Metabolic and endocrine correlates of cognitive function in healthy young women

The Association of Plasma Leptin, Soluble Leptin Receptor and Total and High-Molecular Weight Adiponectin With the Risk of Perioperative Neurocognitive Disorders

BACKGROUND

Perioperative neurocognitive disorders (NCD) are poorly characterized in terms of their risk factor profiles. Leptin and adiponectin are adipose-tissue-derived hormones with a role in inflammation and atherosclerosis whose function in perioperative NCD is unclear. Here, we used a cohort of older adults to examine the association of preoperative plasma concentrations of these biomarkers with the risk of perioperative NCD.

METHODS

Prospective analysis of 768 participants aged ≥ 65 years of the BioCog study. Blood was collected before surgery for measurement of plasma total and high-molecular-weight (hmw) adiponectin, leptin, and soluble leptin receptor (sOB-R). The free leptin index (FLI, leptin:sOB-R) was calculated. Postoperative delirium (POD) was assessed twice daily until postoperative day 7/discharge. Five hundred twenty-six patients (68.5%) returned for 3-month follow-up and provided data on postoperative cognitive dysfunction (POCD). POCD was defined as a decline on six neuropsychological tests that exceeded that of a nonsurgical control group. Logistic regression analyses examined the associations of each exposure with POD and POCD risk, in separate models adjusted for age, sex, fasting, surgery type, and body mass index (BMI).

RESULTS

Of 768 patients, 152 (19.8%) developed POD. Of 526 attendants of the follow-up, 54 (10.3%) had developed POCD. Leptin, sOB-R, and total and hmw adiponectin were each not associated with POD. For POCD, we observed reduced risk in patients in FLI quartile 4 compared with quartile 1 (odds ratio, 0.26; 95% CI 0.08, 0.89). Sensitivity analyses for the outcome POD revealed statistically significant interaction terms of sOB-R and total adiponectin with obesity (BMI≥30kg/m2 versus BMI<30kg/m2). For the outcome POCD, a higher sOB-R was associated with an increased risk in the obese subgroup (odds ratio, 4.00; 95% CI 1.01, 15.86).

CONCLUSIONS

We did not find consistent evidence for the role of leptin, its receptor, and total and hmw adiponectin in POD and POCD risk. Future research should be used to support or refute our findings and to fully characterize any differences in the associations of these hormones with POD/POCD between obese and nonobese individuals.

Cognitive performance in young adult women with a history of premature adrenarche

BACKGROUND

Girls with premature adrenarche (PA) mature earlier than peers and have been found to have greater symptom accounts reflecting anxiety compared to peers. It is not known, however, whether PA effects cognitive development. This longitudinal case-control cohort study aimed: (1) To investigate whether a history of PA leads to measurable changes in adulthood cognitive performance, and (2) to assess whether findings characteristic of PA girls predict adulthood cognitive performance.

METHODS

Twenty-seven girls with PA and 27 age-matched control girls were examined and followed from mid-childhood (mean age 7.2 years) until early adult age (18.5 years). Wechsler Adult Intelligence Scale, Fourth Edition scores were used as main outcome measure.

RESULTS

Allostatic load (AL) scores, which compile multisystem variables to reflect the overall wear and tear of the body from increased and prolonged stress, were higher in the PA group in both prepuberty and adulthood, but there were no differences in WAIS-IV results between the groups (full-scale IQ 92.7 vs. 97.5, p 0.376; no differences in separate indexes). Childhood androgen levels, glucose metabolism biomarkers, and AL scores failed to predict adulthood cognitive performance outcomes.

CONCLUSION

The study suggests that PA does not predispose to adverse adulthood outcomes of cognitive development.

IMPACT

The study suggests that a history of premature adrenarche (PA) does not affect cognitive performance in adult age. Childhood androgen levels and biomarkers of glucose metabolism failed to predict adulthood cognitive outcomes in this study. Allostatic load scores were elevated in the PA group both in childhood and adulthood but did not predict adulthood cognitive outcomes.

Association between the triglyceride-glucose index and cognitive impairment in China: a community population-based cross-sectional study

INTRODUCTION

Insulin resistance (IR) is a feature of metabolic syndrome and plays an important role in cognitive impairment (CI). The triglyceride-glucose (TyG) index is a convenient and cost-effective surrogate for assessing IR. This study aimed to assess the association between the TyG index and CI.

METHODS

This community population-based cross-sectional study used a cluster-sampling methodology. All participants underwent the education-based Mini-Mental State Examination (MMSE), and those with CI were identified using standard thresholds. The fasting blood triglyceride and glucose levels were measured in the morning, and the TyG index was calculated as ln (½ fasting triglyceride level [mg/dL] × fasting blood glucose level [mg/dL]). Multivariable logistic regression and subgroup analysis were used to assess the relationship between the TyG index and CI.

RESULTS

This study included 1484 subjects, of which 93 (6.27%) met the CI criteria. Multivariable logistic regression showed that CI incidence increased by 64% per unit increase in the TyG index (odds ratio [OR] = 1.64, 95% confidence interval [CI]: 1.02-2.63, p = 0.042). CI risk was 2.64-fold higher in the highest TyG index quartile compared to the lowest TyG index quartile (OR = 2.64, 95% CI: 1.19-5.85, p = 0.016). Finally, interaction analysis showed that sex, age, hypertension, and diabetes did not significantly affect the association between the TyG index and CI.

CONCLUSION

The present study suggested that an elevated TyG index was associated with a higher CI risk. Subjects with a higher TyG index should manage and treat at an early stage to alleviate the cognitive decline.

Obesity reduces hippocampal structure and function in older African Americans with the APOE-ε4 Alzheimer's disease risk allele

Introduction

Excess body weight and Alzheimer's disease (AD) disproportionately affect older African Americans. While mid-life obesity increases risk for AD, few data exist on the relationship between late-life obesity and AD, or how obesity-based and genetic risk for AD interact. Although the APOE-ε4 allele confers a strong genetic risk for AD, it is unclear if late-life obesity poses a greater risk for APOE-ε4 carriers compared to non-carriers. Here we assessed: (1) the influence of body mass index (BMI) (normal; overweight; class 1 obese; ≥ class 2 obese) on cognitive and structural MRI measures of AD risk; and (2) the interaction between BMI and APOE-ε4 in older African Americans.

