Loneliness and risk of all-cause, Alzheimer's, vascular, and frontotemporal dementia: a prospective study of 492,322 individuals over 15 years

Prolonged loneliness and risk of incident cognitive decline and dementia: A two-cohort study

BACKGROUND

Loneliness is prevalent currently and could result in increased dementia risks, whereas the associations of prolonged loneliness and its changes with cognitive decline and dementia remain less investigated.

METHODS

Data were from the English Longitudinal Study of Ageing (ELSA) and Health and Retirement Study (HRS). Loneliness was assessed using the Revised UCLA Loneliness Scale. Health risk factors for dementia included unhealthy lifestyles, depressive symptoms, chronic diseases, and functional limitations. Cognitive function was assessed using validated tests in both cohorts, with cognitive decline defined as cognitive z-scores < -1.5. Dementia was identified through self- or proxy-reported physician diagnoses. The Cox proportional hazard regression and Aalen's additive hazard regression were performed to calculate the relative and absolute risk for cognitive decline and dementia, respectively. Covariates including socio-demographic characteristics, social networks, and polygenic scores were adjusted.

RESULTS

Of 6721 ELSA and 10,195 HRS participants aged ≥50y, 2129 (13.7 %) and 612 (3.6 %) developed incident cognitive decline and dementia in about 10 years, respectively. Participants with severe (versus no) cumulative loneliness had 42 % and 98 % higher cognitive decline and dementia risks after pooling, corresponding to 791.6 (477.4-1105.8) and 372.8 (223.6-522.0) excess incidence densities (/105 person-years). Additionally, those who recovered from frequent loneliness (versus persistent frequent) were 9 %-31 % less likely to develop unhealthy lifestyles, depressive symptoms, chronic diseases, and functional limitations, and were at 33 % lower risks of dementia, corresponding to -248.6 (-446.0 ~ -51.2) excess incidence density.

CONCLUSIONS

Prolonged loneliness could increase the risks of incident cognitive decline and ADRD, while alleviating loneliness may help.

Sex differences in the relationship between exercise habits and loneliness among older adults: a cross-sectional study

BACKGROUND

Although loneliness has been associated with reduced physical activity, the association between exercise habits and loneliness remains unclear.

METHODS

This study examined whether exercise habits are associated with loneliness among older adults by sex. This study included 10 152 individuals. The University of California Los Angeles Loneliness Scale was used to measure loneliness, with a score of 44 or more defined as loneliness. Information on exercise habits during the year was obtained using a questionnaire on whether participants performed 14 types of exercise. Binomial logistic regression analysis was conducted, with loneliness as the dependent variable and exercise habits as the independent variable.

RESULTS

Overall, 3591 people (35.4%) were lonely, with more males (43.9%) experiencing loneliness than females (28.3%) (P < 0.05). Binomial logistic regression analysis stratified by sex showed that the following exercise types were associated with loneliness among males (odds ratio (95% confidence interval): golf, 0.77 (0.67-0.89); gymnastics, 0.86 (0.75-0.99); exercise circle, 0.77 (0.65-0.91); and team games, 0.76 (0.63-0.90), P < 0.05). In contrast, no association was found between exercise habits and loneliness among females (P > 0.05).

CONCLUSIONS

Loneliness was reduced among males through certain exercise practices. Group exercise interventions may effectively prevent loneliness among males, who are more likely to feel lonely than females.

Loneliness and Biomarkers of Alzheimer's Disease, Axonal Damage, and Astrogliosis: A Coordinated Analysis of Two Longitudinal Cohorts

OBJECTIVES

Loneliness is associated with an elevated risk of dementia. There is mixed evidence from imaging studies on whether loneliness is associated with neuropathology in dementia-free adults. This study tests whether loneliness is associated with plasma neurobiomarkers of amyloid (Aβ42/Aβ40), phosphorylated tau 181 (pTau181), neurofilament light chain (NfL), and glial fibrillary acidic protein (GFAP) and imaging measures of amyloid and tau.

