Instrumental variable approaches to identifying the causal effect of educational attainment on dementia risk

Entertainment activities and the risk of Alzheimer's disease: a Mendelian randomization analysis

Background

Effective prevention is key to addressing the increasing prevalence and mortality of Alzheimer's disease. Assessing the causal relationship between modifiable entertainment activity factors and the risk of Alzheimer's disease is important for developing public health measures, but establishing causal relationships in epidemiological data may be challenging.

Methods

This study using the two-sample Mendelian randomization analysis aimed to investigate the causal effect of entertainment activity factors on the risk of Alzheimer's disease. Summary statistics from publicly available genome-wide association studies were used to analyze 14 modifiable entertainment activity. The inverse variance weighted random effects method as the primary analytical method to estimate causal effects was used. Additionally performed MR-Egger, weighted median and weighted model methods to assess the robustness of the results. The reliability of our findings was validated through systematic sensitivity analyses and tests for heterogeneity.

Results

We found significant correlation between time spent using computer (odds ratio 0.998; 95% confidence interval 0.996-0.999; p = 0.013) and Alzheimer's disease, compared to other studied entertainment activities that had no significant causal relationship with Alzheimer's disease.

Conclusion

Our findings support the hypothesis that increased computer use may reduce the risk of Alzheimer's disease, providing potential strategic directions for the prevention of neurodegenerative diseases.

Cerebral blood flow regulation and cognitive performance in hypertension

We examined the relation between transcranial Doppler (TCD) markers of cerebral blood flow regulation and cognitive performance in hypertension (HT) patients to evaluate the predictive value of these markers for cognitive decline. We assessed dynamic cerebral autoregulation (dCA), vasoreactivity to carbon dioxide, and neurovascular coupling (NVC) in the middle (MCA) and posterior (PCA) cerebral arteries of 52 patients. Neuropsychological evaluation included the Montreal Cognitive Assessment and tests covering attention, executive function, processing speed, and memory. Notably, reduced rate time in the PCA significantly predicted better processing speed (p = 0.003). Furthermore, reduced overshoot systolic cerebral blood velocity in the PCA and reduced phase in the VLF range in the MCA (p = 0.021 and p = 0.017, respectively) significantly predicted better memory. Intriguingly, enhanced dCA in the MCA predicted poorer memory performance, while reduced NVC in the PCA predicted both superior processing speed and memory performance. These findings suggest that HT-induced changes in cerebral hemodynamics impact cognitive performance. Further research should verify these observations and elucidate whether these changes represent adaptive responses or neurovascular inefficiency. TCD markers might provide insights into HT-related cognitive decline.

My Parent, Myself, or My Child: Whose Education Matters Most for Trajectories of Cognitive Aging in Middle Age?

The growing body of evidence linking intergenerational education and late-life cognitive decline is almost exclusively from high-income countries, despite rapid intergenerational changes in education in low- and middle-income countries (LMICs). We used data from the Mexican Health and Aging Study (n = 8,822), a cohort study of Mexican adults aged ≥50 years (2001-2018), to evaluate whether parental education (none vs. any formal schooling), one's own education (less than primary school vs. completion of primary school), or an adult child's education (less than high school vs. completion of high school) was associated with verbal memory z scores. We used linear mixed models with inverse probability of attrition weights. Educational attainment in all 3 generations was associated with baseline verbal memory scores, independent of the prior generation's education. Lower parental (β = -0.005, 95% confidence interval: -0.009, -0.002) and respondent (β = -0.013, 95% confidence interval: -0.017, -0.010) educational level were associated with faster decline in delayed (but not immediate) verbal memory z scores. Associations between adult child's education and respondent's verbal memory decline varied by exposure specification. The educational attainment of parents and adult children may influence the cognitive aging of middle-aged and older adults in LMICs. These results have important implications given recent structural shifts in educational attainment in many LMICs.

"Hang Ups, Let Downs, Bad Breaks, Setbacks": Impact of Structural Socioeconomic Racism and Resilience on Cognitive Change Over Time for Persons Racialized as Black

Introduction

Older adults racialized as Black experience higher rates of dementia than those racialized as White. Structural racism produces socioeconomic challenges, described by artist Marvin Gaye as "hang ups, let downs, bad breaks, setbacks" that likely contribute to dementia disparities. Robust dementia literature suggests socioeconomic factors may also be key resiliencies.

Methods

We linked state-level data reflecting the racialized landscape of economic opportunity across the 20th Century from the U.S. Census (1930-2010) with individual-level data on cognitive outcomes from the U.S. Health and Retirement Study participants racialized as Black. A purposive sample of participants born after the Brown v. Board ruling (born 1954-59) were selected who completed the modified Telephone Interview for Cognitive Status between 2010 and 2020 (N=1381). We tested associations of exposure to structural racism and resilience before birth, and during childhood, young-adulthood, and midlife with cognitive trajectories in mid-late life using mixed-effects regression models.

Results

Older adults born in places with higher state-level structural socioeconomic racism experienced a more rapid cognitive decline in later life compared to those with lower levels of exposure. In addition, participants born in places with higher levels of state-level structural socioeconomic resilience experienced slower cognitive change over time than their counterparts.

Discussion

These findings reveal the impact of racist U.S. policies enacted in the past that influence cognitive health over time and dementia risk later in life.

Dementia prevention: the Mendelian randomisation perspective

Understanding the causes of Alzheimer's disease and related dementias remains a challenge. Observational studies investigating dementia risk factors are limited by the pervasive issues of confounding, reverse causation and selection biases. Conducting randomised controlled trials for dementia prevention is often impractical due to the long prodromal phase and the inability to randomise many potential risk factors. In this essay, we introduce Mendelian randomisation as an alternative approach to examine factors that may prevent or delay Alzheimer's disease. Mendelian randomisation is a causal inference method that has successfully identified risk factors and treatments in various other fields. However, applying this method to dementia risk factors has yielded unexpected findings. Here, we consider five potential explanations and provide recommendations to enhance causal inference from Mendelian randomisation studies on dementia. By employing these strategies, we can better understand factors affecting dementia risk.

Lifestyle Modulators of Neuroplasticity in Parkinson's Disease: Evidence in Human Neuroimaging Studies

Parkinson's disease (PD) is a neurodegenerative disease characterized by both motor and non-motor symptoms. A progressive neuronal loss and the consequent clinical impairment lead to deleterious effects on daily living and quality of life. Despite effective symptomatic therapeutic approaches, no disease-modifying therapies are currently available. Emerging evidence suggests that adopting a healthy lifestyle can improve the quality of life of PD patients. In addition, modulating lifestyle factors can positively affect the microstructural and macrostructural brain levels, corresponding to clinical improvement. Neuroimaging studies may help to identify the mechanisms through which physical exercise, dietary changes, cognitive enrichment, and exposure to substances modulate neuroprotection. All these factors have been associated with a modified risk of developing PD, with attenuation or exacerbation of motor and non-motor symptomatology, and possibly with structural and molecular changes. In the present work, we review the current knowledge on how lifestyle factors influence PD development and progression and the neuroimaging evidence for the brain structural, functional, and molecular changes induced by the adoption of positive or negative lifestyle behaviours.

Instrumental variables in real-world clinical studies of dementia and neurodegenerative disease: Systematic review of the subject-matter argumentation, falsification test, and study design strategies to justify a valid instrument

OBJECTIVES

We systematically reviewed how investigators argued for and justified the validity of their instrumental variables (IV) in clinical studies of dementia and neurodegenerative disease.

METHODS

We included studies using IV analysis with observational data to investigate causal effects in clinical research studies of dementia and neurodegenerative disease. We reported the subject-matter argumentation, falsification test, and study design strategies used to satisfy the three assumptions of a valid IV: relevance, exclusion restriction, and exchangeability.

RESULTS

Justification for the relevance assumption was performed in all 12 included studies, exclusion restriction in seven studies, and exchangeability in nine studies. Two subject-matter argumentation strategies emerged from seven studies on the relevance of their IV. All studies except one provided quantitative evidence for the strength of the association between the IV and exposure variable. Four argumentation strategies emerged for exclusion restriction from six studies. Four falsification tests were performed across three studies. Three argumentation strategies emerged for exchangeability across four studies. Nine falsification tests were performed across nine studies. Two notable study design strategies were reported.

