Racial and ethnic differences in the association between depressive symptoms and cognitive outcomes in older adults: Findings from KHANDLE and STAR

INTRODUCTION

Depressive symptoms are associated with higher risk of dementia, but how they impact cognition in diverse populations is unclear.

METHODS

Asian, Black, Latino, or White participants (n = 2227) in the Kaiser Healthy Aging and Diverse Life Experiences (age 65+) and the Study of Healthy Aging in African Americans (age 50+) underwent up to three waves of cognitive assessments over 4 years. Multilevel models stratified by race/ethnicity were used to examine whether depressive symptoms were associated with cognition or cognitive decline and whether associations differed by race/ethnicity.

RESULTS

Higher depressive symptoms were associated with lower baseline verbal episodic memory scores (-0.06, 95% CI: -0.12, -0.01; -0.15, 95% CI: -0.25, -0.04), and faster decline annually in semantic memory (-0.04, 95% CI: -0.07, -0.01; -0.10, 95% CI: -0.15, -0.05) for Black and Latino participants. Depressive symptoms were associated with lower baseline but not decline in executive function.

DISCUSSION

Depressive symptoms were associated with worse cognitive outcomes, with some evidence of heterogeneity across racial/ethnic groups.

HIGHLIGHTS

We examined whether baseline depressive symptoms were differentially associated with domain-specific cognition or cognitive decline by race/ethnicity. Depressive symptoms were associated with worse cognitive scores for all racial/ethnic groups across different domains examined. Higher depressive symptoms were associated with faster cognitive decline for semantic memory for Black and Latino participants. The results suggest a particularly harmful association between depressive symptoms and cognition in certain racial/ethnic groups.

Contribution of Global Amyloid-PET Imaging for Predicting Future Cognition in the MEMENTO Cohort

BACKGROUND AND OBJECTIVES

Global amyloid-PET is associated with cognition and cognitive decline, but most research on this association does not account for past cognitive information. We assessed the prognostic benefit of amyloid-PET measures for future cognition when prior cognitive assessments are available, evaluating the added value of amyloid measures beyond information on multiple past cognitive assessments.

METHODS

The French MEMENTO cohort (a cohort of outpatients from French research memory centers to improve knowledge on Alzheimer disease and related disorders) includes older outpatients with incipient cognitive changes, but no dementia diagnosis at inclusion. Global amyloid burden was assessed using positron emission tomography (amyloid-PET) for a subset of participants; semiannual cognitive testing was subsequently performed. We predicted mini-mental state examination (MMSE) scores using demographic characteristics (age, sex, marital status, and education) alone or in combination with information on prior cognitive measures. The added value of amyloid burden as a predictor in these models was evaluated with percent reduction of the mean squared error (MSE). All models were conducted separately for evaluating the added value of dichotomous amyloid positivity status compared with a continuous amyloid-standardized uptake-value ratio.

RESULTS

Our analytic sample comprised 510 individuals who underwent amyloid-PET scans with at least 4 MMSE assessments. The mean age at the PET scan was 71.6 (standard deviation 7.4) years; 60.7% were female. The median follow-up was 4.6 years (interquartile range: 0.9 years). Adding amyloid burden when adjusting for only demographic characteristics reduced the MSE of predictions by 5.08% (95% CI 0.97%-10.86%) and 12.64% (95% CI 3.35%-25.28%) for binary and continuous amyloid, respectively. If the model included 1 past MMSE measure, the MSE improvement was 3.51% (95% CI 1.01%-7.28%) when adding binary amyloid and 8.83% (95% CI 2.63%-16.37%) when adding continuous amyloid. Improvements in model fit were smaller with the addition of amyloid burden when more than 1 past cognitive assessment was included. For all models incorporating past cognitive assessments, differences in predictions amounted to a fraction of 1 MMSE point on average.

DISCUSSION

In a clinical setting, global amyloid burden did not appreciably improve cognitive predictions when past cognitive assessments were available.

