Socioeconomic Inequalities in Cognitive Functioning Only to a Small Extent Attributable to Modifiable Health and Lifestyle Factors in Individuals Without Dementia

Associations of socioeconomic status and healthy lifestyle with incident dementia and cognitive decline: two prospective cohort studies

Background

Little is known about the complex associations of socioeconomic status (SES) and healthy lifestyle with cognitive dysfunction.

Methods

Using data from the Health and Retirement Study (HRS) [2008-2020] and the English Longitudinal Study of Ageing (ELSA) [2004-2018], SES was constructed by latent class analysis using education level, total household income and wealth. Overall healthy lifestyle was derived using information on never smoking, low to moderate alcohol consumption (drinks/day: (0, 1] for women and (0, 2] for men), top tertile of physical activity, and active social contact.

Findings

A total of 12,437 and 6565 participants from the HRS and ELSA were included (40.8% and 46.0% men and mean age 69.3 years and 65.1 years, respectively). Compared with participants of high SES, those of low SES had higher risk of incident dementia (hazard ratio 3.17, 95% confidence interval 2.72-3.69 in the HRS; 1.43, 1.09-1.86 in the ELSA), and the proportions mediated by overall lifestyle were 10.4% (7.3%-14.6%) and 2.7% (0.5%-14.0%), respectively. Compared with participants of high SES and favorable lifestyle, those with low SES and unfavorable lifestyle had a higher risk of incident dementia (4.27, 3.40-5.38 in the HRS; 2.02, 1.25-3.27 in the ELSA) and accelerated rate of global cognitive decline (β = -0.058 SD/year; 95% CI: -0.073, -0.043 in the HRS; β = -0.049 SD/year; 95% CI: -0.063, -0.035 in the ELSA).

Interpretation

Unhealthy lifestyle only mediated a small proportion of the socioeconomic inequality in dementia risk in both US and UK older adults.

Funding

This work was supported by grants from the National Natural Science Foundation of China (82088102 and 82370819), the National Key R&D Program of China (2023YFC2506700), the Shanghai Municipal Government (22Y31900300), the Shanghai Clinical Research Center for Metabolic Diseases (19MC1910100), the Innovative Research Team of High-Level Local Universities in Shanghai, the Special Project for Clinical Research in Health Industry of Shanghai Municipal Health Commission (202340084), and Ruijin Hospital Youth Incubation Project (KY20240805). Y.X. is supported by the National Top Young Talents program.

Impact of the South African Child Support Grant on memory decline and dementia probability in rural and low-income mothers, 2014-2021

INTRODUCTION

Aging populations across sub-Saharan Africa are rapidly expanding, leading to an increase in the burden of Alzheimer's disease and related dementias (ADRD). Cash transfer interventions are one plausible mechanism to combat ADRD at a population-level in low-income settings. We exploited exogenous variation in eligibility for South Africa's Child Support Grant (CSG) to estimate the longitudinal association between potential CSG benefit and cognitive trajectories in rural mothers with <10 children (n = 1090).

METHODS

South Africa's CSG delivers monthly cash payments to primary caregivers, predominantly mothers, to offset the costs associated with child rearing. This study implemented a quasi-experimental design using data (2014-2022) from a rural, low-income cohort in the Agincourt research area, South Africa. We fit linear mixed effects models and generalized linear models to estimate the association of potential CSG benefit per eligible child with memory decline and dementia probability, respectively. We stratified all models by the mother's total number of children (1-4 and 5-9) and examined effect modification by household wealth and the mother's education level.

RESULTS

Having above median CSG per eligible child was associated with higher baseline memory scores (β = 0.12 SD units, 95% CI = 0.02, 0.22) but steeper memory decline (β = -0.02 SD units, 95% CI = -0.04, -0.00) compared to below median CSG. Within stratified analyses, this effect was primarily observed among mothers with 5-9 children. No associations were observed between potential CSG per eligible child and dementia probability.

CONCLUSIONS

Our findings support the use of large-scale cash transfers as a promising intervention to promote healthy cognitive aging in mid-life women within rural, low-income settings. However, we found evidence that the CSG in its current structure may not be sufficient support for women to sustain measurable cognitive benefits over the long-term.

