Dorsal Raphe Dopamine Neurons Represent the Experience of Social Isolation.

The motivation to seek social contact may arise from either positive or negative emotional states, as social interaction can be rewarding and social isolation can be aversive. While ventral tegmental area (VTA) dopamine (DA) neurons may mediate social reward, a cellular substrate for the negative affective state of loneliness has remained elusive. Here, we identify a functional role for DA neurons in the dorsal raphe nucleus (DRN), in which we observe synaptic changes following acute social isolation. DRN DA neurons show increased activity upon social contact following isolation, revealed by in vivo calcium imaging. Optogenetic activation of DRN DA neurons increases social preference but causes place avoidance. Furthermore, these neurons are necessary for promoting rebound sociability following an acute period of isolation. Finally, the degree to which these neurons modulate behavior is predicted by social rank, together supporting a role for DRN dopamine neurons in mediating a loneliness-like state. PAPERCLIP.

Mental health concerns during the COVID-19 pandemic as revealed by helpline calls.

Mental health is an important component of public health, especially in times of crisis. However, monitoring public mental health is difficult because data are often patchy and low-frequency1-3. Here we complement established approaches by using data from helplines, which offer a real-time measure of 'revealed' distress and mental health concerns across a range of topics4-9. We collected data on 8 million calls from 19 countries, focusing on the COVID-19 crisis. Call volumes peaked six weeks after the initial outbreak, at 35% above pre-pandemic levels. The increase was driven mainly by fear (including fear of infection), loneliness and, later in the pandemic, concerns about physical health. Relationship issues, economic problems, violence and suicidal ideation, however, were less prevalent than before the pandemic. This pattern was apparent both during the first wave and during subsequent COVID-19 waves. Issues linked directly to the pandemic therefore seem to have replaced rather than exacerbated underlying anxieties. Conditional on infection rates, suicide-related calls increased when containment policies became more stringent and decreased when income support was extended. This implies that financial relief can allay the distress triggered by lockdown measures and illustrates the insights that can be gleaned from the statistical analysis of helpline data.

Chronic social isolation signals starvation and reduces sleep in Drosophila.

Social isolation and loneliness have potent effects on public health1-4. Research in social psychology suggests that compromised sleep quality is a key factor that links persistent loneliness to adverse health conditions5,6. Although experimental manipulations have been widely applied to studying the control of sleep and wakefulness in animal models, how normal sleep is perturbed by social isolation is unknown. Here we report that chronic, but not acute, social isolation reduces sleep in Drosophila. We use quantitative behavioural analysis and transcriptome profiling to differentiate between brain states associated with acute and chronic social isolation. Although the flies had uninterrupted access to food, chronic social isolation altered the expression of metabolic genes and induced a brain state that signals starvation. Chronically isolated animals exhibit sleep loss accompanied by overconsumption of food, which resonates with anecdotal findings of loneliness-associated hyperphagia in humans. Chronic social isolation reduces sleep and promotes feeding through neural activities in the peptidergic fan-shaped body columnar neurons of the fly. Artificial activation of these neurons causes misperception of acute social isolation as chronic social isolation and thereby results in sleep loss and increased feeding. These results present a mechanistic link between chronic social isolation, metabolism, and sleep, addressing a long-standing call for animal models focused on loneliness7.

Changes in well-being among socially isolated older people during the COVID-19 pandemic: An outcome-wide analysis.

Older adults experienced major changes during the COVID-19 pandemic and ensuing restrictions, and it might be expected that those who were already socially isolated before the pandemic were particularly vulnerable. We apply an outcome-wide longitudinal design on 4,636 participants (mean age 66.8 y) from the English Longitudinal Study of Ageing, observed in 2018/19 and early (June/July 2020) and later (November/December 2020) in the pandemic. Social isolation is defined using an index including marital status, social contact, and social participation in 2018/19. Using mixed models, we compare changes in well-being, health, health behaviors, financial well-being, and Internet use, between isolated and nonisolated participants. From before to during the pandemic, isolated participants (29%) experienced smaller declines in life satisfaction and quality of life and a smaller increase in loneliness. They showed greater declines in smoking and physical activity and were more likely to remain worried about their future financial situation. They also did not change in their likelihood of regular Internet use, contrasting with nonisolated participants who increased in this regard. The groups followed a similar trend for general health and sleep quality (no change), depression and anxiety (increase), and expectations of future financial difficulties (decrease). Although isolated older adults generally show poorer outcomes than their socially connected counterparts, they were somewhat protected during the pandemic on some fronts. Our findings highlight the need to continually care for isolated older adults but also to be attentive in times of unexpected crises to those experiencing extreme changes related to necessary policy responses.

