Building your best day for healthy brain aging-The neuroprotective effects of optimal time use

Blood brain barrier dysfunction in healthy aging and dementia: Why, how, what for?

The blood brain barrier (BBB) is an indispensable structure that maintains the central nervous system (CNS) microenvironment for a correct neuronal function. It is composed by highly specialized microvessels, surrounded by astrocytes, pericytes, neurons and microglia cells, which tightly control the influx and efflux of substances to the brain parenchyma. During aging, the BBB becomes impaired, and it may contribute to the development of neurodegenerative and neurological disorders including Alzheimer's disease and other dementias. Restoring the BBB can be a strategy to prevent disease onset and development, reducing the symptoms of these conditions. This work critically reviews the major mechanisms underlying BBB breakdown in healthy and unhealthy aging, as well as biomarkers and methodologies that accurately assess its impairment. Complementarily, potential therapeutic targets are discussed as new strategies to restore the normal function of the BBB in aging.

Cross-sectional associations between 24-hour time-use composition, grey matter volume and cognitive function in healthy older adults

BACKGROUND

Increasing physical activity (PA) is an effective strategy to slow reductions in cortical volume and maintain cognitive function in older adulthood. However, PA does not exist in isolation, but coexists with sleep and sedentary behaviour to make up the 24-hour day. We investigated how the balance of all three behaviours (24-hour time-use composition) is associated with grey matter volume in healthy older adults, and whether grey matter volume influences the relationship between 24-hour time-use composition and cognitive function.

METHODS

This cross-sectional study included 378 older adults (65.6 ± 3.0 years old, 123 male) from the ACTIVate study across two Australian sites (Adelaide and Newcastle). Time-use composition was captured using 7-day accelerometry, and T1-weighted magnetic resonance imaging was used to measure grey matter volume both globally and across regions of interest (ROI: frontal lobe, temporal lobe, hippocampi, and lateral ventricles). Pairwise correlations were used to explore univariate associations between time-use variables, grey matter volumes and cognitive outcomes. Compositional data analysis linear regression models were used to quantify associations between ROI volumes and time-use composition, and explore potential associations between the interaction between ROI volumes and time-use composition with cognitive outcomes.

RESULTS

After adjusting for covariates (age, sex, education), there were no significant associations between time-use composition and any volumetric outcomes. There were significant interactions between time-use composition and frontal lobe volume for long-term memory (p = 0.018) and executive function (p = 0.018), and between time-use composition and total grey matter volume for executive function (p = 0.028). Spending more time in moderate-vigorous PA was associated with better long-term memory scores, but only for those with smaller frontal lobe volume (below the sample mean). Conversely, spending more time in sleep and less time in sedentary behaviour was associated with better executive function in those with smaller total grey matter volume.

CONCLUSIONS

Although 24-hour time use was not associated with total or regional grey matter independently, total grey matter and frontal lobe grey matter volume moderated the relationship between time-use composition and several cognitive outcomes. Future studies should investigate these relationships longitudinally to assess whether changes in time-use composition correspond to changes in grey matter volume and cognition.

Differentiating the influence of sedentary behavior and physical activity on brain health in late adulthood

Public health messaging calls for individuals to be more physically active and less sedentary, yet these lifestyle behaviors have been historically studied independently. Both physical activity (PA) and sedentary behavior (SB) are linked through time-use in a 24-hour day and are related to health outcomes, such as neurocognition. While the benefits of PA on brain health in late adulthood have been well-documented, the influence of SB remains to be understood. The purpose of this paper was to critically review the evolving work on SB and brain health in late adulthood and emphasize key areas of consideration to inform potential research. Overall, the existing literature studying the impact of SB on the components and mechanisms of brain health are mixed and inconclusive, provided largely by cross-sectional and observational work employing a variety of measurement techniques of SB and brain health outcomes. Further, many studies did not conceptually or statistically account for the role of PA in the proposed relationships. Therefore, our understanding of the way in which SB may influence neurocognition in late adulthood is limited. Future efforts should include more prospective longitudinal and randomized clinical trials with intentional methodological approaches to better understand the relationships between SB and the brain in late adulthood, and how these potential links are differentiated from PA.

How are combinations of physical activity, sedentary behaviour and sleep related to cognitive function in older adults? A systematic review

The relationships between cognitive function and each of physical activity, sleep and sedentary behaviour in older adults are well documented. However, these three "time use" behaviours are co-dependent parts of the 24-hour day (spending time in one leaves less time for the others), and their best balance for cognitive function in older adults is still largely unknown. This systematic review summarises the existing evidence on the associations between combinations of two or more time-use behaviours and cognitive function in older adults. Embase, Pubmed, PsycInfo, Medline and Emcare databases were searched in March 2020 and updated in May 2021, returning a total of 25,289 papers for screening. A total of 23 studies were included in the synthesis, spanning >23,000 participants (mean age 71 years). Findings support previous evidence that spending more time in physical activity and limiting sedentary behaviour is broadly associated with better cognitive outcomes in older adults. Higher proportions of moderate-vigorous physical activity in the day were most frequently associated with better cognitive function. Some evidence suggests that certain types of sedentary behaviour may be positively associated with cognitive function, such as reading or computer use. Sleep duration appears to share an inverted U-shaped relationship with cognition, as too much or too little sleep is negatively associated with cognitive function. This review highlights considerable heterogeneity in methodological and statistical approaches, and encourages a more standardised, transparent approach to capturing important daily behaviours in older adults. Investigating all three time-use behaviours together against cognitive function using suitable statistical methodology is strongly recommended to further our understanding of optimal 24-hour time-use for brain function in aging.

