Effect size for the main cognitive function determinants in a large cross-sectional study

A prospective investigation into the association between the gut microbiome composition and cognitive performance among healthy young adults

Background

There is emerging evidence that the gut microbiome composition is associated with several human health outcomes, which include cognitive performance. However, only a few prospective epidemiological studies exist and none among young adults. Here we address the gap in the literature by investigating whether the gut microbiome composition is prospectively linked to fluid intelligence among healthy young adults.

Methods

Forty individuals (65% females, 26 years) from the DOrtmund Nutritional and Anthropometric Longitudinally Designed (DONALD) study provided a fecal sample for gut microbiome composition and subsequently (average of 166 days) completed a cognitive functioning test using the Cattell’s Culture Fair Intelligence Test, revised German version (CFT 20-R). The assessment of the gut microbiome at the genera level was by 16S rRNA V3-V4 Illumina sequencing. The relative abundance of 158 genera was summarized into bacterial communities using a novel data-driven dimension reduction, amalgamation. The fluid intelligence score was regressed on the relative abundance of the bacterial communities and adjusted for selected covariates.

Results

The 158 genera were amalgamated into 12 amalgams (bacterial communities), which were composed of 18, 6, 10, 14, 8, 10, 16, 13, 12, 12, 3, and 11 genera. Only the 14-genera bacterial community, named the “Ruminococcaceae- and Coriobacteriaceae-dominant community” was positively associated with fluid intelligence score (β = 7.8; 95% CI: 0.62, 15.65, P = 0.04).

Conclusion

Among healthy young adults, the abundance of a gut bacterial community was associated with fluid intelligence score. This study suggests that cognitive performance may potentially benefit from gut microbiome-based intervention.

Outdoor air pollution exposure and cognitive performance: findings from the enrolment phase of the CONSTANCES cohort

BACKGROUND

Air pollution exposure is one of the modifiable risk factors of cognitive decline. We aimed to test the association between exposure to several outdoor air pollutants and domain-specific cognitive performance.

METHODS

In this cross-sectional study, we used data from the enrolment phase of the French CONSTANCES cohort. From the 220 000 people (aged 18-69 years) randomly recruited in the French CONSTANCES cohort, participants aged 45 years old or older (104 733 people) underwent a comprehensive cognitive assessment (verbal episodic memory, language skills, and executive functions). After exclusion of those who were not suitable for our analysis, 61 462 participants with available data were included in the analyses. We used annual mean concentrations at residential addresses, derived from land-use regression models, to assign exposure to particulate matter with aerodynamic diameters less than 2·5 μm (PM_2·5), nitrogen dioxide (NO₂), and black carbon. We used multiple linear regression models with different covariate adjustments to test the associations between each pollutant and cognitive outcomes. We did several sensitivity analyses, including multilevel modelling, meta-analysis by centre of recruitment, and exclusion of specific population groups.

FINDINGS

We found significantly poorer cognitive function, especially on semantic fluency and domains of executive functions, with an increase in exposure to black carbon and NO₂. Exposure to PM_2·5 was mainly significant for the semantic fluency test. We found that decrease in cognitive performance with an increase of one interquartile range of exposure ranged from 1% to nearly 5%. The largest effect size (percentage decrease) for both PM_2.5 and NO₂ was found for the semantic fluency test (PM_2.5 4·6%, 95% CI 2·1-6·9 and NO₂ 3·8%, 1·9-5·7), whereas for black carbon, the largest effect size was found for the digit symbol substitution test of the domains of executive functions (4·5%, 2·7-6·3). Monotonic and linear exposure-response associations were found between air pollution exposure and cognitive performance, starting from a low level of exposures.

INTERPRETATION

Significantly poorer cognitive performance was associated with exposure to outdoor air pollution even at low levels of exposure. This highlights the importance of further efforts to reduce exposure to air pollution.

FUNDING

The Caisse Nationale d'Assurance Maladie, and partly funded by Merck Sharp & Dohme and L'Oréal, the French National Research Agency, and Fondation de France.

TRANSLATION

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

Association Between Occupational Exposure to Formaldehyde and Cognitive Impairment

OBJECTIVE

To our knowledge, no study has investigated the effect of exposure to formaldehyde on cognition in the general population. Our objective was to examine the association between occupational exposure to formaldehyde and cognitive impairment in middle-aged and young- old adults (≥45 years).