TRIAL REGISTRATION INFORMATION

ClinicalTrials.gov Identifier: NCT02164643.

Spouses of individuals living with mild cognitive impairment or dementia in the United States: A descriptive, population-based study

BACKGROUND

Little is known about the population of individuals who live with a spouse with cognitive impairment (CI) or dementia.

METHODS

Using the US Health and Retirement Study, 2000 to 2018, we estimated the population of adults ≥ 50 years old co-residing with a spouse with probable CI/dementia. We described their socio-demographic and health characteristics and quantified socio-demographic inequities.

RESULTS

Among community-dwelling adults ≥ 50 years old, 6% of women and 4% of men co-resided with a spouse with probable CI/dementia. Among those who were married/partnered, the prevalence of spousal dementia was greater for Black and Hispanic adults compared to their White counterparts, and for those with lower versus higher educational attainment. Among spouses, activities of daily living disability, depression, and past 2-year hospitalization was common.

DISCUSSION

Millions of older adults, disproportionately Black and Hispanic people and people with lower levels of educational attainment, live with a spouse with CI while also facing their own major health challenges.

Association between social vulnerability and place of death during the first 2 years of COVID-19 in Massachusetts

We investigated the relationship between individual-level social vulnerability and place of death during the infectious disease emergency of the COVID-19 pandemic in Massachusetts. Our research represents a unique contribution by matching individual-level death certificates with COVID-19 test data to analyse differences in distributions of place of death.

Does a Cancer Diagnosis in Mid-to-Later Life Modify Racial Disparities in Memory Aging?

BACKGROUND

It is unknown whether an incident cancer diagnosis differentially impacts acute and long-term memory aging between older White and Black Americans.

METHODS

Incident cancer diagnoses and memory (immediate and delayed recall, combined with proxy-reported memory) were assessed at biennial study interviews in the US Health and Retirement Study (N=14,235, 1998-2016). We used multivariable segmented linear mixed-effects models to evaluate the rate of change in standardized memory score (SD/decade) in the years before, acutely at the time of, and in the years following an incident cancer diagnosis, compared to cancer-free adults, by race.

RESULTS

Black participants experienced faster memory decline than White participants (cancer-free group: -1.211 vs. -1.077; P<0.0001). An incident cancer diagnosis was associated with an acute memory drop in White, but not Black participants (-0.065 vs. 0.024; P<0.0001). However, White cancer survivors experienced slower memory decline than cancer-free White adults before and after diagnosis, but this memory advantage was not observed among Black cancer survivors.

CONCLUSIONS

Racial disparities in memory aging are not modified by an incident cancer diagnosis. The acute cancer-related memory decline and long-term memory advantage experienced by White, but not Black, cancer survivors relative to cancer-free older adults, requires further investigation.

Tutorial on directed acyclic graphs

Directed acyclic graphs (DAGs) are an intuitive yet rigorous tool to communicate about causal questions in clinical and epidemiologic research and inform study design and statistical analysis. DAGs are constructed to depict prior knowledge about biological and behavioral systems related to specific causal research questions. DAG components portray who receives treatment or experiences exposures; mechanisms by which treatments and exposures operate; and other factors that influence the outcome of interest or which persons are included in an analysis. Once assembled, DAGs - via a few simple rules - guide the researcher in identifying whether the causal effect of interest can be identified without bias and, if so, what must be done either in study design or data analysis to achieve this. Specifically, DAGs can identify variables that, if controlled for in the design or analysis phase, are sufficient to eliminate confounding and some forms of selection bias. DAGs also help recognize variables that, if controlled for, bias the analysis (e.g., mediators or factors influenced by both exposure and outcome). Finally, DAGs help researchers recognize insidious sources of bias introduced by selection of individuals into studies or failure to completely observe all individuals until study outcomes are reached. DAGs, however, are not infallible, largely owing to limitations in prior knowledge about the system in question. In such instances, several alternative DAGs are plausible, and researchers should assess whether results differ meaningfully across analyses guided by different DAGs and be forthright about uncertainty. DAGs are powerful tools to guide the conduct of clinical research.