The Mediating Role of Lifestyle Activities in the Association Between Social Deprivation and Cognition in Older Adulthood: Results From the Health and Retirement (HRS) Study

Objectives: We aimed to investigate the mediating role of lifestyle activities in the association between social deprivation and cognition. Methods: To investigate, we analysed data of 3867 respondents (Mean Age: 73.37, SD: 5.57) in the U.S. Health and Retirement Study (HRS) using growth curve and path analysis, adjusted for demographic and health covariates. Results: Being in the high (vs. moderate) Social Deprivation Index group was associated with lower cognition scores (β = -2.63, [95 % CI: -2.90, -2.36]). Conversely, higher (vs. lower) Lifestyle Index scores were associated with higher cognition scores (β = 1.17, [95 % CI: 0.72, 1.63]). In mediation analysis, the Lifestyle Index score explained 27 % of the association of So Dep Index group on cognition at the final follow-up. Discussion: While lifestyle activities did mediate the association between social deprivation and cognition, factors not investigated accounted for the majority of the variation. These may include systemic disadvantages.

The dilution effect of healthy lifestyles on the risk of cognitive function attributed to socioeconomic status among Chinese older adults: A national wide prospective cohort study

Background

Lower socioeconomic status (SES) is a risk factor for poor cognitive function, while a healthy lifestyle is associated with better cognitive function. We examined the complex relationship between SES and a healthy lifestyle and cognitive function among older Chinese adults.

Methods

We used a national prospective cohort of the Chinese Longitudinal Healthy Longevity Survey (CLHLS) from 2008-18, aged 65 years and older with normal cognition at baseline. Participants were categorised into the favourable group if they had four to six healthy lifestyle factors and the unfavourable group for zero to three factors. SES was classified as higher and lower by assessing the socioeconomic vulnerability index (SEVI) with six components. Cognitive function was measured using the Mini-Mental State Examination (MMSE) scores and the standardised Z-scores. We applied the linear mixed effects and time-dependent Cox regression models to explore associations and further stratified the analysis by healthy lifestyles.

Results

A total of 6851 participants were included (the mean age was 80.87, 43.44% had a favourable lifestyle, and 49.29% had higher SES). Over the 10-year follow-up period, SES status and lifestyle profiles significantly affected the decline in the standardised Z-scores (P < 0.05). The higher SES group with favourable lifestyles exhibited a slower cognitive decline than those with lower SES (by 0.031 points per year, P < 0.05). The association was not observed in those in the unfavourable group (0.010 points per year, P > 0.05). During a follow-up, 25.06% of participants developed cognitive impairment (MMSE<18). We also observed a significant interaction between SES and healthy lifestyles (P < 0.05), with the corresponding associations of SES being more pronounced among participants with unfavourable lifestyles (hazard ratio (HR) = 0.821; 95% confidence interval (CI) = 0.701-0.960) than those with favourable lifestyles (HR = 1.006; 95% CI = 0.844-1.200).

Conclusions

A healthy lifestyle may attenuate the adverse impacts of lower SES on cognitive function among older adults. This study might provide important information for protecting cognitive function, especially in low- and middle-income countries.

Associations of socioeconomic status and healthy lifestyle with incident early-onset and late-onset dementia: a prospective cohort study

BACKGROUND

Modifiable risk factor estimates are sparse for early-onset dementia incidence. This study aimed to estimate and compare the risk factor profiles of early-onset dementia and late-onset dementia, and to explore the complex relationships between socioeconomic status, lifestyles, and early-onset dementia risk.

METHODS

In this prospective cohort study, we used data from the UK Biobank for analysis of early-onset dementia and late-onset dementia. For early-onset dementia analyses, data were collected on those aged younger than 60 years without prevalent dementia at baseline. For late-onset dementia analyses, data were collected on those aged 65 years or older at the end of follow-up. Participants with missing information on socioeconomic factors were excluded. Two models were used to test associations between early-onset dementia incidence and socioeconomic status. The first model tested associations between socioeconomic status and early-onset and late-onset dementia incidence, adjusting for covariates. Participant socioeconomic status was defined using education level, income, and employment status via latent class analysis. The second model additionally included a healthy lifestyle score, which was constructed using data on smoking, alcohol consumption, physical activity, and the Healthy Diet Index. Incident early-onset dementia was defined as a dementia case diagnosed before 65 years of age. Multivariable-adjusted Cox proportional hazard regression models were used to estimate the hazard ratio (HR) for risk of dementia. We used multivariable-adjusted Cox proportional-hazard regression models to estimate the HR for risk of both early-onset dementia and late-onset dementia.