Methods

Seventy cognitively normal older African American participants (Mage = 69.50 years; MBMI = 31.01 kg/m2; 39% APOE-ε4 allele carriers; 86% female) completed anthropometric measurements, physical assessments, saliva collection for APOE-ε4 genotyping, cognitive testing, health and lifestyle questionnaires, and structural neuroimaging [volume/surface area (SA) for medial temporal lobe subregions and hippocampal subfields]. Covariates included age, sex, education, literacy, depressive symptomology, and estimated aerobic fitness.

Results

Using ANCOVAs, we observed that individuals who were overweight demonstrated better hippocampal cognitive function (generalization of learning: a sensitive marker of preclinical AD) than individuals with normal BMI, p = 0.016, ηp2 = 0.18. However, individuals in the obese categories who were APOE-ε4 non-carriers had larger hippocampal subfield cornu Ammonis region 1 (CA1) volumes, while those who were APOE-ε4 carriers had smaller CA1 volumes, p = 0.003, ηp2 = 0.23.

Discussion

Thus, being overweight by BMI standards may preserve hippocampal function, but obesity reduces hippocampal structure and function in older African Americans with the APOE-ε4 Alzheimer's disease risk allele.

Possible cognition changes in women with polycystic ovary syndrome: a narrative review

Nowadays, polycystic ovary syndrome (PCOS) and cognitive dysfunction are major health problems among female. This narrative review aimed to investigate cognitive dysfunction in female with PCOS. English and Persian articles published in PubMed, Scopus, Web of Science, Google Scholar, PsycINFO, Scientific Information Database, and Cochrane Database of Systematic Reviews until May 2022 were searched. Sixteen studies involving 850 female with PCOS and 974 controls were assessed. In these studies, the association between biochemical factors and symptoms of PCOS and memory, attention, executive functioning, information processing speed, and visuospatial skills was evaluated. The literature review revealed the possible cognitive changes in female with PCOS. This study summarized the different aspects of cognitive function in female with PCOS due to medication, psychological problems (mood disorders caused by disease symptoms and complications), and biochemical markers, such as metabolic and sex hormone abnormalities. Considering the existing scientific gap regarding the possibility of cognitive complications in female with PCOS, further biological studies should be conducted to evaluate the potential mechanisms involved.

Relationships Between Body Composition and Cognitive Impairment in Hospitalised Middle-Aged Type 2 Diabetic Patients

Objective

The aim of this study was to elucidate the relationship between specific body composition and the risk of Cognitive Impairment (CI) in middle-aged Type 2 Diabetes Mellitus (T2DM) patients.

Methods

This cross-sectional study included 504 hospitalized patients with T2DM from the Department of Endocrinology and Metabolism of the Tianjin Union Medical Center. Subjects were grouped by sex, and cognitive status was assessed using the Montreal Cognitive Assessment (MoCA). The relationship between body composition and cognitive ability was investigated with the use of linear regression analysis. The association between body composition and CI risk was determined by logistic regression analysis.

Results

The prevalence of CI was 39.3% in middle-aged T2DM patients. After adjusting for age, education, marriage status, carotid atherosclerosis, cerebrovascular disease and hemoglobin, multiple linear regression analysis showed that lean mass index (LMI), body mass index (BMI) and appendicular skeletal muscle index (SMI) were significant predictors for the MoCA scores in men (p < 0.05). In addition, BMI (OR 0.913, 95% CI 0.840-0.992) and LMI (OR 0.820, 95% CI 0.682-0.916) were independent protective factors for CI in males. After adjusted for age, education, marriage status, dietary control of diabetes and cerebrovascular disease, visceral obesity (VO, OR 1.950, 95% CI 1.033-3.684) and abdominal obesity (AO, OR 2.537, 95% CI 1.191-5.403) were risk factors for CI in female patients.

Conclusion

The results suggest that there may be different mechanisms underlying the relationship of body compositions and cognitive performance between middle-aged male and female patients with T2DM. In addition, our finding of potential determinants of cognitive impairment may facilitate the development of intervention programs for middle-aged type 2 diabetic patients. Nevertheless, more large prospective studies looking at cognition and changes in body composition over time are needed in the future to further support their association.

Review of the effects of polycystic ovary syndrome on Cognition: Looking beyond the androgen hypothesis

Polycystic-ovary syndrome (PCOS) is the most common endocrine disorder affecting women of reproductive age, and many features associated with PCOS - such as elevated androgens, insulin resistance and inflammation - are known to affect cognition. However, effects of PCOS on cognition are not well-understood. Here we review the current literature on PCOS and cognition, note the extent of PCOS symptomatology studied in relation to cognitive outcomes, and identify key research gaps and common methodological concerns. Findings indicate a pattern of worse performance across cognitive domains and brain measures in women with PCOS relative to non-PCOS controls, as well as a lack of evidence for the common assumption that women with PCOS will have higher performance on tasks with a demonstrated male-advantage due to high testosterone levels. We suggest strategies for moving beyond the focus on elevated androgens, in favor of research practices that account for the nuances and heterogeneity of PCOS symptoms.

Endophenotypic correlates of cognitive function in reproductive-age individuals with polycystic ovary syndrome

Objective

To characterize cognitive performance in relation to hormonal and metabolic factors in women with polycystic ovary syndrome (PCOS).

Design

Cross-sectional study.

Setting

Tertiary university center.

Patients

A total of 48 individuals, aged 21-46 years, with PCOS according to the Rotterdam criteria.

Interventions

Complete history and physical examinations, endovaginal ultrasounds, dermatologic assessments, neuropsychological assessments, and metabolic and hormonal serum tests.

Main Outcome Measures

Sample-based z-scores on a comprehensive cognitive test battery.

Results

Subjects were defined as having an androgenic (n = 31) or a nonandrogenic (n = 17) PCOS phenotype. Compared with their nonandrogenized counterparts, subjects with hyperandrogenism demonstrated lower relative performance on the tests of executive function (β-coefficient for the executive function composite z-score, -0.44; 95% confidence interval, -0.79 to -0.09), despite similar performance on the tests of memory, verbal reasoning, and perceptual reasoning. These differences were independent of age, years of education, and obesity. In an exploratory analysis in which subjects were stratified by the presence of insulin resistance (IR), subjects with PCOS with both IR and hyperandrogenism showed the lowest performance on a composite score of executive function, followed by those with hyperandrogenism alone.

