The impact of type 2 diabetes and body mass index on cerebral structure is modulated by brain reserve

Associations of Glucose Metabolism Status with Brain Macrostructure and Microstructure: Findings from the UK Biobank

CONTEXT

Evidence linking glucose metabolism status with brain macro- and microstructure is limited and inconsistent.

OBJECTIVE

We aim to investigate the associations of glucose metabolism status with brain macrostructure and microstructure, including brain volumes, subcortical gray matter volumes, and white matter microstructural metrics.

METHODS

This study enrolled 29 251 participants from the UK Biobank. Glucose metabolism status was classified into normal glucose metabolism (NGM), prediabetes, type 2 diabetes (T2D) with HbA1c <7%, and T2D with HbA1c ≥7%. Brain macrostructural metrics included volumes of total and subcortical gray matter, white matter, white matter hyperintensity (WMH), cerebrospinal fluid, and brain stem. Brain microstructural metrics included fractional anisotropy (FA) and mean diffusivity in white matter tracts. Multivariable linear regression models were used to estimate β values and 95% CI.

RESULTS

After multivariable adjustment including demographic and lifestyle factors, medical history, and total intracranial volume, those with prediabetes had smaller total and subcortical gray matter volumes than participants with NGM, while atrophy of total and subcortical gray matter was more pronounced in those with T2D (all P trend < .05). Moreover, participants with T2D had larger volumes of white matter and WMH (both P trend < .05). For brain microstructure, participants with prediabetes had lower FA values in commissural fibers (β -0.04; 95% CI -0.08, -0.003). Global and tract-specific microstructural abnormalities of white matter were observed in participants with T2D, especially for T2D with HbA1c ≥ 7% (all P trend < .05), except for FA values in projection fibers.

CONCLUSION

These findings suggest that interventions for hyperglycemia at an earlier stage may help protect brain health.

Association between Type 2 Diabetes Mellitus and Brain Atrophy: A Meta-Analysis

BACKGROUND

Type 2 diabetes mellitus (T2DM) is known to be associated with cognitive decline and brain structural changes. This study systematically reviews and estimates human brain volumetric differences and atrophy associated with T2DM.

METHODS

PubMed, PsycInfo and Cochrane Library were searched for brain imaging studies reporting on brain volume differences between individuals with T2DM and healthy controls. Data were examined using meta-analysis, and association between age, sex, diabetes characteristics and brain volumes were tested using meta-regression.

RESULTS

A total of 14,605 entries were identified; after title, abstract and full-text screening applying inclusion and exclusion criteria, 64 studies were included and 42 studies with compatible data contributed to the meta-analysis (n=31,630; mean age 71.0 years; 44.4% male; 26,942 control; 4,688 diabetes). Individuals with T2DM had significantly smaller total brain volume, total grey matter volume, total white matter volume and hippocampal volume (approximately 1% to 4%); meta-analyses of smaller samples focusing on other brain regions and brain atrophy rate in longitudinal investigations also indicated smaller brain volumes and greater brain atrophy associated with T2DM. Meta-regression suggests that diabetes-related brain volume differences start occurring in early adulthood, decreases with age and increases with diabetes duration.

CONCLUSION

T2DM is associated with smaller total and regional brain volume and greater atrophy over time. These effects are substantial and highlight an urgent need to develop interventions to reduce the risk of T2DM for brain health.

Factors Influencing Change in Brain-Predicted Age Difference in a Cohort of Healthy Older Individuals

Background

There is considerable variability in the rate at which we age biologically, and the brain is particularly susceptible to the effects of aging.

Objective

We examined the test-retest reliability of brain age at one- and three-year intervals and identified characteristics that predict the longitudinal change in brain-predicted age difference (brain-PAD, defined by deviations of brain age from chronological age).

Methods

T1-weighted magnetic resonance images were acquired at three timepoints from 497 community-dwelling adults (73.8±3.5 years at baseline, 48% were female). Brain age was estimated from whole brain volume, using a publicly available algorithm trained on an independent dataset. Linear mixed models were used, adjusting for sex, age, and age2.

