Sedentary behavior as a risk factor for cognitive decline? A focus on the influence of glycemic control in brain health

Glycaemic variability in diabetes: clinical and therapeutic implications

Glycaemic variability is an integral component of glucose homoeostasis. Although it has not yet been definitively confirmed as an independent risk factor for diabetes complications, glycaemic variability can represent the presence of excess glycaemic excursions and, consequently, the risk of hyperglycaemia or hypoglycaemia. Glycaemic variability is currently defined by a large and increasing number of metrics, representing either short-term (within-day and between-day variability) or long-term glycaemic variability, which is usually based on serial measurements of HbA_1c or other measures of glycaemia over a longer period of time. In this Review, we discuss recent evidence examining the association between glycaemic variability and diabetes-related complications, as well as non-pharmacological and pharmacological strategies currently available to address this challenging aspect of diabetes management.

Television viewing and cognitive decline in older age: findings from the English Longitudinal Study of Ageing

There has been significant interest in the effects of television on cognition in children, but much less research has been carried out into the effects in older adults. This study aimed to explore whether television viewing behaviours in adults aged 50 or over are associated with a decline in cognition. Using data from the English Longitudinal Study of Aging involving 3,662 adults aged 50+, we used multivariate linear regression models to explore longitudinal associations between baseline television watching (2008/2009) and cognition 6 years later (2014/2015) while controlling for demographic factors, socio-economic status, depression, physical health, health behaviours and a range of other sedentary behaviours. Watching television for more than 3.5 hours per day is associated with a dose-response decline in verbal memory over the following six years, independent of confounding variables. These results are found in particular amongst those with better cognition at baseline and are robust to a range of sensitivity analyses exploring reverse causality, differential non-response and stability of television viewing. Watching television is not longitudinally associated with changes in semantic fluency. Overall our results provide preliminary data to suggest that television viewing for more than 3.5 hours per day is related to cognitive decline.

Blood-Brain Barrier: From Physiology to Disease and Back

The blood-brain barrier (BBB) prevents neurotoxic plasma components, blood cells, and pathogens from entering the brain. At the same time, the BBB regulates transport of molecules into and out of the central nervous system (CNS), which maintains tightly controlled chemical composition of the neuronal milieu that is required for proper neuronal functioning. In this review, we first examine molecular and cellular mechanisms underlying the establishment of the BBB. Then, we focus on BBB transport physiology, endothelial and pericyte transporters, and perivascular and paravascular transport. Next, we discuss rare human monogenic neurological disorders with the primary genetic defect in BBB-associated cells demonstrating the link between BBB breakdown and neurodegeneration. Then, we review the effects of genes underlying inheritance and/or increased susceptibility for Alzheimer's disease (AD), Parkinson's disease (PD), Huntington's disease, and amyotrophic lateral sclerosis (ALS) on BBB in relation to other pathologies and neurological deficits. We next examine how BBB dysfunction relates to neurological deficits and other pathologies in the majority of sporadic AD, PD, and ALS cases, multiple sclerosis, other neurodegenerative disorders, and acute CNS disorders such as stroke, traumatic brain injury, spinal cord injury, and epilepsy. Lastly, we discuss BBB-based therapeutic opportunities. We conclude with lessons learned and future directions, with emphasis on technological advances to investigate the BBB functions in the living human brain, and at the molecular and cellular level, and address key unanswered questions.