Characterising activity and diet compositions for dementia prevention: protocol for the ACTIVate prospective longitudinal cohort study

INTRODUCTION

Approximately 40% of late-life dementia may be prevented by addressing modifiable risk factors, including physical activity and diet. Yet, it is currently unknown how multiple lifestyle factors interact to influence cognition. The ACTIVate Study aims to (1) explore associations between 24-hour time-use and diet compositions with changes in cognition and brain function; and (2) identify duration of time-use behaviours and the dietary compositions to optimise cognition and brain function.

METHODS AND ANALYSIS

This 3-year prospective longitudinal cohort study will recruit 448 adults aged 60-70 years across Adelaide and Newcastle, Australia. Time-use data will be collected through wrist-worn activity monitors and the Multimedia Activity Recall for Children and Adults. Dietary intake will be assessed using the Australian Eating Survey food frequency questionnaire. The primary outcome will be cognitive function, assessed using the Addenbrooke's Cognitive Examination-III. Secondary outcomes include structural and functional brain measures using MRI, cerebral arterial pulse measured with diffuse optical tomography, neuroplasticity using simultaneous transcranial magnetic stimulation and electroencephalography, and electrophysiological markers of cognitive control using event-related potential and time frequency analyses. Compositional data analysis, testing for interactions between time point and compositions, will assess longitudinal associations between dependent (cognition, brain function) and independent (time-use and diet compositions) variables.

CONCLUSIONS

The ACTIVate Study will be the first to examine associations between time-use and diet compositions, cognition and brain function. Our findings will inform new avenues for multidomain interventions that may more effectively account for the co-dependence between activity and diet behaviours for dementia prevention.

ETHICS AND DISSEMINATION

Ethics approval has been obtained from the University of South Australia's Human Research Ethics committee (202639). Findings will be disseminated through peer-reviewed manuscripts, conference presentations, targeted media releases and community engagement events.

TRIAL REGISTRATION NUMBER

Australia New Zealand Clinical Trials Registry (ACTRN12619001659190).

Daily activities are associated with non-invasive measures of neuroplasticity in older adults

OBJECTIVE

We aimed to determine the association between daily activities (sleep, sedentary behavior and physical activities) and neuroplasticity in older adults by measuring motor evoked potential amplitudes (MEPs) elicited after a single and spaced continuous theta burst stimulation (cTBS) paradigm, targeting the primary motor cortex.

METHODS

MEPs were recorded from the right first dorsal interosseous muscle of 34 older adults (66.9 ± 4.5 years) by delivering single-pulse TMS before, between and at 0, 10, 20, 40 and 60 min after the application of spaced-cTBS separated by 10 min. Habitual activity was assessed by accelerometry for 24 h/day over 7-days. Multiple linear regression models determined if the time-use composition (sleep, sedentary behavior and physical activities) was associated with neuroplasticity response.

RESULTS

More physical activity at the equal expense of sleep and sedentary behaviors was associated with greater motor cortical neuroplasticity. Associations appeared to be driven by more time spent in light- but not moderate-to-vigorous- physical activities.

CONCLUSIONS

Engaging in light physical activity at the expense of sleep and sedentary behavior was associated with greater LTD-like motor cortex neuroplasticity (as measured with cTBS) in older adults.

SIGNIFICANCE

These findings suggest the promotion of physical activity among older adults to support brain neuroplasticity.

Compositional Data Analysis in Time-Use Epidemiology: What, Why, How

In recent years, the focus of activity behavior research has shifted away from univariate paradigms (e.g., physical activity, sedentary behavior and sleep) to a 24-h time-use paradigm that integrates all daily activity behaviors. Behaviors are analyzed relative to each other, rather than as individual entities. Compositional data analysis (CoDA) is increasingly used for the analysis of time-use data because it is intended for data that convey relative information. While CoDA has brought new understanding of how time use is associated with health, it has also raised challenges in how this methodology is applied, and how the findings are interpreted. In this paper we provide a brief overview of CoDA for time-use data, summarize current CoDA research in time-use epidemiology and discuss challenges and future directions. We use 24-h time-use diary data from Wave 6 of the Longitudinal Study of Australian Children (birth cohort, n = 3228, aged 10.9 ± 0.3 years) to demonstrate descriptive analyses of time-use compositions and how to explore the relationship between daily time use (sleep, sedentary behavior and physical activity) and a health outcome (in this example, adiposity). We illustrate how to comprehensively interpret the CoDA findings in a meaningful way.