Childhood social class and cognitive aging in the Swedish Adoption/Twin Study of Aging

Socioeconomic inequalities in cardiovascular disease: a causal perspective

Socioeconomic inequalities in cardiovascular disease (CVD) persist in high-income countries despite marked overall declines in CVD-related morbidity and mortality. After decades of research, the field has struggled to unequivocally answer a crucial question: is the association between low socioeconomic position (SEP) and the development of CVD causal? We review relevant evidence from various study designs and disciplinary perspectives. Traditional observational, family-based and Mendelian randomization studies support the widely accepted view that low SEP causally influences CVD. However, results from quasi-experimental and experimental studies are both limited and equivocal. While more experimental and quasi-experimental studies are needed to aid causal understanding and inform policy, high-quality descriptive studies are also required to document inequalities, investigate their contextual dependence and consider SEP throughout the lifespan; no simple hierarchy of evidence exists for an exposure as complex as SEP. The COVID-19 pandemic illustrates the context-dependent nature of CVD inequalities, with the generation of potentially new causal pathways linking SEP and CVD. The linked goals of understanding the causal nature of SEP and CVD associations, their contextual dependence, and their remediation by policy interventions necessitate a detailed understanding of society, its change over time and the phenotypes of CVD. Interdisciplinary research is therefore key to advancing both causal understanding and policy translation.

Cognitive aging and the life course: A new look at the Scaffolding theory

Our understanding of human neurocognitive aging, its developmental roots, and life course influences has been transformed by brain imaging technologies, increasing availability of longitudinal data sets, and analytic advances. The Scaffolding Theory of Aging and Cognition is a life course model, proposed originally in 2009, featuring adaptivity and compensatory potential as lifelong mechanisms for meeting neurocognitive challenges posed by the environment and by developing or declining brain circuitry. Here, we review the scaffolding theory in relation to new evidence addressing when during the life course potentially enriching and depleting factors exert their effects on brain health and scaffolding, and we consider the implications for separable, and potentially reciprocal, influences on the level of cognitive function and the rate of decline in later life.

Direct and indirect associations between childhood socioeconomic status and cognitive function in the middle-aged and older adults in China

OBJECTIVES

To investigate whether childhood socioeconomic status (SES) is associated with cognitive function, and what factors might mediate the associations.

METHOD

Using data from the China Health and Retirement Longitudinal Study (CHARLS) and within frameworks of the latency model, the pathway model and the accumulation model, we quantified direct and indirect pathways between childhood SES and cognitive function for Chinese middle-aged and older adults aged 45+ by structural equations modeling.

RESULTS

We found significant direct, indirect and total effects of childhood SES on cognitive function at baseline. The indirect effects were mediated through educational attainment, household consumption, smoking behaviors and social engagement. At follow-ups, cognitive enhancement can be made by indirect pathways through educational attainment, improvement of household consumption and social engagement.

CONCLUSION

Our results supported the latency model, the pathway model and the accumulation model when considering pathways linking childhood SES to cognitive function. The findings underscored the value of taking early interventions to improve SES and cognitive function, especially among those with low childhood SES.

Education and Income Show Heterogeneous Relationships to Lifespan Brain and Cognitive Differences Across European and US Cohorts

Higher socio-economic status (SES) has been proposed to have facilitating and protective effects on brain and cognition. We ask whether relationships between SES, brain volumes and cognitive ability differ across cohorts, by age and national origin. European and US cohorts covering the lifespan were studied (4-97 years, N = 500 000; 54 000 w/brain imaging). There was substantial heterogeneity across cohorts for all associations. Education was positively related to intracranial (ICV) and total gray matter (GM) volume. Income was related to ICV, but not GM. We did not observe reliable differences in associations as a function of age. SES was more strongly related to brain and cognition in US than European cohorts. Sample representativity varies, and this study cannot identify mechanisms underlying differences in associations across cohorts. Differences in neuroanatomical volumes partially explained SES-cognition relationships. SES was more strongly related to ICV than to GM, implying that SES-cognition relations in adulthood are less likely grounded in neuroprotective effects on GM volume in aging. The relatively stronger SES-ICV associations rather are compatible with SES-brain volume relationships being established early in life, as ICV stabilizes in childhood. The findings underscore that SES has no uniform association with, or impact on, brain and cognition.