Racial/Ethnic Disparities in Young Adulthood and Midlife Cardiovascular Risk Factors and Late-life Cognitive Domains: The Kaiser Healthy Aging and Diverse Life Experiences (KHANDLE) Study

BACKGROUND

Midlife cardiovascular risk factors (CVRF) increase dementia risk. Less is known about whether CVRF identified before midlife impact late-life cognition in diverse populations.

METHODS

Linear regression models examined hypertension, hyperlipidemia, and overweight/obesity at ages 30 to 59 with late-life executive function, semantic memory, verbal episodic memory, and global cognition in a cohort of Asians, blacks, Latinos, and whites (n=1127; mean age=75.8, range=65 to 98). Models adjusted for age at CVRF, age at cognitive assessment, sex, race/ethnicity, participant education, and parental education.

RESULTS

Overall, 34% had 1 CVRF at ages 30 to 59; 19% had 2+. Blacks (26%) and Latinos (23%) were more likely to have 2+ CVRF than Asians (14%) or whites (13%). Having 2+ CVRF was associated with lower global cognition [β=-0.33; 95% confidence interval (CI)=-0.45, -0.21], executive function (β=-0.26; 95% CI=-0.39, -0.13), verbal episodic memory (β=-0.34; 95% CI=-0.48, -0.20), and semantic memory (β=-0.20; 95% CI=-0.33, -0.07). Interaction by age (P=0.06) indicated overweight/obesity was negatively associated with executive function at ages 30 to 39 but not at ages 40 to 59. Race/ethnic-specific effects showed disparities in CVRF prevalence impact population disparities in late-life cognition.

CONCLUSION

Being overweight/obese in early adulthood and having 2+ CVRF in early adulthood/midlife are modifiable targets to redress racial/ethnic disparities in cognitive impairment and dementia.

Elevated Depressive Symptoms and the Risk of Stroke among the Mexican Older Population

BACKGROUND/OBJECTIVES

Several longitudinal studies in high-income countries suggest that depression increases stroke risk. However, few prior studies have evaluated this association in low- and middle-income countries (LMICs), where rapidly aging populations may have markedly different vascular risk profiles.

DESIGN

Prospective cohort study.

SETTING

The Mexican Health and Aging Study is a national population-based study of older adults in Mexico.

PARTICIPANTS

A total of 10,693 Mexican adults aged 50 and older enrolled in 2001 with no history of prior stroke.

MEASUREMENTS

Depressive symptoms were assessed with a modified 9-item Centers for Epidemiologic Studies Depression Scale (elevated depressive symptom cutoff ≥5) in 2001 and 2003. We evaluated associations between baseline and short-term (2-year) changes in elevated depressive symptoms (categorized as stable low, recently remitted, recent-onset, or stable high symptoms) with incident self-reported or next-of-kin reported doctor-diagnosed stroke through 2015 using Cox proportional hazards models and sensitivity analyses applying inverse probability weights.

RESULTS

Over an average follow-up of 11.4 years (standard deviation = 4.2), 10,693 respondents reported 546 incident strokes. Individuals with elevated baseline depressive symptoms experienced a moderately higher hazard of incident stroke (hazard ratio [HR] = 1.13; 95% confidence interval [CI] = .95-1.36) compared with those without elevated baseline depressive symptoms. In analyses of short-term changes in elevated depressive symptoms (n = 8,808; 414 incident stokes), participants with recent-onset (HR = 1.38; 95% CI = 1.06-1.81) or stable high (HR = 1.42; 95% CI = 1.10-1.84) elevated depressive symptoms had a greater hazard of incident stroke compared to those with stable low/no depressive symptoms, whereas recently remitted (HR = 1.01; 95% CI = .74-1.37) symptoms was not associated with stroke hazard.

CONCLUSION

Strategies to reduce depressive symptoms merit evaluation as approaches to prevent stroke in middle-income countries. Findings are similar to those in high-income countries but should be replicated in other LMICs.