Results

Excellent retest reliability of brain age was observed over one and three years. We identified a significant sex difference in brain-PAD, where a faster rate of brain aging (worsening in brain age relative to chronological age) was observed in men, and this finding replicated in secondary analyses. The effect size, however, was relatively weak, equivalent to 0.16 years difference per year. A higher score in physical health related quality of life and verbal fluency were associated with a faster rate of brain aging, while depression was linked to a slower rate of brain aging, but these findings were not robust.

Conclusion

Our study provides consistent evidence that older men have slightly faster brain atrophy than women. Given the sparsity of longitudinal research on brain age in older populations, future prospective studies are needed to confirm our findings.

Gait and balance impairments in patients with subcortical vascular cognitive impairment

Background

Subcortical vascular cognitive impairment (SVCI) is a subtype of vascular cognitive impairment associated with extensive cerebral small vessel diseases (CSVDs) imaging biomarkers. The objectives of this work were to study the existence and patterns of gait and balance impairments in patients with SVCI due to CSVDs.

Methods

The study was conducted on 28 newly diagnosed SVCI patients and 22 healthy control subjects (HCS) submitted to the advanced activity of daily living scale (AADLs), Berg balance test (BBT), Montreal Cognitive Assessment Scale (MoCA), computerized dynamic posturography (CDP), vision-based 3-D skeletal data gait analysis, and brain MRI volumetric assessment.

Results

SVCI patients showed a significant decrease in AADLs as well as total cerebral white matter volume, total cerebral cortical volume, and mean cortical thickness which were proportional to the degree of cognitive impairment as measured by the MoCA score. Regarding CDP analysis, patients with SVCI revealed prolongation of cancelation time and spectral power for mid- and high frequencies in dynamic positions. In respect to gait analysis, there were significant decreases in mean stride length and mean cadence as well as increases in mean step width and left to right step length difference in the SVCI group compared to HCS while doing a single task. These variables get highly significant during the dual-task performance with a p value < 0.001 for each one.

Conclusion

Patients with SVCI suffer from gait and balance impairments that are proportional to the severity of their cognitive decline and greatly impair their ADLs.

A multimodal meta-analysis of regional structural and functional brain alterations in type 2 diabetes

Neuroimaging studies have identified brain structural and functional alterations of type 2 diabetes mellitus (T2DM) patients; however, there is no systematic information on the relations between abnormalities in these two domains. We conducted a multimodal meta-analysis of voxel-based morphometry and regional resting-state functional MRI studies in T2DM, including fifteen structural datasets (693 patients and 684 controls) and sixteen functional datasets (378 patients and 358 controls). We found, in patients with T2DM compared to controls, conjoint decreased regional gray matter volume (GMV) and altered intrinsic activity mainly in the default mode network including bilateral superior temporal gyrus/Rolandic operculum, left middle and inferior temporal gyrus, and left supramarginal gyrus; decreased GMV alone in the limbic system; and functional abnormalities alone in the cerebellum, insula, and visual cortex. This meta-analysis identified complicated patterns of conjoint and dissociated brain alterations in T2DM patients, which may help provide new insight into the neuropathology of T2DM.

Higher Framingham Risk Scores are associated with greater loss of brain volume over time in multiple sclerosis

BACKGROUND

Few studies have evaluated the association between comorbidities associated with increased vascular risk and brain volume changes in multiple sclerosis (MS). To date, findings have not been consistent with respect to which comorbidities are associated with lower brain volumes or whether comorbidities associated with increased vascular risk are associated with greater brain volume loss over time.

OBJECTIVES

We aimed to evaluate the association between the Framingham Risk Score (FRS) which evaluates vascular risk and normalized whole brain volume in MS.