The long arm of childhood socioeconomic deprivation on mid- to later-life cognitive trajectories: A cross-cohort analysis

Introduction

Earlier studies of the effects of childhood socioeconomic status (SES) on later-life cognitive function consistently report a social gradient in later-life cognitive function. Evidence for their effects on cognitive decline is, however, less clear.

Methods

The sample consists of 5324 participants in the Whitehall II study, 8572 in the Health and Retirement Study (HRS), and 1413 in the Kame Project, who completed self-report questionnaires on their early life experiences and underwent repeated cognitive assessments. We characterized cognitive trajectories using latent class mixed models, and explored associations between childhood SES and latent class membership using logistic regressions.

Results

We identified distinct trajectories classes for all cognitive measures examined. Childhood socioeconomic deprivation was associated with an increased likelihood of being in a lower trajectory class.

Discussion

Our findings support the notions that cognitive aging is a heterogeneous process and early life circumstances may have lasting effects on cognition across the life-course.

Gene Expression Profile in Different Age Groups and Its Association with Cognitive Function in Healthy Malay Adults in Malaysia

The mechanism of cognitive aging at the molecular level is complex and not well understood. Growing evidence suggests that cognitive differences might also be caused by ethnicity. Thus, this study aims to determine the gene expression changes associated with age-related cognitive decline among Malay adults in Malaysia. A cross-sectional study was conducted on 160 healthy Malay subjects, aged between 28 and 79, and recruited around Selangor and Klang Valley, Malaysia. Gene expression analysis was performed using a HumanHT-12v4.0 Expression BeadChip microarray kit. The top 20 differentially expressed genes at p < 0.05 and fold change (FC) = 1.2 showed that PAFAH1B3, HIST1H1E, KCNA3, TM7SF2, RGS1, and TGFBRAP1 were regulated with increased age. The gene set analysis suggests that the Malay adult's susceptibility to developing age-related cognitive decline might be due to the changes in gene expression patterns associated with inflammation, signal transduction, and metabolic pathway in the genetic network. It may, perhaps, have important implications for finding a biomarker for cognitive decline and offer molecular targets to achieve successful aging, mainly in the Malay population in Malaysia.

Role of sex in the association between childhood socioeconomic position and cognitive ageing in later life

We aimed to explore sex differences in the association of childhood socioeconomic position (SEP) with the level of cognitive performance and the rate of cognitive decline. We studied 84,059 individuals (55% women; mean age 64 years) from the Survey on Health, Ageing and Retirement in Europe. Sex differences in the association of childhood SEP (household characteristics at age 10) with the level of cognitive performance (verbal fluency, immediate recall, delayed recall) were analysed using multilevel linear regression. Structural equation modelling tested education, depressive symptoms and physical state as mediators. The relationship between childhood socioeconomic advantage and disadvantage and the rate of cognitive decline was assessed using linear mixed-effects models. Higher childhood SEP was associated with a higher level of cognitive performance to a greater extent in women (B = 0.122; 95% CI 0.092–0.151) than in men (B = 0.109; 95% CI 0.084–0.135). The strongest mediator was education. Childhood socioeconomic disadvantage was related to a higher rate of decline in delayed recall in both sexes, with a greater association in women. Strategies to prevent impaired late-life cognitive functioning, such as reducing childhood socioeconomic disadvantages and improving education, might have a greater benefit for women.

Drivers of Frailty from Adulthood into Old Age: Results from a 27-Year Longitudinal Population-Based Study in Sweden

BACKGROUND

Frailty is a strong predictor of adverse outcomes. However, longitudinal drivers of frailty are not well understood. This study aimed at investigating the longitudinal trajectories of a frailty index (FI) from adulthood to late life and identifying the factors associated with the level and rate of change in FI.

METHODS

An age-based latent growth curve analysis was performed in the Swedish Adoption/Twin Study of Aging (N = 1,842; aged 29-102 years) using data from up to 15 measurement waves across 27 years. A 42-item FI was used to measure frailty at each wave.