Conclusions

In this small study, subjects with hyperandrogenic PCOS demonstrated lower performance on the tests of executive function than subjects with nonandrogenic PCOS. Additional research is needed to confirm these findings in larger cohorts and investigate the role of modifiable factors, including IR, on cognitive outcomes.

Visceral adiposity, inflammation, and hippocampal function in obesity

The 'apple-shaped' anatomical pattern that accompanies visceral adiposity increases risk for multiple chronic diseases, including conditions that impact the brain, such as diabetes and hypertension. However, distinguishing between the consequences of visceral obesity, as opposed to visceral adiposity-associated metabolic and cardiovascular pathologies, presents certain challenges. This review summarizes current literature on relationships between adipose tissue distribution and cognition in preclinical models and highlights unanswered questions surrounding the potential role of tissue- and cell type-specific insulin resistance in these effects. While gaps in knowledge persist related to insulin insensitivity and cognitive impairment in obesity, several recent studies suggest that cells of the neurovascular unit contribute to hippocampal synaptic dysfunction, and this review interprets those findings in the context of progressive metabolic dysfunction in the CNS. Signalling between cerebrovascular endothelial cells, astrocytes, microglia, and neurons has been linked with memory deficits in visceral obesity, and this article describes the cellular changes in each of these populations with respect to their role in amplification or diminution of peripheral signals. The picture emerging from these studies, while incomplete, implicates pro-inflammatory cytokines, insulin resistance, and hyperglycemia in various stages of obesity-induced hippocampal dysfunction. As in the parable of the five blind wanderers holding different parts of an elephant, considerable work remains in order to assemble a model for the underlying mechanisms linking visceral adiposity with age-related cognitive decline.

Insulin resistance and NAFLD may influence memory performance in obese patients with prediabetes or newly-diagnosed type 2 diabetes

BACKGROUND AND AIMS

Diabetes has consistently been shown to increase risk for cognitive decline. Cognitive deficits may occur at the very earliest stages of diabetes. We sought to estimate the determinants of memory function in a group of middle-aged obese subjects with prediabetes or newly-diagnosed type 2 diabetes mellitus.

METHODS AND RESULTS

Sixty-two obese patients in treatment with metformin-with prediabetes (n = 41) or newly diagnosed T2DM (n = 21), were studied. Short- and long-term memory function was assessed through a neuropsychological assessment consisting of two tests and a composite domain z score was calculated. Cardiometabolic variables, such as abdominal MRI quantification of subcutaneous (SAT) and visceral (VAT) adipose tissue content, and of intra-hepatocellular lipid content, as well as insulin sensitivity (Matsuda Index, HOMA-IR) and beta cell performance (Beta Index), by multiple sampling, 8-point oral glucose tolerance test, were also evaluated. Age, non-alcoholic fatty liver disease (NAFLD), and lnHOMA-IR together explained 18% (R square) of the variance in memory domain. Including NAFLD increased the explained variance by 8% and including lnHOMA-IR by 9.1%, whereas the contribution of age and other factors was negligible.

CONCLUSION

Preventing and managing insulin resistance in precocious and possibly earlier stages of diabetes might provide benefit in slowering down future cognitive decline.

Eight Days of Water-Only Fasting Promotes Favorable Changes in the Functioning of the Urogenital System of Middle-Aged Healthy Men

The aim of this study was to determine whether, after 8 days of water-only fasting, there are changes in the efficiency of the lower urinary tract, the concentration of sex hormones, and the symptoms of prostate diseases in a group of middle-aged men (n = 14). For this purpose, before and after 8 days of water-only fasting (subjects drank ad libitum moderately mineralized water), and the following somatic and blood concentration measurements were made: total prostate specific antigen (PSA-T), free prostate specific antigen (PSA-F), follicle stimulating hormone (FSH), luteotropic hormone (LH), prolactin (Pr), total testosterone (T-T), free testosterone (T-F), dehydroepiandrosterone (DHEA), sex hormone globulin binding (SHGB), total cholesterol (Ch-T), β-hydroxybutyrate (β-HB). In addition, prostate volume (PV), volume of each testis (TV), total volume of both testes (TTV), maximal urinary flow rate (Qmax), and International Prostate Symptom Score (IPSS) values were determined. The results showed that after 8 days of water-only fasting, Qmax and IPSS improved but PV and TTV decreased significantly. There was also a decrease in blood levels of PSA-T, FSH, P, T-T, T-F, and DHEA, but SHGB concentration increased significantly. These results indicate that 8 days of water-only fasting improved lower urinary tract functions without negative health effects.

Plasma leptin, but not adiponectin, is associated with cognitive impairment in older adults

BACKGROUND

Leptin and adiponectin are adipose-tissue derived hormones primarily involved in glucose, lipid, and energy metabolism, inflammation, and atherosclerosis. Both adipokines may cross the blood-brain barrier but evidence on their roles in cognitive impairment is limited and conflicting. Here, we determined associations of plasma adipokine concentration with cognitive impairment in older adults.

METHODS

Cross-sectional analysis of baseline data from 669 participants aged ≥65 years of the Biomarker Development for Postoperative Cognitive Impairment in the Elderly (BioCog) study were recruited 2014-2017 at study sites in Berlin, Germany and Utrecht, the Netherlands. Cognitive impairment was defined as the lowest tertile of a cognitive summary score derived from six neuropsychological tests.

RESULTS

After adjustment for age, sex, fasting, BMI, diabetes, hypertension, cerebrovascular disease, and coronary heart disease, higher leptin concentrations and a higher leptin/adiponectin ratio (LAR) were associated with a higher odds of cognitive impairment (OR per 1 SD higher leptin concentration, 1.33; 95 % CI 1.05, 1.69; p = 0.02; OR per 1 SD higher LAR, 1.26; 95 % CI 1.01, 1.57; p = 0.04). Sensitivity analyses determined that these findings were driven by the non-obese group (BMI < 30 kg/m²), whereas leptin and LAR were not associated with cognitive impairment in the obese group (BMI ≥ 30 kg/m²). Soluble leptin receptor, leptin/soluble leptin receptor ratio, total adiponectin and high-molecular weight adiponectin concentrations were each not associated with impairment.