Association of cumulative loneliness with all-cause mortality among middle-aged and older adults in the United States, 1996 to 2019.

Loneliness is a growing public health concern worldwide. We characterized the association between cumulative loneliness and subsequent all-cause mortality, using data from 9,032 participants aged 50+ in the population-based US Health and Retirement Study (HRS) from 1996 to 2019. Loneliness status (yes; no) was measured biennially from 1996 to 2004, and we categorized the experience of cumulative loneliness over the 8-y period as never, one time point, two time points, and ≥three time points. A multivariable-adjusted age-stratified Cox proportional hazards regression model was fitted to examine the association between cumulative loneliness from 1996 to 2004 and all-cause mortality from 2004 to 2019. Excess deaths due to each category of cumulative loneliness were calculated. Compared to those who never reported loneliness from 1996 to 2004, participants experiencing loneliness at one time point, two time points, and ≥three time points respectively had 1.05 (95% CI: 0.96 to 1.15), 1.06 (95% CI: 0.95 to 1.19), and 1.16 (95% CI: 1.02 to 1.33) times higher hazards of mortality from 2004 to 2019 (P trend = 0.01). These results correspond to 106 (95% CI: 68 to 144), 202 (95% CI: 146 to 259), and 288 (95% CI: 233 to 343) excess deaths per 10,000 person-years, for those experiencing loneliness at each of one, two, or ≥three time points from 1996 to 2004. Cumulative loneliness in mid-to-later life may thus be a mortality risk factor with a notable impact on excess mortality. Loneliness may be an important target for interventions to improve life expectancy in the United States.

Mental health, financial, and social outcomes among older adults with probable COVID-19 infection: A longitudinal cohort study.

We investigated the immediate and longer-term impact (over 4-6 months) of probable COVID-19 infection on mental health, wellbeing, financial hardship, and social interactions among older people living in England. Data were analysed from 5146 older adults participating in the English Longitudinal Study of Ageing who provided data before the pandemic (2018-19) and at two COVID-19 assessments in 2020 (June-July and November-December). The associations of probable COVID-19 infection (first COVID-19 assessment) with depression, anxiety, poor quality of life (QoL), loneliness, financial hardship, and social contact with family/friends at the first and second COVID-19 assessments were tested using linear/logistic regression and were adjusted for pre-pandemic outcome measures. Participants with probable infection had higher levels of depression and anxiety, poorer QoL, and greater loneliness scores compared with those without probable infection at both the first (ORdepression = 1.62, P-value = 0.005; ORanxiety = 1.59, P-value = 0.049; bpoorQoL = 1.34, P < 0.001; bloneliness = 0.49, P < 0.001) and second (ORdepression = 1.56, P-value = 0.003; ORanxiety = 1.55, P-value = 0.041; bpoorQoL = 1.38, P-value < 0.001; bloneliness = 0.31, P-value = 0.024) COVID-19 assessments. Participants with probable infection also experienced greater financial difficulties than those without infection at the first assessment (OR = 1.50, P-value = 0.011). Probable COVID-19 infection is associated with longer-term deterioration of mental health and wellbeing and short-term increases in financial hardship among older adults. It is important to monitor the mental health of older people affected by COVID-19 and provide additional support to those in need.

Exercise to socialize? Bidirectional relationships between physical activity and loneliness in middle-aged and older American adults.

Physical inactivity and loneliness are both associated with health risks and can affect each other through various social and behavioral mechanisms. However, current evidence on this relationship is equivocal and mostly based on cross-sectional data. This longitudinal study aimed to determine whether current levels of physical activity (moderate and vigorous intensity) and loneliness are associated with future respective states of themselves and each other. We used data from waves 6-14 (2002-2018) of the Health and Retirement Study (n = 20 134) in a mixed-effects and random-intercept cross-lagged panel model. Analysis showed that current loneliness and physical activity were associated with each future respective state. Additionally, weekly participation in moderate-intensity, but not vigorous-intensity, physical activity was associated with a lower likelihood of becoming lonely in the future (relative risk [RR] = 0.94; 95% CI, 0.90-0.99). However, changes in physical activity were not associated with deviation from a person's typical level of loneliness (for vigorous intensity, mean deviation [MD] = 0.00; 95% CI: -0.04 to 0.03; for moderate-intensity, MD = 0.01; 95% CI: -0.03 to 0.04). Loneliness was not associated with moderate- or vigorous-intensity physical activity in subsequent waves. This suggests that while lower physical activity levels can be associated with future loneliness, changing levels of physical activity has little impact on loneliness at the individual level.

