationship between loneliness and cognitive function in the rest of the studies. There was substantial variation across studies in the measures of loneliness and cognitive function. Furthermore, many studies relied on cognitive screening tools to identify cognitive outcomes, which may not be sensitive to subtle cognitive changes that precede dementia. Future studies should consider using validated and sensitive measures of loneliness and cognitive function, and examining these relationships prospectively, in order to, assess these relationships in a more robust way.