RESULTS

A bilinear, two-slope model with a turning point at age 65 best described the age-related change in FI, showing that the increase in frailty was more than twice as fast after age 65. Underweight, obesity, female sex, overweight, being separated from one's co-twin during childhood, smoking, poor social support, and low physical activity were associated with a higher FI at age 65, with underweight having the largest effect size. When tested as time-varying covariates, underweight and higher social support were associated with a steeper increase in FI before age 65, whereas overweight and obesity were associated with less steep increase in FI after age 65.

CONCLUSIONS

Factors associated with the level and rate of change in frailty are largely actionable and could provide targets for intervention. As deviations from normal weight showed the strongest associations with frailty, future public health programs could benefit from monitoring of individuals with abnormal BMI, especially those who are underweight.

The Relationship between Life Course Socioeconomic Conditions and Objective and Subjective Memory in Older Age

While objective memory performance in older adults was primarily shown to be affected by education as indicator of life course socioeconomic conditions, other life course socioeconomic conditions seem to relate to subjective memory complaints. However, studies differ in which life course stages were investigated. Moreover, studies have explored these effects in an isolated way, but have not yet investigated their unique effect when considering several stages of the life course simultaneously. This study, therefore, examined the respective influence of socioeconomic conditions from childhood up to late-life on prospective memory (PM) performance as an objective indicator of everyday memory as well as on subjective memory complaints (SMC) in older age using structural equation modeling. Data came from two waves of the Vivre-Leben-Vivere aging study (n=993, Mage=80.56). The results indicate that only socioeconomic conditions in adulthood significantly predicted late-life PM performance. PM performance was also predicted by age and self-rated health. In contrast, SMC in older age were not predicted by socioeconomic conditions at any stage of the life course but were predicted by level of depression. In line with the cognitive reserve hypothesis, present results highlight the significance of education and occupation (adulthood socioeconomic conditions) for cognitive functioning in later life.

Childhood Socioeconomic Status and Cognitive Function Later in Life: Evidence From a National Survey in Indonesia

INTRODUCTION

Social and economic conditions in childhood have been found to predict cognitive ability in midlife and old age in high-income countries. This study examines the long-term effect of childhood conditions on cognition among a nationally representative sample of older adults in a low- and middle-income country.

MATERIALS AND METHODS

Data were obtained from the 2014 to 2015 Indonesia Family Life Survey Wave 5 (6676 respondents, aged 50 years and older). Cognitive function was assessed based on total score on a series of tests adapted from the Telephone Interview for Cognitive Status. Retrospective information was collected on childhood poverty, with questions including whether respondents ever experienced hunger before age 15, whether basic facilities were available, and the number of books in the childhood home. We used linear regression to examine the association between childhood conditions and cognitive function in later life.

RESULTS

The findings show that the numbers of facilities and books available in childhood homes are substantially associated with cognition in later life after taking adulthood characteristics into account. Childhood hunger has no significant association with cognitive ability in later life. Belonging to an older birth cohort and living in a rural area were shown to have negative associations with cognitive ability in Indonesia.

CONCLUSIONS

Our findings suggest that childhood poverty, birth cohort, and living in a rural area may contribute to cognitive aging in Indonesia. Policies and interventions that target childhood poverty in developing countries may also recognize the rural-urban divide in access to educational and other socioeconomic resources.

Early-Life Conditions and Cognitive Function in Middle-and Old-Aged Chinese Adults: A Longitudinal Study

A range of previous studies have suggested that early-life conditions (ELCs) are associated with various health problems throughout life in Western societies. The aim of this study was to investigate whether, and how, early-life conditions predicted the level and trajectory of cognitive function in middle- and old-aged Chinese adults. Data were obtained from China Health and Retirement Longitudinal Study which comprised 16,258 adults at baseline. Cognitive function was assessed using mental intactness and episodic memory and ELCs were measured by early parental death, childhood socioeconomic status (SES), food deprivation, and childhood health. Growth curve modeling was used to examine the trajectory of cognitive function (three waves in a 6-year period)with particular attention paid to the effects of ELCs on cognition. The results show that early maternal death is associated with the baseline cognitive level among middle- and old-aged Chinese adults (β range between −0.44 and −0.35, p < 0.05), but that this association is also largely attenuated by adulthood education. Higher childhood SES predicts an enhanced level of baseline cognition in both age groups (β range between 0.08 and 1.27, p < 0.001), but only protects against cognitive decline at baseline in middle-aged adults. Participants who were less healthy during childhood tended to have lower cognitive performance than those who had enjoyed good health (β range between −0.36 and −0.14, p < 0.05). The results of this study highlight the detrimental impact of deleterious ELCs on cognitive function throughout later life.