METHODS

In the French CONSTANCES cohort, cognitive function was assessed with a standardized battery of seven cognitive tests to evaluate global cognitive function, episodic verbal memory, language abilities and executive functions (e.g., Digit Symbol Substitution Test, DSST). A global cognitive score was created using principal component analysis. Cognitive impairment was assessed in reference to norms of neuropsychological battery according to age, sex and education. Lifetime exposure to formaldehyde was assessed using a French job-exposure matrix created in the framework of the Matgéné project. After performing multiple imputation, separate modified Poisson regression models were used to evaluate the association between cognitive impairment (<25^th percentile) and formaldehyde exposure (exposed/never exposed), exposure duration, cumulative exposure index (CEI), and combination of CEI and time of last exposure.

RESULTS

Among 75 322 participants (median age: 57.5 years, women: 53%), 8% were exposed to formaldehyde during their professional life. These participants were at higher risk of global cognitive impairment (for global cognitive score: adjusted relative risk, aRR, 1.17, 95% confidence interval, CI: 1.11-1.23), after adjusting for confounders (age, sex, education, income, solvent exposure, Effort-Reward Imbalance, night-shift, repetitive, and noisy work). They were at higher risk of cognitive impairment for all cognitive domains explored. Longer exposure duration and high CEI were associated with cognitive impairment, with a dose-effect relationship for exposure duration. Recent exposure was associated with impairment in all cognitive domains. Time did not fully attenuate formaldehyde-associated cognitive deficits especially in highly exposed individuals (for DSST: high past exposure aRR 1.23, 95%CI: 1.11-1.36; high recent exposure: aRR 1.24, 95%CI: 1.13-1.35).

CONCLUSION

Our findings highlight the long-term detrimental effect of formaldehyde exposure on cognitive health in a relatively young population.

Do Cardiovascular Risk Factors and Cardiovascular Disease Explain Sex Differences in Cognitive Functioning in Old Age?

Background:

Sex differences in cognitive functioning in old age are known to exist yet are still poorly understood.

Objective:

This study examines to what extent differences in cardiovascular risk factors and cardiovascular disease between men and women explain sex differences in cognitive functioning.

Methods:

Data from 2,724 older adults from the Longitudinal Aging Study Amsterdam were used. Information processing speed and episodic memory, measured three times during six years of follow-up, served as outcomes. The mediating role of cardiovascular risk factors and cardiovascular disease was examined in single and multiple mediator models. Determinant-mediator effects were estimated using linear or logistic regression, and determinant-outcome and mediator-outcome effects were estimated using linear mixed models. Indirect effects were estimated using the product-of-coefficients estimator.

Results:

Women scored 1.58 points higher on information processing speed and 1.53 points higher on episodic memory. Several cardiovascular risk factors had small mediating effects. The sex difference in information processing speed was mediated by smoking, depressive symptoms, obesity, and systolic blood pressure. The sex difference in episodic memory was mediated by smoking, physical activity, and depressive symptoms. Effects of smoking, LDL cholesterol, and diabetes mellitus on information processing speed differed between men and women.

Conclusion:

Differences in cardiovascular risk factors between women and men partially explained why women had better cognitive functioning. A healthy cardiovascular lifestyle seems beneficial for cognition and sex-specific strategies may be important to preserve cognitive functioning at older age.

Similarities in cognitive abilities in older couples: a study of mutual influences

Objective: Similarities between spouses in cognitive functions have been mainly explained by the assortative mating phenomenon and the convergence for age and education. The mutual influence between spouses is another explanation particularly relevant in the elderly population. Today, it remains difficult to determine whether cognitive similarities exclusively result from the convergence effect or from the mutual influence. Using a novel methodology, the present study aimed to assess the impact of the marital relationship on cognitive similarities among elderly couples.Methods: 1723 couples from the Three-City Cohort Study were classified in two groups of couples with homogeneous and heterogeneous age and education. We also constituted two groups of pseudo-couples by a random association of individuals, with homogeneous and heterogeneous age and education. Dyadic analyses were conducted in the four groups, regarding the similarities in lexicosemantic abilities, executive functions, memory and global cognitive functioning.Results: Similarities were found on lexicosemantic abilities both in mate-assorted couples and in couples heterogeneous in age and education but no similarity was found in pseudo-couples.Discussion: Beyond the convergence effect, the fact that the spouses co-construct their lifestyles may contribute to cognitive similarities in the lexicosemantic domain.

Individual and neighbourhood socioeconomic inequalities in cognitive impairment: cross-sectional findings from the French CONSTANCES cohort

OBJECTIVES

Despite the recent awareness of the environment impact on brain ageing, the influence of the neighbourhood socioeconomic status on cognitive impairment remains unclear. Here, we investigated the effects of individual and neighbourhood deprivation on cognitive impairment in middle-aged and young-old people.