Community-Based Activity and Sedentary Patterns Are Associated With Cognitive Performance in Mobility-Limited Older Adults

Over the last few decades, considerable evidence shows that greater levels of aerobic exercise and cardiovascular fitness benefit cognitive performance. However, the degree to which free-living activity in community settings is related to cognitive performance remains unclear, particularly in older adults vulnerable to disability. Also, it is unknown whether the manner in which daily physical activity (PA) and sedentary time are accumulated throughout the day is associated with cognition. Cross-sectional associations between accelerometer-characterized PA and sedentary patterns and cognitive performance were examined in 1,274 mobility-limited older adults. Percent time spent in various bout lengths of PA (≥1, ≥2, and ≥5 min) and sedentary (≥1, ≥30, and ≥60 min) was defined as the number of minutes registered divided by total wear time × 100. Percent time was then tertiled for each bout length. Multiple linear regression models were used to estimate the associations between accelerometer bout variables and separate cognitive domains that included processing speed (Digit Symbol Coding; DSC), immediate and delayed recall (Hopkins Verbal Learning Test; HVLT), information processing and selective attention (Flanker), working memory (n-back), reaction time (switch and non-switch reaction time), and a composite score that averaged results from all cognitive tests. After adjusting for demographics, behavioral factors, and morbid conditions, more time spent in PA was associated with higher DSC for all bout lengths (p < 0.03 for all). Higher PA was associated with higher HVLT and global cognition scores but only for longer bout lengths (p < 0.05 for all). The association was largely driven by participants who spent the lowest amount of time performing activity while awake (p < 0.04). An inverse linear relationship was observed between total sedentary time and DSC (p = 0.02), but not for other measures of cognition. These results suggest that, while higher PA was associated with higher cognitive performance, PA’s association with memory was sensitive to bout duration. The time, but not the manner, spent in sedentary behaviors showed a minor association with executive function. Further research is warranted to characterize longitudinal changes in daily activity and sedentary patterns as potential biophysical markers of cognitive status in older adults.

Dimensions of sedentary behavior and objective cognitive functioning in breast cancer survivors

PURPOSE

To examine associations between dimensions of sedentary behavior and cognitive function in breast cancer survivors.

METHODS

Sedentary behavior variables were measured using thigh-worn activPALs, and included total daily sitting time, time in long sitting bouts, sit-to-stand transitions, and standing time. Cognitive function was assessed using the NIH Toolbox Cognitive Domain. Separate multivariable linear regression models were used to examine associations between sedentary behavior variables with the cognitive domain scores of attention, executive functioning, episodic memory, working memory, and information processing speed.

RESULTS

Thirty breast cancer survivors with a mean age of 62.2 (SD = 7.8) years who were 2.6 (SD = 1.1) years since diagnosis completed study assessments. In multivariable linear regression models, more time spent standing was associated with faster information processing (b: 5.78; p = 0.03), and more time spent in long sitting bouts was associated with worse executive function (b: -2.82; p = 0.02), after adjustment for covariates. No other sedentary behavior variables were statistically significantly associated with the cognitive domains examined in this study.

CONCLUSIONS

Two important sedentary constructs that are amenable to intervention, including time in prolonged sitting bouts and standing time, may be associated with cognitive function in breast cancer survivors. More research is needed to determine whether modifying these dimensions of sedentary behavior will improve cognitive function in women with a history of breast cancer, or prevent it from declining in breast cancer patients.

Regular walking breaks prevent the decline in cerebral blood flow associated with prolonged sitting

Decreased cerebrovascular blood flow and function are associated with lower cognitive functioning and increased risk of neurodegenerative diseases. Prolonged sitting impairs peripheral blood flow and function, but its effects on the cerebrovasculature are unknown. This study explored the effect of uninterrupted sitting and breaking up sitting time on cerebrovascular blood flow and function of healthy desk workers. Fifteen participants (10 male, 35.8 ± 10.2 yr, body mass index: 25.5 ± 3.2 kg/m2) completed, on separate days, three 4-h conditions in a randomized order: 1) uninterrupted sitting (SIT), 2) sitting with 2-min light-intensity walking breaks every 30 min (2WALK), or 3) sitting with 8-min light-intensity walking breaks every 2 h (8WALK). At baseline and 4 h, middle cerebral artery blood flow velocity (MCAv) and CO2 reactivity (CVR) of the MCA and carotid artery were measured using transcranial Doppler (TCD) and duplex ultrasound, respectively. Cerebral autoregulation (CA) was assessed with TCD using a squat-stand protocol and analyzed to generate values of gain and phase in the very low, low, and high frequencies. There was a significant decline in SIT MCAv (−3.2 ± 1.2 cm/s) compared with 2WALK (0.6 ± 1.5 cm/s, P = 0.02) but not between SIT and 8WALK (−1.2 ± 1.0 cm/s, P = 0.14). For CA, the change in 2WALK very low frequency phase (4.47 ± 4.07 degrees) was significantly greater than SIT (−3.38 ± 2.82 degrees, P = 0.02). There was no significant change in MCA or carotid artery CVR ( P > 0.05). Results indicate that prolonged uninterrupted sitting in healthy desk workers reduces cerebral blood flow; however, this is offset when frequent short-duration walking breaks are incorporated.