CONCLUSION

Our results reinforce IV analysis as a feasible option for clinical researchers in dementia and neurodegenerative disease by clarifying known strategies used to validate an IV.

Effect of Duration of Education on Sexual Activity and the Mediating Role of Illness in Later Life: A Natural Experiment in English Schooling Reform

This study aimed to examine the effect of increases in the duration of education on sexual activity in later life using the instrumental variable approach. Cross-sectional data were obtained from the English Longitudinal Study of Ageing, Wave 6 (2012/2013) for the analysis. The effect of the duration of education on a binary variable for sexual activity in the past month was examined by two-stage least squares estimation using the 1947 schooling reform as the instrument. A total of 1493 participants were included. The 1947 schooling reform significantly extended the duration of education by a mean of 0.86 years (95% confidence interval (CI), 0.52-1.20; F = 24.70) for men and 0.81 years for women (95% CI, 0.54-1.09; F = 33.82). The second-stage regression showed that an additional year of education increased the probability of having sexual activity in the past month by 0.16 points (95% CI, 0.07-0.25) for men and decreased the probability of having sexual activity in the past month by 0.18 points (95% CI, - 0.30- - 0.05) for women. The causal mediation analysis revealed that long-standing illness mediated the mechanism between education and sexual activity, but the mediational effect was clearly observed only for men: the indirect effect for men was 0.10 (95% CI, 0.01-0.20; the proportion mediated, 78.1%) and for women was - 0.16 (95% CI, - 1.23-0.90; the proportion mediated, 97.8%), respectively. This study confirmed the causal effect of education on sexual activity. However, the effect for men and women was completely opposite.

The causal effects of education on adult health, mortality and income: evidence from Mendelian randomization and the raising of the school leaving age

BACKGROUND

On average, educated people are healthier, wealthier and have higher life expectancy than those with less education. Numerous studies have attempted to determine whether education causes differences in later health outcomes or whether another factor ultimately causes differences in education and subsequent outcomes. Previous studies have used a range of natural experiments to provide causal evidence. Here we compare two natural experiments: a policy reform, raising the school leaving age in the UK in 1972; and Mendelian randomization.

METHODS

We used data from 334 974 participants of the UK Biobank, sampled between 2006 and 2010. We estimated the effect of an additional year of education on 25 outcomes, including mortality, measures of morbidity and health, ageing and income, using multivariable adjustment, the policy reform and Mendelian randomization. We used a range of sensitivity analyses and specification tests to assess the plausibility of each method's assumptions.

RESULTS

The three different estimates of the effects of educational attainment were largely consistent in direction for diabetes, stroke and heart attack, mortality, smoking, income, grip strength, height, body mass index (BMI), intelligence, alcohol consumption and sedentary behaviour. However, there was evidence that education reduced rates of moderate exercise and increased alcohol consumption. Our sensitivity analyses suggest that confounding by genotypic or phenotypic confounders or specific forms of pleiotropy are unlikely to explain our results.

CONCLUSIONS

Previous studies have suggested that the differences in outcomes associated with education may be due to confounding. However, the two independent sources of exogenous variation we exploit largely imply consistent causal effects of education on outcomes later in life.

Sufficient component cause simulations: an underutilized epidemiologic teaching tool

Simulation studies are a powerful and important tool in epidemiologic teaching, especially for understanding causal inference. Simulations using the sufficient component cause framework can provide students key insights about causal mechanisms and sources of bias, but are not commonly used. To make them more accessible, we aim to provide an introduction and tutorial on developing and using these simulations, including an overview of translation from directed acyclic graphs and potential outcomes to sufficient component causal models, and a summary of the simulation approach. Using the applied question of the impact of educational attainment on dementia, we offer simple simulation examples and accompanying code to illustrate sufficient component cause-based simulations for four common causal structures (causation, confounding, selection bias, and effect modification) often introduced early in epidemiologic training. We show how sufficient component cause-based simulations illuminate both the causal processes and the mechanisms through which bias occurs, which can help enhance student understanding of these causal structures and the distinctions between them. We conclude with a discussion of considerations for using sufficient component cause-based simulations as a teaching tool.

Marital Histories and Associations With Later-Life Dementia and Mild Cognitive Impairment Risk in the HUNT4 70+ Study in Norway

Objectives: Earlier studies suggest that being married in later life protects against dementia, and that being single in old age increases the risk of dementia. In this study, we examine midlife marital status trajectories and their association with dementia and mild cognitive impairment (MCI) at ages 70 plus using a large population based sample from Norway. Methods: Based on a general population sample linked to population registries (N = 8706), we used multinomial logistic regression to examine the associations between six types of marital trajectories (unmarried, continuously divorced, intermittently divorced, widowed, continuously married, intermittently married) between age 44 and 68 years from national registries and a clinical dementia or a MCI diagnosis after age 70. We estimated relative risk ratios (RRR) and used mediation analyses adjusting for education, number of children, smoking, hypertension, obesity, physical inactivity, diabetes, mental distress, and having no close friends in midlife. Inverse probability weighting and multiple imputations were applied. The population attributable fraction was estimated to assess the potential reduction in dementia cases due to marital histories. Results: Overall, 11.6% of the participants were diagnosed with dementia and 35.3% with MCI. Dementia prevalence was lowest among the continuously married (11.2%). Adjusting for confounders, the risk of dementia was higher for the unmarried (RRR = 1.73; 95% CI: 1.24, 2.40), continuously divorced (RRR = 1.66; 95% CI: 1.14, 2.43), and intermittently divorced (RRR = 1.50; 95% CI: 1.09, 2.06) compared to the continuously married. In general, marital trajectory was less associated with MCI than with dementia. In the counterfactual scenario, where all participants had the same risk of receiving a dementia diagnosis as the continuously married group, there would be 6.0% fewer dementia cases. Discussion: Our data confirm that staying married in midlife is associated with a lower risk of dementia and that divorced people account for a substantial share of dementia cases.

The challenge of dementia prevention trials and the role of quasi-experimental studies

Observational studies have shown consistently that modifiable risk factors during life are associated with increased dementia risk in old age but randomized controlled trials (RCTs) on dementia prevention evaluating the treatment of these risk factors did not find consistent effects on cognitive outcomes. The discrepancy in findings is potentially attributable to inherent differences between the two study designs. Although RCTs are the gold standard for establishing causality, designing and conducting an RCT for dementia prevention is complex. Quasi-experimental studies (QESs) may contribute to investigating causality without randomization. QESs use variation in exposure to a risk factor or intervention in an observational setting to deduct causal effects. Design-specific approaches are used to control for confounding, the main caveat of QESs. In this article we address the challenges, opportunities, and limitations of QESs for research into dementia prevention. HIGHLIGHTS: Despite consistent associations between modifiable risk factors and dementia, the mostly neutral effects of randomized controlled trials (RCTs) challenge the causality of these associations. RCTs in the field of dementia prevention are often problematic due to ethical, practical, or financial constraints, and their results may have limited generalizability. Four quasi-experimental study (QES) designs may be suitable to study causality between risk factors and dementia; we critically appraise these study designs for dementia-prevention studies. We describe how specific QES designs can be used to study the effects of risk-factor modification for 12 known risk factors for dementia.

State-Level Indicators of Childhood Educational Quality and Incident Dementia in Older Black and White Adults

Importance

Higher educational attainment is associated with reduced dementia risk, but the role of educational quality is understudied, presenting a major evidence gap, especially as it may contribute to racial inequities.

Objective

To evaluate the association between state-level educational quality during childhood and dementia risk.

Design, Setting, and Participants

This cohort study analyzed longitudinal data collected from January 1, 1997, through December 31, 2019 (23-year follow-up period). The sample comprised members of Kaiser Permanente Northern California (KPNC), a large integrated health care delivery system, who completed an optional survey during 1964-1972. Eligible individuals were US born; non-Hispanic Black or non-Hispanic White; aged 65 years or older as of January 1, 1996; were still alive; and did not have a dementia diagnosis or lapse in KPNC membership greater than 90 days between January 1 and December 31, 1996.