Gut Bacterial Diversity and Growth among Preschool Children in Burkina Faso

There is a lack of empirical, prospective human data on the gut microbiome and its relationship with growth, especially in low- and middle-income countries. We prospectively assessed the association between gut microbial diversity and short-term growth in a cohort of preschool children in Burkina Faso to better characterize whether there is any evidence that changes in gut microbial diversity may affect growth. Data were obtained from a randomized controlled trial evaluating the effect of antibiotic administration on gut microbial diversity in preschool children. We followed up the enrolled children for 35 days, with anthropometric measurements at baseline and day 35 and microbial diversity measured at baseline and day 9 (analytic sample, N = 155). We estimated linear mixed-effects regression models with household random intercepts to assess the association of Simpson's and Shannon's alpha diversity with measures of change in anthropometry (e.g., ponderal growth since baseline) and absolute anthropometric measurements (e.g., day 35 weight). We did not find evidence that alpha gut microbial diversity was associated with growth or absolute anthropometric measurements after adjusting for confounding variables. Effect estimates were close to the null (P ≥ 0.15 for all fully adjusted comparisons), with the association between Simpson's alpha diversity and day 35 height (cm) farthest from the null (coefficient = -0.03, 95% CI: -0.07, 0.01). The change in gut microbial diversity also was not associated with the change in anthropometry in crude or adjusted models. Future research is needed to explore whether gut diversity has an impact on growth over a longer time period, in both healthy and malnourished children.

Abstract WP482: Early Life Exposure to the Stroke Belt and Later Life Incident Cognitive Impairment: The Reasons for Geographic and Racial Differences in Stroke (REGARDS) Study

Introduction: Incidence of cognitive impairment is higher for residents of the Stroke Belt (SB) compared to those living outside it, but the importance of timing of SB residence is unclear.

Methods: Participants were aged 45+ yrs, and enrolled in 2003-2007 in REGARDS. Cognition was assessed annually, by telephone, using the Six-Item Screener (SIS) in 11,488 black or white stroke-free participants currently living in the SB, and 8,949 currently living outside of the SB. Incident cognitive impairment was defined as SIS score of < 4 at last assessment among participants with initial SIS >4. Exposures were defined as SB residence all years, some years, or no years of childhood (ages 0-18) and early adulthood (ages 19-30). Demographic adjusted logistic regression models were stratified by SB residence at enrollment, and were used to estimate the demographic-adjusted odds of incident cognitive impairment.

Results: Among those currently residing in the SB, childhood residence outside the SB for some (OR = 0.82; 95% CI: 0.68 - 0.99) or all (OR = 0.76; 95% CI: 0.65 - 0.90) of the time predicted lower odds of incident cognitive impairment. Similarly, early adulthood residence outside the SB for some (OR = 0.86; 95% CI: 0.74 - 0.98) or all (OR = 0.70; 95% CI: 0.58 - 0.84) of the time predicted lower incident cognitive impairment. Conversely, for those currently living outside the SB, the risk of incident cognitive impairment was higher for those who had spent their entire early adulthood in the SB (OR = 1.51; 95% CI: 1.01 - 2.57), with non-significant increased risk for childhood exposure or some early adulthood exposure to the SB (table).

Conclusions: These findings suggest that early residence in the SB during childhood or early adulthood increases the risk of cognitive impairment regardless of place of residence in later adulthood. Further research is needed to determine the characteristics of early SB life that are linked to later adult cognitive impairment.

Will biomarker-based diagnosis of Alzheimer's disease maximize scientific progress? Evaluating proposed diagnostic criteria

A recently published framework for the diagnosis of Alzheimer's disease (AD) in research studies would allow diagnosis on the sole basis of two biomarkers (β-amyloid and pathologic tau), even in people with no objective or subjective memory or cognitive changes. This revision will have substantial implications for future Alzheimer's research, and the changes should be rigorously evaluated before widespread adoption. We propose three principles for evaluating any revision to diagnostic frameworks for AD: (1) does the revision improve the validity of the diagnosis; (2) does the revision improve the reliability or reduce the expense of the diagnosis; and (3) will the revision foster innovative and rigorous research across populations. The new diagnostic framework is unlikely to achieve any of these goals. Instead, it has the potential to handicap future researchers, and slow progress towards identifying effective strategies to prevent or treat AD.