The impact of loneliness and social isolation on the development of cognitive decline and Alzheimer's Disease.

Alzheimer's Disease (AD) is the leading cause of dementia, observed at a higher incidence in women compared with men. Treatments aimed at improving pathology in AD remain ineffective to stop disease progression. This makes the detection of the early intervention strategies to reduce future disease risk extremely important. Isolation and loneliness have been identified among the major risk factors for AD. The increasing prevalence of both loneliness and AD emphasizes the urgent need to understand this association to inform treatment. Here we present a comprehensive review of both clinical and preclinical studies that investigated loneliness and social isolation as risk factors for AD. We discuss that understanding the mechanisms of how loneliness exacerbates cognitive impairment and AD with a focus on sex differences will shed the light for the underlying mechanisms regarding loneliness as a risk factor for AD and to develop effective prevention or treatment strategies.

Loneliness and Depressive Symptoms Are High Among Older Adults With Digestive Disease and Associated With Lower Perceived Health.

BACKGROUND & AIMS: Current approaches to managing digestive disease in older adults fail to consider the psychosocial factors contributing to a person's health. We aimed to compare the frequency of loneliness, depression, and social isolation in older adults with and without a digestive disease and to quantify their association with poor health. METHODS: We conducted an analysis of Health and Retirement Study data from 2008 to 2016, a nationally representative panel study of participants 50 years and older and their spouses. Bivariate analyses examined differences in loneliness, depression, and social isolation among patients with and without a digestive disease. We also examined the relationship between these factors and health. RESULTS: We identified 3979 (56.0%) respondents with and 3131 (44.0%) without a digestive disease. Overall, 60.4% and 55.6% of respondents with and without a digestive disease reported loneliness (P < .001), 12.7% and 7.5% reported severe depression (P < .001), and 8.9% and 8.7% reported social isolation (P = NS), respectively. After adjusting for covariates, those with a digestive disease were more likely to report poor or fair health than those without a digestive disease (odds ratio [OR], 1.25; 95% CI, 1.11-1.41). Among patients with a digestive disease, loneliness (OR, 1.43; 95% CI, 1.22-1.69) and moderate and severe depression (OR, 2.93; 95% CI, 2.48-3.47; and OR, 8.96; 95% CI, 6.91-11.63, respectively) were associated with greater odds of poor or fair health. CONCLUSIONS: Older adults with a digestive disease were more likely than those without a digestive disease to endorse loneliness and moderate to severe depression and these conditions are associated with poor or fair health. Gastroenterologists should feel empowered to screen patients for depression and loneliness symptoms and establish care pathways for mental health treatment.

Bidirectional Associations Between Loneliness, Emotional Support, and Sleep in Daily Life.

OBJECTIVE: Evidence suggests a link between positive social relationship perceptions and improved sleep (e.g., quality, efficiency) across the life span. Less work has probed the directionality of these relationships. Here, we report findings from the first study to examine bidirectional between- and within-person associations between loneliness and emotional support with daily life measures of sleep. METHODS: Participants were 389 healthy adults aged 40 to 64 years (61% female) who completed hourly surveys assessing loneliness and perceptions of emotional support over the course of 4 days. Measures of actigraphy-assessed sleep and nightly sleep quality were also assessed for 7 to 10 days. RESULTS: Individuals with lower average daily loneliness showed higher sleep quality and efficiency than individuals with higher loneliness (r = -0.19, p < .001; r = -0.14, p = .008, respectively), and greater average emotional support was likewise linked with better sleep quality (r = 0.18, p < .001). Controlling for neuroticism attenuated the effects of average loneliness on sleep. Within-person analyses showed unexpected bidirectional effects. Specifically, days in which people felt relatively lonelier were followed by nights with greater sleep efficiency (γ = 1.08, p = .015), and nights when people reported relatively poorer sleep quality were followed by days with greater emotional support (γ = -0.04, p = .013). These unexpected findings are probed in exploratory analyses. CONCLUSIONS: Individuals with higher loneliness and lower emotional support report poorer sleep quality and efficiency, on average. Day-to-day fluctuations in perceptions of social relationships may affect the following night's sleep, and vice versa.