NEW & NOTEWORTHY Prolonged uninterrupted sitting in healthy desk workers reduces cerebral blood flow. However, this reduction in cerebral blood flow is offset when frequent short-duration walking breaks are incorporated into this sitting period. For those who engage in long periods of sedentary behavior, chronically breaking up these sitting periods with frequent active break strategies may have important implications for cerebrovascular health; however, further research should explore this hypothesis.

Dementia Patients Are More Sedentary and Less Physically Active than Age- and Sex-Matched Cognitively Healthy Older Adults

AIMS

The aim of this study was to examine physical activity and sedentary behaviour characteristics of ambulatory and community-dwelling patients with dementia compared to cognitively healthy age-, sex- and weight-matched controls.

METHODS

In this cross-sectional study, we included community-dwelling dementia patients (n = 45, age 79.6 ± 5.9 years, Mini-Mental State Examination [MMSE] 22.8 ± 3.2) and matched controls (n = 49, age 80.0 ± 7.7 years, MMSE 29.0 ± 1.2). Participants wore a wrist accelerometer for 7 days to assess sedentary time, sedentary bout duration and time spent in very light, light-to-moderate and moderate-to-vigorous physical activities.

RESULTS

Relative sedentary time and sedentary bout duration was significantly higher in dementia patients than in controls (median [interquartile range] 57% [49-68] vs. 55% [47-59] and 18.3 [16.4-21.1] min vs. 16.6 [15.3-18.4] min, p = 0.042 and p = 0.008, respectively). In addition, dementia patients spent a lower percentage of their waking time in light-to-moderate and moderate-to-vigorous intensity physical activities (20% [15-23] vs. 22% [18-25] and 5% [2-10] vs. 10% [5-13], p = 0.017 and p = 0.001, respectively).

CONCLUSION

We revealed that dementia patients are more sedentary and perform less physical activity than cognitively healthy controls. This may have clinically important consequences, given the observation that sedentary behaviour and little physical activity independently predict all-cause mortality and morbidity.

A more comprehensive investigation of disability and associated factors among older adults receiving home-based care in rural Dongguan, China

Background

No previous study has evaluated disability in older persons according to the International Classification of Functioning, Disability and Health Framework guidelines. We conducted a more comprehensive investigation of disability and associated factors among older adults receiving home-based care in rural Dongguan, a city in the central Guangdong Province of Southern China.

Methods

A total of 819 individuals aged ≥60 years were recruited from Dongguan home-based care system of via a two-stage selection process. We interviewed participants and assessed their ability level using the Ability Assessment for Older Adults, which defined by a combination of activity of daily living, sensory perception, mental status and social involvement. Conditional probability and Logistic regression approaches were used to assess the strength of association between each pair of conditions. Factors significantly associated with disability were identified via χ² tests and multinomial ordinal logistic regression.