Compartmental Model Diagrams as Causal Representations in Relation to DAGs

Compartmental model diagrams have been used for nearly a century to depict causal relationships in infectious disease epidemiology. Causal directed acyclic graphs (DAGs) have been used more broadly in epidemiology since the 1990s to guide analyses of a variety of public health problems. Using an example from chronic disease epidemiology, the effect of type 2 diabetes on dementia incidence, we illustrate how compartmental model diagrams can represent the same concepts as causal DAGs, including causation, mediation, confounding, and collider bias. We show how to use compartmental model diagrams to explicitly depict interaction and feedback cycles. While DAGs imply a set of conditional independencies, they do not define conditional distributions parametrically. Compartmental model diagrams parametrically (or semiparametrically) describe state changes based on known biological processes or mechanisms. Compartmental model diagrams are part of a long-term tradition of causal thinking in epidemiology and can parametrically express the same concepts as DAGs, as well as explicitly depict feedback cycles and interactions. As causal inference efforts in epidemiology increasingly draw on simulations and quantitative sensitivity analyses, compartmental model diagrams may be of use to a wider audience. Recognizing simple links between these two common approaches to representing causal processes may facilitate communication between researchers from different traditions.

Post-traumatic stress disorder and cardiometabolic disease: improving causal inference to inform practice

Post-traumatic stress disorder (PTSD) has been declared 'a life sentence' based on evidence that the disorder leads to a host of physical health problems. Some of the strongest empirical research - in terms of methodology and findings - has shown that PTSD predicts higher risk of cardiometabolic diseases, specifically cardiovascular disease (CVD) and type 2 diabetes (T2D). Despite mounting evidence, PTSD is not currently acknowledged as a risk factor by cardiovascular or endocrinological medicine. This view is unlikely to change absent compelling evidence that PTSD causally contributes to cardiometabolic disease. This review suggests that with developments in methods for epidemiological research and the rapidly expanding knowledge of the behavioral and biological effects of PTSD the field is poised to provide more definitive answers to questions of causality. First, we discuss methods to improve causal inference using the observational data most often used in studies of PTSD and health, with particular reference to issues of temporality and confounding. Second, we consider recent work linking PTSD with specific behaviors and biological processes, and evaluate whether these may plausibly serve as mechanisms by which PTSD leads to cardiometabolic disease. Third, we evaluate how looking more comprehensively into the PTSD phenotype provides insight into whether specific aspects of PTSD phenomenology are particularly relevant to cardiometabolic disease. Finally, we discuss new areas of research that are feasible and could enhance understanding of the PTSD-cardiometabolic relationship, such as testing whether treatment of PTSD can halt or even reverse the cardiometabolic risk factors causally related to CVD and T2D.

Frailty modifies effectiveness of psychosocial intervention in recovery from stroke

Objective : To evaluate the impact of a psychosocial intervention on instrumental activities of daily living, physical performance, cognition and mortality after stroke.

Design : A randomized clinical trial.

Setting : Patients were recruited from hospitals and rehabilitation centres; the intervention took place in subjects' homes.

Subjects : Two-hundred and ninety-one stroke survivors over age 45. One-hundred and forty-six subjects were assigned to the intervention and 145 subjects were assigned to usual care.

Intervention : Up to 16 meetings conducted over six months in the patient's home (approximately weekly for 12 weeks, followed by tri-weekly sessions for another 12 weeks). Sessions lasted approximately 1 hour and included, when possible, the entire support system (stroke survivor, primary caregiver, additional family and friends, and professional caregivers).

