Sex differences in cognitive aging and the role of socioeconomic status: Evidence from multi-cohort studies

Life-course socioeconomic inequalities, social mobility and healthy aging in older adults: A multi-cohort study

OBJECTIVE

To investigate how socioeconomic positions at different life stages, their relative importance, and social mobility influence IC across the USA, UK, Europe, China, and Japan among adults aged ≥50 years.

METHODS

We included 54,217 participants from five nationally representative cohorts in the USA, UK, Europe, China, and Japan. Life-course socioeconomic positions were assessed in early-life (childhood socioeconomic positions), early-adulthood (education), and late-adulthood (household wealth). Healthy aging was measured by intrinsic capacity including cognition, psychological health, locomotion, vitality, and sensory functions. Linear mixed models were used to estimate the associations of intrinsic capacity with each socioeconomic position indicator and social mobility.

FINDINGS

Higher levels of education and wealth were both significantly associated with better intrinsic capacity (p < 0.05 in all cohorts). Education had a stronger impact on intrinsic capacity than wealth in the USA, Europe, China, and Japan. Middle and high childhood socioeconomic positions were significantly linked to better intrinsic capacity compared with the low group (p < 0.05 in all cohorts). Compared to stable groups, upward and downward social mobility groups were associated with better and worse intrinsic capacity, respectively.

CONCLUSION

Socioeconomic measures throughout the life course can predict healthy aging in the USA, Europe, and Asia. The long-term negative impact of disadvantaged childhood socioeconomic positions on healthy aging can be partially mitigated by upward mobility later in life. Policies need to narrow the social inequalities from early life and prevent adults from experiencing downward mobility, thereby reducing disparities in healthy aging.

Teeth, Health, and Mind: Understanding the Interplay of Social Determinants and Cognitive Decline in Older Adults

The study examines the association between social determinants of health, tooth loss, and cognitive decline. Using regression models, the 2020 Behavioral Risk Factor Surveillance data examined the study objective; it included 32,663 older adults who reported on cognitive status. Results suggested that older adults missing more than five teeth or unable to work are 1.61 times and 6.84 times more likely to report cognitive decline, respectively. Older adults with higher education and higher household incomes are less likely to report cognitive decline. Results suggested that older adults with no diabetes or who never smoked are 31% and 39% less likely to report a cognitive decline. The results suggested a significant association between tooth loss and cognitive decline among social determinants of health. A comprehensive approach to affect cognitive decline should include oral and social health strategies.

Multivariate decomposition of gender differentials in cognitive impairment among older adults in India based on Longitudinal Ageing Study in India, 2017-2018

BACKGROUND

Increasing life expectancy and declining fertility rates have increased the ageing population around the world. The literature lacks a consensus regarding the risk of cognitive impairments by gender.

OBJECTIVE

Our study aims to examine the differences in cognition impairments between male and female older adults in India.

METHODOLOGY

We utilized data from the first wave of the Longitudinal Ageing Study in India (LASI) (2017-18), analyzing 31,464 older adults aged 60 years and above (15,098 males and 16,366 females). Cognitive impairment is measured using the Harmonized Cognitive Assessment Protocol (HCAP) which includes five broad domains (memory, orientation, arithmetic function, executive function, and object naming). A multivariate decomposition analysis was performed using STATA 17 software to identify covariates'contributions, which explain the group differences to average predictions.

FINDINGS

The prevalence of cognitive impairment was significantly higher among females (19.8%) than males (6.4%) (p < 0.001). Gender disparities were more pronounced among the oldest-old (41.5% vs. 15.9%), widowed individuals (24.6% vs. 9.8%), those with no education (25.1% vs. 11.8%), and individuals living alone (23.4% vs. 5.0%). Decomposition analysis revealed that 62% of the gender gap in cognitive impairment was attributable to differences in compositional factors, primarily education (42%), marital status (6%), working status (6%), difficulty in instrumental activities of daily living (3%), and physical activity (2%). The remaining 38% of the disparity was due to differences in how these factors impacted men and women.

CONCLUSION

The findings indicate that cognitive impairments are more pronounced among women. Gender-responsive interventions improving education access among the female gender would bring relevant and desired results.