METHODS

Participants were cognitively unimpaired older adults from the Baltimore Longitudinal Study on Aging (BLSA; N = 1,028 individuals and up to 2,277 neurobiomarker measurements; Baseline mean age = 66, SD = 15 years) and the UK Biobank (N = 1,263 individuals and up to 2,526 neurobiomarker measurements; Baseline mean age = 60, SD = 7 years). Single-item measures of loneliness and the Quanterix Single Molecule Array assays were used in both samples. In a subset of BLSA participants, positron emission tomography (PET) was used to assess cerebral amyloid burden (n = 220) and tau in the entorhinal cortex (n = 102).

RESULTS

In both samples and meta-analyses, loneliness was unrelated to plasma measures of Aβ42/Aβ40, pTau181, NfL, and GFAP. Changes in loneliness were also unrelated to changes in the plasma neurobiomarkers, and no consistent evidence of moderation by age, sex, or APOE ε4 allele was found. Loneliness was also unrelated to PET-based measures of amyloid and tau.

DISCUSSION

This study found no associations between loneliness and measures of Alzheimer's disease pathology, axonal damage, or astrogliosis.

A Meta-analysis of Loneliness and Risk of Dementia using Longitudinal Data from >600,000 Individuals

Loneliness is one critical risk factor for cognitive health. Combining data from ongoing aging studies and the published literature, we provided the largest meta-analysis on the association between loneliness and dementia (k = 21 samples, N = 608,561) and cognitive impairment (k = 16, N = 103,387). Loneliness increased risk for all-cause dementia (HR = 1.306, 95% CI [1.197,1.426]), Alzheimer's disease (HR = 1.393, 95% CI [1.290,1.504]; k = 5), vascular dementia (HR = 1.735, 95% CI [1.483,2.029]; k = 3), and cognitive impairment (HR = 1.150, 95% CI [1.113,1.189]). The associations persisted when models controlled for depression, social isolation, and/or other modifiable risk factors for dementia. The large heterogeneity across studies was partly due to differences in loneliness measures and ascertainment of cognitive status. Results underscored the importance to further examine type/sources of loneliness and cognitive symptoms to develop effective interventions that reduce the risk of dementia.

Loneliness, cerebrovascular and Alzheimer's disease pathology, and cognition

INTRODUCTION

Loneliness has a rising public health impact, but research involving neuropathology and representative cohorts has been limited.

METHODS

Inverse odds of selection weights were generalized from the autopsy sample of Rush Alzheimer's Disease Center cohorts (N = 680; 89 ± 9 years old; 25% dementia) to the US-representative Health and Retirement Study (N = 8469; 76 ± 7 years old; 5% dementia) to extend external validity. Regressions tested cross-sectional associations between loneliness and (1) Alzheimer's disease (AD) and cerebrovascular pathology; (2) five cognitive domains; and (3) relationships between pathology and cognition, adjusting for depression.

RESULTS

In weighted models, greater loneliness was associated with microinfarcts, lower episodic and working memory in the absence of AD pathology, lower working memory in the absence of infarcts, a stronger association of infarcts with lower episodic memory, and a stronger association of microinfarcts with lower working and semantic memory.

DISCUSSION

Loneliness may relate to AD through multiple pathways involving cerebrovascular pathology and cognitive reserve.

HIGHLIGHTS

Loneliness was associated with worse cognition in five domains. Loneliness was associated with the presence of microinfarcts. Loneliness moderated cognition-neuropathology associations. Transportability methods can provide insight into selection bias.

Life Events and Incident Dementia: A Prospective Study of 493,787 Individuals Over 16 Years

OBJECTIVES

Life events can be stressful and have a detrimental impact on health, but evidence is inconclusive regarding life events and dementia risk. The present study tests whether life events are associated with incident dementia, whether experiencing multiple events has cumulative effects, and whether the associations vary across age, sex, race/ethnicity, socioeconomic status, and genetic vulnerability.

METHODS

UK Biobank participants (N = 493,787) reported on 6 life events that occurred within the past 2 years: serious illness, injury, assault to yourself or close relative, death of a spouse/partner or close relative, marital separation/divorce, and financial problems. Incident all-cause dementia was ascertained through health records from the UK National Health Service over a 16-year follow-up.

RESULTS

Serious illness, injury, or assault to yourself, marital separation/divorce, and financial difficulties were associated with a higher risk of dementia; serious illness, injury, or assault of a close relative was associated with a lower risk of dementia. When combined, experiencing 3-4 events was associated with a more than 2-fold increase in dementia risk. The association for marital separation/divorce was stronger within the first 5 years of follow-up (consistent with reverse causality). Death of a spouse/partner or close relative was mostly unrelated to dementia risk. With few exceptions, the associations were similar across age, sex, race/ethnicity, socioeconomic status, and apolipoprotein E e4 status groups.