Results

Of the 819 included participants (mean age 87 ±4.7 years), 75.5% were female, 76.7% had any disability, and 62.3% had a mild disability. The occurrence of any deficits significantly increased the likelihood of the co-occurrence of other deficits (odds ratio [OR] > 1, P < 0.05), with the lowest prevalence odds ratio observed among individuals with sensory and communication deficiency (OR: 2.99; 95% confidence interval [CI]: 2.21–4.05). Multivariable ordinal logistic regression analysis indicated that physical activity (OR: 0.96; 95% CI: 0.93–0.99), sedentary behavior (OR: 1.25; 95% CI: 1.13–1.38), not watching television (OR: 1.7; 95% CI: 1.07–2.72) and age (OR: 1.09; 95% CI: 1.02–1.17) were significantly associated with disability.

Conclusions

Impairment of ADL, sensory perception, mental status or social involvement increased the likelihood of risk of the co-occurrence of other deficits. Comprehensive disability among older adults receiving home-based care is associated with age, sedentariness, physical activity and TV viewing.

Electronic supplementary material

The online version of this article (10.1186/s12877-018-0852-x) contains supplementary material, which is available to authorized users.

Feasibility, acceptability, and potential efficacy of a childcare-based intervention to reduce sitting time among pre-schoolers: A pilot randomised controlled trial

The aim of this study was to test the feasibility, acceptability and potential efficacy of a childcare-based intervention to reduce total and prolonged sitting time in pre-schoolers. Four centres and 115 pre-schoolers (44 % boys; 4.1y) participated in a 3-month, 2-arm pilot cluster randomised controlled trial. Feasibility and acceptability were assessed through observations and semi-structured interviews. Sitting time, and breaks and bouts of sitting during childcare were assessed using an activPAL accelerometer over a one-week period at pre- and post-test (12wks). EF (inhibition, working memory and shifting) was assessed using the Early Years Toolbox. Intervention fidelity was high for both intervention centres (77 % vs 70 %) and educators reacted positively to the intervention. Proportion of sitting time per day reduced significantly at post-test in both intervention (-5.3%/day,[2.13, 8.50]) and control centres (-6.45 %,[4.20, 8.71]), resulting in a non- significant between-group difference (p = 0.51[2.4, 4.9]). EF scores did not significantly differ between groups (p > 0.05). Modifications to the childcare environment to reducing sitting, particularly the standing workstations, were feasible and acceptable to educators and children. No differences in sitting time between groups were seen; additional changes and longer-term trials are needed to reduce sitting time in pre-schoolers.

Sedentary behavior associated with reduced medial temporal lobe thickness in middle-aged and older adults

Atrophy of the medial temporal lobe (MTL) occurs with aging, resulting in impaired episodic memory. Aerobic fitness is positively correlated with total hippocampal volume, a heavily studied memory-critical region within the MTL. However, research on associations between sedentary behavior and MTL subregion integrity is limited. Here we explore associations between thickness of the MTL and its subregions (namely CA1, CA23DG, fusiform gyrus, subiculum, parahippocampal, perirhinal and entorhinal cortex,), physical activity, and sedentary behavior. We assessed 35 non-demented middle-aged and older adults (25 women, 10 men; 45-75 years) using the International Physical Activity Questionnaire for older adults, which quantifies physical activity levels in MET-equivalent units and asks about the average number of hours spent sitting per day. All participants had high resolution MRI scans performed on a Siemens Allegra 3T MRI scanner, which allows for detailed investigation of the MTL. Controlling for age, total MTL thickness correlated inversely with hours of sitting/day (r = -0.37, p = 0.03). In MTL subregion analysis, parahippocampal (r = -0.45, p = 0.007), entorhinal (r = -0.33, p = 0.05) cortical and subiculum (r = -0.36, p = .04) thicknesses correlated inversely with hours of sitting/day. No significant correlations were observed between physical activity levels and MTL thickness. Though preliminary, our results suggest that more sedentary non-demented individuals have less MTL thickness. Future studies should include longitudinal analyses and explore mechanisms, as well as the efficacy of decreasing sedentary behaviors to reverse this association.