Exposures

Historical state-level administrative indicators of school quality (school term length, student-teacher ratio, and attendance rates) linked to participants using birth state and birth year (with a 6-year lag) and divided into tertiles using the pooled sample.

Main Outcomes and Measures

Dementia diagnoses from electronic health records between 1997 and 2019 were analyzed between March 1 and August 31, 2022. The associations of educational quality with incident dementia were estimated using Cox proportional hazards regression models.

Results

Among 21 450 KPNC members who participated in the optional survey, individuals born before availability of educational quality records (n = 87) and missing educational attainment (n = 585) were excluded. The final analytic sample was 20 778 individuals (56.5% women, 43.5% men; mean [SD] age, 74.7 [6.5] years; 18.8% Black; 81.2% White; 41.0% with less than high school education). Among Black individuals, 76.2% to 86.1% (vs 20.8%-23.3% of White individuals) attended schools in states in the lowest educational quality tertiles. Highest (vs lowest) educational quality tertiles were associated with lower dementia risk (student-teacher ratio: hazard ratio [HR], 0.88 [95% CI, 0.83-0.94]; attendance rates: HR, 0.80 [95% CI, 0.73-0.88]; term length: HR, 0.79 [95% CI, 0.73-0.86]). Effect estimates did not differ by race and were not attenuated by adjustment for educational attainment.

Conclusions and Relevance

In this cohort study, lower state-average educational quality was more common among Black individuals and associated with higher dementia risk. Differential investment in high-quality education due to structural racism may contribute to dementia disparities.

High school quality is associated with cognition 58 years later

We leveraged a unique school-based longitudinal cohort-the Project Talent Aging Study-to examine whether attending higher quality schools is associated with cognitive performance among older adults in the United States (mean age = 74.8). Participants (n = 2,289) completed telephone neurocognitive testing. Six indicators of high school quality, reported by principals at the time of schooling, were predictors of respondents' cognitive function 58 years later. To account for school-clustering, multilevel linear and logistic models were applied. We found that attending schools with a higher number of teachers with graduate training was the clearest predictor of later-life cognition, and school quality mattered especially for language abilities. Importantly, Black respondents (n = 239; 10.5 percentage) were disproportionately exposed to low quality high schools. Therefore, increased investment in schools, especially those that serve Black children, could be a powerful strategy to improve later life cognitive health among older adults in the United States.

Comparison of sex differences in cognitive function in older adults between high- and middle-income countries and the role of education: a population-based multicohort study

BACKGROUND

The extent to which education explains variations in sex differences in cognitive function between countries at different levels of economic development is unknown. We examined the role of education in sex differences in four cognitive domains in high- and middle-income countries.

METHODS

Analyses were based on 70,846 participants, aged 60 years and older, in cohort studies from a high-income (United States) and four middle-income countries (Mexico, Brazil, China, and India). We used weighted linear models to allow nationally-representative comparisons of sex differences in orientation, memory, attention, and fluency using the United States as the reference, before and after adjustment for education, and after stratification by education.

RESULTS

Females had lower levels of education than males in all countries, particularly in India. Before adjustment for education, sex differences in orientation and attention in all middle-income countries, memory in Brazil, China, and India, and fluency in India were less favourable to females than in the United States (P < 0.010). For example, females outperformed males in memory in the United States (mean difference [male-female scores] = -0.26 standard deviations [95% CI -0.30, -0.22]) but not in China (0.15 [0.09, 0.21]) or India (0.16 [0.13, 0.19]). Adjustment for education attenuated these sex differences. In analyses stratified by education, there were minimal sex differences in the high education group in all countries.

CONCLUSION

Education contributes to larger female disadvantages in cognitive function at older ages in middle-income countries compared with the United States. Gender equity in education is an important target to reduce sex disparities in cognitive function globally.

Duration of Education and Back Pain: Lessons From English Schooling Reforms

This study aimed to examine the associations of increases in the duration of education with back pain using the exogenous variation generated by the English schooling reforms of 1947 and 1972. We analyzed cross-sectional data derived from 9 waves (waves 1-9; 2002-2019) of the English Longitudinal Study of Ageing. An instrumental variables regression using 2-stage least squares with the 2-way cluster-robust standard error was used. The mean severity of back pain, measured using the Numerical Rating Scale, was used as the outcome. A total of 22,868 observations from 5,070 participants were included (the 1947 reform = 16,565 observations from 3,231 participants, mean age = 74.5 years; the 1972 reform = 6,303 observations from 1,839 participants, mean age = 59.3 years). The schooling reforms significantly extended years of school attendance by a mean of 0.57 years for the 1942 reform cohort and 0.66 years for 1972 reform cohort. For participants born within 5 years of the pivotal cohorts, an additional year of education decreased the severity of back pain by 0.78 points (95% confidence interval: 0.65, 0.92) for the 1972 reform cohort. Our finding underscores the importance of the length of education in the reduction of back pain in middle-aged individuals.

Differences in the Cognitive Function of Mexican Adults Aged 60 and Older with Self-Reported Diabetes in 2001 and 2018

BACKGROUND

The prevalence of type 2 diabetes in Mexico has nearly doubled for adults aged ≥60. Increases in education and healthcare resources to manage chronic conditions have contributed to population-level increases in the cognitive functioning of older adults. However, research has not focused on older adults with chronic conditions such as diabetes.

OBJECTIVE

Our objective was to compare the cognitive functioning of Mexican adults aged ≥60 with diabetes in 2001 and 2018.

METHODS

Data came from Mexican Health and Aging Study. Our study used a cross-sectional design and included participants aged ≥60 with self-reported diabetes during the 2001 (n = 1,052, mean age = 68.4, female = 59.6%) and 2018 (n = 2,469, mean age = 70.6, female = 62.0%) observation waves. Five cognitive tests were used to create a score of global cognition. Generalized estimating equations were used to compare global cognition in 2001 to 2018.

RESULTS

Older adults in 2018 had more education and were more likely than older adults in 2001 to take oral medication for diabetes, insulin, and to check blood sugar weekly. Older adults in 2018 had higher global cognition than in 2001 when adjusting for age, gender, education, and health insurance coverage (b = 0.38, SE = 0.02). This statistically significant difference remained after adjusting for health conditions, health behaviors, and diabetes management behaviors.

CONCLUSIONS

Older adults in Mexico with self-reported diabetes in 2018 had higher cognitive function than in 2001. Future research is needed to investigate causes of the cohort differences in cognitive functioning among Mexican older adults with self-reported diabetes.

The long-term relation between physical activity and executive function in the Rotterdam Study

BACKGROUND

Research on the association between physical inactivity and cognitive decline and dementia is dominated by studies with short-term follow-up, that might be biased by reverse causality.

OBJECTIVE

Investigate the long-term association between physical activity, cognition, and the rate of age-associated cognitive decline.

METHODS

We investigated the association between late-life physical activity and executive functioning and rate of decline of executive abilities during follow-up of up to 16 years, in 3553 participants of the prospective Rotterdam Study cohort. Measurement took place in 1997-1999, 2002-2004, 2009-2011, and 2014-2015.

RESULTS

At baseline (age ± 72 years), higher levels of physical activity were associated with higher levels of executive functioning (adjusted mean difference = 0.03, 95% CI: 0.00 ; 0.06, p = 0.03). This difference remained intact up to 16 years of follow-up. The level of physical activity at baseline was unrelated to the rate of decline of executive abilities over time, in the whole group (adjusted mean difference in change_{time*physical activity} = 0.00, 95% CI: -0.00 ; 0.01, p = 0.31). However, stratification by APOE genotype showed that the accelerated decline of executive abilities observed in those with the ApoE-ε4 allele might be attenuated by higher levels of physical activity in late adulthood (ApoE-ε4 carriers: B_{time*physical activity} = 0.01, 95% CI: 0.00 ; 0.01, p = 0.03).