DISCUSSION

Severe illness, injury, or personal assault, marital separation or divorce, and financial hardships may raise risk of dementia, particularly when these events occur together.

Estimating risk of loneliness in adulthood using survey-based prediction models: A cohort study

It is widely accepted that loneliness is associated with health problems, but less is known about the predictors of loneliness. In this study, we constructed a model to predict individual risk of loneliness during adulthood. Data were from the prospective population-based FinHealth cohort study with 3444 participants (mean age 55.5 years, 53.4% women) who responded to a 81-item self-administered questionnaire and reported not to be lonely at baseline in 2017. The outcome was self-reported loneliness at follow-up in 2020. Predictive models were constructed using bootstrap enhanced LASSO regression (bolasso). The C-index from the final model including 11 predictors from the best bolasso -models varied between 0.65 (95% CI 0.61 to 0.70) and 0.71 (95% CI 0.67 to 0.75) the pooled C -index being 0.68 (95% CI 0.61 to 0.75). Although survey-based individualised prediction models for loneliness achieved a reasonable C-index, their predictive value was limited. High detection rates were associated with high false positive rates, while lower false positive rates were associated with low detection rates. These findings suggest that incident loneliness during adulthood. may be difficult to predict with standard survey data.

Unraveling the dynamics of loneliness and cognition in late life: a cross-lagged panel model

Introduction

Loneliness and cognitive decline are pressing concerns among older adults, yet little research has explored cognition as a predictor of loneliness. This study investigates the dynamic relationship between loneliness and cognitive function in older adults using the random intercept cross-lagged panel model (RI-CLPM).

Methods

Data were drawn from Waves 9-14 of the Health and Retirement Study (HRS), encompassing 8,473 individuals aged 65 years and older. Loneliness was assessed using the UCLA Loneliness Scale, and cognitive function was measured using immediate and delayed word recall and serial 7s from the HRS RAND file. Age, gender, education, marital status, self-health report, and depression were included as covariates. Using Mplus, we computed RI-CLPMs. The first three models were conducted on loneliness and cognitive functions. Then unconditional RI-CLPMs with no exogenous predictors were computed.

Results

Three conditional model results showed that age, gender, marital status, self-health report, and depression were significantly associated with loneliness in the first wave, but only age and self-health report were significantly associated with immediate and delayed word recall at the first wave, not with serial 7s. For carry-over effects, loneliness showed significant positive associations across consecutive waves, but cognitive functions showed significant positive associations just in the last two waves. Some spill-over effects were found between loneliness and cognitive functions. For within-person effects, although initially non-significant, a negative association between loneliness and immediate and delayed word recall emerged in later waves (11-12 and 13-14). The conditional models indicated that older age, not being married, male gender, low self-reported health, and high depression levels were positively associated with loneliness. However, only older age and lower self-reported health were positively linked to cognitive functions.

Discussion

This study underscores the link between loneliness and cognitive function decline in older adults, emphasizing the need to address loneliness to potentially reduce cognitive decline. Insights into demographic predictors of loneliness and cognitive function could inform targeted interventions for promoting successful aging.

A translational neuroscience perspective on loneliness: Narrative review focusing on social interaction, illness and oxytocin

This review addresses key findings on loneliness from the social, neurobiological and clinical fields. From a translational perspective, results from studies in humans and animals are included, with a focus on social interaction, mental and physical illness and the role of oxytocin in loneliness. In terms of social interactions, lonely individuals tend to exhibit a range of abnormal behaviors based on dysfunctional social cognitions that make it difficult for them to form meaningful relationships. Neurobiologically, a link has been established between loneliness and the hypothalamic peptide hormone oxytocin. Since social interactions and especially social touch regulate oxytocin signaling, lonely individuals may have an oxytocin imbalance, which in turn affects their health and well-being. Clinically, loneliness is a predictor of physical and mental illness and leads to increased morbidity and mortality. There is evidence that psychopathology is both a cause and a consequence of loneliness. The final section of this review summarizes the findings from social, neurobiological and clinical perspectives to present a new model of the complex construct of loneliness.