CONCLUSIONS

With leptin as a known promoter of atherosclerosis and inflammation, our findings point to a pathogenic role of leptin in age-related cognitive impairment that may be limited to non-obese individuals and warrants further investigation.

Relationship Between Psychological Distress and Cognitive Function Differs as a Function of Obesity Status in Inpatient Heart Failure

Heart failure (HF) is a chronic medical condition rapidly growing in prevalence. Evidence links HF to cognitive decline, obesity, and psychological distress. The current study examined the association between cognitive function and ejection fraction (EF%), anxiety, depression, and obesity in inpatient HF. Patients completed the Generalized Anxiety Disorder 7-Item Scale (GAD-7), Patient Health Questionnaire 9-Item Scale (PHQ-9), and Mini-Cog while hospitalized for HF. Additional demographic and medical information was gathered via chart review. All models controlled for age. Of 117 patients assessed (49% male), 55% (n = 64) were obese. ANCOVA analyses were conducted comparing those with obesity and without on cognitive function: model A included EF%, model B included depression, and model C included anxiety. All three models were significantly related to cognitive function. There was a significant interaction effect of EF% and obesity and of anxiety and obesity to predict Mini-Cog scores. Post hoc partial correlational analyses revealed that anxiety was negatively associated with Mini-Cog scores among only patients without obesity. Depression was not significantly related to cognitive function in either group. However, patients with obesity demonstrated higher depression and anxiety than patients without. Results suggest that at lower EF%, and with higher anxiety, patients without obesity may be at greater risk of cognitive dysfunction than those with obesity. Cognitive dysfunction among HF patients with obesity may be independent of psychological distress. These findings may reflect the “obesity paradox” observed among HF patients, in that patients with obesity may have a different biopsychosocial presentation, which may lead to unexpected clinical outcomes. Further research is necessary to articulate the relationship of obesity and cognitive function in HF.

Metabolic and Neurocognitive Changes Following Lifestyle Modification: Examination of Biomarkers from the ENLIGHTEN Randomized Clinical Trial

BACKGROUND

Previous studies have demonstrated that aerobic exercise (AE) and the Dietary Approaches to Stop Hypertension (DASH) diet can improve neurocognition. However, the mechanisms by which lifestyle improves neurocognition have not been widely studied. We examined the associations between changes in metabolic, neurotrophic, and inflammatory biomarkers with executive functioning among participants from the Exercise and Nutritional Interventions for Neurocognitive Health Enhancement (ENLIGHTEN) trial.

OBJECTIVE

To examine the association between changes in metabolic function and neurocognition among older adults with cognitive impairment, but without dementia (CIND) participating in a comprehensive lifestyle intervention.

METHODS

ENLIGHTEN participants were randomized using a 2×2 factorial design to receive AE, DASH, both AE+DASH, or a health education control condition (HE) for six months. Metabolic biomarkers included insulin resistance (homeostatic model assessment [HOMA-IR]), leptin, and insulin-like growth factor (IGF-1); neurotrophic biomarkers included brain derived neurotrophic factor (BDNF) and vascular endothelial growth factor (VEGF); and inflammatory biomarkers included interleukin-6 (IL-6) and C-Reactive Protein (CRP).

RESULTS

Participants included 132 sedentary older adults (mean age = 65 [SD = 7]) with CIND. Results demonstrated that both AE (d = 0.48, p = 0.015) and DASH improved metabolic function (d = 0.37, p = 0.039), without comparable improvements in neurotrophic or inflammatory biomarkers. Greater improvements in metabolic function, including reduced HOMA-IR (B = -2.3 [-4.3, -0.2], p = 0.033) and increased IGF-1 (B = 3.4 [1.2, 5.7], p = 0.004), associated with increases in Executive Function.

CONCLUSION

Changes in neurocognition after lifestyle modification are associated with improved metabolic function.

Dysglycemia, Not Altered Sex Steroid Hormones, Affects Cognitive Function in Polycystic Ovary Syndrome

Context

Polycystic ovary syndrome (PCOS) is a complex endocrine condition characterized by multiple reproductive and metabolic abnormalities. Because individual reproductive and metabolic abnormalities modulate working memory in the general population, there is growing interest in whether cognitive function is dually and negatively affected in PCOS.

Objective

To examine the association of reproductive and metabolic features with cognitive function in women with and without PCOS.

Design

An observational, cross-sectional study was conducted at an academic clinical research center in North America between 2006 and 2009. Common tests of working memory (i.e., manual dexterity, perceptual speed, and visuospatial ability) were performed by women with PCOS (n = 40) and control subjects (n = 40). Markers of sex steroid hormones, ovulatory function, and cardiometabolic health were also assessed.

Results

Reduced visuospatial ability was observed in women with PCOS compared with control subjects (P < 0.01). Reduced visuospatial ability was linked to higher levels of hemoglobin A1c in the entire study cohort, independent of body mass index or PCOS status. No associations were observed between visuospatial ability and reproductive features, after controlling for confounding variables.

Conclusion

Our findings support a role for glycemic control, and not PCOS per se, in cognitive dysfunction in women of reproductive age. Additional studies are needed to understand the short- and long-term effects of dysglycemia on brain health in women with PCOS, given their increased propensity for metabolic comorbidities, compared with control subjects.

Associations of insulin resistance with cognition in individuals without diagnosed diabetes: Results from the Hispanic Community Health Study/Study of Latinos

AIMS

Insulin resistance (IR) adversely impacts memory and executive functioning in non-Hispanic whites without diabetes. Less is known in Hispanics/Latinos, despite the fact that Hispanics/Latinos have higher rates of insulin resistance than non-Hispanic whites. We investigated the association between IR and cognition and its variation by age.

METHODS

Data from 5987 participants 45-74 years old without diabetes from the Hispanic Community Health Study/Study of Latinos. IR was considered continuously using homeostasis model assessment for insulin resistance (HOMA-IR) and also dichotomized based on clinically relevant thresholds for hyperinsulinemia (fasting insulin > 84.73 pmol/L or HOMA-IR > 2.6) and sample-based norms (75th percentile of fasting insulin or HOMA-IR). Cognitive testing included the Brief Spanish English Verbal Learning Test (B-SEVLT), Verbal Fluency, and Digit Symbol Substitution.