CONCLUSION

Higher levels of physical activity in late adulthood are related to higher levels of executive functioning, up to 16 years of follow-up. Accelerated decline of executive abilities observed in those with the ApoE-ε4 allele might be mitigated by higher levels of physical activity.

Observational studies in Alzheimer disease: bridging preclinical studies and clinical trials

Recent high-profile failures of Alzheimer disease treatments at the clinical trial stage have led to renewed efforts to identify and test novel interventions for Alzheimer disease and related dementias (ADRD). In this Perspective, we highlight the importance of including well-designed observational studies as part of these efforts. Observational research is an important cornerstone for gathering evidence on risk factors and causes of ADRD; this evidence can then be combined with data from preclinical studies and randomized controlled trials to inform the development of effective interventions. Observational study designs can be particularly beneficial for hypothesis generation, posing questions that are unethical or impractical for a trial setting, studying life-course associations, research in populations typically not included in trials, and public health surveillance. Here, we discuss each of these situations in the specific context of ADRD research. We also highlight novel approaches to enhance causal inference and provide a timely discussion on how observational epidemiological studies help provide a bridge between preclinical studies and successful interventions for ADRD.

Educational Attainment Polygenic Scores: Examining Evidence for Gene-Environment Interplay with Adolescent Alcohol, Tobacco and Cannabis Use

Genes associated with educational attainment may be related to or interact with adolescent alcohol, tobacco and cannabis use. Potential gene-environment interplay between educational attainment polygenic scores (EA-PGS) and adolescent alcohol, tobacco, and cannabis use was evaluated with a series of regression models fitted to data from a sample of 1871 adult Australian twins. All models controlled for age, age², cohort, sex and genetic ancestry as fixed effects, and a genetic relatedness matrix was included as a random effect. Although there was no evidence that adolescent alcohol, tobacco or cannabis use interacted with EA-PGS to influence educational attainment, there was a significant, positive gene-environment correlation with adolescent alcohol use at all PGS thresholds (ps <.02). Higher EA-PGS were associated with an increased likelihood of using alcohol as an adolescent (ΔR² ranged from 0.5% to 1.1%). The positive gene-environment correlation suggests a complex relationship between educational attainment and alcohol use that is due to common genetic factors.

The impact of women's off-farm employment on depressive symptoms: Evidence from rural China

While China's economy has grown rapidly in recent decades, urban-rural inequalities in mental health have persisted, and depression is more prevalent among rural women. Using a nationally-representative survey data in China, this paper investigates the impact of women's off-farm employment on their depressive symptoms. Results from instrumental variable and individual fixed effects estimation show that women's participation in off-farm employment leads to a significant reduction in depressive symptoms. We further take into account the confounding effects of working conditions, and the main results are robust. Moreover, off-farm employment enhances women's mental health mainly through pathways including increased absolute income, higher self-perceived relative income, more frequent healthy behaviors, increased likelihood of health investment, and obtaining more formal social support. Further evidence suggests that the depression-reducing effect of off-farm employment is more effective for those with more severe depressive symptoms, middle-aged and elderly persons, and women with lower body mass index. The findings have important implications for preventing depressive disorders and improving mental health in China and other developing countries.

The causes and consequences of Alzheimer's disease: phenome-wide evidence from Mendelian randomization

Alzheimer's disease (AD) has no proven causal and modifiable risk factors, or effective interventions. We report a phenome-wide association study (PheWAS) of genetic liability for AD in 334,968 participants of the UK Biobank study, stratified by age. We also examined the effects of AD genetic liability on previously implicated risk factors. We replicated these analyses in the HUNT study. PheWAS hits and previously implicated risk factors were followed up in a Mendelian randomization (MR) framework to identify the causal effect of each risk factor on AD risk. A higher genetic liability for AD was associated with medical history and cognitive, lifestyle, physical and blood-based measures as early as 39 years of age. These effects were largely driven by the APOE gene. The follow-up MR analyses were primarily null, implying that most of these associations are likely to be a consequence of prodromal disease or selection bias, rather than the risk factor causing the disease.

Variation in Population Attributable Fraction of Dementia Associated With Potentially Modifiable Risk Factors by Race and Ethnicity in the US

IMPORTANCE

Identifying modifiable risk factors that are associated with dementia burden across racial and ethnic groups in the population can yield insights into the potential effectiveness of interventions in preventing dementia and reducing disparities.

OBJECTIVE

To calculate the population attributable fraction (PAF) of dementia associated with 12 established modifiable risk factors for all US adults, as well as separately by race and ethnicity.

DESIGN, SETTING, AND PARTICIPANTS

This cross-sectional study used survey data from nationally representative samples of US adults. PAFs were calculated using relative risks and prevalence estimates for 12 risk factors. Relative risks were taken from meta-analyses, as reported in a 2020 systematic review. Prevalence estimates for risk factors were derived from nationally representative cross-sectional survey data collected between 2011 and 2018. Combined PAFs were adjusted for risk factor communality using weights derived from the Atherosclerosis Risk in Communities (ARIC) study (1987-2018). Analyses were conducted May through October 2021.

EXPOSURES

Low education, hearing loss, traumatic brain injury, hypertension, excessive alcohol consumption, obesity, smoking, depression, social isolation, physical inactivity, diabetes, and air pollution.

MAIN OUTCOMES AND MEASURES

PAF for each dementia risk factor, a combined PAF, and the decrease in the number of prevalent dementia cases in 2020 that would be expected given a 15% proportional decrease in each exposure.

RESULTS

Among all US adults, an estimated 41.0% (95% CI, 22.7%-55.9%) of dementia cases were attributable to 12 risk factors. A 15% proportional decrease in each risk factor would reduce dementia prevalence in the population by an estimated 7.3% (95% CI, 3.7%-10.9%). The estimated PAF was greater for Black and Hispanic than it was for White and Asian individuals. The greatest attributable fraction of dementia cases was observed for hypertension (PAF, 20.2%; 95% CI, 6.3%-34.4%), obesity (PAF, 20.9%; 95% CI, 13.0%-28.8%), and physical inactivity (PAF, 20.1%; 95% CI, 9.1%-29.6%). These factors were also highest within each racial and ethnic group, although the proportions varied.

CONCLUSIONS AND RELEVANCE

A large fraction of dementia cases in the US were associated with potentially modifiable risk factors, especially for Black and Hispanic individuals. Targeting and reducing these risk factors may curb the projected rise in dementia cases over the next several decades.

Geospatial Analysis of a COVID-19 Outbreak at the University of Wisconsin - Madison: Potential Role of a Cluster of Local Bars

We combined smartphone mobility data with census track-based reports of positive case counts to study a coronavirus disease 2019 (COVID-19) outbreak at the University of Wisconsin–Madison campus, where nearly 3000 students had become infected by the end of September 2020. We identified a cluster of twenty bars located at the epicentre of the outbreak, in close proximity to campus residence halls. Smartphones originating from the two hardest-hit residence halls (Sellery-Witte), where about one in five students were infected, were 2.95 times more likely to visit the 20-bar cluster than smartphones originating in two more distant, less affected residence halls (Ogg-Smith). By contrast, smartphones from Sellery-Witte were only 1.55 times more likely than those from Ogg-Smith to visit a group of 68 restaurants in the same area [rate ratio 1.91, 95% confidence interval (CI) 1.29–2.85, P < 0.001]. We also determined the per-capita rates of visitation to the 20-bar cluster and to the 68-restaurant comparison group by smartphones originating in each of 21 census tracts in the university area. In a multivariate instrumental variables regression, the visitation rate to the bar cluster was a significant determinant of the per-capita incidence of positive severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) tests in each census tract (elasticity 0.88, 95% CI 0.08–1.68, P = 0.032), while the restaurant visitation rate showed no such relationship. The potential super-spreader effects of clusters or networks of places, rather than individual sites, require further attention.

Sex-related associations between body height and cognitive impairment among low-income elderly adults in rural China: a population-based cross-sectional study

BACKGROUND

Body height is a marker of childhood health and cumulative net nutrition during growth periods. However, sex-specific associations between body height and cognitive impairment are not well known in northern rural China.

