Understanding the Individual and Combined Impacts of Social Isolation and Loneliness on Memory: A Sequential Explanatory Mixed Methods Study

Abstract

Social isolation (SI) and loneliness (LON) are important risk factors for cognitive health; however, their combined effects on memory, a key cognitive domain, are under-researched. This thesis is the first sequential, explanatory, mixed methods study to examine how SI and LON individually and together affect memory in middle-aged and older adults. Using three waves of data from the Canadian Longitudinal Study on Aging (CLSA), spread over six years, LON was measured by the loneliness frequency question from the 10-item Center for Epidemiologic Studies Depression Scale. SI was measured by an index based on marital/cohabiting status, retirement status, social activity participation, and number/frequency of social network contacts. Memory was evaluated with combined immediate- and delayed-recall z-scores from the Rey Auditory Verbal Learning Test. Primary analyses utilized all available data across the three waves of CLSA data and retained participants with missing covariate data (n = 14,208). Linear mixed models to account for all three waves of data were used to regress combined memory scores onto SI and LON, adjusting for sociodemographic, health, functional ability, and lifestyle variables. Results showed that combined SI and LON had the greatest negative impact on memory (least-squares mean: -0.80 [95% confidence-interval: -1.22, -0.39]), followed by LON alone (-0.73 [-1.13, -0.34]), then SI alone (-0.69 [1.09, -0.29]), and lastly by experiencing neither (-0.65 [-1.05, -0.25]). Two sensitivity analyses – one excluding participants with missing covariate data from the primary analysis sample and another employing a multiple imputation approach – both confirmed these findings. The qualitative phase involved phenomenological, semi-structured interviews with ten individuals – recruited through purposive and snowball sampling – to explain the quantitative results from the perspective of middle-aged and older adults. Based on thematic analysis, qualitative participants believed that LON has a stronger negative impact on memory than SI because individuals can still engage in mental stimulation while isolated, but are less motivated to do so when feeling lonely. Participants also believed that the combination of SI and LON is most detrimental to memory, as these conditions can exacerbate each other in a feedback loop, leading those who experience both to be more prone to self-destructive behaviours. This research highlights the need for targeted interventions involving multimodal brain health programs, which simultaneously address multiple risk factors for cognitive decline – such as SI and LON – through actionable steps, including staying socially connected, finding meaning in life, engaging in cognitively stimulating physical/leisure activities, managing medical conditions, and adopting healthy lifestyle choices.