RESULTS

There was 90% overlap in participant categorization comparing clinically relevant and sample-based thresholds. In separate fully-adjusted linear regression models, age modified the association between HOMA-IR and Digit Symbol Substitution (p = 0.02); advancing age combined with higher HOMA-IR levels resulted in higher scores. Age also modified the association between clinically relevant hyperinsulinemia and B-SEVLT recall (p = 0.03); with increasing age came worse performance for individuals with hyperinsulinemia.

CONCLUSION

The relationship of IR with cognition in Hispanics/Latinos without diabetes may reflect an age- and test-dependent state.

Association Between Insulin Resistance, Plasma Leptin, and Neurocognition in Vascular Cognitive Impairment

BACKGROUND

Greater body weight has been associated impairments in neurocognition and greater dementia risk, although the mechanisms linking weight and neurocognition have yet to be adequately delineated.

OBJECTIVE

To examine metabolic mechanisms underlying the association between obesity and neurocognition.

METHODS

We conducted a secondary analysis of weight, neurocognition, and the potentially mediating role of metabolic and inflammatory biomarkers among 160 participants from the ENLIGHTEN trial of vascular cognitive impairment, no dementia (CIND). Neurocognition was assessed using a 45-minute assessment battery assessing Executive Function, Verbal and Visual Memory. We considered three metabolic biomarkers: insulin resistance (homeostatic model assessment [HOMA-IR]), plasma leptin, and insulin-like growth factor (IGF-1). Inflammation was assessed using C-reactive protein. Multiple regression analyses were used.

RESULTS

Participants included 160 sedentary older adults with CIND. Participants tended to be overweight or obese (mean BMI = 32.5 [SD = 4.8]). Women exhibited higher BMI (p = 0.043), CRP (p < 0.001), and leptin (p < 0.001) compared with men. Higher BMI levels were associated with worse performance on measures of Executive Function (β= -0.16, p = 0.024) and Verbal Memory (β= -0.16, p = 0.030), but not Visual Memory (β= 0.05, p = 0.500). Worse metabolic biomarker profiles also were associated with lower Executive Function (β= -0.12, p = 0.050). Mediation analyses suggested leptin was a plausible candidate as a mediator between BMI and Executive Function.

CONCLUSIONS

In overweight and obese adults with vascular CIND, the association between greater weight and poorer executive function may be mediated by higher leptin resistance.

Evolutionary perspective on sex differences in the expression of neurological diseases

Sex-specific brain and cognitive deficits emerge with malnutrition, some infectious and neurodegenerative diseases, and often with prenatal or postnatal toxin exposure. These deficits are described in disparate literatures and are generally not linked to one another. Sexual selection may provide a unifying framework that integrates our understanding of these deficits and provides direction for future studies of sex-specific vulnerabilities. Sexually selected traits are those that have evolved to facilitate competition for reproductive resources or that influence mate choices, and are often larger and more complex than other traits. Critically, malnutrition, disease, chronic social stress, and exposure to man-made toxins compromise the development and expression of sexually selected traits more strongly than that of other traits. The fundamental mechanism underlying vulnerability might be the efficiency of mitochondrial energy capture and control of oxidative stress that in turn links these traits to current advances in neuroenergetics, stress endocrinology, and toxicology. The key idea is that the elaboration of these cognitive abilities, with more underlying gray matter or more extensive inter-modular white matter connections, makes them particularly sensitive to disruptions in mitochondrial functioning and oxidative stress. A framework of human sexually selected cognitive abilities and underlying brain systems is proposed and used to organize what is currently known about sex-specific vulnerabilities.

Cognitive dysfunction and metabolic comorbidities in mood disorders: A repurposing opportunity for glucagon-like peptide 1 receptor agonists?

Major depressive disorder and bipolar disorder are highly prevalent and disabling conditions. Cognition is considered a core domain of their psychopathology and a principle mediator of psychosocial impairment, disproportionately accounting for overall illness-associated costs. There are few interventions with replicated evidence of efficacy in treating cognitive deficits in mood disorders. Evidence also indicates that cognitive deficits are associated with obesity and involve significant impairment across multiple domains. Conversely, weight-loss interventions, such as physical exercise and bariatric surgery, have been shown to beneficially affect cognitive function. This convergent phenomenology suggests that currently available agents that target metabolic systems may also be capable of mitigating deficits in cognitive functions, and are, therefore, candidates for repurposing. The incretin glucagon-like peptide-1 (GLP-1) is a hormone secreted by intestinal epithelial cells. GLP-1 receptors (GLP-1R) are widely expressed in the central nervous system. Activation of GLP-1R leads to facilitation of glucose utilization and antiapoptotic effects in various organs. Pre-clinical trials have demonstrated significant neuroprotective effects of GLP-1, including protection from cell death, promotion of neuronal differentiation and proliferation; and facilitation of long-term potentiation. Liraglutide is a GLP-1R agonist that has been approved for the treatment of type 2 diabetes mellitus and obesity. Convergent preclinical and clinical evidence, including a proof-of-concept pilot study from group, has suggested that liraglutide may improve objective measures of cognitive function in adults with mood disorders. The safety and availability of GLP-1R agonists indicate that they are promising candidates for repurposing, and that they may be viable therapeutic options for mood disorders. This article is part of the Special Issue entitled 'Metabolic Impairment as Risk Factors for Neurodegenerative Disorders.'