Contributions of loneliness to cognitive impairment and dementia in older adults are independent of other risk factors and Alzheimer's pathology: a narrative review

Loneliness significantly contributes to cognitive impairment and dementia in older adults. Loneliness is a distressing feeling resulting from a perceived lack of social connection (i.e., a discrepancy between desired and actual social relationships), while social isolation is a related term that can be defined by number and type of social relationships. Importantly, loneliness is distinct from social isolation in that it is associated with a distressing self-perception. The primary focus of this narrative review is the impact of chronic loneliness on cognitive impairment and dementia among older adults. Loneliness has a significant association with many factors that are related to worse cognition, and therefore we include discussion on health, mental health, as well as the physiological effects of loneliness, neuropathology, and potential treatments. Loneliness has been shown to be related to development of dementia with a hazard ratio (HR) risk comparable to having a single APOE4 gene. The relationship of dementia to loneliness appears to be at least partially independent of other known dementia risk factors that are possibly associated with loneliness, such as depression, educational status, social isolation, and physical activity. Episodic memory is not consistently impacted by loneliness, which would be more typically impaired if the mild cognitive impairment (MCI) or dementia was due to Alzheimer's disease (AD) pathology. In addition, the several longitudinal studies that included neuropathology showed no evidence for a relationship between loneliness and AD neuropathology. Loneliness may decrease resilience, or produce greater cognitive change associated with the same level of AD neuropathology. Intervention strategies to decrease loneliness in older adults have been developed but need to consider key treatment targets beyond social isolation. Loneliness needs to be assessed in all studies of cognitive decline in elders, since it significantly contributes to the variance of cognitive function. It will be useful to better define the underlying mechanism of loneliness effects on cognition to determine if it is similar to other psychological factors related to excessive stress reactivity, such as neuroticism or even depression, which are also associated with cognitive decline. It is important from a health perspective to develop better strategies to decrease loneliness in older adults.

Role of the Exposome in Neurodegenerative Disease: Recent Insights and Future Directions

Neurodegenerative diseases are increasing in prevalence and place a significant burden on society. The causes are multifactorial and complex, and increasing evidence suggests a dynamic interplay between genes and the environment, emphasizing the importance of identifying and understanding the role of lifelong exposures, known as the exposome, on the nervous system. This review provides an overview of recent advances toward defining neurodegenerative disease exposomes, focusing on Parkinson's disease, amyotrophic lateral sclerosis, and Alzheimer's disease. We present the current state of the field based on emerging data, elaborate on key themes and potential mechanisms, and conclude with limitations and future directions. ANN NEUROL 2024;95:635-652.

Social isolation, loneliness, and the risk of incident acute kidney injury in middle-aged and older adults: A prospective cohort study

OBJECTIVE

The relationships of social isolation and loneliness with acute kidney injury (AKI) risk remained uncertain. We aimed to investigate the associations of social isolation and loneliness with incident AKI.

METHODS

450,868 participants without prior AKI were included from the UK Biobank. The social isolation index was constructed based on living alone, social contact, and participation in social activities. Loneliness was assessed by asking about "Do you often feel lonely?". The study outcome was incident AKI.

RESULTS

During a median follow-up of 12.0 years, 18,679 (4.1%) participants developed AKI, including 18,428 participants ascertained by hospital admission records with a median duration of hospitalization of 3 (25th-75th, 1-8) days. The hazard ratio for incident AKI for social isolation compared with no social isolation was 1.50 (95% CI: 1.44-1.55) after adjusting for age and race (minimally adjusted), and was 1.10 (95% CI: 1.06-1.14) after further adjusting for socioeconomic factors, health behaviors, biological and health-related factors, psychologic factors, and loneliness (fully adjusted). The minimally adjusted and fully adjusted hazard ratios for incident AKI for loneliness compared with no loneliness was 1.57 (95% CI: 1.52-1.62), and 1.10 (95% CI: 1.06-1.15), respectively. In the fully adjusted models, the highest risk of AKI was found in those with both social isolation and loneliness. Living alone and less social contact, rather than less participation in social activities, were significantly associated with a higher risk of incident AKI.

CONCLUSIONS

Both social isolation and loneliness were independently and significantly associated with a higher risk of incident AKI.