Muscular strength, endothelial function and cognitive disorders: state of the art

In recent years, the ageing population has increasingly grown. This process carries a range of pathophysiological changes involving alterations in the skeletal muscle, vascular endothelium and brain function, becoming an important risk factor for developing cognitive disorders and cardiovascular diseases. With ageing, there is a decrease in muscle mass and muscle strength, and a relationship between muscle strength decrease and cognitive decline has been shown. Lower handgrip strength has been linked to memory impairment, lower global cognitive function, decreased attention and reduced visuospatial abilities in the elderly, but understanding of the underlying mechanisms that explain the link between altered skeletal muscle function and structure, endothelial dysfunction, and the role of endothelial dysfunction in the onset of cognitive disorders has been scarcely explored. This review aims to detail the cellular and molecular mechanisms by which the progressive changes associated with ageing can alter healthy skeletal muscle and endothelial function, creating an environment of oxidative stress, inflammation and mitochondrial dysfunction. These changes can lead to reduced muscle strength, and the secretion of detrimental endothelial factors, resulting in endothelial dysfunction, blood-brain barrier disruption, and damage to neurons and microglia, ultimately accelerating the onset of cognitive disorders in the elderly. In addition, we aimed to describe the mechanisms that potentially explain how preserving muscular function with resistance training could prevent brain function deterioration, including the production of different factors that allow an improved endothelial function, haemodynamic parameters and brain plasticity, ultimately delaying the onset of cognitive impairment and chronic diseases.

Multimorbidity, lifestyle, and cognitive function: A cross-cultural study on the role of diabetes, cardiovascular disease, cancer, and chronic respiratory diseases

BACKGROUND

The effect of lifestyle factors on cognitive function related to four major noncommunicable diseases (NCDs) including diabetes, cardiovascular disease, cancer, and chronic respiratory diseases, and the relationship between these NCDs and cognitive function have not been fully studied. We aimed to investigate the longitudinal associations between these NCDs and cognitive function in middle-aged and older people, and the combined effects of lifestyle factors.

METHODS

By employing the data from three large-scale cohort studies from the U.S. Health and Retirement Study (2010-2019), English Longitudinal Study of Aging (2014-2019), and China Health and Retirement Longitudinal Study (2011-2019), this study carried out a multi-cohort analysis to 77, 210 participants. Fixed-effects regression models were used to examine associations between NCD status and cognitive function. Margin plots were used to illustrate the effect of lifestyle factors.

RESULTS

Our findings revealed the dose-dependent association between mounting these NCDs and declining cognitive performance, ranging from one NCD (β = -0.05, 95 % CI: -0.08 to -0.02) to four NCDs (β = -0.51, 95 % CI: -0.75 to -0.28). Decline in cognitive function associated with NCDs was exacerbated with physical inactivity, current smoking status, and an increase in unhealthy lifestyle behaviors.

LIMITATIONS

The observational study design precludes causal interrogation of lifestyles and four NCDs on cognitive function.

CONCLUSIONS

An increasing number of these NCDs were dose-dependently associated with the decline in cognitive function score. Unhealthy lifestyle factors expedite decline in cognitive function linked to these NCDs.

The associations of socioeconomic position with structural brain damage and connectivity and cognitive functioning: The Maastricht Study

BACKGROUND

Socioeconomic inequalities in cognitive impairment may partly act through structural brain damage and reduced connectivity. This study investigated the extent to which the association of early-life socioeconomic position (SEP) with later-life cognitive functioning is mediated by later-life SEP, and whether the associations of SEP with later-life cognitive functioning can be explained by structural brain damage and connectivity.

METHODS

We used cross-sectional data from the Dutch population-based Maastricht Study (n = 4,839; mean age 59.2 ± 8.7 years, 49.8% women). Early-life SEP was assessed by self-reported poverty during childhood and parental education. Later-life SEP included education, occupation, and current household income. Participants underwent cognitive testing and 3-T magnetic resonance imaging to measure volumes of white matter hyperintensities, grey matter, white matter, cerebrospinal fluid, and structural connectivity. Multiple linear regression analyses tested the associations between SEP, markers of structural brain damage and connectivity, and cognitive functioning. Mediation was tested using structural equation modeling.

RESULTS

Although there were direct associations between both indicators of SEP and later-life cognitive functioning, a large part of the association between early-life SEP and later-life cognitive functioning was explained by later-life SEP (72.2%). The extent to which structural brain damage or connectivity acted as mediators between SEP and cognitive functioning was small (up to 5.9%).