Androgen Regulation of the Mesocorticolimbic System and Executive Function

Multiple lines of evidence indicate that androgens, such as testosterone, modulate the mesocorticolimbic system and executive function. This review integrates neuroanatomical, molecular biological, neurochemical, and behavioral studies to highlight how endogenous and exogenous androgens alter behaviors, such as behavioral flexibility, decision making, and risk taking. First, we briefly review the neuroanatomy of the mesocorticolimbic system, which mediates executive function, with a focus on the ventral tegmental area (VTA), nucleus accumbens (NAc), medial prefrontal cortex (mPFC), and orbitofrontal cortex (OFC). Second, we present evidence that androgen receptors (AR) and other steroid receptors are expressed in the mesocorticolimbic system. Using sensitive immunohistochemistry and quantitative polymerase chain reaction (qPCR) techniques, ARs are detected in the VTA, NAc, mPFC, and OFC. Third, we describe recent evidence for local androgens ("neuroandrogens") in the mesocorticolimbic system. Steroidogenic enzymes are expressed in mesocorticolimbic regions. Furthermore, following long-term gonadectomy, testosterone is nondetectable in the blood but detectable in the mesocorticolimbic system, using liquid chromatography tandem mass spectrometry. However, the physiological relevance of neuroandrogens remains unknown. Fourth, we review how anabolic-androgenic steroids (AAS) influence the mesocorticolimbic system. Fifth, we describe how androgens modulate the neurochemistry and structure of the mesocorticolimbic system, particularly with regard to dopaminergic signaling. Finally, we discuss evidence that androgens influence executive functions, including the effects of androgen deprivation therapy and AAS. Taken together, the evidence indicates that androgens are critical modulators of executive function. Similar to dopamine signaling, there might be optimal levels of androgen signaling within the mesocorticolimbic system for executive functioning. Future studies should examine the regulation and functions of neurosteroids in the mesocorticolimbic system, as well as the potential deleterious and enduring effects of AAS use.

Treatment with a GLP-1R agonist over four weeks promotes weight loss-moderated changes in frontal-striatal brain structures in individuals with mood disorders

Cognitive deficits are a core feature across psychiatric disorders. Emerging evidence indicates that metabolic pathways are highly relevant for the substrates and phenomenology of the cognitive domain. Herein, we aimed to determine the effects of liraglutide, a GLP-1R agonist, on brain structural/volumetric parameters in adults with a mood disorder. This is the secondary analysis of a 4-week, pilot, proof-of-concept, open-label study. Participants (N=19) exhibiting impairments in executive function with either major depressive disorder (MDD) or bipolar disorder (BD) were recruited. Liraglutide 1.8mg/day was added as an adjunct to existing pharmacotherapy. Structural magnetic resonance imaging (MRI) scanning was obtained at baseline and endpoint. Results showed that at endpoint there was significant weight loss (mean: 3.15%; p<0.001). Changes in frontal and striatal volumes were significantly correlated with changes in body mass index (BMI), indicating the weight loss was associated with volume increase in most regions (e.g. r=-0.561, p=0.042 in the left superior frontal area). After adjusting for intracranial volume, age, gender, and BMI, we observed significant changes from baseline to endpoint in multiple regions (e.g. RR: 1.011, p=0.049 in the left rostral middle frontal area). Changes in regional volumes were associated with improvement in executive function (e.g. r=0.698, p=0.003 for the right superior frontal area). Adjunctive liraglutide results in clinically significant weight loss, with corresponding improvement in cognitive function; changes in cognitive function were partially moderated by changes in brain morphometry, underscoring the interrelationship between weight and brain structure/function.

The Body Fat-Cognition Relationship in Healthy Older Individuals: Does Gynoid vs Android Distribution Matter?

OBJECTIVE

To examine the relationship between regional and whole body fat accumulation and core cognitive executive functions.

DESIGN

Cross-sectional study.

SETTINGS AND PARTICIPANTS

78 healthy men and women aged between 65 and 75 years recruited through consumer's database.

MEASUREMENTS

DXA measured percentage total body fat, android, gynoid distribution and android/gynoid ratio; inhibition and working memory updating through Random Number Generation test and cognitive flexibility by Trail Making test. First-order partial correlations between regional body fat and cognitive executive function were computed partialling out the effects of whole body fat. Moderation analysis was performed to verify the effect of gender on the body fat-cognition relationship.

RESULTS

Results showed a differentiated pattern of fat-cognition relationship depending on fat localization and type of cognitive function. Statistically significant relationships were observed between working memory updating and: android fat (r = -0.232; p = 0.042), gynoid fat (r = 0.333; p = 0.003) and android/gynoid ratio (r = -0.272; p = 0.017). Separating genders, the only significant relationship was observed in females between working memory updating and gynoid fat (r = 0.280; p = 0.045). In spite of gender differences in both working memory updating and gynoid body fat levels, moderation analysis did not show an effect of gender on the relationship between gynoid fat and working memory updating.

CONCLUSIONS

Results suggest a protective effect of gynoid body fat and a deleterious effect of android body fat. Although excessive body fat increases the risk of developing CDV, metabolic and cognitive problems, maintaining a certain proportion of gynoid fat may help prevent cognitive decline, particularly in older women. Guidelines for optimal body composition maintenance for the elderly should not target indiscriminate weight loss, but weight maintenance through body fat/lean mass control based on non-pharmacological tools such as physical exercise, known to have protective effects against CVD risk factors and age-related cognitive deterioration.

Liraglutide promotes improvements in objective measures of cognitive dysfunction in individuals with mood disorders: A pilot, open-label study

BACKGROUND

There is a paucity of treatments that are capable of reliably and robustly improving cognitive function in adults with mood disorders. Glucagon-like peptide-1 is synthesized centrally and its receptors are abundantly expressed in neural circuits subserving cognitive function. We aimed to determine the effects of liraglutide, a GLP-1 receptor (GLP-1R) agonist, on objective measures of cognition in adults with a depressive or bipolar disorder.

METHODS

In this 4-week, pilot, open-label, domain-based study (e.g. cognition), we recruited 19 individuals with major depressive disorder (MDD) or bipolar disorder (BD) and an impairment in executive function, defined as a below-average performance in the Trail Making Test-B (TMTB). Liraglutide 1.8mg/day was added as an adjunct to existing pharmacotherapy.

RESULTS

Participants had significant increases from baseline to week 4 in the TMTB standard score (age and education corrected) (Cohen's d=0.64, p=0.009) and in a composite Z-score comprising multiple cognitive tests (i.e. Digit Symbol Substitution Test, Rey Auditory Verbal Learning Test, Stroop test) (Cohen's d=0.77, p<0.001). Neither changes in mood rating scales nor metabolic parameters were associated with changes in cognitive performance (all p>0.05); however baseline insulin resistance (IR) and body mass index (BMI) moderated the changes in the composite Z-score (p=0.021 and p=0.046, respectively), indicating larger responses in individuals with higher IR and BMI at baseline. There was a significant increase in lipase (p<0.001), but individual values were above the upper limit of normality.