Main outcome measures : Instrumental activities of daily living, physical performance, and cognition were assessed six months post stroke; mortality was assessed at an average of 47 months post stroke.

Results : No significant differences in outcomes were observed between the intervention and usual care groups when analysing the total study population. Among non-frail participants (n = 156), subjects randomized to treatment had better scores on instrumental activities of daily living (mean score among treated = 12.4 (standard deviation (SD) = 2.1), mean score among usual care subjects = 11.3 (SD = 2.9), P-value for difference in means = 0.01) and reduced risk of mortality (P = 0.03) than subjects randomized to usual care.

Conclusion : While there is evidence that the treatment benefited healthier subgroups, results also show evidence that the treatment was not effective, and possibly harmful, in frail subgroups.

Body mass index and cognitive function: the potential for reverse causation

OBJECTIVE

Higher late life body mass index (BMI) is unrelated to or even predicts lower risk of dementia in late life, a phenomenon that may be explained by reverse causation due to weight loss during preclinical phases of dementia. We aim to investigate the association of baseline BMI and changes in BMI with dementia in a large prospective cohort, and to examine whether weight loss predicts cognitive function.

METHODS

Using a national cohort of adults average age 58 years at baseline in 1994 (n=7029), we investigated the associations between baseline BMI in 1994 and memory scores from 2000 to 2010. We also examined the association of BMI change from 1994 to 1998 with memory scores from 2000 to 2010. Last, to investigate reverse causation, we examined whether memory scores in 1996 predicted BMI trajectories from 2000 to 2010.

RESULTS

Baseline overweight predicted better memory scores 6 to 16 years later (β=0.012, 95% confidence interval (CI)=0.001; 0.023). Decline in BMI predicted lower memory scores over the subsequent 12 years (β=-0.026, 95% CI= -0.041; -0.011). Lower memory scores at mean age 60 years in 1996 predicted faster annual rate of BMI decline during follow-up (β=-0.158 kg m(-2) per year, 95% CI= -0.223; -0.094).

CONCLUSION

Consistent with reverse causation, greater decline in BMI over the first 4 years of the study was associated with lower memory scores over the next decade and lower memory scores was associated with a decline in BMI. These findings suggest that preclinical dementia predicts weight loss for people as early as their late 50s.

Do genetic risk scores for body mass index predict risk of phobic anxiety? Evidence for a shared genetic risk factor

BACKGROUND

Obesity and anxiety are often linked but the direction of effects is not clear.

METHOD

Using genetic instrumental variable (IV) analyses in 5911 female participants from the Nurses' Health Study (NHS, initiated 1976) and 3697 male participants from the Health Professional Follow-up Study (HPFS, initiated 1986), we aimed to determine whether obesity increases symptoms of phobic anxiety. As instrumental variables we used the fat mass and obesity-associated (FTO) gene, the melanocortin 4 receptor (MC4R) gene and a genetic risk score (GRS) based on 32 single nucleotide polymorphisms (SNPs) that significantly predict body mass index (BMI). 'Functional' GRSs corresponding with specific biological pathways that shape BMI (adipogenesis, appetite and cardiopulmonary) were considered. The main outcome was phobic anxiety measured by the Crown Crisp Index (CCI) in 2004 in the NHS and in 2000 in the HPFS.

RESULTS

In observational analysis, a 1-unit higher BMI was associated with higher phobic anxiety symptoms [women: β = 0.05, 95% confidence interval (CI) 0.030-0.068; men: β = 0.04, 95% CI 0.016-0.071). IV analyses showed that BMI was associated with higher phobic anxiety symptoms in the FTO-instrumented analysis (p = 0.005) but not in the GRS-instrumented analysis (p = 0.256). Functional GRSs showed heterogeneous, non-significant effects of BMI on phobic anxiety symptoms.

CONCLUSIONS

Our findings do not provide conclusive evidence in favor of the hypothesis that higher BMI leads to higher levels of phobic anxiety, but rather suggest that genes that influence obesity, in particular FTO, may have direct effects on phobic anxiety, and hence that obesity and phobic anxiety may share common genetic determinants.