DESIGN

Cross-sectional study.

SETTINGS

21 Health Screening Centres in the entire French metropolitan territory.

PARTICIPANTS

A total of 44 648 participants (age range: 45 to 69 years) from the French CONSTANCES cohort were included in the analyses.

MAIN OUTCOMES

Associations between the overall cognitive score (based on a standardised battery of cognitive tests administered by neuropsychologists) and individual deprivation (Evaluation of Deprivation and Inequalities in Health Screening Centres; EPICES score) and geographical deprivation (French Deprivation Index; FDep index).

RESULTS

Based on the EPICES score (validated cut-off ≥30.17), 12% of participants were considered to be deprived. After mutual adjustment, individual and geographical deprivation were associated with higher cognitive impairment in a multilevel logistic regression analysis that was also adjusted for sociodemographic, lifestyle and health factors. Specifically, individual deprivation was associated with an odds increase of 55% (OR=1.55, 95% CI: 1.45 to 1.66). The risk of global cognitive impairment progressively increased with the neighbourhood deprivation level, evaluated by the FDep index (reference Q1; Q2: OR=1.09, 95% CI: 0.98 to 1.20; Q3: OR=1.15, 95% CI: 1.04 to 1.27; Q4: OR=1.15, 95% CI: 1.04 to 1.28; Q5: OR=1.25, 95% CI: 1.13 to 1.39).

CONCLUSION

Our results suggest that the neighbourhood socioeconomic deprivation level is associated with cognitive impairment, independently of the individual deprivation level. A better understanding of this association could help to define new prevention strategies to target high-risk residents and high-risk geographical areas in order to reduce social health inequalities.

Increased Prevalence of Neurocognitive Impairment in Aging People Living With Human Immunodeficiency Virus: The ANRS EP58 HAND 55–70 Study

Background

There are limited data on the comparative prevalence of neurocognitive impairment (NCI) in aging people living with human immunodeficiency virus (PLHIV) and people not living with HIV.

Methods

This was a cross-sectional study of PLHIV randomly matched by age (±4 years), gender, and education with 5 HIV-uninfected individuals from the CONSTANCES cohort. PLHIV were fluent in French and sequentially included during routine outpatient visits if aged 55–70 years, with HIV viral load &lt;50 copies/mL, and lymphocyte T-CD4 level ≥200 cells/µL in the past 24 and 12 months, respectively. The primary outcome was NCI as defined by the Frascati criteria. Multivariate normative comparison (MNC) and −1.5 standard deviations in ≥2 neurocognitive domains were secondary outcomes of NCI.

Results

Two hundred PLHIV were matched with 1000 controls. Median age was 62 years, and 85% were men. In PLHIV, the median T-CD4 lymphocyte level was 650 cells/µL, and median nadir T-CD4 lymphocyte level was 176 cells/µL. NCI was found in 71 (35.5%) PLHIV and in 242 (24.2%) controls (odds ratio [OR], 1.74; 95% confidence interval [CI], 1.25, 2.41). After adjusting for confounders, HIV remained significantly associated with NCI (OR, 1.50; 95% CI, 1.04, 2.16). Adjusted results were similar with NCI defined by MNC (ORMNC, 2.95; 95% CI, 1.13, 3.50) or −1.5 SD (OR−1.5, 2.24; 95% CI, 1.39, 3.62).

Conclusions

In this matched study of aging individuals, HIV was significantly associated with an increased risk of NCI after adjusting for major confounders. Results were confirmed with more stringent NCI classifications.

Clinical Trials Registration

NCT02592174.

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.

Is effort-reward imbalance at work associated with different domains of health functioning? Baseline results from the French CONSTANCES study

PURPOSE

Despite its importance a comprehensive assessment of health functioning has rarely been included in epidemiological investigations of work-related health outcomes. In this study, we analyzed associations of a health-adverse psychosocial work environment with a comprehensive set of subjective and objective measures of health functioning that cover the three domains of affective, cognitive, and physical functioning.

METHODS

Baseline data from the French CONSTANCES cohort study were used with a sample of 24,327 employed men and women aged 45-60. Psychosocial work environment was measured by the short version of the effort-reward imbalance (ERI) questionnaire. Measures of health functioning were depressive symptoms, semantic fluency, verbal memory, walking speed, standing balance and lung function.

RESULTS

First, we replicated main psychometric properties of the ERI questionnaire in the French cohort. Second, ERI scales revealed consistent associations with depressive symptoms, but less consistent links to cognitive and physical function. Among men, we observed an association of stressful work with reduced lung function.

