The association between kidney function, cognitive function, and structural brain abnormalities in community-dwelling individuals aged 50+ is mediated by age and biomarkers of cardiovascular disease

AIMS

Cognitive impairment has been associated with kidney function and chronic kidney disease. Whether this association is due to accelerated cardiovascular disease (CVD) or an independent specific kidney function effect related to toxins is unclear. We investigated the impact of an array of clinical factors, inflammatory biomarkers, and cardiovascular biomarkers on the association between kidney function, cognitive function, and structural brain abnormalities.

METHODS AND RESULTS

We used data from the first and third waves of the TILDA Study, a population-representative prospective cohort of Irish adults aged 50 years and over, based on stratified random sampling (n = 3774). The MRI sub-study included participants who consented to MRI brain imaging in addition to the health assessment. Multivariable linear and mixed-effect longitudinal regression models were fitted separately for each kidney marker/estimated glomerular filtration rate (eGFR) equation after adjusting for baseline age and demographics, clinical vascular risk factors, and biomarkers. Unadjusted analyses showed an association between low eGFR, cognitive dysfunction, and cognitive decline (P < 0.001 for all kidney markers). Kidney function markers were also associated with white matter disease [OR = 3.32 (95% CI: 1.11, 9.98)], total grey matter volume (β = -0.17, 95% CI -0.27 to -0.07), and regional grey matter volumes within areas particularly susceptible to hypoxia (P < 0.001 for all). All the associations decreased after adjusting for age and were also diminished after adjusting for CVD biomarkers. Age and CVD-biomarker score were significant mediators of the adjusted associations between eGFR and cognitive status. These results remained consistent for cross-sectional and longitudinal outcomes and specific cognitive domains.

CONCLUSION

Decreased kidney function was associated with cerebrovascular disease. The association appeared to be mediated predominantly by age and the combination of CVD markers [namely N-terminal pro-B-type natriuretic peptide (NT-proBNP) and Growth Differentiation Factor 15 (GDF15)], supporting the idea that shared biological pathways underline both diseases. Further mechanistic studies of the specific molecular mechanisms that lead to both kidney and cognitive decline are warranted.

The bi-directional association between loneliness and depression among older adults from before to during the COVID-19 pandemic

BACKGROUND

Older adults have both the highest risk of contracting SARS-CoV-2 and in many jurisdictions have had additional restrictions placed on the social interactions. As a result, the COVID-19 pandemic has led to increased depression and loneliness among older adults. Using data from an established cohort of older adults, the aims of this study was to describe changes in loneliness and depression and to examine the directionality of the association between depression and loneliness over a 5-year period that included the early months of the pandemic.

METHODS

Data were from The Irish Longitudinal Study on Ageing (TILDA), a large cohort of community-dwelling adults aged 54+. We applied an auto-regressive cross-lagged panel modelling approach to estimate the effect of depression on loneliness and vice versa over three time points.

RESULTS

Both depression and loneliness increased significantly in the early months of the pandemic. While the association between loneliness and depression was bi-directional, loneliness was a stronger predictor of depression.

CONCLUSION

The strength and bi-directionality of the association between loneliness and depression suggests that interventions to alleviate loneliness may also help reduce depressive symptoms and vice versa.

Associations between Cardiovascular Signal Entropy and Cognitive Performance over Eight Years

In this study, the relationship between non-invasively measured cardiovascular signal entropy and global cognitive performance was explored in a sample of community-dwelling older adults from The Irish Longitudinal Study on Ageing (TILDA), both cross-sectionally at baseline (n = 4525; mean (SD) age: 61.9 (8.4) years; 54.1% female) and longitudinally. We hypothesised that signal disorder in the cardiovascular system, as quantified by short-length signal entropy during rest, could provide a marker for cognitive function. Global cognitive function was assessed via Mini Mental State Examination (MMSE) across five longitudinal waves (8 year period; n = 4316; mean (SD) age: 61.9 (8.4) years; 54.4% female) and the Montreal Cognitive Assessment (MOCA) across two longitudinal waves (4 year period; n = 3600; mean (SD) age: 61.7 (8.2) years; 54.1% female). Blood pressure (BP) was continuously monitored during supine rest at baseline, and sample entropy values were calculated for one-minute and five-minute sections of this data, both for time-series data interpolated at 5 Hz and beat-to-beat data. Results revealed significant associations between BP signal entropy and cognitive performance, both cross-sectionally and longitudinally. Results also suggested that as regards associations with cognitive performance, the entropy analysis approach used herein potentially outperformed more traditional cardiovascular measures such as resting heart rate and heart rate variability. The quantification of entropy in short-length BP signals could provide a clinically useful marker of the cardiovascular dysregulations that potentially underlie cognitive decline.