The relation of poor mastication with cognition and dementia risk: a population-based longitudinal study

We investigated the effect of poor masticatory ability on cognitive trajectories and dementia risk in older adults. 544 cognitively intact adults aged ≥50 were followed for up to 22 years. Cognitive domains (verbal, spatial/fluid, memory, and perceptual speed) were assessed at baseline and follow-ups. Dementia was ascertained according to standard criteria. Masticatory ability was assessed using the Eichner Index and categorized according to the number of posterior occlusal zones: A (all four), B (3-1), and C (none).

At baseline, 147 (27.0%) participants were in Eichner category A, 169 (31.1%) in B and 228 (41.9%) in C. After the age of 65, participants in Eichner category B and C showed an accelerated decline in spatial/fluid abilities (β: -0.16, 95% CI: -0.30 to -0.03) and (β: -0.15, 95% CI: -0.28 to -0.02), respectively. Over the follow-up, 52 incident dementia cases were identified. Eichner categories B or C were not associated with an increased risk of dementia, compared to category A (Hazard Ratio [HR]: 0.83, 95% CI: 0.39 to 1.76 and HR: 0.63, 95% CI: 0.30 to 1.29, respectively).

Poor masticatory ability is associated with an accelerated cognitive decline in fluid/spatial abilities, however it was not related to a higher risk of dementia.

Education and age-related decline in cognitive performance: Systematic review and meta-analysis of longitudinal cohort studies

Central theories of cognitive aging propose that education is an important protective factor for decline in cognitive performance in older age. We conducted a systematic review and meta-analysis of reported estimates of an association between educational attainment and change in performance in six cognitive domains (episodic memory, processing speed, verbal fluency, crystallized intelligence, fluid intelligence, and global ability) in the general population of older individuals. The systematic search (11^th of October 2019) identified 92 eligible articles. The episodic memory domain had the highest number of estimates (37 estimates from 18 articles, n = 109,281) included in the meta-analysis. The fewest estimates (6 estimates from 6 articles, n = 5263) were included for fluid intelligence. Pooled mean estimates from an inverse-variance weighted random effects analysis were not statistically significant and indicated that any association between education and change in cognitive performance is likely of a negligible magnitude. The estimates for education's role (one additional year) for change in cognitive performance ranged from -0.019 (95 % confidence interval, CI = -0.047, 0.010) to 0.004SD (CI = -0.003, 0.012) per decade. Even if the larger positive point estimates (i.e., protective effects) are selectively considered, the influence of education on change is still at least 12 times less important for the cognitive functioning of an older individual than the association between education and level of cognitive performance. Sensitivity analyses did not substantially alter these results. However, heterogeneity was substantial, and remained largely unexplained by mean age, mean educational attainment, Gini coefficient, GDP per capita, maximum follow-up period, and publication year. Overall, education is an important factor in aging due to its robust association with level of performance, but the current base of empirical evidence is not revealing a consistent and substantial association between educational attainment and changes in cognitive performance in the general population. Theories of cognitive aging must be updated to incorporate this pattern of findings.

Early-life socioeconomic circumstances explain health differences in old age, but not their evolution over time

BACKGROUND

Early-life socioeconomic circumstances (SEC) are associated with health in old age. However, epidemiological evidences on the influence of these early-life risk factors on trajectories of healthy ageing are inconsistent, preventing drawing solid conclusion about their potential influence. Here, to fill this knowledge gap, we used a statistical approach adapted to estimating change over time and an outcome-wide epidemiology approach to investigate whether early-life SEC were associated with the level of and rate of decline of physical, cognitive and emotional functioning over time.