Genetic vulnerability to diabetes and obesity: does education offset the risk?

The prevalence of type 2 diabetes (T2D) and obesity has recently increased dramatically. These common diseases are likely to arise from the interaction of multiple genetic, socio-demographic and environmental risk factors. While previous research has found genetic risk and education to be strong predictors of these diseases, few studies to date have examined their joint effects. This study investigates whether education modifies the association between genetic background and risk for type 2 diabetes (T2D) and obesity. Using data from non-Hispanic Whites in the Health and Retirement Study (HRS, n = 8398), we tested whether education modifies genetic risk for obesity and T2D, offsetting genetic effects; whether this effect is larger for individuals who have high risk for other (unobserved) reasons, i.e., at higher quantiles of HbA1c and BMI; and whether effects differ by gender. We measured T2D risk using Hemoglobin A1c (HbA1c) level, and obesity risk using body-mass index (BMI). We constructed separate genetic risk scores (GRS) for obesity and diabetes respectively based on the most current available information on the single nucleotide polymorphism (SNPs) confirmed as genome-wide significant predictors for BMI (29 SNPs) and diabetes risk (39 SNPs). Linear regression models with years of schooling indicate that the effect of genetic risk on HbA1c is smaller among people with more years of schooling and larger among those with less than a high school (HS) degree compared to HS degree-holders. Quantile regression models show that the GRS × education effect systematically increased along the HbA1c outcome distribution; for example the GRS × years of education interaction coefficient was -0.01 (95% CI = -0.03, 0.00) at the 10th percentile compared to -0.03 (95% CI = -0.07, 0.00) at the 90th percentile. These results suggest that education may be an important socioeconomic source of heterogeneity in responses to genetic vulnerability to T2D.

Occupational solvent exposure and cognition: does the association vary by level of education?

OBJECTIVE

Chronic occupational solvent exposure is associated with long-term cognitive deficits. Cognitive reserve may protect solvent-exposed workers from cognitive impairment. We tested whether the association between chronic solvent exposure and cognition varied by educational attainment, a proxy for cognitive reserve.

METHODS

Data were drawn from a prospective cohort of French national gas and electricity (GAZEL) employees (n = 4,134). Lifetime exposure to 4 solvent types (chlorinated solvents, petroleum solvents, benzene, and nonbenzene aromatic solvents) was assessed using a validated job-exposure matrix. Education was dichotomized at less than secondary school or below. Cognitive impairment was defined as scoring below the 25th percentile on the Digit Symbol Substitution Test at mean age 59 (SD 2.8; 88% of participants were retired at testing). Log-binomial regression was used to model risk ratios (RRs) for poor cognition as predicted by solvent exposure, stratified by education and adjusted for sociodemographic and behavioral factors.

RESULTS

Solvent exposure rates were higher among less-educated patients. Within this group, there was a dose-response relationship between lifetime exposure to each solvent type and RR for poor cognition (e.g., for high exposure to benzene, RR = 1.24, 95% confidence interval 1.09-1.41), with significant linear trends (p < 0.05) in 3 out of 4 solvent types. Recency of solvent exposure also predicted worse cognition among less-educated patients. Among those with secondary education or higher, there was no significant or near-significant relationship between any quantification of solvent exposure and cognition.

CONCLUSIONS

Solvent exposure is associated with poor cognition only among less-educated individuals. Higher cognitive reserve in the more-educated group may explain this finding.

Depressive symptoms predict incident stroke independently of memory impairments

BACKGROUND

We evaluated whether depressive symptoms predict the onset of first stroke independently of memory impairment. We conceptualized memory impairment as a marker of preexisting cerebrovascular disease. We hypothesized that if depressive symptoms are causally related to stroke through mechanisms unrelated to cerebrovascular disease, depressive symptoms should predict stroke independently of memory impairment.