CONCLUSIONS

We observed substantial SEP differences in later-life cognitive functioning. Associations of structural brain damage and connectivity with cognitive functioning were relatively small, and only marginally explained the SEP gradients in cognitive functioning.

Longitudinal trajectories of cognitive aging

PURPOSE OF REVIEW

This review summarizes recent evidence related to the cognitive trajectories of aging, the factors associated with the different trajectories, and the effect of sex on cognitive decline.

RECENT FINDINGS

Trajectories of cognitive aging identified in different studies vary in number, in the proportion of individuals falling into each of the classes and in the predictors of class membership. Trajectories observed include types with 'rapid decline', those with 'gradual decline' and those with 'maintenance of high level' of cognitive performance. Predictors of decline and predictors of maintenance of cognitive performance may be different. While factors such as education were in general associated with high performance, and reversely with low performance, other factors, such as depression were predictors only for some groups, particularly the declining ones. Sex differences in cognitive trajectories and the associated predictive factors have also been identified.

SUMMARY

The findings on education may be particularly important in populations with low educational level, especially among women and the findings on depression have special interest in preventing cognitive decline in women. Further work is required to explain intriguing inconsistencies observed in the literature.

Factors affecting the GABAergic synapse function in Alzheimer's disease: Focus on microRNAs

Alzheimer's disease (AD) is a progressive neurological disease characterized by the loss of cognitive function, confusion, and memory deficit. Accumulation of abnormal proteins, amyloid beta (Aß), and phosphorylated Tau (p-tau) forms plaques and tangles that deteriorate synapse function, resulting in neurodegeneration and cognitive decline in AD. The human brain is composed of different types of neurons and/or synapses that are functionally defective in AD. The GABAergic synapse, the most abundant inhibitory neuron in the human brain was found to be dysfunctional in AD and contributes to disrupting neurological function. This study explored the types of GABA receptors associated with neurological dysfunction and various biological and environmental factors that cause GABAergic neuron dysfunction in AD, such as Aβ, p-tau, aging, sex, astrocytes, microglia, APOE, mental disorder, diet, physical activity, and sleep. Furthermore, we explored the role of microRNAs (miRNAs) in the regulation of GABAergic synapse function in neurological disorders and AD states. We also discuss the molecular mechanisms underlying GABAergic synapse dysfunction with a focus on miR-27b, miR-30a, miR-190a/b, miR-33, miR-51, miR-129-5p, miR-376-3p, miR-376c, miR-30b and miR-502-3p. The purpose of our article is to highlight the recent research on miRNAs affecting the regulation of GABAergic synapse function and factors that contribute to the progression of AD.

Socioeconomic inequalities in physical, psychological, and cognitive multimorbidity in middle-aged and older adults in 33 countries: a cross-sectional study

BACKGROUND

Many physical, psychological, and cognitive disorders are highly clustered among populations with low socioeconomic status. However, the extent to which socioeconomic status is associated with different combinations of these disorders is unclear, particularly outside high-income countries. We aimed to evaluate these associations in 33 countries including high-income countries, upper-middle-income countries, and one lower-middle-income country.

METHODS

This cross-sectional multi-region study pooled individual-level data from seven studies on ageing between 2017 and 2020. Education and total household wealth were used to measure socioeconomic status. Physical disorder was defined as having one or more of the self-reported chronic conditions. Psychological and cognitive disorders were measured by study-specific instruments. The outcome included eight categories: no disorders, physical disorder, psychological disorder, cognitive disorder, and their four combinations. Multivariable-adjusted logistic regression models were used to estimate odds ratios (ORs) and 95% CIs for the associations of socioeconomic status with these outcomes separately for high-income countries, upper-middle-income countries, and the lower-middle-income country.

FINDINGS

Among 167 376 individuals aged 45 years and older, the prevalence of multimorbidity was 24·5% in high-income countries, 33·9% in upper-middle-income countries, and 8·1% in the lower-middle-income country (India). Lower levels of education, household wealth, and a combined socioeconomic status score were strongly associated with physical, psychological, and cognitive multimorbidity in high-income countries and upper-middle-income countries, with ORs (low vs high socioeconomic status) for physical-psychological-cognitive multimorbidity of 12·36 (95% CI 10·29-14·85; p<0·0001) in high-income countries and of 23·84 (18·85-30·14; p<0·0001) in upper-middle-income countries. The associations in the lower-middle-income country were mixed. Participants with both a low level of education and low household wealth had the highest odds of multimorbidity (eg, OR for physical-psychological-cognitive multimorbidity 21·21 [15·95-28·19; p<0·0001] in high-income countries, 37·07 [25·66-53·56; p<0·0001] in upper-middle-income countries, and 54·96 [7·66-394·38; p<0·0001] in the lower-middle-income country).