METHODS

We used data on more than 23 000 adults in older age from the Survey of Health, Ageing and Retirement in Europe, a 12-year large-scale longitudinal study with repeated measurements of multiple health indicators of the same participants over time (2004 -2015, assessments every 2 years). Confounder-adjusted linear growth curve models were used to examine the associations of early-life SEC with the evolution of muscle strength, lung function, cognitive function, depressive symptoms and well-being over time.

RESULTS

We consistently found an association between early-life SEC and the mean levels of all health indicators at age 63.5, with a critical role played by the cultural aspect of disadvantage. These associations were only partly explained by adult-life SEC factors. By contrast, evidences supporting an association between early-life SEC and the rate of change in health indicators were weak and inconsistent.

CONCLUSIONS

Early-life SEC are associated with health in old age, but not with trajectories of healthy ageing. Conceptual models in life course research should consider the possibility of a limited influence of early-life SEC on healthy ageing trajectories.

Advantaged socioeconomic conditions in childhood are associated with higher cognitive functioning but stronger cognitive decline in older age

There is increasing evidence that socioeconomic conditions early in life have an impact on cognitive functioning in later life. Based on the large longitudinal sample from SHARE we find a clear pattern in cognitive functioning in old age, related to childhood socioeconomic conditions: Those from more affluent households show higher levels of fluid intelligence in old age and experience stronger decline over time in executive functions. The latter phenomenon is not often documented. Although modifications in cognitive functioning with aging are inevitable, life course socioeconomic circumstances impact the timing of this process. We conclude that the etiology of cognitive aging is the result of multiple social processes, defined by the socioeconomic conditions in childhood and all along the life course.

Cognitive aging is characterized by large heterogeneity, which may be due to variations in childhood socioeconomic conditions (CSC). Although there is substantial evidence for an effect of CSC on levels of cognitive functioning at older age, results on associations with cognitive decline are mixed. We examined by means of an accelerated longitudinal design the association between CSC and cognitive trajectories from 50 to 96 years. Cognition included two functions generally found to decline with aging: delayed recall and verbal fluency. Data are from six waves of the Survey of Health, Aging, and Retirement in Europe (SHARE), conducted between 2004 and 2015 (n = 24,066 at baseline; 56% female, age 50+). We found a consistent CSC pattern in levels of cognitive functioning in later life. Older people with disadvantaged CSC had lower levels of cognitive functioning than those with more advantaged CSC. We also find that decline is almost 1.6 times faster in the most advantaged group compared with the most disadvantaged group. The faster decline for people with more advantaged CSC becomes less pronounced when we additionally control for adulthood socioeconomic conditions and current levels of physical activity, depressive symptoms, and partner status. Our findings are in line with the latency, pathway, and cumulative model and lend support to theories of cognitive reserve, stating that neuronal loss can no longer be repaired in people with more cognitive reserve once the underlying pathology is substantial and speed of decline is accelerated.

Cohort by Education Interactions in Longitudinal Changes in Functional Abilities

Objective: Investigations of cohort differences in relationships between education and health tend to focus on mortality or self-reported health. We report one of the first analyses of cohort differences in relationships between education and objective measures of functional abilities across the lifespan. Method: Up to 26 years of follow-up data were available from 859 adults from the Swedish Adoption/Twin Study of Aging. The sample was divided into two cohorts by birth year: 1900-1924 and 1925-1948. Latent growth curve models (LGCM) were compared across cohort and educational levels. Results: LGCM indicated divergence between adults with lower and higher educational attainment in longitudinal trajectories of change with age in the Balance and Flexibility factors for the later born cohort only. Discussion: Results support the cumulative advantage theory and suggest that education-health disparities are increasing in recent cohorts, even in counties with national health care systems and strong support of education.

Childhood socioeconomic status and genetic risk for poorer cognition in later life