Obesity is associated with reduced cerebral blood flow - modified by physical activity

This study examined the associations of body mass index (BMI), waist-to-hip ratio (WHR), waist circumference (WC), and physical activity (PA) with gray matter cerebral blood flow (CBF_GM) in older adults. Cross-sectional data was used from the Irish Longitudinal Study on Ageing (n = 495, age 69.0 ±7.4 years, 52.1% female). Whole-brain CBF_GM was quantified using arterial spin labeling MRI. Results from multivariable regression analysis revealed that an increase in BMI of 0.43 kg/m², WHR of 0.01, or WC of 1.3 cm were associated with the same reduction in CBF_GM as 1 year of advancing age. Participants overweight by BMI or with high WHR/WC reporting low/moderate PA had up to 3 ml/100g/min lower CBF_GM (p ≤ .011); there was no significant reduction for those reporting high PA. Since PA could potentially moderate obesity/CBF associations, this may be a cost-effective and relatively easy way to help mitigate the negative impact of obesity in an older population, such as cerebral hypoperfusion, which is an early mechanism in vascular dementia and Alzheimer's disease.

Cardiovascular Profiles for Phenotyping Cognitive Trajectories in the Irish Longitudinal Study on Ageing

Cardiovascular risk factors are increasingly recognized as modifiable risks for cognitive decline and dementia in later life. The Life’s Simple 7, an ideal CV health scoring system, has been recently put forward as a tool for the promotion of brain health. This study aims to evaluate the LS7 as risk prediction tool for cognitive decline trajectories (MMSE, immediate/delayed recall and verbal fluency) in 2,739 adults aged ≥50 years from TILDA. We investigate if indices of muscular strength (grip strength), mobility (Time Up and Go, walking speed) and physiological stress (e.g. orthostatic blood pressure and heart rate recovery) as add-ons to the LS7 improves prediction of cognitive trajectories; and, in a subcohort, we assess CV health score in association with multimodal brain measures. Identifying the factors that influence the onset and trajectory of cognitive decline in a multifactorial perspective is critical toward lowering dementia risks and developing adequate intervention and treatment.

Cardiovascular Health, Functional Disability, and Leisure Activities Profiles in Relation to Mental Aging

We investigated cardiovascular health, functional disability and leisure activities profiles independently and in relation to cognitive decline and dementia in high and low-medium income countries using data from the English Longitudinal Study of Ageing, Irish Longitudinal Study on Ageing and Brazilian Bambui Cohort Study of Aging. Functional loss among older Brazilians has shown a hierarchical sequence over the 15-year follow-up, with the highest incidence in functional disability reported for dressing, followed by getting out of bed, bathing/showering, walking across a room, using the toilet and eating (de Oliveira). Using the Life’s Simple 7, an ideal cardiovascular health scoring system evaluating the muscular strength, mobility and physiological stress, we showed a reliable prediction of cognitive trajectories in a representative sample of Irish individuals (De Looze). Within the same cohort, we report discrepancies between men and women in functional decline driven by domestic tasks, rather than determining differential cognitive trajectories (McGarrigle). In an English representative sample, we found that participants with an increasing number of functional impairments over almost a decade were more likely to be classified with subsequent dementia compared with those with no impairments and this may imply a more comprehensive ascertainment during the prodromal stage of dementia (Cadar). In contrast, a reduced risk of dementia was found for individuals with higher levels of engagement in cognitively stimulating activities, that may preserve cognitive reserve until later in life (Almeida). Identifying factors that influence cognitive aging and dementia risk in a multifactorial perspective is critical toward developing adequate intervention and treatment.

Changes in Speech Chunking in Reading Aloud is a Marker of Mild Cognitive Impairment and Mild-to-Moderate Alzheimer's Disease

BACKGROUND

Speech and Language Impairments, generally attributed to lexico-semantic deficits, have been documented in Mild Cognitive Impairment (MCI) and Alzheimer's disease (AD). This study investigates the temporal organisation of speech (reflective of speech production planning) in reading aloud in relation to cognitive impairment, particularly working memory and attention deficits in MCI and AD. The discriminative ability of temporal features extracted from a newly designed read speech task is also evaluated for the detection of MCI and AD.

METHOD

Sixteen patients with MCI, eighteen patients with mild-to-moderate AD and thirty-six healthy controls (HC) underwent a battery of neuropsychological tests and read a set of sentences varying in cognitive load, probed by manipulating sentence length and syntactic complexity.

RESULTS

Our results show that Mild-to-Moderate AD is associated with a general slowness of speech, attributed to a higher number of speech chunks, silent pauses and dysfluences, and slower speech and articulation rates. Speech chunking in the context of high cognitive-linguistic demand appears to be an informative marker of MCI, specifically related to early deficits in working memory and attention. In addition, Linear Discriminant Analysis shows the ROC AUCs (Areas Under the Receiver Operating Characteristic Curves) of identifying MCI vs. HC, MCI vs. AD and AD vs. HC using these speech characteristics are 0.75, 0.90 and 0.94 respectively.

CONCLUSION

The implementation of connected speech-based technologies in clinical and community settings may provide additional information for the early detection of MCI and AD.