An Early and Unequal Decline: Life Course Trajectories of Cognitive Aging in the United States

Objectives: Cognitive aging is a lifelong process with implications for Alzheimer's disease and dementia. This study aims to fill major gaps in research on the natural history of and social disparities in aging-related cognitive decline over the life span. Methods: We conducted integrative data analysis of four large U.S. population-based longitudinal studies of individuals aged 12 to 105 followed over two decades and modeled age trajectories of cognitive function in multiple domains. Results: We found evidence for the onset of cognitive decline in the 4th decade of life, varying gender differences with age, and persistent disadvantage among non-Hispanic Blacks, Hispanics, and those without college education. We further found improvement in cognitive function across 20th century birth cohorts but widening social inequalities in more recent cohorts. Discussion: These findings advance an understanding of early life origins of dementia risk and invite future research on strategies for promoting cognitive health for all Americans.

Associations Between Traumatic Brain Injury and Cognitive Decline Among Older Male Veterans: A Twin Study

BACKGROUND AND OBJECTIVES

Traumatic brain injuries (TBIs) are associated with increased risk of dementia, but whether lifetime TBI influences cognitive trajectories in later life is less clear. Cognitive interventions after TBI may improve cognitive trajectories and delay dementia. Because twins share many genes and environmental factors, we capitalize on the twin study design to examine the association between lifetime TBI and cognitive decline.

METHODS

Participants were members of the National Academy of Sciences-National Research Council's Twin Registry of male veterans of World War II with self or proxy-reported history of TBI and with up to 4 observations over 12 years of the modified Telephone Interview for Cognitive Status (TICS-m). We used linear random-effects mixed models to analyze the association between TBI and TICS-m in the full sample and among co-twins discordant for TBI. Additional TBI predictor variables included number of TBIs, severity (loss of consciousness [LOC]), and age of first TBI (age <25 vs 25+ years [older age TBI]). Models were adjusted for age (centered at 70 years), age-squared, education, wave, twin pair, lifestyle behaviors, and medical conditions.

RESULTS

Of 8,662 participants, 25% reported TBI. History of any TBI (β = -0.56, 95% CI -0.73 to -0.39), TBI with LOC (β = -0.51, 95% CI -0.71 to -0.31), and older age TBI (β = -0.66, 95% CI -0.90 to -0.42) were associated with lower TICS-m scores at 70 years. TBI with LOC (β = -0.03, 95% CI -0.05 to -0.001), more than one TBI (β = -0.05, 95% CI -0.09 to -0.002,), and older age TBI (β = -0.06, 95% CI -0.09 to -0.03) were associated with faster cognitive decline. Among monozygotic pairs discordant for TBI (589 pairs), history of any TBI (β = -0.55, 95% CI -0.91 to -0.19) and older age TBI (β = -0.74, 95% CI -1.22 to -0.26) were associated with lower TICS-m scores at 70 years. Those with more than one TBI (β = -0.13, 95% CI -0.23 to -0.03) and older age TBI (β = -0.07, 95% CI -0.13 to -0.002) showed greater cognitive decline compared with their co-twin without TBI.

DISCUSSION

These findings support an association of the effect of TBI on cognitive score and the rapidity of cognitive decline in later life. The results in monozygotic pairs, who share all genes and many exposures, particularly in early life, provide additional evidence of a causal relationship between TBI and poorer late-life cognitive outcomes.

ORGANOCHLORINE EXPOSURES AND COGNITIVE FUNCTION IN OLDER LIFE: THE ROLE OF RACE/ETHNICITY

Organochlorines (OCs) are persistent pesticides that remain in the environment and body for extended periods after exposure. Little is known about their long-term impact on cognition in later life. Some studies, but not all, have shown that higher levels of selected OCs are associated with lower cognitive function (CF). Using weighted linear generalized estimating equations, we explored whether the association between lipid-adjusted levels of 8 OCs and global CF is modified by race/ethnicity in 985 adults age 60+ from the National Health and Nutrition Examination Surveys (2011-2014). Adjusting for covariates, results indicated that higher levels of grouped-OCs are not associated with lower CF (p=0.121), but higher levels of specific OCs were associated with lower CF: Mirex[p=0.029]; Oxychlordane[p=0.036]; p,p’-DDE[p=0.009]; p,p’-DDT[p=0.003]; and trans-Nonachlor[p=0.023]. These associations did not differ by race/ethnicity. Disentangling the complex impact of OCs on late-life cognition—whether in combination or singularly—may lead to more equitable environmental health policies.