Beneficial Effect of Societal Factors on APOE-ε2 and ε4 Carriers' Brain Health: A Systematic Review

BACKGROUND

Apolipoprotein-E (APOE) ε4 and ε2 are the most prevalent risk-increasing and risk-reducing genetic predictors of Alzheimer's disease, respectively. However, the extent to which societal factors can reduce the harmful impact of APOE-ε4 and enhance the beneficial impact of APOE-ε2 on brain health has not yet been examined systematically.

METHODS

To fill this gap, we conducted a systematic review searching for studies in MEDLINE, Embase, PsycINFO, and Scopus until June 2023, that included: (a) 1 of 5 social determinants of health (SDH) identified by Healthy People 2030, (b) APOE-ε2 or APOE-ε4 allele carriers, (c) cognitive or brain-biomarker outcomes, and (d) studies with an analysis of how APOE-ε2 and/ or APOE-ε4 carriers differ on outcomes when exposed to SDH.

RESULTS

From 14 076 articles retrieved, 124 met the inclusion criteria. In most of the studies, exposure to favorable SDH reduced APOE-ε4's detrimental effect and enhanced APOE-ε2's beneficial effect on cognitive and brain-biomarker outcomes (cognition: 70.5%, n: 74/105; brain-biomarkers: 71.4%, n: 20/28). A similar pattern of results emerged in each of the 5 Healthy People 2030 SDH categories, where finishing high school, having resources to satisfy basic needs, less air pollution, less negative external stimuli that can generate stress (eg, negative age stereotypes), and exposure to multiple favorable SDH were associated with better cognitive and brain health among APOE-ε4 and APOE-ε2 carriers.

CONCLUSIONS

Societal factors can reduce the harmful impact of APOE-ε4 and enhance the beneficial impact of APOE-ε2 on cognitive outcomes. This suggests that plans to reduce dementia should include community-level policies promoting favorable SDH.

Psycho-social and health predictors of loneliness in older primary care patients and mediating mechanisms linking comorbidities and loneliness

BACKGROUND

Aging is associated with many personal, social, and environmental challenges that increase the risk of loneliness. Loneliness is a painful emotional experience associated with a perceived lack of connection and intimacy. Loneliness accelerates health deterioration, but the presence of chronic health conditions (comorbidities) in older individuals may potentiate the feeling of loneliness. The relationships between health status and loneliness in older individuals have not been assessed in an integrated manner, although it is necessary for planning efficient interventions. The aim of this study was to fill in this knowledge gap, by attempting to create an integrated model of loneliness in older individuals.

METHODS

The sample consisted of 189 (58% F) older individuals (> 60 years) (mean ± SD, 78.47 ± 6.65), attendees in Primary Health Care. Different factors associated with loneliness in the older population were assessed, and classified as demographic, environmental, physical (health-related), and psychological, in addition to functional abilities. A set of standard questionnaires was used to assess psychological factors and functional abilities. The hierarchical regression model assessed the effect of particular blocks of factors on status loneliness. The second aim was to analyze how psychological factors mediate associations between health status (comorbidity level) and loneliness.

RESULTS

Indicated that increasing comorbidity, anxiety, lack of positive moods, not having hobbies/activities, low perception of social support, impaired cognitive function, and suppression of emotion expression, are significant predictors of loneliness. Mediation analysis informed us of how to help patients with comorbidities feel less lonely. Interventions that were suggested were those that can reduce anxiety and depression, improve cognitive abilities and emotional regulation control, and enhance social support.

CONCLUSIONS

Results can help understand the pathophysiology loops linking poor health status (comorbidity level) of older individuals and loneliness, and have significant potentials from the translational perspectives, as a decision-support tool.

Loneliness and Risk of Parkinson Disease

Importance

Loneliness is associated with morbidity and mortality, including higher risk of neurodegenerative diseases. To our knowledge, no study has examined whether the association between loneliness and detrimental outcomes extends to Parkinson disease (PD).

Objective

To assess whether loneliness is associated with risk of incident PD and whether the association is independent of other risk factors or modified by age, sex, and genetic vulnerability.

Design, Setting, and Participants

This prospective cohort study included a population-based sample of UK Biobank participants aged 38 to 73 years with loneliness data and without a diagnosis of PD at baseline who were first assessed from March 13, 2006, to October 1, 2010, and followed up to October 9, 2021.