LIMITATIONS

Small sample size, open-label design, lack of a placebo group.

CONCLUSIONS

Liraglutide was safe and well tolerated by a sample of non-diabetic individuals with mood disorders and had beneficial effects on objective measures of cognitive function. Larger studies with controlled trial designs are necessary to confirm and expand the results described herein.

Obesity Weighs down Memory through a Mechanism Involving the Neuroepigenetic Dysregulation of Sirt1

Aberrant gene expression within the hippocampus has recently been implicated in the pathogenesis of obesity-induced memory impairment. Whether a dysregulation of epigenetic modifications mediates this disruption in gene transcription has yet to be established. Here we report evidence of obesity-induced alterations in DNA methylation of memory-associated genes, including Sirtuin 1 (Sirt1), within the hippocampus, and thus offer a novel mechanism by which SIRT1 expression within the hippocampus is suppressed during obesity. Forebrain neuron-specific Sirt1 knock-out closely recapitulated the memory deficits exhibited by obese mice, consistent with the hypothesis that the high-fat diet-mediated reduction of hippocampal SIRT1 could be responsible for obesity-linked memory impairment. Obese mice fed a diet supplemented with the SIRT1-activating molecule resveratrol exhibited increased hippocampal SIRT1 activity and preserved hippocampus-dependent memory, further strengthening this conclusion. Thus, our findings suggest that the memory-impairing effects of diet-induced obesity may potentially be mediated by neuroepigenetic dysregulation of SIRT1 within the hippocampus.

SIGNIFICANCE STATEMENT

Previous studies have implicated transcriptional dysregulation within the hippocampus as being a relevant pathological concomitant of obesity-induced memory impairment, yet a deeper understanding of the basis for, and etiological significance of, transcriptional dysregulation in this context is lacking. Here we present the first evidence of epigenetic dysregulation (i.e., altered DNA methylation and hydroxymethylation) of memory-related genes, including Sirt1, within the hippocampus of obese mice. Furthermore, experiments using transgenic and pharmacological approaches strongly implicate reduced hippocampal SIRT1 as being a principal pathogenic mediator of obesity-induced memory impairment. This paper offers a novel working model that may serve as a conceptual basis for the development of therapeutic interventions for obesity-induced memory impairment.

Association between adiposity and cognitive function in young men: Hormonal mechanisms

OBJECTIVE

To determine the association between adiposity, hormones, and cognition in young men with abdominal obesity.

METHODS

In this cross-sectional observational study, 53 nondiabetic men with abdominal obesity (mean body mass index, 37.3 kg/m(2) ; age, 22-45 years) and normal intelligence underwent detailed measures of body composition, hormonal profiles, and cognition. Age- and education-adjusted performance in five cognitive domains was examined.

RESULTS

Total fat percentage was negatively associated with visuospatial skills (P = 0.002) and visual memory (P = 0.012). Insulin resistance (homeostatic model assessment of insulin resistance) was also negatively associated with these domains (P = 0.05 and trend, P = 0.06, respectively). Total testosterone levels were negatively associated with executive function and verbal learning and memory (P = 0.04 for each), but free testosterone was not. Sex hormone-binding globulin (SHBG) was also inversely associated with performance in these domains (P = 0.015 and trend, P = 0.09, respectively). In a stepwise regression model including percentage fat, homeostatic model assessment of insulin resistance, SHBG, and free testosterone, SHBG was the only variable selected for executive function (P = 0.05) and showed a trend for verbal learning and memory (P = 0.09).

CONCLUSIONS

Adiposity and insulin resistance were associated with worse function in visual domains. An unexpected negative association is reported between SHBG and cognitive measures, which seemed to be independent of free testosterone levels.

Effect of obesity on cognition in adults with and without a mood disorder: study design and methods

INTRODUCTION

Obesity is a common medical illness that is increasingly recognised as conferring risk of decline in cognitive performance, independent of other comorbid medical conditions. Individuals with mood disorders (bipolar disorder (BD) or major depressive disorder (MDD)) display an increased prevalence of both obesity and risk factors for cardiovascular diseases. Moreover, BD and MDD are associated with impairment in cognitive functioning across multiple domains. The independent contribution of obesity to cognitive decline in this population has not been explored. This study examines the impact of obesity on cognition by comparing neuropsychological performance in obese individuals, with or without a mood disorder before and after undergoing bariatric surgery.

METHODS AND ANALYSIS

This study compares measures of declarative memory, executive functioning and attention in obese individuals (body mass index >35 kg/m(2)) with BD or MDD, and 2 control populations (obese individuals without a psychiatric illness and healthy non-obese controls) prior to and following bariatric surgery. Participants (ages 18-60) receive a psychiatric diagnosis via the Structured Clinical Interview for the Diagnostic and Statistical Manual of Mental Disorders, Fourth Edition (DSM-IV; SCID). Mood ratings, physical measurements, nutritional and health questionnaires are also administered. A standardised battery of neuropsychological tests aimed at establishing performance in areas of declarative memory, executive functioning and attention are administered. Warrington's Recognition Memory Task (RMT) and an N-Back Task are performed in a 3 T functional MRI to investigate patterns of neural activation during cognitive performance. Additionally, anatomical MRI data are obtained to investigate potential changes in neural structures. Baseline data will be analysed for between-group differences and later compared with postsurgical data to investigate cognitive change.

ETHICS AND DISSEMINATION

This study has been approved by the Hamilton Integrated Research Ethics Board (09-3254). Results will be available in peer-reviewed scientific publications and scientific meetings presentations, and released in lay form to media.

Regional Brain Glucose Hypometabolism in Young Women with Polycystic Ovary Syndrome: Possible Link to Mild Insulin Resistance

Objective

To investigate whether cerebral metabolic rate of glucose (CMR_glu) is altered in normal weight young women with polycystic ovary syndrome (PCOS) who exhibit mild insulin resistance.

Materials and methods

Seven women with PCOS were compared to eleven healthy female controls of similar age, education and body mass index. Regional brain glucose uptake was quantified using FDG with dynamic positron emission tomography and magnetic resonance imaging, and its potential relationship with insulin resistance assessed using the updated homeostasis model assessment (HOMA2-IR). A battery of cognitive tests was administered to evaluate working memory, attention and executive function.