The Preventing Alzheimer's with Cognitive Training (PACT) randomized clinical trial

BACKGROUND

To address the rising prevalence of Alzheimer's disease and related dementias, effective interventions that can be widely disseminated are warranted. The Preventing Alzheimer's with Cognitive Training study (PACT) investigates a commercially available computerized cognitive training program targeting improved Useful Field of View Training (UFOVT) performance. The primary goal is to test the effectiveness of UFOVT to reduce incidence of clinically defined mild cognitive impairment (MCI) or dementia with a secondary objective to examine if effects are moderated by plasma β-amyloid level or apolipoprotein E e4 (APOE e4) allele status.

METHODS/DESIGN

This multisite study utilizes a randomized, controlled experimental design with blinded assessors and investigators. Individuals who are 65 years of age and older are recruited from the community. Eligible participants who demonstrate intact cognitive status (Montreal Cognitive Assessment score > 25) are randomized and asked to complete 45 sessions of either a commercially available computerized-cognitive training program (UFOVT) or computerized games across 2.5 years. After three years, participants are screened for cognitive decline. For those demonstrating decline or who are part of a random subsample, a comprehensive neuropsychological assessment is completed. Those who perform below a pre-specified level are asked to complete a clinical evaluation, including an MRI, to ascertain clinical diagnosis of normal cognition, MCI, or dementia. Participants are asked to provide blood samples for analyses of Alzheimer's disease related biomarkers.

DISCUSSION

The PACT study addresses the rapidly increasing prevalence of dementia. Computerized cognitive training may provide a non-pharmaceutical option for reducing incidence of MCI or dementia to improve public health.

REGISTRATION

The PACT study is registered at http://Clinicaltrials.govNCT03848312.

Traumatic brain injury and dementia risk in male veteran older twins-Controlling for genetic and early life non-genetic factors

INTRODUCTION

This study leveraged the twin study design, which controls for shared genetic and early life exposures, to investigate the association between traumatic brain injury (TBI) and dementia.

METHODS

Members of the National Academy of Sciences-National Research Council's Twins Registry of World War II male veterans were assigned a cognitive outcome based on a multi-step assessment protocol. History of TBI was obtained via interviews.

RESULTS

Among 8302 individuals, risk of non-Alzheimer's disease (non-AD) dementia was higher in those with TBI (hazard ratio [HR] = 2.00, 95% confidence interval [CI], 0.97-4.12), than for AD (HR = 1.23, 95% CI, 0.76-2.00). To add more control of genetic and shared environmental factors, we analyzed 100 twin pairs discordant for both TBI and dementia onset, and found TBI-associated risk for non-AD dementia increased further (McNemar odds ratio = 2.70; 95% CI, 1.27-6.25).

DISCUSSION

These findings suggest that non-AD mechanisms may underlie the association between TBI and dementia, potentially providing insight into inconsistent results from prior studies.

Sex Differences in the Association Between Metabolic Dysregulation and Cognitive Aging: The Health and Retirement Study

BACKGROUND

Dysregulation of some metabolic factors increases the risk of dementia. It remains unclear if overall metabolic dysregulation, or only certain components, contribute to cognitive aging and if these associations are sex specific.

METHODS

Data from the 2006-2016 waves of the Health and Retirement Study (HRS) was used to analyze 7 103 participants aged 65 and older at baseline (58% women). We created a metabolic-dysregulation risk score (MDRS) composed of blood pressure/hypertension status, glycosylated hemoglobin (HbA1c)/diabetes status, total cholesterol (TC), high-density lipoprotein cholesterol (HDL-C), and waist circumference, and assessed cognitive trajectories from repeated measures of the HRS-Telephone Interview for Cognitive Status (HRS-TICS) over 10 years of follow-up. Linear mixed-effects models estimated associations between MDRS or individual metabolic factors (biomarkers) with mean and change in HRS-TICS scores and assessed sex-modification of these associations.

RESULTS

Participants with higher MDRSs had lower mean HRS-TICS scores, but there were no statistically significant differences in rate of decline. Sex stratification showed this association was present for women only. MDRS biomarkers revealed heterogeneity in the strength and direction of associations with HRS-TICS. Lower HRS-TICS levels were associated with hypertension, higher HbA1c/diabetes, and lower HDL-C and TC, whereas faster rate of cognitive decline was associated with hypertension, higher HbA1c/diabetes, and higher TC. Participants with higher HbA1c/diabetes presented worse cognitive trajectories. Sex differences indicated that women with higher HbA1c/diabetes to have lower HRS-TICS levels, whereas hypertensive males presented better cognitive trajectory.