METHODS

We included 98 participants with MS who underwent two brain MRIs two years apart, from which whole brain volumes were calculated. Each participant reported their comorbidities and medications taken. Blood pressure, height and weight were recorded and we calculated the FRS. We tested the association between the FRS at baseline and brain volume at the second time point using quantile regression adjusting for baseline normalized brain volume, age, gender and use of disease-modifying therapy.

RESULTS

As the FRS increased, brain volume was lower, both at enrollment (β= -0.24; 95%CI: -0.42, -0.04) and at follow-up (-0.27; 95%CI: -0.45, -0.08). After further adjustment for age, gender, and use of disease modifying therapy, higher FRS remained associated with lower brain volume at follow-up at the 90th percentile of brain volume (β= -2.22; 95%CI: -3.40, -1.04) but not at the 10th or 50th percentiles.

CONCLUSION

Higher FRS were associated with lower brain volumes in persons with MS at baseline, and with brain volume loss over time. This effect was most pronounced for persons with higher brain volumes at baseline, which suggests that prevention, detection and effective management of comorbidities associated with vascular risk in people with MS is particularly important early in the disease course.

Brain deficits in prediabetic adults: A systematic review

Previous findings on the relationship between prediabetes (the precursor stage of type 2 diabetes) and brain health in humans are inconsistent. Thus, this systematic review of cross-sectional and longitudinal studies aimed to summarize what is currently known about brain deficits in prediabetic adults. Following the PRISMA reporting standards for systematic reviews, we conducted a comprehensive review of peer-reviewed journal articles published from 2009 to present, focusing on studies that assessed brain volume, structural connectivity, and cerebrovascular health in prediabetic adults and older adults (i.e., 18 years or older). We systematically searched PsychINFO, Scopus, Web of Science, Ovid MEDLINE, CINAHL, and EMbase databases. Quality assessment was based on the NIH Quality Assessment Tool for Observational and Cross-sectional Studies. In total, 19 studies were included in our review. Results from these studies show that prediabetes may be associated with deficits in brain structure and pathology, however, several studies also refute these findings. Moreover, we identified clear inconsistencies in study methodologies, including diabetes measures and classification, across studies that may account for these conflicting findings.

Cognitive and balance impairments in people with incidental white matter hyperintensities

Background

White matter hyperintensities (WMHs) is the most frequent type of cerebral small vessel diseases and a common incidental finding in MRI films of the geriatric population. The objectives of this work were to study the existence of occult cognitive and balance impairments in subjects with accidentally discovered WMHs.

Methods

The study was conducted on 44 subjects with accidentally discovered WMHs and 24 non-WMHs subjects submitted to the advanced activity of daily living scale (AADLs), a neurocognitive battery assessing different cognitive domains, Berg balance test (BBT), computerized dynamic posturography (CDP), and brain MRI diffusion tensor tractography (DTT).

Results

WMHs subjects showed a significant decrease in AADLs as well as visual and vestibular ratios of CDP. Regarding the neurocognitive battery, there were significant decreases in MoCA as well as arithmetic test and block design of Wechsler adult intelligence scale-IV in WMHs compared to non-WMHs subjects’ groups (p value < 0.001). Concerning Wisconsin Card Sorting subtests, each preservative response, preservative errors, non-preservative errors and trials to complete the 1st category showed a highly significant increase in WMHs compared to non-WMHs subjects (p values < 0.001). DTT showed a substantial reduction in fractional anisotropy (FA) of each corticospinal tract, thalamocortical connectivity, and arcuate fasciculi.

Conclusion

Subjects with WMHs have lower cognitive performance and subtle balance impairment which greatly impair their ADLs.

Higher BMI is associated with smaller regional brain volume in older adults with type 2 diabetes

AIMS/HYPOTHESIS

There are established relationships between adiposity (obesity) and higher dementia risk, faster cognitive decline and associated neural injury. Type 2 diabetes is strongly linked to greater adiposity and has been consistently associated with neural injury and poor cognitive outcomes. However, although obesity is a major cause of type 2 diabetes, there is limited evidence on the association of adiposity with brain atrophy among individuals with type 2 diabetes.