How Loneliness Gets Under the Skin: Inflammation Mediates the Relationship Between Loneliness and Gait Speed.

OBJECTIVE: Loneliness is linked to interleukin 6 (IL-6), a marker of systemic inflammation, which chronically has deleterious effects on physical and mental health across the adult life span. This study investigated cross-sectional relationships among loneliness, IL-6, demographics, multimorbidity, depression, obesity, friendship quantity, and slowed gait. METHODS: Data from the Midlife Development in the United States Biomarker Project, a national adult sample ( N = 822; age range, 26-78 years) was used for this study. The PROCESS macro tested the hypothesis that IL-6 would mediate the relationship between loneliness and gait, after adjusting for demographic and health risk factors. RESULTS: Age ( ß = 0.292, p < .001), sex ( ß = 0.197, p < .001), body mass index (BMI, ß = 0.374, p < .001), waist-hip ratio ( ß = 0.242, p < .001), and loneliness ( ß = 0.089, p = .025) but not multimorbidity ( ß = 0.043, p = .20), depression history ( ß = 0.022, p = .47), depression symptoms ( ß = 0.036, p = .28), and number of friends ( ß = 0.022, p = .46) contributed to the variance in IL-6. Serial mediation analyses supported the chained effect of loneliness on walking time through BMI and IL-6. Results also showed specific indirect effects of BMI and IL-6 on walking time, suggesting more than one pathway by which loneliness influences health. CONCLUSIONS: These results suggest that loneliness may increase the risk of systemic inflammation, leading to slowed gait and adverse health outcomes. Psychosocial interventions that address loneliness may provide an optimal treatment target for reducing inflammation and preventing declines in health.

Do We Become More Lonely With Age? A Coordinated Data Analysis of Nine Longitudinal Studies.

Loneliness is a pervasive experience with adverse impacts on health and well-being. Despite its significance, notable gaps impede a full understanding of how loneliness changes across the adult life span and what factors influence these changes. To address this, we conducted a coordinated data analysis of nine longitudinal studies encompassing 128,118 participants ages 13 to 103 from over 20 countries. Using harmonized variables and models, we examined loneliness trajectories and predictors. Analyses revealed that loneliness follows a U-shaped curve, decreasing from young adulthood to midlife and increasing in older adulthood. These patterns were consistent across studies. Several baseline factors (i.e., sex, marital status, physical function, education) were linked to loneliness levels, but few moderated the loneliness trajectories. These findings highlight the dynamic nature of loneliness and underscore the need for targeted interventions to reduce social disparities throughout adulthood.

Interventions to Reduce Loneliness in Community-Living Older Adults: a Systematic Review and Meta-analysis.

BACKGROUND: The problem of loneliness has garnered increased attention from policymakers, payors, and providers due to higher rates during the pandemic, particularly among seniors. Prior systematic reviews have in general not been able to reach conclusions about effectiveness of interventions. METHODS: Computerized databases were searched using broad terms such as "loneliness" or "lonely" or "social isolation" or "social support" from Jan 1, 2011 to June 23, 2021. We reference mined existing systematic reviews for additional and older studies. The Social Interventions Research & Evaluation Network database and Google were searched for gray literature on Feb 4, 2022. Eligible studies were RCTs and observational studies of interventions to reduce loneliness in community-living adults that used a validated loneliness scale; studies from low- or middle-income countries were excluded, and studies were excluded if restricted to populations where all persons had the same disease (such as loneliness in persons with dementia). RESULTS: A total of 5971 titles were reviewed and 60 studies were included in the analysis, 36 RCTs and 24 observational studies. Eleven RCTs and 5 observational studies provided moderate certainty evidence that group-based treatment was associated with reduced loneliness (standardized mean difference for RCTs = - 0.27, 95% CI - 0.48, - 0.08). Five RCTs and 5 observational studies provided moderate certainty evidence that internet training was associated with reduced loneliness (standardized mean difference for RCTs = - 0.22, 95% CI - 0.30, - 0.14). Low certainty evidence suggested that group exercises may be associated with very small reductions in loneliness. Evidence was insufficient to reach conclusions about group-based activities, individual in-person interactions, internet-delivered interventions, and telephone-delivered interventions. DISCUSSION: Low-to-moderate certainty evidence exists that group-based treatments, internet training, and possibly group exercises are associated with modest reductions in loneliness in community-living older adults. These findings can inform the design of supplemental benefits and the implementation of evidence-based interventions to address loneliness. SYSTEMATIC REVIEW REGISTRATION NUMBER: PROSPERO ( CRD42021272305 ).