CONCLUSIONS

Our results demonstrate that metabolic dysregulation is more strongly associated with cognition in women compared with men, though sex differences vary by individual biomarker.

Life-course trajectories of body mass index from adolescence to old age: Racial and educational disparities

No research exists on how body mass index (BMI) changes with age over the full life span and social disparities therein. This study aims to fill the gap using an innovative life-course research design and analytic methods to model BMI trajectories from early adolescence to old age across 20th-century birth cohorts and test sociodemographic variation in such trajectories. We conducted the pooled integrative data analysis (IDA) to combine data from four national population-based NIH longitudinal cohort studies that collectively cover multiple stages of the life course (Add Health, MIDUS, ACL, and HRS) and estimate mixed-effects models of age trajectories of BMI for men and women. We examined associations of BMI trajectories with birth cohort, race/ethnicity, parental education, and adult educational attainment. We found higher mean levels of and larger increases in BMI with age across more recent birth cohorts as compared with earlier-born cohorts. Black and Hispanic excesses in BMI compared with Whites were present early in life and persisted at all ages, and, in the case of Black-White disparities, were of larger magnitude for more recent cohorts. Higher parental and adulthood educational attainment were associated with lower levels of BMI at all ages. Women with college-educated parents also experienced less cohort increase in mean BMI. Both race and education disparities in BMI trajectories were larger for women compared with men.

Racially diverse participant registries to facilitate the recruitment of African Americans into presymptomatic Alzheimer's disease studies

INTRODUCTION

The Alzheimer's Disease Prevention Registry (ADPR) of the Joseph and Kathleen Bryan Alzheimer's Disease Research Center at Duke University has been successful in achieving a racially diverse and "research ready" cohort of cognitively healthy volunteers.

METHODS

The ADPR is based on an infrastructure that includes: (1) an administrative leadership team; (2) a coordinating center; (3) an IT management team; (4) a community engagement team; and (5) collaborations with study partners across disciplines.

RESULTS

The ADPR currently has more than 4677 members, 26% of whom are African American. The ADPR has supported 21 studies including 8 biomarker studies, 7 clinical trials, 4 cognitive neuroscience studies, and 2 studies assessing novel computerized measures.

DISCUSSION

We describe our experiences establishing and maintaining a diverse ADPR as well as insights on recruitment strategies to increase the representation of African Americans in Alzheimer's disease studies.

The NAS-NRC Twin Registry and Duke Twins Study of Memory in Aging: An Update

The National Academy of Sciences-National Research Council (NAS-NRC) Twin Registry is one of the oldest, national population-based twin registries in the USA. It comprises 15,924 White male twin pairs born in the years 1917-1927 (N = 31.848), both of whom served in the armed forces, chiefly during World War II. This article updates activities in this registry since the most recent report in Twin Research and Human Genetics (Page, 2006). Records-based data include information from enlistment charts and Veterans Administration data linkages. There have been three major epidemiologic questionnaires and an education and earnings survey. Separate data collection efforts with the NAS-NRC registry include the National Heart, Lung, and Blood Institute (NHLBI) subsample, the Duke Twins Study of Memory in Aging and a clinically based study of Parkinson's disease. Progress has been made on consolidating the various data holdings of the NAS-NRC Twin Registry. Data that had been available through the National Academy of Sciences are now freely available through National Archive of Computerized Data on Aging (NACDA).

VALIDATING SILICONE WRISTBANDS TO MEASURE PESTICIDE EXPOSURES AMONG OLDER ADULTS -- PROOF-OF-CONCEPT STUDY

Silicone wristbands have been used to measure exposure to pesticides and other chemicals among children and younger farm workers, but not in older adults. Thus, we aimed to examine exposure to pesticides using silicone wristbands in a small cohort of older adults living on agricultural land, with variable contact with fields and pesticides. We also investigated correlations between pesticide levels on wristbands and urinary pesticide metabolites. Organophosphate (OPH) pesticides and several organochlorines were measured in wristbands worn by 15 males age 70+ (10 farmers using pesticides and 5 non-farmers with no recent pesticide use). Wristbands were worn continuously for 5-days. End-of-day urine samples were collected on days 1-3-5. Spearman correlations and Wilcoxon Scores were calculated. Five pesticides were quantified in the wristbands and detection frequencies ranged from 40-90%. In urine,12 OPH metabolites were quantified, but only 5 were detected in >50% of the samples. None of 5 urinary herbicides were detected. Imputation was performed by dividing minimum-detect by square-root-2. Malathion was only detected in farmers compared to non-farmers. Correlations between OPH urinary metabolites and wristband were examined but only two were significant and were negative in direction. Notably, organochlorine DDE on the wristbands was significantly correlated with 3 OPH metabolites. These unexpected relationships, based on small numbers, suggest a need to replicate this work in a larger study sample to explore potential for confounding or mixtures in future studies of pesticides and health in older farmers.