METHODS

We assessed sex differences in the association between body height and cognitive impairment in a low-income elderly population in rural China. A population-based cross-sectional study was conducted from April 2014 to August 2014 to collect basic information from elderly residents aged 60 years and older in rural areas of Tianjin, China. Body height and Mini Mental State Examination (MMSE) scores were measured, and the relationships between these variables were assessed.

RESULTS

A total of 1081 residents with a mean age of 67.7 years were enrolled in this study. After adjusting for age, educational attainment, smoking status, drinking status, and the presence of hypertension, diabetes, and hypercholesterolemia, higher body height was found to be associated with a decreased prevalence of cognitive impairment in elderly men. Each 1-dm increase in height was associated with a 37% decrease in the prevalence of cognitive impairment. However, there was no significant association between body height and cognitive impairment among elderly women.

CONCLUSION

In conclusion, shorter body height was related to cognitive impairment independently of age, educational attainment, lifestyle factors, and health-related comorbid factors among low-income elderly men in rural China. Accordingly, shorter elderly men may be targeted for effective dementia prevention in rural China.

Dementia and disadvantage in the USA and England: population-based comparative study

OBJECTIVES

To compare dementia prevalence and how it varies by socioeconomic status (SES) across the USA and England.

DESIGN

Population-based comparative study.

SETTING

Non-Hispanic whites aged over 70 population in the USA and England.

PARTICIPANTS

Data from the Health and Retirement Study and the English Longitudinal Study of Ageing, which are harmonised, nationally representative panel studies. The sample includes 5330 and 3147 individuals in the USA and England, respectively.

MAIN OUTCOME MEASURES

Between country differences in age-gender standardised dementia prevalence, across the SES gradient. Dementia prevalence was estimated in each country using an algorithm based on an identical battery of demographic, cognitive and functional measures.

RESULTS

Dementia prevalence is higher among the disadvantaged in both countries, with the USA being more unequal according to four measures of SES. Overall prevalence was lower in England at 9.7% (95% CI 8.9% to 10.6%) than the USA at 11.2% (95% CI 10.6% to 11.8%), a difference of 1.4 percentage points (pp) (p=0.0055). Most of the between country difference is driven by the bottom of the SES distribution. In the lowest income decile individuals in the USA had 7.3 pp (p<0.0001) higher prevalence than in England. Once past health factors and education were controlled for, most of the within country inequalities disappeared; however, the cross-country difference in prevalence for those in lowest income decile remained disproportionately high.

CONCLUSIONS

There is inequality in dementia prevalence according to income, wealth and education in both the USA and England. England has lower dementia prevalence and a less steep SES gradient. Most of the cross-country difference is concentrated in the lowest SES group, which provides evidence that disadvantage in the USA is a disproportionately high risk factor for dementia.

Does Prolonged Education Causally Affect Dementia Risk When Adult Socioeconomic Status Is Not Altered? A Swedish Natural Experiment in 1.3 Million Individuals

Intervening on modifiable risk factors to prevent dementia is of key importance, since progress-modifying treatments are not currently available. Education is inversely associated with dementia risk, but causality and mechanistic pathways remain unclear. We aimed to examine the causality of this relationship in Sweden using, as a natural experiment, data on a compulsory schooling reform that extended primary education by 1 year for 70% of the population between 1936 and 1949. The reform introduced substantial exogenous variation in education that was unrelated to pupils' characteristics. We followed 18 birth cohorts (n = 1,341,842) from 1985 to 2016 (up to ages 79-96 years) for a dementia diagnosis in the National Inpatient and Cause of Death registers and fitted Cox survival models with stratified baseline hazards at the school-district level, chronological age as the time scale, and cohort indicators. Analyses indicated very small or negligible causal effects of education on dementia risk (main hazard ratio = 1.01, 95% confidence interval: 0.98, 1.04). Multiple sensitivity checks considering only compliers, the pre-/post- design, differences in health-care-seeking behavior, and the impact of exposure misclassification left the results essentially unaltered. The reform had limited effects on further adult socioeconomic outcomes, such as income. Our findings suggest that without mediation through adult socioeconomic position, education cannot be uncritically considered a modifiable risk factor for dementia.

Do the Benefits of Educational Attainment for Late-life Cognition Differ by Racial/Ethnic Group?: Evidence for Heterogenous Treatment Effects in the Kaiser Healthy Aging and Diverse Life Experience (KHANDLE) Study

INTRODUCTION

Educational attainment is associated with late-life cognitive performance and dementia; few studies have examined diverse racial/ethnic groups to assess whether the association differs by race/ethnicity.

METHODS

We investigated whether the association between educational attainment and cognition differed between White, Black, Asian, and Latino participants in the Kaiser Healthy Aging and Diverse Life Experiences study (n=1348). Covariate-adjusted multivariable linear regression models examined domains of verbal episodic memory, semantic memory, and executive functioning.

RESULTS

We observed significant effect heterogeneity by race/ethnicity only for verbal episodic memory (P=0.0198), for which any schooling between high school and college was beneficial for White, Asian, and Black participants, but not Latino participants. We found no evidence of heterogeneity for semantic memory or executive function.

DISCUSSION

With the exception of Latino performance on verbal episodic memory, more education consistently predicted better cognitive scores to a similar extent across racial/ethnic groups, despite likely heterogenous educational and social experiences.

Sex differences and the role of education in cognitive ageing: analysis of two UK-based prospective cohort studies

BACKGROUND

Previous studies have shown an excess risk of Alzheimer's disease and related dementias among women. Education is thought to have a causal association with dementia onset. We aimed to investigate the role of education in influencing sex differences in cognitive ageing.

METHODS

We analysed data from two prospective cohort studies in the UK; the English Longitudinal Study of Ageing (ELSA) and the Whitehall II study, to assess sex differences in cognitive performance and cognitive decline by birth cohort (birth year 1930-38, 1939-45, or 1946-55), before and after adjustment for education, and by high and low education level. Memory was assessed using immediate recall, for which data were available from all waves of the ELSA (2002-14) and Whitehall II (1997-2015) studies. Fluency was assessed using a semantic fluency test based on an animal naming task, with data available from all waves of the Whitehall II study and waves one to five (2002-10) and wave seven (2014) of the ELSA study. Cognitive scores were standardised separately in each study based on the mean and SD of the corresponding test among participants aged 50-59 years with secondary education.

FINDINGS

15 924 participants were included from the two studies. In pooled analyses, women had better memory scores than men in all birth cohorts, irrespective of adjustment for education (eg, at age 60 years, birth cohort 1930-38, mean difference between sexes [male scores minus female scores] -0·25 SDs [95% CI -0·32 to -0·19] after adjustment for education), and in both education level groups. Memory decline was faster in men than in women (at age 60 years, birth cohort 1946-55, mean difference in 13-year change -0·15 SDs [-0·20 to -0·09]; after adjustment for education -0·14 SDs [-0·20 to -0·08]). Men had better fluency scores than women in earlier birth cohorts and in the low education group (at age 60 years, birth cohort 1930-38, mean difference 0·20 SDs [95% CI 0·05 to 0·36]); but women had better fluency scores than men in later birth cohorts and in the high education group (at age 60 years, birth cohort 1946-55, mean difference -0·17 SDs [-0·24 to -0·10]). No sex differences were observed for fluency decline.

INTERPRETATION

Our findings suggest that decreasing disparities between sexes in education, due to secular increases in educational opportunities, could attenuate sex differences in dementia risk and cognitive decline in the future.

FUNDING

National Institute on Aging, National Institutes of Health; UK Medical Research Council; British Heart Foundation; and National Institute for Health Research.