Exposure

Feeling lonely and covariates that are known risk factors for or prodromal features of PD.

Main Outcome and Measure

Incident PD was ascertained through UK National Health Service health records.

Results

Of 491 603 participants (mean [SD] age, 56.54 [8.09] years; 54.4% female), 2822 developed PD during the 15-year follow-up. Individuals who reported being lonely had a higher risk of PD (hazard ratio [HR], 1.37; 95% CI, 1.25-1.51), an association that remained after accounting for demographic factors, socioeconomic status, social isolation, PD polygenetic risk score, smoking, physical activity, body mass index, diabetes, hypertension, stroke, myocardial infarction, depression, and ever seeing a psychiatrist (fully adjusted model: HR 1.25; 95% CI, 1.12-1.39). The association between loneliness and incident PD was not moderated by sex (HR for interaction, 0.98; 95% CI, 95% CI, 0.81-1.18), age (HR for interaction, 0.99; 95% CI, 0.98-1.01), or polygenic risk score (HR for interaction, 0.93; 95% CI, 0.85-1.02). Contrary to expectations for a prodromal syndrome, when stratified by time, loneliness was not associated with risk for incident PD during the first 5 years (HR, 1.15; 95% CI, 0.91-1.45) but was associated with PD risk during the subsequent 10 years (HR, 1.32; 95% CI, 1.19-1.46).

Conclusions and Relevance

This large cohort study found that loneliness was associated with risk of incident PD across demographic groups and independent of depression and other prominent risk factors and genetic risk. The findings add to the evidence that loneliness is a substantial psychosocial determinant of health.

The relationship between social isolation, social support, and loneliness with cardiovascular disease and shared risk factors: A narrative review

BACKGROUND

Cardiovascular disease (CVD) is the greatest contributor to global morbidity and mortality. Poor social health plays a critical role in CVD incidence. Additionally, the relationship between social health and CVD may be mediated through CVD risk factors. However, the underlying mechanisms between social health and CVD are poorly understood. Certain social health constructs (social isolation, low social support and loneliness) have complicated the characterisation of a causal relationship between social health and CVD.

AIM

To provide an overview of the relationship between social health and CVD (and its shared risk factors).

METHOD

In this narrative review, we examined published literature on the relationship between three social health constructs (social isolation, social support, and loneliness) and CVD. Evidence was synthesised in a narrative format, focusing on the potential ways in which social health affects CVD, including shared risk factors.

RESULTS

The current literature highlights an established relationship between social health and CVD with a likelihood for bi-directionality. However, there is speculation and varied evidence regarding how these relationships may be mediated through CVD risk factors.

CONCLUSIONS

Social health can be considered an established risk factor for CVD. However, the potential bi-directional pathways of social health with CVD risk factors are less established. Further research is needed to understand whether targeting certain constructs of social health may directly improve the management of CVD risk factors. Given the health and economic burdens of poor social health and CVD, improvements to addressing or preventing these interrelated health conditions would have societal benefits.

Affective Neuroscience of Loneliness: Potential Mechanisms underlying the Association between Perceived Social Isolation, Health, and Well-Being

Loneliness, or the subjective feeling of social isolation, is an important social determinant of health. Loneliness is associated with poor physical health, including higher rates of cardiovascular disease and dementia, faster cognitive decline, and increased risk of mortality, as well as disruptions in mental health, including higher levels of depression, anxiety, and negative affect. Theoretical accounts suggest loneliness is a complex cognitive and emotional state characterized by increased levels of inflammation and affective disruptions. This review examines affective neuroscience research on social isolation in animals and loneliness in humans to better understand the relationship between perceptions of social isolation and the brain. Loneliness associated increases in inflammation and neural changes consistent with increased sensitivity to social threat and disrupted emotion regulation suggest interventions targeting maladaptive social cognitions may be especially effective. Work in animal models suggests the neural changes associated with social isolation may be reversible. Therefore, ameliorating loneliness may be an actionable social determinant of health target. However, more research is needed to understand how loneliness impacts healthy aging, explore the role of inflammation as a potential mechanism in humans, and determine the best time to deliver interventions to improve physical health, mental health, and well-being across a diverse array of populations.