The Impact of Multiple Dimensions of Socioeconomic Status on Physical Functioning Across the Life Course

Objective: We used the Physical Performance Across the LifeSpan Study to investigate the relationships of multiple indicators of socioeconomic status (SES), both in early life and late life, with physical function. Method: We examined associations between multiple early and late life SES indicators with physical function measured by aerobic endurance, gait speed, and lower body strength. Results: Higher participant education and household income were associated with increased physical function. In our age-stratified analysis, we observed widening SES disparities with increasing age among those in the two younger strata with lower SES associated with worse physical function. Finally, we observed an association between socioeconomic trend and gait speed, aerobic endurance, and lower body strength. There was also an association between lower aerobic endurance and being in a downward socioeconomic trend. Discussion: These findings highlight the significance of considering multiple dimensions of the social environment as important correlates of physical functioning across the life course.

The Association Between Lipoproteins, Disability, and Physical Function Among Older Costa Rican Adults

OBJECTIVE

To examine the relationship between total cholesterol (TC), triglycerides (TG), and high-density lipoprotein cholesterol (HDL-C) with disability and physical performance.

METHOD

Wave 1 data were from Costa Rican Longevity and Healthy Aging Study ( n = 2,827). Lipoprotein profiles were measured using blood samples. Disability and physical functioning were measured with activities of daily living/instrumental activities of daily living (ADLs/IADLs) and objective assessment of physical performance.

RESULTS

Lower HDL-C was associated with greater ADL disability, and lower TC with longer time to pick-a-pencil and Time-Up-Go (TUG) test. Age interacted between (a) TG and lung function, chair stands, and pick-a-pencil, and (b) HDL-C and TUG. Stratification showed lower TG and longer time picking up a pencil only for those above 84 years. Based on significant interactions with sex, lower TC was associated with slower chair stand time in women and higher HDL-C with slower chair stand time in men.

DISCUSSION

Lower levels of lipoproteins may suggest worse physical function, but the association may differ by sex.

Dementia: a barrier to receiving percutaneous coronary intervention for elderly patients with ST-elevated myocardial infarction

OBJECTIVE

Percutaneous coronary intervention (PCI) is the first line of treatment for ST-elevated myocardial infarction (STEMI). This study evaluates the role of dementia in diagnostic cardiac catheterization (to receive PCI) in STEMI patients ≥65 years old admitted to high annual volume PCI hospitals.

METHODS

Participants were registered in Florida's comprehensive inpatient surveillance system for the years 2006-2007 with principal diagnosis of STEMI. Dementia was defined using ICD-9 codes for presenile, senile, and Alzheimer's type dementia.

RESULTS

Data from 8331 STEMI patients were used. Of these, 77.2% were catheterized, 67.2% received PCI, and 9.3% had coronary artery bypass graft (CABG). The mean age of the cohort was 76.3 years (SD 7.8 years.); with 43.3% female, 83.4% white, 4.6% black, and 12% Hispanic/other. Of the 248 (3%) patients with dementia, 42% were catheterized. After adjustment for age, gender, and race/ethnicity, patients with dementia were less likely to be catheterized (RR 0.30, 95% CI 0.30-0.50) than non-demented patients. However, among patients who were catheterized, there was no difference in the use of PCI or CABG for patients with versus without dementia (p = 0.56). Of those with dementia, being older and arriving to the hospital in the afternoon were associated with lower likelihood of being catheterized (RR 0.08, 95% CI 0.02-0.28, and RR 0.30, 95% CI 0.10-0.88, respectively). However, having hyperlipidemia increased the probability of catheterization (RR 3.60, 95% CI 1.86-6.98).

CONCLUSION

ST-elevated myocardial infarction patients with dementia were much less likely to receive diagnostic cardiac catheterization, thereby limiting the possibility for receiving optimal care including PCI or CABG.