Association of Late Life Depression, (Non-) Modifiable Risk and Protective Factors with Dementia and Alzheimer's Disease: Literature Review on Current Evidences, Preventive Interventions and Possible Future Trends in Prevention and Treatment of Dementia

The number of people living with dementia and Alzheimer’s disease is growing rapidly, making dementia one of the biggest challenges for this century. Many studies have indicated that depression plays an important role in development of dementia, including Alzheimer’s disease; depression, especially, during the late life may either increase the risk of dementia or even being its prodromal stage. Despite a notably large number of carried observational studies and/or clinical trials, the association between the late life depression and dementia remains, due to the complexity of their relationship, still unclear. Moreover, during past two decades multiple other (non-)modifiable risk and possibly protective factors such as the hypertension, social engagement, obesity, level of education or physical (in)activity have been identified and their relationship with the risk for development of dementia and Alzheimer’s disease has been extensively studied. It has been proposed that to understand mechanisms of dementia and Alzheimer’s disease pathogeneses require their multifactorial nature represented by these multiple factors to be considered. In this review, we first summarize the recent literature findings on roles of the late life depression and the other known (non-)modifiable risk and possibly protective factors in development of dementia and Alzheimer’s disease. Then, we provide evidences supporting hypotheses that (i) depressive syndromes in late life may indicate the prodromal stage of dementia (Alzheimer’s disease) and, (ii) the interplay among the multiple (non-)modifiable risk and protective factors should be considered to gain a better understanding of dementia and Alzheimer’s disease pathogeneses. We also discuss the evidences of recently established interventions considered to prevent or delay the prodromes of dementia and provide the prospective future directions in prevention and treatment of dementia and Alzheimer’s disease using both the single-domain and multidomain interventions.

Social contact, social support, and cognitive health in a population-based study of middle-aged and older men and women in rural South Africa

BACKGROUND

Several theories seek to explain how social connections and cognitive function are interconnected in older age. These include that social interaction protects against cognitive decline, that cognitive decline leads to shedding of social connections and that cognitive decline leads to increased instrumental support. We investigated how patterns of social contact, social support and cognitive health in rural South Africa fit with these three theories.

METHOD

We used data from the baseline of "Health and Aging in Africa: a Longitudinal Study of an INDEPTH community in South Africa" (HAALSI), a population-based study of 5059 individuals aged ≥ 40 years. We evaluated how a range of egocentric social connectedness measures varied by respondents' cognitive function.

RESULTS

We found that respondents with lower cognitive function had smaller, denser social networks that were more local and more kin-based than their peers. Lower cognitive function was associated with receipt of less social support generally, but this difference was stronger for emotional and informational support than for financial and physical support. Impairment was associated with greater differences among those aged 40-59 and those with any (versus no) educational attainment.

CONCLUSIONS

The patterns we found suggest that cognitively impaired older adults in this setting rely on their core social networks for support, and that theories relating to social connectedness and cognitive function developed in higher-income and higher-education settings may also apply in lower-resource settings elsewhere.

Cognitive Resilience to Alzheimer's Disease Pathology in the Human Brain

BACKGROUND

Past research has focused on risk factors for developing dementia, with increasing recognition of "resilient" people who live to old age with intact cognitive function despite pathological features of Alzheimer's disease (AD).

OBJECTIVE

To evaluate demographic factors, mid-life characteristics, and non-AD neuropathology findings that may be associated with cognitive resilience to AD pathology.

METHODS

We analyzed data from 276 autopsy cases with intermediate or high levels of AD pathology from the Adult Changes in Thought study. We defined cognitive resilience as having Cognitive Abilities Screening Instrument scores ≥86 within two years of death and no clinical dementia diagnosis; non-resilient people had dementia diagnoses from AD or other causes before death. We compared mid-life characteristics, demographics, and additional neuropathology findings between resilient and non-resilient people. We used multivariable logistic regression to estimate odds ratios (ORs) with 95% confidence intervals (CIs) for being resilient compared to not being resilient adjusting for demographic and neuropathology factors.

RESULTS

We classified 68 (25%) people as resilient and 208 (75%) as not resilient. A greater proportion of resilient people had a college degree (50%) compared with non-resilient (32%, p = 0.01). The odds of being resilient were significantly increased among people with a college education (OR = 2.01, 95% CI = 1.01-3.99) and significantly reduced among people with additional non-AD neuropathology findings such as hippocampal sclerosis (OR = 0.28, 95% CI = 0.09-0.89) and microinfarcts (OR = 0.34, 95% CI = 0.15-0.78).

CONCLUSION

Increased education and absence of non-AD pathology may be independently associated with cognitive resilience, highlighting the importance of evaluating co-morbid factors in future research on mechanisms of cognitive resilience.

Accelerating the Search for Interventions Aimed at Expanding the Health Span in Humans: The Role of Epidemiology

BACKGROUND

Extensive work in basic and clinical science suggests that biological mechanisms of aging are causally related to the development of disease and disability in late life. Modulation of the biological mechanisms of aging can extend both life span and health span in animal models, but translation to humans has been slow.

METHODS

Summary of workshop proceedings from the 2018-2019 Epidemiology of Aging Workshop hosted by the Intramural Research Program at the National Institute on Aging.

RESULTS

Epidemiologic studies play a vital role to progress in this field, particularly in evaluating new risk factors and measures of biologic aging that may influence health span, as well as developing relevant outcome measures that are robust and relevant for older individuals.

CONCLUSIONS

Appropriately designed epidemiological studies are needed to identify targets for intervention and to inform study design and sample size estimates for future clinical trials designed to promote health span.

Education and adolescent cognitive ability as predictors of dementia in a cohort of Danish men

BACKGROUND

An association between education and dementia is well-established but it is unclear whether education is associated with dementia after accounting for early life cognitive ability and whether there is a joint effect, such that the risk associated with one of the exposures depends on the value of the other. We examined separate and joint associations of adolescent cognitive ability and educational attainment with risk of dementia among Danish men born between 1939 and 1959.

METHODS

Men (N = 477,421) from the Danish Conscription Database were followed for dementia from the age 60 for up to 17 years via patient and prescription registry linkages. Exposure measures included cognitive ability assessed at the conscript board examination around age 18 and highest educational level (low: 0-10 year, medium: 10-13 years, high: ≥13 years) at age 30 from registry records. Associations with dementia diagnosis were estimated in Cox proportional hazards models adjusted for birth year and age at conscript board examination. Interaction was assessed on the multiplicative scale by including a product term between the two exposure measures and on the additive scale by calculating relative excess risk due to interaction (RERI) between different levels of the exposure measures.

RESULTS

Compared to men in the high education group hazard ratio [HR] for men in the medium and low group were 1.21 (95% confidence interval [CI]: 1.13, 1.30) and 1.34 (95% CI: 1.24, 1.45), respectively when not adjusting for cognitive ability. Additional adjustment for cognitive ability attenuated the magnitude of the associations, but they remained significant (education medium: HR = 1.10, 95% CI: 1.02, 1.19 and education low: HR = 1.12, 95% CI: 1.02, 1.22). A 10% higher cognitive ability score was associated with a 3.8% lower hazard of dementia (HR = 0.962; 95% CI: 0.957, 0.967), and the magnitude of the association only changed marginally after adjustment for education. Men in the low education group with relatively low cognitive ability were identified as a high-risk subgroup for dementia. The increased risk associated with exposure to both risk factors did, however, not significantly depart from the sum of risk experienced by men only exposed to one of the risk factors (estimates of RERI were not significantly different from 0) and no significant evidence of either additive or multiplicative interactions was found.

CONCLUSIONS

In conclusion, the results suggest that education and cognitive ability protect against the risk of dementia independently of one another and that increases in educational attainment may at least partially offset dementia risk due to low cognitive ability.

Influence of age and education on a performance-based measure of everyday functioning

Sociodemographic variables, such as age and education, influence the determination of impairment on neuropsychological tests, but their influence on impairment determinations for tests of everyday functioning is less well defined. Existing studies suggest that older age and lower education levels are associated with worse everyday functioning when assessed by self- or collateral-report. This relationship, however, has not been thoroughly investigated with performance-based methods of everyday functioning. This study aimed to determine the influence of sociodemographic factors on the Functional Impact Assessment (FIA), a performance-based measure of everyday functioning that includes measures of both accuracy and speed. Seventy-three healthy individuals, ages 42 - 88 years, completed the FIA and an additional everyday functioning self-report questionnaire (Functional Activities Questionnaire). Using a multiple regression statistical approach, age and education predicted overall FIA accuracy, while age alone predicted FIA speed. Sociodemographic variables continued to predict FIA performance when controlling for overall cognitive functioning. Sociodemographic variables were unrelated to FAQ scores. These findings indicate that age and education are associated with scores on a performance-based test of everyday functioning. Demographic corrections may improve accuracy in determining functional impairment, but more research is needed given the complex relationships among demographic factors, healthy aging, and dementia risk.