METHODS

Incidence of first stroke was assessed with self or proxy reports from 19,087 participants in the Health and Retirement Study cohort (1,864 events). Elevated depressive symptoms (3+ on an 8-item Centers for the Epidemiologic Study of Depression scale) and memory impairment (score of ≤6 on a combined immediate and delayed recall of a 10-word list) were used as predictors of incident stroke in Cox survival models with adjustment for sociodemographic and cardiovascular risk factors.

RESULTS

After adjustment for sociodemographic and cardiovascular risk factors, elevated depressive symptoms (hazard ratio = 1.25; 95% confidence interval 1.12-1.39) and memory impairment (hazard ratio = 1.26; 95% confidence interval 1.13-1.41) each predicted stroke incidence in separate models. Hazard ratios were nearly unchanged and remained significant (1.23 for elevated depressive symptoms and 1.25 for memory impairment) when models were simultaneously adjusted for both elevated depressive symptoms and memory impairment. Elevated depressive symptoms also predicted stroke when restricting analyses to individuals with median memory score or better.

CONCLUSIONS

Memory impairments and depressive symptoms independently predict stroke incidence. Memory impairment may reflect undiagnosed cerebrovascular disease. These results suggest that depressive symptoms might be directly related to stroke rather than merely indicating preexisting cerebrovascular disease.

Does childhood schooling affect old age memory or mental status? Using state schooling laws as natural experiments

BACKGROUND

The association between schooling and old age cognitive outcomes such as memory disorders is well documented but, because of the threat of reverse causation, controversy persists over whether education affects old age cognition. Changes in state compulsory schooling laws (CSL) are treated as natural experiments (instruments) for estimating the effect of education on memory and mental status among the elderly. Changes in CSL predict changes in average years of schooling completed by children who are affected by the new laws. These educational differences are presumably independent of innate individual characteristics such as IQ.

METHODS

CSL-induced changes in education were used to obtain instrumental variable (IV) estimates of education's effect on memory (n = 10,694) and mental status (n = 9751) for white, non-Hispanic US-born Health and Retirement Survey participants born between 1900 and 1947 who did not attend college.

RESULTS

After adjustment for sex, birth year, state of birth and state characteristics, IV estimates of education's effect on memory were large and statistically significant. IV estimates for mental status had very wide confidence intervals, so it was not possible to draw meaningful conclusions about the effect of education on this outcome.

CONCLUSIONS

Increases in mandatory schooling lead to improvements in performance on memory tests many decades after school completion. These analyses condition on individual states, so differences in memory outcomes associated with CSL changes cannot be attributed to differences between states. Although unmeasured state characteristics that changed contemporaneously with CSL might account for these results, unobserved genetic variation is unlikely to do so.

APOE epsilon 4 allele predicts faster cognitive decline in mild Alzheimer disease

OBJECTIVE

To determine whether APOE epsilon 4 predicts rate of cognitive change in incident and prevalent Alzheimer disease (AD).

METHODS

Individuals were recruited from two longitudinal cohort studies-the Washington Heights and Inwood Columbia Aging Project (WHICAP; population-based) and the Predictors Study (clinic-based)--and were followed for an average of 4 years. Three samples of participants diagnosed with AD, with diverse demographic characteristics and baseline cognitive functioning, were studied: 1) 199 (48%) of the incident WHICAP cases; 2) 215 (54%) of the prevalent WHICAP cases; and 3) 156 (71%) of the individuals diagnosed with AD in the Predictors Study. Generalized estimating equations were used to test whether rate of cognitive change, measured using a composite cognitive score in WHICAP and the Mini-Mental State Examination in Predictors, varied as a function of epsilon 4 status in each sample.

RESULTS

The presence of at least one epsilon 4 allele was associated with faster cognitive decline in the incident population-based AD group (p = 0.01). Parallel results were produced for the two prevalent dementia samples only when adjusting for disease severity or excluding the most impaired participants from the analyses.

CONCLUSION

APOE epsilon 4 may influence rate of cognitive decline most significantly in the earliest stages of Alzheimer disease.