INTERPRETATION

In study populations from high-income countries, upper-middle-income countries, and the lower-middle-income country, the odds of multimorbidity, which included physical, psychological, and cognitive disorders, were more than ten times greater in individuals with low socioeconomic status. Equity-oriented policies and programmes that reduce social inequalities in multimorbidity are urgently needed to achieve Sustainable Development Goals.

FUNDING

Zhejiang University, Fundamental Research Funds for the Central Universities, The Key Laboratory of Intelligent Preventive Medicine of Zhejiang Province, Wellcome Trust, Medical Research Council, National Institute on Aging, and Academy of Finland.

TRANSLATION

For the Chinese translation of the abstract see Supplementary Materials section.

Cholinergic-estrogen interaction is associated with the effect of education on attenuating cognitive sex differences in a Thai healthy population

The development of human brain is shaped by both genetic and environmental factors. Sex differences in cognitive function have been found in humans as a result of sexual dimorphism in neural information transmission. Numerous studies have reported the positive effects of education on cognitive functions. However, little work has investigated the effect of education on attenuating cognitive sex differences and the neural mechanisms behind it based on healthy population. In this study, the Wisconsin Card Sorting Test (WCST) was employed to examine sex differences in cognitive function in 135 Thai healthy subjects, and label-free quantitative proteomic method and bioinformatic analysis were used to study sex-specific neurotransmission-related protein expression profiles. The results showed sex differences in two WCST sub-scores: percentage of Total corrects and Total errors in the primary education group (Bayes factor>100) with males performed better, while such differences eliminated in secondary and tertiary education levels. Moreover, 11 differentially expressed proteins (DEPs) between men and women (FDR<0.1) were presented in both education groups, with majority of them upregulated in females. Half of those DEPs interacted directly with nAChR3, whereas the other DEPs were indirectly connected to the cholinergic pathways through interaction with estrogen. These findings provided a preliminary indication that a cholinergic-estrogen interaction relates to, and might underpin, the effect of education on attenuating cognitive sex differences in a Thai healthy population.

Associations of metabolic syndrome, its severity with cognitive impairment among hemodialysis patients

BACKGROUND

In the general population, metabolic syndrome (MetS) is associated with increased risk of cognitive impairment, including global and specific cognitive domains. These associations are not well studied in patients undergoing hemodialysis and were the focus of the current investigation.

METHODS

In this multicenter cross-sectional study, 5492 adult hemodialysis patients (3351 men; mean age: 54.4 ± 15.2 years) treated in twenty-two dialysis centers of Guizhou, China were included. The Mini-Mental State Examination (MMSE) was utilized to assess mild cognitive impairment (MCI). MetS was diagnosed with abdominal obesity, hypertension, hyperglycemia, and dyslipidemia. Multivariate logistic and linear regression models were used to examine the associations of MetS, its components, and metabolic scores with the risk of MCI. Restricted cubic spline analyses were performed to explore the dose-response associations.

RESULTS

Hemodialysis patients had a high prevalence of MetS (62.3%) and MCI (34.3%). MetS was positively associated with MCI risk with adjusted ORs of 1.22 [95% confidence interval (CI) 1.08-1.37, P = 0.001]. Compared to no MetS, adjusted ORs for MCI were 2.03 (95% CI 1.04-3.98) for 22.51 (95% CI 1.28-4.90) for 3, 2.35 (95% CI 1.20-4.62) for 4, and 2.94 (95% CI 1.48-5.84) for 5 components. Metabolic syndrome score, cardiometabolic index, and metabolic syndrome severity score were associated with increased risk of MCI. Further analysis showed that MetS was negatively associated with MMSE score, orientation, registration, recall and language (P < 0.05). Significant interaction effect of sex (P for interaction = 0.012) on the MetS-MCI was observed.

CONCLUSION

Metabolic syndrome was associated with MCI in hemodialysis patients in a positive dose-response effect.