CONCLUSIONS

This study demonstrated consistent associations of stressful work in terms of effort-reward imbalance with affective functioning in a large sample of male and female employees. Relationships with physical functioning were less consistent and restricted to men, and cognitive functioning was only marginally associated with stressful work. We also established the psychometric properties of the French short version of the ERI questionnaire, thus offering a tool for guiding and harmonizing further research in this field.

Anticholinergic drug use and cognitive performances in middle age: findings from the CONSTANCES cohort

BACKGROUND

Previous studies have shown associations between the use of anticholinergics (AC) and cognitive performance in the elderly, considering AC as a homogeneous set of drugs. The present study aims to assess the relationship between exposure to AC drugs and cognitive performance in middle-aged adults according to AC potency and drug class.

METHODS

Our cross-sectional study used baseline data of 34 267 participants aged 45-70 from the Consultants des centres d'examen de santé de la sécurité sociale (CONSTANCES) cohort. The cumulative exposure to AC was measured using national reimbursement databases over the 3-year period preceding assessment of cognitive performance. Eight classes of AC drugs were differentiated. Episodic verbal memory, language abilities and executive functions were evaluated by validated neuropsychological tests. Analyses were controlled on lifestyle and health status variables.

RESULTS

This study showed a negative association between overall cumulative AC exposure and cognitive performances after adjustment. The use of drugs with possible AC effect according to the Anticholinergic Cognitive Burden scale (ACB-1 score) was only associated with executive functions. Analyses of AC exposure across drug classes showed a negative association between the use of AC antipsychotics and all cognitive functions assessed. Heterogeneous associations were found for the use of AC anxiolytics, AC opioids and AC drugs targeting the gastrointestinal tract or metabolism. We did not find significant associations between the use of antihistamines, antidepressants, cardiovascular system or other AC medications and cognitive function.

CONCLUSION

Association between AC drugs and cognitive performance was highly heterogeneous across drug classes; this heterogeneity will have to be considered by future studies.

Predicting dementia using socio-demographic characteristics and the Free and Cued Selective Reminding Test in the general population

BACKGROUND

Our study aimed to determine whether the consideration of socio-demographic features improves the prediction of Alzheimer's dementia (AD) at 5 years when using the Free and Cued Selective Reminding Test (FCSRT) in the general older population.

METHODS

Our analyses focused on 2558 subjects from the prospective Three-City Study, a cohort of community-dwelling individuals aged 65 years and over, with FCSRT scores. Four "residual scores" and "risk scores" were built that included the FCSRT scores and socio-demographic variables. The predictive performance of crude, residual and risk scores was analyzed by comparing the areas under the ROC curve (AUC).

RESULTS

In total, 1750 subjects were seen 5 years after completing the FCSRT. AD was diagnosed in 116 of them. Compared with the crude free-recall score, the predictive performances of the residual score and of the risk score were not significantly improved (AUC: 0.83 vs 0.82 and 0.88 vs 0.89 respectively).

CONCLUSION

Using socio-demographic features in addition to the FCSRT does not improve its predictive performance for dementia or AD.

CONSTANCES: a general prospective population-based cohort for occupational and environmental epidemiology: cohort profile

WHY THE COHORT WAS SET UP?: CONSTANCES is a general-purpose cohort with a focus on occupational and environmental factors.

COHORT PARTICIPANTS

CONSTANCES was designed as a randomly selected sample of French adults aged 18-69 years at inception; 200 000 participants will be included.

DATA COLLECTION PHASES

At enrolment, the participants are invited to complete questionnaires and to attend a health screening centre (HSC) for a health examination. A biobank will be set up. The follow-up includes an yearly self-administered questionnaire, a periodic visit to an HSC and linkage to social and national health administrative databases.

MAIN TYPES OF DATA COLLECTED

Data collected for participants include social and demographic characteristics, socioeconomic status, life events and behaviours. Regarding occupational and environmental factors, a wealth of data on organisational, chemical, biological, biomechanical and psychosocial lifelong exposure, as well as residential characteristics, are collected at enrolment and during follow-up. The health data cover a wide spectrum: self-reported health scales, reported prevalent and incident diseases, long-term chronic diseases and hospitalisations, sick-leaves, handicaps, limitations, disabilities and injuries, healthcare usage and services provided, and causes of death.

CONTROL OF SELECTION EFFECTS

To take into account non-participation and attrition, a random cohort of non-participants was set up and will be followed through the same national databases as participants.

DATA ACCESS

Inclusions begun at the end of 2012 and more than 110 000 participants were already included by September 2016. Several projects on occupational and environmental risks already applied to a public call for nested research projects.