State School Policies as Predictors of Physical and Mental Health: A Natural Experiment in the REGARDS Cohort

We used differences in state school policies as natural experiments to evaluate the joint influence of educational quantity and quality on late-life physical and mental health. Using US Census microsample data, historical measures of state compulsory schooling and school quality (term length, student-teacher ratio, and attendance rates) were combined via regression modeling on a scale corresponding to years of education (policy-predicted years of education (PPYEd)). PPYEd values were linked to individual-level records for 8,920 black and 14,605 white participants aged ≥45 years in the Reasons for Geographic and Racial Differences in Stroke study (2003-2007). Linear and quantile regression models estimated the association between PPYEd and Physical Component Summary (PCS) and Mental Component Summary (MCS) from the Short Form Health Survey. We examined interactions by race and adjusted for sex, birth year, state of residence at age 6 years, and year of study enrollment. Higher PPYEd was associated with better median PCS (β = 1.28, 95% confidence interval (CI): 0.40, 1.49) and possibly better median MCS (β = 0.46, 95% CI: -0.01, 0.94). Effect estimates were higher among black (vs. white) persons (PCS × race interaction, β = 0.22, 95% CI: -0.62, 1.05, and MCS × race interaction, β = 0.18; 95% CI: -0.08, 0.44). When incorporating both school quality and duration, this quasiexperimental analysis found mixed evidence for a causal effect of education on health decades later.

Cohort differences on the CVLT-II and CVLT3: Evidence of a negative Flynn effect on the attention/working memory and learning trials

OBJECTIVE

Although cohort effects on IQ measures have been investigated extensively, studies exploring cohort differences on verbal memory tests, and the extent to which they are influenced by socioenvironmental changes across decades (e.g. educational attainment; ethnic makeup), have been limited.

METHOD

We examined differences in performance between the normative samples of the CVLT-II from 1999 and the CVLT3 from 2016 to 2017 on the immediate- and delayed-recall trials, and we explored the degree to which verbal learning and memory skills might be influenced by the cohort year in which norms were collected versus demographic factors (e.g. education level).

RESULTS

Multivariate analysis of variance tests and follow-up univariate tests yielded evidence for a negative cohort effect (also referred to as negative Flynn effect) on performance, controlling for demographic factors (p = .001). In particular, findings revealed evidence of a negative Flynn effect on the attention/working memory and learning trials (Trial 1, Trial 2, Trial 3, Trials 1-5 Total, List B; ps < .007), with no significant cohort differences found on the delayed-recall trials. As expected, education level, age group, and ethnicity were significant predictors of CVLT performance (ps < .01). Importantly, however, there were no interactions between cohort year of norms collection and education level, age group, or ethnicity on performance.

CONCLUSIONS

The clinical implications of the present findings for using word list learning and memory tests like the CVLT, and the potential role of socioenvironmental factors on the observed negative Flynn effect on the attention/working memory and learning trials, are discussed.

Educational attainment and allostatic load in later life: Evidence using genetic markers

Education is strongly correlated with health outcomes in older adulthood. Whether the impact of education expansion improves health remains unclear due to a lack of clarity over the causal relationship. Previous health research within the social sciences has tended to use specific activities of daily living or self-reported health status. This study uses a broader and objective health measure - allostatic load (AL) - to take into consideration the exposures that accumulate throughout the life course. This paper applies a Mendelian Randomization (MR) approach to identify causality in relation to education on health as measured by AL. Using the Health and Retirement Study 2008 (N=3935), we adopt a polygenic score built from genetic variants associated with years of education. To test whether our analyses violate the exclusion assumption, we further run MR Egger regressions to test for bias from pleiotropy. We also explore the potential pathways between education and AL, including smoking, drinking, marital length, health insurance, etc. Using this genetic instrument, we find a 0.3 unit (19% of a standard deviation) reduction in AL per year of schooling. The effect is mainly driven by BMI and Hba1c. Smoking and marital stability are two potential pathways that also causally influenced by education. If our main and sensitivity analyses are valid, the results find support that a higher level of education is causally related to better health in older adulthood.

School Context in Adolescence and Cognitive Functioning 50 Years Later

To advance understanding of how social inequalities from childhood might contribute to cognitive aging, we examined the extent to which school context in adolescence was associated with individuals' cognitive performance more than 50 years later. Using data from 3,012 participants in the Wisconsin Longitudinal Study (WLS), we created an aggregate measure of school-level structural advantage, with indicators such as the proportion of teachers who had at least five years of teaching experience and spending per pupil. Multilevel models indicated that secondary school advantage was associated with small benefits in language/executive function at age 65 among older adults who had lower academic achievement in secondary school. Findings suggest that school advantage is a developmental context of adolescence that has modest implications for intracohort differences in aspects of later life cognition.

Who dies early? Education, mortality and causes of death in Norway

We estimated the effects of education on mortality and causes of death in Norway. We identified causal effects by exploiting the staggered implementation of a school reform that increased the length of compulsory education from seven to nine years. The municipality-level education data were combined with complete records of all deaths from 1960 to 2015 from the Norwegian Cause of Death Registry. These data covered the entire life span of persons aged 16-64. One additional year of education caused a reduction in mortality of about 10% for men. The effect was negligible for women. For men, a large part of the effect was due to fewer accidental deaths. We suggest two explanations for this finding. First, there are differences in risk-taking behaviour between people with a high level of education and those with a low level. Second, more education leads to upward occupational mobility. This mobility is mainly from occupations for which the risk of accidents is high to occupations for which the risk is low. Our results supported the fundamental cause theory. This is because education had a stronger effect on mortality for causes of death that are preventable than for causes of death that are not preventable. More education had no effect on the probability of dying of diseases that were amenable to medical intervention only. This gives some support to our results that patients are treated equally, independent of their level of education. This may be due to the large public involvement in financing and provision of health services.

Understanding the correlation between Alzheimer's Disease polygenic risk, wealth, and the composition of wealth holdings

We investigate how the genetic risk of developing Alzheimer's Disease (AD) relates to saving behavior. Using nationally representative data from the 1996-2014 Health and Retirement Study (HRS), we find that genetic predisposition for AD correlates with, but is not causally related to how older individuals' hold wealth in different asset types. People with a higher AD polygenic risk score (PGS) hold roughly 20 per cent less wealth in IRAs and contribute about 24 percent less to IRAs between survey periods. We hypothesize that people with a high risk of AD choose different portfolios: (i) because they know their genetic risk of developing AD from parental history, (ii) because they have the lower cognitive capacity, and (iii) because they indirectly learn about their genetic predisposition for AD as they age. Our extended model results show that the first two hypotheses do not account for the observed correlation. Consistent with the third hypothesis, the interaction between age and the AD PGS accounts for the correlation between genetic traits and asset holdings. Our findings have far-reaching implications for researchers using genetic data: when indirect learning about own predispositions is possible, correlations between genes and choices must be interpreted with caution.

Cognitive Performance Among Older Persons in Japan and the United States

OBJECTIVE

To compare cognitive performance among Japanese and American persons, aged 68 years and older, using two nationally representative studies and to examine whether differences can be explained by differences in the distribution of risk factors or in their association with cognitive performance.

DESIGN

Nationally representative studies with harmonized collection of data on cognitive functioning.

SETTING

Nihon University Japanese Longitudinal Study of Aging and the US Health and Retirement Study.

PARTICIPANTS

A total of 1953 Japanese adults and 2959 US adults, aged 68 years or older.

MEASUREMENTS

Episodic memory and arithmetic working memory are measured using immediate and delayed word recall and serial 7s.