METHODS

We examined the association of BMI (a measure of adiposity), and of long-term trajectories of BMI (three empirically identified groups of trajectories-'normal', 'overweight' and 'obese'-using SAS macro PROC TRAJ), with regional brain volume, in a sample of older individuals (aged 64-84) with type 2 diabetes participating in the Israel Diabetes and Cognitive Decline Study (n = 198).

RESULTS

Using linear regression, we found that greater BMI was associated with smaller volumes of the inferior frontal gyrus (IFG) (r = -0.25, p = 0.001) and the middle temporal gyrus (r = -0.19; p = 0.010) after adjusting for sociodemographic covariates and total intracranial volume. In addition, there were significant differences between BMI trajectory groups in IFG volume (F = 4.34, p = 0.014), such that a long-term trajectory of obesity was associated with a smaller volume. Additional adjustment for cardiovascular and diabetes-related potential confounders did not substantively alter the results. There were no associations of adiposity with superior frontal gyrus, middle frontal gyrus or total grey matter volumes.

CONCLUSIONS/INTERPRETATION

In older adults with type 2 diabetes, long-term adiposity may have a detrimental impact on volume of brain regions relevant to cognitive functioning. Further studies to identify the underlying mechanisms are warranted. Graphical abstract.

Prediabetes and structural brain abnormalities: Evidence from observational studies

Type 2 diabetes mellitus has been linked to structural brain abnormalities, but evidence of the association among prediabetes and structural brain abnormalities has not been systematically evaluated. Comprehensive searching strategies and relevant studies were systematically retrieved from PubMed, Embase, Medline and web of science. Twelve articles were included overall. Stratified analyses and regression analyses were performed. A total of 104 468 individuals were included. The risk of infarct was associated with continuous glycosylated haemoglobin (HbA_1c ) [adjusted odds ratio (OR) 1.19 (95% confidence interval [CI]: 1.05-1.34)], or prediabetes [adjusted OR 1.13 (95% CI: 1.00-1.27)]. The corresponding ORs associated with white matter hyperintensities were 1.08 (95%CI: 1.04-1.13) for prediabetes, and 1.10 (95%CI: 1.08-1.12) for HbA_1c . The association was significant between the decreased risk of brain volume with continuous HbA_1c (the combined OR 0.92, 95% CI: 0.87-0.98). Grey matter volume and white matter volume were inversely associated with prediabetes [weighted mean deviation (WMD), -9.65 (95%CI: -15.25 to -4.04) vs WMD, -9.25 (95%CI: -15.03 to -3.47)]. There were no significant association among cerebral microbleeds, hippocampal volume, continuous total brain volume, and prediabetes. Our findings demonstrated that (a) both prediabetes and continuous HbA_1c were significantly associated with increasing risk of infarct or white matter hyperintensities; (b) continuous HbA_1c was associated with a decreased risk of brain volume; (c) prediabetes was inversely associated with grey matter volume and white matter volume. To confirm these findings, further studies on early diabetes onset and structural brain abnormalities are needed.

Sugar in mind: Untangling a sweet and sour relationship beyond type 2 diabetes

It is widely recognised that type 2 diabetes (T2D) represents a major disease burden but it is only recently that its role in neurodegeneration has attracted more attention. This research has shown that T2D is associated with impaired cerebral health, cognitive decline and dementia. However, the impact on the brain of progressive metabolic changes associated with the pre-clinical development of the disease is less clear. The aim of this review is to comprehensively summarise how the emergence of risk factors and co-morbid conditions linked to the development of T2D impact cerebral health. Particular attention is directed at characterising how normal but elevated blood glucose levels in individuals without T2D contribute to neurodegenerative processes, and how the main risk factors for T2D including obesity, physical activity and diet modulate these effects. Where available, evidence from the animal and human literature is contrasted, and sex differences in risk and outcomes are highlighted.