The ε4 allele of the APOE gene is associated with poorer cognition in later life. This study aimed to advance understanding of how environments potentially moderate this genetic risk by focusing on childhood socioeconomic status (SES). Previous research across diverse national contexts has found that older adults from higher-SES families in childhood demonstrate better cognitive functioning than their lower-SES counterparts. Nevertheless, few studies have examined whether higher childhood SES might also promote later life cognition by mitigating the effects of ε4 carrier status. To address this gap, we used data from 3017 participants in the Wisconsin Longitudinal Study, which has followed a random sample of people who graduated from Wisconsin high schools in 1957. Childhood SES included parents' educational attainment, father's occupational status, and household income in adolescence. We constructed measures of memory and of language/executive functioning using scores from neurocognitive tests administered when participants were approximately ages 65 and 72. APOE ε4 status was measured through saliva samples. Results from cross-controlled multilevel models indicated that APOE ε4 status-and not childhood SES-independently predicted memory, whereas childhood SES-and not APOE ε4 status-independently predicted language/executive functioning. Moreover, a statistical interaction between APOE ε4 status and childhood SES for memory indicated that at baseline, higher childhood SES protected against the risk of APOE ε4 status, whereas lower childhood SES exacerbated the risk of APOE ε4 status. However, by follow-up, these moderating effects dissipated, and APOE ε4 status alone was associated with memory. We interpret these results in light of theorizing on differential susceptibility for poorer cognition across the life course.

Blunted cortisol stress reactivity in low-income children relates to lower memory function

Lower socioeconomic status (SES) environments are marked by higher stress that is hypothesized to alter cortisol secretion in children, thereby damaging hippocampal volume and memory performance. However, empirical evidence demonstrating these putative links is lacking. We assessed the diurnal cortisol awakening response (CAR) on two mornings and cortisol stress reactivity (CSR) with the Trier Social Stress Test for Children in 102 healthy, socio-demographically diverse 6-to-7-year-old children (46% female). Children performed a hippocampal-dependent item-location associative memory task and 60 of these children underwent structural MRI scanning for hippocampal volume. Cortisol values were modeled with latent-change structural equation models to represent overall levels and change. We found lower income is associated with a flatter CAR, blunted reactivity and recovery to acute stress, and smaller hippocampal volume. Furthermore, hyporeactivity in CSR was related to lower memory among lower-income children, whereas there was no reliable association of CSR and memory among higher-income children (an income x cortisol interaction). We found no evidence that smaller hippocampal volume in lower income was associated with poorer memory performance. Notably, hyporeactivity in both CAR and CSR was specific to using income as the SES predictor. The income x cortisol interaction and smaller hippocampal effects, however, were replicated with education and an SES composite score. This suggests that hyporeactivity to acute stress may function as a mediator in SES-cognition associations at the lower end of the SES spectrum, but it does not imply environmental- or genetically-mediated causation.

Mediators of the Effect of Childhood Socioeconomic Status on Late Midlife Cognitive Abilities: A Four Decade Longitudinal Study

BACKGROUND AND OBJECTIVES

Childhood socioeconomic status (cSES) is found to predict later-life cognitive abilities, yet the mechanisms underlying these associations remain unclear. The objective of this longitudinal study was to examine the direct and indirect paths through which cSES influences late midlife cognitive outcomes.

RESEARCH DESIGN AND METHODS

Participants were 1,009 male twins in the Vietnam Era Twin Study of Aging (VETSA). At mean ages 20 and 62, participants completed a standardized test for general cognitive ability (GCA). The age 62 cognitive assessment also included in-person tests of processing speed, episodic memory, abstract reasoning, working memory, verbal fluency, visual-spatial ability, and executive functions. At mean age 56, participants were interviewed regarding their own and their parents' education and occupation, and completed questionnaires about cognitive leisure activities and sociodemographic information. Multiple mediation analyses were conducted to examine the direct path effects and indirect path effects of cSES through age 20 GCA, adult SES, and cognitive leisure activities on seven cognitive outcomes at age 62, adjusting for age, ethnicity, and non-independence of observations.

RESULTS

Total (direct plus indirect) effects were significant for all measures with the exception of executive functions. Men from lower cSES backgrounds had poorer cognitive functioning in late midlife. The direct effect of cSES was partially mediated for abstract reasoning, and was fully mediated for the remaining six cognitive outcomes. Total indirect effects accounted for at least half of the total effects in each model, with paths through age 20 GCA explaining most of the total indirect effects.

DISCUSSION AND IMPLICATIONS

cSES predicted cognitive functioning in late middle age Using multiple mediation models, we show that lower cSES predicts poorer cognition in late midlife primarily through young adult cognitive ability and to a lesser extent through SES in adulthood and engagement in cognitively stimulating activities.