RESULTS

Americans have higher scores on episodic memory than Japanese people (0.72 points on a 20-point scale); however, when education is controlled, American and Japanese people did not differ. Level of working memory was higher in Japan (0.36 on a 5-point scale) than in the United States, and the effect of education on working memory was stronger among Americans than Japanese people. There are no differences over the age of 85 years.

CONCLUSION

Even with large differences in educational attainment and a strong effect of education on cognitive functioning, the overall differences in cognitive functioning between the United States and Japan are modest. Differences in health appear to have little effect on national differences in cognition. J Am Geriatr Soc 68:354-361, 2020.

Quality and quantity: The association of state-level educational policies with later life cardiovascular disease

Education is a powerful predictor of cardiovascular morbidity and mortality. While the majority of the literature has focused on years of educational attainment or degree attainment, fewer studies examine the role of educational quality in the prevention of cardiovascular disease (CVD). We tested the hypothesis that average state-level educational quality was associated with CVD, linking state-level data on educational quality with individual demographic and health data from multiple waves of the National Health and Nutrition Examination Survey (N = 34,770). We examined thirteen CVD-related outcomes-including blood pressure, cholesterol, and heart attack-to understand the multiple pathways through which educational quality may influence CVD. The primary predictor was a composite index of educational quality, combining state-level measures of student-teacher ratios, per-pupil expenditures, and school term length. We fit multivariable models, regressing each outcome on the educational quality composite index and adjusting for individual- and state-level covariates. We also assessed whether the association between state educational quality and CVD differed for less educated individuals. Overall, higher educational quality was associated with less smoking (OR = 0.86, 95%CI: 0.77, 0.97), but there was no statistically significant association for the other 12 outcomes. Interaction tests indicated that less educated individuals benefited less from higher educational quality relative to those with more education for several outcomes. Our study suggests that state-level educational quality is not strongly associated with CVD, and that this null association overall may mask heterogeneous benefits that accrue disproportionately to those with higher levels of education.

The role of education in a vascular pathway to episodic memory: brain maintenance or cognitive reserve?

Educational attainment is associated with cognition among older adults, but this association is complex and not well understood. While associated with better cognition among healthy adults, more education predicts faster decline in older adults with cognitive impairment. Education may influence cognitive functioning through mechanisms involving brain maintenance (BM: reduced age-related pathology) or cognitive reserve (CR: altered pathology-cognition association). We examined evidence for each mechanism by quantifying main and interaction effects of education within a well-studied pathway involving systolic blood pressure, white matter hyperintensities (WMH), and episodic memory in 2 samples without dementia at the baseline (total N = 1136). There were no effects of education on systolic blood pressure or WMH, suggesting a lack of evidence for BM. In the sample less likely to progress to dementia, education attenuated the effect of WMH on memory at the baseline. In the sample more likely to progress to dementia, education exacerbated this effect at the baseline. These moderations provide evidence for a CR mechanism and are consistent with previous findings of faster decline once CR is depleted.

Differential associations between state-level educational quality and cardiovascular health by race: Early-life exposures and late-life health

Cardiovascular diseases (CVD) are patterned by educational attainment but educational quality is rarely examined. Educational quality differences may help explain racial disparities. Health and Retirement Study respondent data (1992-2014; born 1900-1951) were linked to state- and year-specific educational quality measures when the respondent was 6 years old. State-level educational quality was a composite of state-level school term length, student-to-teacher ratio, and per-pupil expenditure. CVD-related outcomes were self-reported (N = 24,339) obesity, heart disease, stroke, ever-smoking, high blood pressure, diabetes and objectively measured (N = 10,704) uncontrolled blood pressure, uncontrolled blood sugar, total cholesterol, high-density lipoprotein cholesterol (HDL), and C-reactive protein. Race/ethnicity was classified as White, Black, or Latino. Cox models fit for dichotomous time-to-event outcomes and generalized estimating equations for continuous outcomes were adjusted for individual and state-level confounders. Heterogeneities by race were evaluated using state-level educational quality by race interaction terms; race-pooled, race by educational quality interaction, and race-specific estimates were calculated. In race-pooled analyses, higher state-level educational quality was protective for obesity (HR = 0.92; 95%CI(0.87,0.98)). In race-specific estimates for White Americans, state-level educational quality was protective for high blood pressure (HR = 0.95; 95%CI(0.91,0.99). Differential relationships among Black compared to White Americans were observed for obesity, heart disease, stroke, smoking, high blood pressure, and HDL cholesterol. In race-specific estimates for Black Americans, higher state-level educational quality was protective for obesity (HR = 0.88; 95%CI(0.84,0.93)), but predictive of heart disease (HR = 1.07; 95%CI(1.01,1.12)), stroke (HR = 1.20; 95%CI(1.08,1.32)), and smoking (HR = 1.05; 95%CI(1.02,1.08)). Race-specific hazard ratios for Latino and Black Americans were similar for obesity, stroke, and smoking. Better state-level educational quality had differential associations with CVD by race. Among minorities, better state-level educational quality was predominately associated with poorer CVD outcomes. Results evaluate the 1900-1951 birth cohorts; secular changes in the racial integration of schools since the 1950s, means results may not generalize to younger cohorts.

Which Risk Factors Causally Influence Dementia? A Systematic Review of Mendelian Randomization Studies

Background:

Numerous risk factors for dementia are well established, though the causal nature of these associations remains unclear.

Objective:

To systematically review Mendelian randomization (MR) studies investigating causal relationships between risk factors and global cognitive function or dementia.

Methods:

We searched five databases from inception to February 2017 and conducted citation searches including MR studies investigating the association between any risk factor and global cognitive function, all-cause dementia or dementia subtypes. Two reviewers independently assessed titles and abstracts, full-texts, and study quality.

Results:

We included 18 MR studies investigating education, lifestyle factors, cardiovascular factors and related biomarkers, diabetes related and other endocrine factors, and telomere length. Studies were of predominantly good quality, however eight received low ratings for sample size and statistical power. The most convincing causal evidence was found for an association of shorter telomeres with increased risk of Alzheimer’s disease (AD). Causal evidence was weaker for smoking quantity, vitamin D, homocysteine, systolic blood pressure, fasting glucose, insulin sensitivity, and high-density lipoprotein cholesterol. Well-replicated associations were not present for most exposures and we cannot fully discount survival and diagnostic bias, or the potential for pleiotropic effects.

Conclusions:

Genetic evidence supported a causal association between telomere length and AD, whereas limited evidence for other risk factors was largely inconclusive with tentative evidence for smoking quantity, vitamin D, homocysteine, and selected metabolic markers. The lack of stronger evidence for other risk factors may reflect insufficient statistical power. Larger well-designed MR studies would therefore help establish the causal status of these dementia risk factors.

Long-term effects of compulsory schooling on physical, mental and cognitive ageing: a natural experiment

BACKGROUND

Longer schooling is associated with better physical, mental and cognitive functioning, but there is controversy as to whether these associations are causal. We examine the long-term health impact of a policy that increased compulsory schooling by 2 years in France for cohorts born on or after January 1953, offering a natural experiment.

METHODS

Data came from Constances, a randomly selected cohort of the French population assessed for cognition, depressive symptoms and physical functioning at ages 45 and older (n=18 929). We use a Regression Discontinuity Design to estimate the impact of increased schooling duration on health. Cognition was measured based on five validated neuropsychological tests and combined into an overall score. The Center for Epidemiological Studies Depression scale was used to assess depressive symptoms levels. Physical functioning was included as finger tapping, hand grip strength and walking speed.

RESULTS

The reform increased average schooling, particularly among participants from disadvantaged families. Estimates suggest that for men, this reform improved cognitive scores (β=0.15, 95% CI 0.02 to 0.27), but had no impact on physical functioning. Among women, the reform did not increase cognitive scores or physical functioning but led to higher levels of depressive symptoms (β=1.52, 95% CI 0.32 to 2.72). Results were robust to a range of sensitivity analyses.

CONCLUSION

These findings highlight the need to carefully consider the potential limits of policies that increase the length of compulsory schooling as strategies to improve population health.