The silent epidemic of loneliness: identifying the antecedents of loneliness using a lagged exposure-wide approach.

BACKGROUND: A large and accumulating body of evidence shows that loneliness is detrimental for various health and well-being outcomes. However, less is known about potentially modifiable factors that lead to decreased loneliness. METHODS: We used data from the Health and Retirement Study to prospectively evaluate a wide array of candidate predictors of subsequent loneliness. Importantly, we examined if changes in 69 physical-, behavioral-, and psychosocial-health factors (from t0;2006/2008 to t1;2010/2012) were associated with subsequent loneliness 4 years later (t2;2014/2016). RESULTS: Adjusting for a large range of covariates, changes in certain health behaviors (e.g. increased physical activity), physical health factors (e.g. fewer functioning limitations), psychological factors (e.g. increased purpose in life, decreased depression), and social factors (e.g. greater number of close friends) were associated with less subsequent loneliness. CONCLUSIONS: Our findings suggest that subjective ratings of physical and psychological health and perceived social environment (e.g. chronic pain, self-rated health, purpose in life, anxiety, neighborhood cohesion) are more strongly associated with subsequent loneliness. Yet, objective ratings (e.g. specific chronic health conditions, living status) show less evidence of associations with subsequent loneliness. The current study identified potentially modifiable predictors of subsequent loneliness that may be important targets for interventions aimed at reducing loneliness.

Stress-related gene regulation: Do isolated and connected individuals differ?

BACKGROUND: Social isolation and loneliness (known as social disconnection, collectively) lead to serious downstream health effects, including shortening of lifespan and higher risk for cardiac disease. We must better understand how isolation and loneliness lead to these negative health outcomes. Previous literature has demonstrated that social motivation and social ability are contributors to the likelihood of social isolation and loneliness. We examined the effect of the above social factors on immune gene expression in socially-connected and -isolated individuals. METHODS: Recruitment occurred via two online advertisements, one for socially isolated individuals and another for general research participants. Participants (n = 102) were separated into groups (isolated versus connected) based on which ad they responded to, and provided data on isolation, loneliness, social motivation, and social ability. The Conserved Transcriptional Response to Adversity (CTRA) stress gene regulation program was assessed with genome-wide transcriptional profiling. RESULTS: CTRA gene expression patterns were reversed between connected and isolated groups across several variables. Social isolation was associated with higher CTRA levels in the connected group, but lower levels in the isolated group. Social approach was associated with lower CTRA levels in the connected group, but higher in the isolated group, and the converse was true for social avoidance. CTRA levels were minimally affected by social ability measures. CONCLUSION: Prior work on social isolation and loneliness has focused on loneliness and has identified many negative downstream health effects. In this study we demonstrate that objective social isolation may not be associated with the same negative downstream health effects, and in fact, social interaction may be more stressful than social isolation for some socially-isolated individuals.

Social isolation, loneliness, and inflammation: A multi-cohort investigation in early and mid-adulthood.

Social isolation and loneliness have been associated with poor health and increased risk for mortality, and inflammation might explain this link. We used data from the Danish TRIAGE Study of acutely admitted medical patients (N = 6,144, mean age 60 years), and from two population-representative birth cohorts: the New Zealand Dunedin Longitudinal Study (N = 881, age 45) and the UK Environmental Risk (E-Risk) Longitudinal Twin Study (N = 1448, age 18), to investigate associations of social isolation with three markers of systemic inflammation: C-reactive protein (CRP), interleukin-6 (IL-6), and a newer inflammation marker, soluble urokinase plasminogen activator receptor (suPAR), which is thought to index systemic chronic inflammation. In the TRIAGE Study, socially isolated patients (those living alone) had significantly higher median levels of suPAR (but not CRP or IL-6) compared with patients not living by themselves. Social isolation prospectively measured in childhood was longitudinally associated with higher CRP, IL-6, and suPAR levels in adulthood (at age 45 in the Dunedin Study and age 18 in the E-Risk Study), but only suPAR remained associated after controlling for covariates. Dunedin Study participants who reported loneliness at age 38 or age 45 had elevated suPAR at age 45. In contrast, E-Risk Study participants reporting loneliness at age 18 did not show any elevated markers of inflammation. In conclusion, social isolation was robustly associated with increased inflammation in adulthood, both in medical patients and in the general population. It was associated in particular with systemic chronic inflammation, evident from the consistently stronger associations with suPAR than other inflammation biomarkers.