FINDINGS

Between 2007 and 2010, 257 345 individuals were included in the analysis of early-onset dementia, and 294 133 older individuals were included in the analysis of late-onset dementia. During a mean follow-up of 11·9-12·5 years, 502 early-onset dementia cases and 5768 late-onset dementia cases were documented. Risk factor profiles were typically dissimilar between early-onset dementia and late-onset dementia. For instance, the age and sex adjusted HR for low socioeconomic status (vs high) was 4·40 (95% CI 3·43-5·65) for early-onset dementia and 1·90 (1·74-2·07) for late-onset dementia, yielding a ratio of HRs of 2·32 (1·78-3·02). After adjusting for various risk factors, participants with low socioeconomic status (vs high) had increased risk for early-onset dementia (3·38, 2·61-4·37), and overall lifestyle mediated 3·2% (1·8-5·7) of the association. Individuals with both low socioeconomic status and unhealthy lifestyles had a higher risk of early-onset dementia (5·40, 3·66-7·97). No significant interaction was observed between lifestyle and socioeconomic status. The association between socioeconomic status and early-onset dementia seemed to be more pronounced in individuals with type 2 diabetes (HR 11·21, 95% CI 2·70-46·57).

INTERPRETATION

Early-onset dementia and late-onset dementia might have different risk factor profiles; although risk factors were similar, the magnitude of associations between risk factors and dementia incidence was greater for early-onset dementia. Only a small proportion of the socioeconomic inequity in dementia risk was mediated by healthy lifestyles, which indicates that measures other than healthy lifestyle promotion to improve social determinants of health are warranted.

FUNDING

The National Key Research and Development Program of China, the National Natural Science Foundation of China, the Hubei Province Science Fund for Distinguished Young Scholars, and the Fundamental Research Funds for the Central Universities.

Socioeconomic position, modifiable dementia risk and cognitive decline: results of 12-year Maastricht Aging Study

OBJECTIVES

This study investigated whether the association between modifiable dementia risk and rate of cognitive decline differs across socioeconomic status (SES) strata.

DESIGN, SETTING AND PARTICIPANTS

Data were used from Maastricht Aging Study, a prospective cohort study with a 12-year follow-up. The baseline sample consisted of 1023 adults over 40 years old.

MEASUREMENTS

The "LIfestyle for BRAin health" (LIBRA) index was used to assess modifiable dementia risk. Cognitive performance was assessed at baseline, 6 and 12 years, and measured in the domains of information processing speed, executive functioning and verbal memory function. An SES score was calculated from equivalent income and educational level (tertiles). Linear mixed models were used to study the association between LIBRA, SES and their interaction on the rate of cognitive decline.

RESULTS

Participants in the lowest SES tertile displayed more decline in information processing speed (vs. middle SES: X2 = 7.08, P = 0.029; vs. high SES: X2 = 9.49, P = 0.009) and verbal memory (vs. middle SES: X2 = 9.28, P < 0.001; vs. high SES: X2 = 16.68, P < 0.001) over 6 years compared to their middle- and high-SES counterparts. Higher (unhealthier) LIBRA scores were associated with more decline in information processing speed (X2 = 12.66, P = 0.002) over 12 years and verbal memory (X2 = 4.63, P = 0.032) over 6 years. No consistent effect modification by SES on the association between LIBRA and cognition was found.

CONCLUSIONS

Results suggest that lifestyle is an important determinant of cognitive decline across SES groups. Yet, people with low SES had a more unfavorable modifiable risk score suggesting more potential for lifestyle-based interventions.

[What does the population know about risk and protective factors for dementia? An international review of the current state of knowledge in various countries]

BACKGROUND

The scientific state of knowledge on modifiable risk factors for dementia has greatly improved in recent years. The established risk and protective factors include physical and social inactivity, hypertension, diabetes mellitus, excessive alcohol consumption and smoking; however, it is assumed that this knowledge is so far insufficiently disseminated among the general population, indicating untapped potential for primary prevention of dementia.

OBJECTIVE

To assess the state of knowledge on established risk and protective factors for dementia in the general population.

MATERIAL AND METHODS

Based on a systematic literature search in the PubMed database, international studies that investigated the knowledge on modifiable risk and/or protective factors for dementia in samples from the general population were identified.

RESULTS AND CONCLUSION

A total of 21 publications were included in the review. The majority of publications (n = 17) collated risk and protective factors using closed questions, while n = 4 studies used open questions. Lifestyle factors, e.g. cognitive, social and physical activity, were most frequently named as protective against dementia. Furthermore, many participants recognized depression as a risk factor for dementia. Knowledge of cardiovascular risk constellations for dementia, such as hypertension, hypercholesterolemia or diabetes mellitus were much less known among the participants. The results indicate that there is a need for a targeted clarification of the role of pre-existing cardiovascular diseases as risk factors for dementia. Studies assessing the state of knowledge on social and environmental risk and protective factors for dementia are currently scarce.