The reciprocal associations between social deficits, social engagement, and inflammation: Longitudinal evidence comparing venous blood samples and dried blood spots and mapping the modifying role of phenotypic and genotypic depression.

BACKGROUND: Social psychoneuroimmunology suggests an interplay between social deficits (loneliness and isolation) and chronic inflammation, but the direction of these relationships remains unclear. We estimated the reciprocal associations of social deficits and social engagement with levels of C-reactive protein (CRP), compared the consistency of the findings depending on the biological sampling method used, and examined the modifying role of phenotypic and genotypic depression. METHODS: We used longitudinal nationally representative data from the US (Health and Retirement Study, 3 waves, 2006-16) and England (English Longitudinal Study of Ageing, 4 waves, 2004-18). Loneliness, social isolation, and social engagement were self-reported. CRP was measured using dried blood spots (US) and venous blood samples (England). Cross-lagged panel models were fitted and tested interactions with phenotypic depression (above-threshold depressive symptom scores) and genotypic depression (polygenic score for major depressive disorder). RESULTS: We included 15,066 participants (mean age = 66.1 years, SD = 9.8) in the US and 10,290 (66.9 years, SD = 10.5) in England. We found reciprocal associations between loneliness and CRP using dried blood spots and venous blood samples. Higher CRP predicted higher subsequent loneliness and higher loneliness predicted elevated CRP. Both phenotypic and genotypic depression modified this reciprocal association. There were also reciprocal associations for social engagement in venous blood samples: higher CRP predicted lower social engagement and greater social engagement predicted lower subsequent CRP. Associations between social isolation and CRP were inconsistent and unidirectional. CONCLUSIONS: Loneliness may increase chronic inflammation, whereas social engagement may reduce inflammation. As these relationships were reciprocal, there may be a loop between inflammation, loneliness, and social engagement. This loop was stronger in those with depression or at high genetic risk for major depressive disorder. This relationship for loneliness was present in both blood sampling methods despite contrasting methods of CRP measurement, indicating that the finding is not attributable to measurement bias in biomarkers.

Psychological and neurobiological mechanisms involved in the relationship between loneliness and cognitive decline in older adults.

Loneliness, among older adults, is one of the risk factors for developing dementia. Still, little is known about the neurobiological and psychological conditions that link loneliness to cognitive decline. The current study investigated several research aims: First, it sought to identify neurobiological and psychological pathways that may account for the relationship between loneliness and decline across several cognitive domains. These pathways included depressive symptoms, total gray matter volume, and conditional analyses of pro-inflammatory cytokines and brain-derived neurotrophic factor (BDNF) expression. Second, it examined loneliness as a predictor of mild cognitive impairment (MCI) and Alzheimer's disease (AD). Third, it sought to determine whether the relationship between loneliness and cognitive decline is sex-specific in older adults. Longitudinal data were collected from 2130 Rush Memory and Aging Project participants. Participants underwent annual cognitive and psychological assessments and neuroimaging procedures every year. BDNF gene expression was measured in the dorsolateral prefrontal cortex, cytokines were measured in serum, and the final consensus clinical diagnosis was identified at the time of death. All linear mixed and multinomial logistic regression models controlled for age at baseline, education, sex, and APOE genotype. Participants were largely women (73 %), and Caucasian (93 %). The average education was 14.93 (SD = 3.34). The average age at baseline was 80.05 (SD = 7.57). Results showed that gray matter volume and depressive symptoms partially mediated the relationship between loneliness and cognitive decline. There was a significant interaction between loneliness and BDNF expression in relation to cognitive decline. Higher levels of BDNF expression was associated with slower decline in semantic memory and visuospatial ability. Finally, the current study also established that higher levels of loneliness was positively associated with the incidence of AD and other dementias. The present findings support the growing literature, which tends to show that the consequence of loneliness goes beyond the feeling of being isolated. Loneliness may induce physiological changes in our brains, leading to cognitive decline. Future research can explore a wide range of biological and psychological expressions of loneliness to clarify how loneliness relates to dementia.