Results

The PCOS group had 10% higher fasting glucose and 40% higher HOMA2-IR (p ≤ 0.035) compared to the Controls. The PCOS group had 9–14% lower CMR_glu in specific regions of the frontal, parietal and temporal cortices (p ≤ 0.018). A significant negative relation was found between the CMR_glu and HOMA2-IR mainly in the frontal, parietal and temporal cortices as well as in the hippocampus and the amygdala (p ≤ 0.05). Globally, cognitive performance was normal in both groups but scores on the PASAT test of working memory tended to be low in the PCOS group.

Conclusions

The PCOS group exhibited a pattern of low regional CMR_glu that correlated inversely with HOMA2-IR in several brain regions and which resembled the pattern seen in aging and early Alzheimer’s disease. These results suggest that a direct association between mild insulin resistance and brain glucose hypometabolism independent of overweight or obesity can exist in young adults in their 20s. Further investigation of the influence of insulin resistance on brain glucose metabolism and cognition in younger and middle-aged adults is warranted.

Relationship between Insulin-Resistance Processing Speed and Specific Executive Function Profiles in Neurologically Intact Older Adults

This study investigated the relationship between insulin-resistance and constituent components of executive function in a sample of neurologically intact older adult subjects using the homeostasis model assessment (HOMA-IR) and latent factors of working memory, cognitive control and processing speed derived from confirmatory factor analysis. Low-density lipoprotein (LDL), mean arterial pressure (MAP), along with body mass index (BMI) and white matter hypointensity (WMH) were used to control for vascular risk factors, adiposity and cerebrovascular injury. The study included 119 elderly subjects recruited from the University of California, San Francisco Memory and Aging Center. Subjects underwent neuropsychological assessment, fasting blood draw and brain magnetic resonance imaging (MRI). Partial correlations and linear regression models were used to examine the HOMA-IR-executive function relationship. Pearson correlation adjusting for age showed a significant relationship between HOMA-IR and working memory (rp = -.18; p = .047), a trend with cognitive control (rp = -.17; p = .068), and no relationship with processing speed (rp = .013; p = .892). Linear regression models adjusting for demographic factors (age, education, and gender), LDL, MAP, BMI, and WMH indicated that HOMA-IR was negatively associated with cognitive control (r = -.256; p = .026) and working memory (r = -.234; p = .054). These results suggest a greater level of peripheral insulin-resistance is associated with decreased cognitive control and working memory. After controlling for demographic factors, vascular risk, adiposity and cerebrovascular injury, HOMA-IR remained significantly associated with cognitive control, with working memory showing a trend. These findings substantiate the insulin-resistance-executive function hypothesis and suggest a complex interaction, demonstrated by the differential impact of insulin-resistance on processing speed and specific aspects of executive function.

Potential factors associated with perceived cognitive impairment in breast cancer survivors

PURPOSE

This cross-sectional study was designed to explore potential factors associated with perceived cognitive impairment (PCI) in breast cancer survivors compared to controls and gain insight into perceived levels of severity for cognitive complaints.

METHODS

Women (N = 363, 317: breast cancer, 46: healthy controls) completed demographic questionnaire, MD Anderson Symptom Inventory, Attentional Function Index, and Functional Assessment for Cancer Therapy-Cognition. Group classification included pre-chemotherapy, current chemotherapy, and postchemotherapy (<1, >1- < 2, >2- < 5, >5 years).

RESULTS

A significant group effect was seen for PCI (F 6, 355 = 7.01, p < 0.0001). Controls reported less PCI than all other groups. Neuropathy was inversely correlated with PCI (r = -0.23; p < 0.0001) for participants with breast cancer. A significant association was demonstrated between exercise frequency and PCI in women exposed to chemotherapy (F 3, 135 = 3.78, p < 0.05). A multiple linear regression model built using forward selection methods explained 24 % of the variance (adjusted R (2)) for PCI in breast cancer participants and included group, body mass index (BMI), exercise, fatigue, and distress. Exercise frequency moderated the relationship between BMI and PCI for breast cancer participants (F 3, 198 = 2.4, p = 0.07) and reduced the negative effects of high BMI. The moderating effect of exercise was significant (F 3, 133 = 3.1, p = 0.03) when limited to participants exposed to chemotherapy.

CONCLUSIONS

PCI decreased for women >5 years postchemotherapy. Overweight survivors who exercised frequently reported less PCI than sedentary survivors. Study results provide support for a relationship between BMI and PCI in breast cancer survivors and exercise as a potential intervention for cognitive complaints. Further investigation of the influence of weight and exercise on cognitive function is warranted.

Obesity-associated biomarkers and executive function in children

There is a growing focus on links between obesity and cognitive decline in adulthood, including Alzheimer's disease. It is also increasingly recognized that obesity in youth is associated with poorer cognitive function, specifically executive functioning skills such as inhibitory control and working memory, which are critical for academic achievement. Emerging literature provides evidence for possible biological mechanisms driven by obesity; obesity-associated biomarkers such as adipokines, obesity-associated inflammatory cytokines, and obesity-associated gut hormones have been associated with learning, memory, and general cognitive function. To date, examination of obesity-associated biology with brain function has primarily occurred in animal models. The few studies examining such biologically mediated pathways in adult humans have corroborated the animal data, but this body of work has gone relatively unrecognized by the pediatric literature. Despite the fact that differences in these biomarkers have been found in association with obesity in children, the possibility that obesity-related biology could affect brain development in children has not been actively considered. We review obesity-associated biomarkers that have shown associations with neurocognitive skills, specifically executive functioning skills, which have far-reaching implications for child development. Understanding such gut-brain associations early in the lifespan may yield unique intervention implications.

Menopause Analytical Hormonal Correlate Outcome Study (MAHCOS) and the association to brain electrophysiology (P300) in a clinical setting

Various studies have demonstrated that increased leptin levels and obesity are inversely related to cognitive decline in menopausal women. It is hypothesized that adiposity is inversely correlated with cognitive decline, as women with increased weight are less vulnerable to diminishing cognition. However, it is increasingly observed that menopausal women, even with increased adiposity, experience significant cognitive decline. Positron emission tomography (PET) has been used to analyze cognitive function and processing in menopausal women. Evoked potentials (P300) and neurophysiologic tests have validated brain metabolism in cognitively impaired patients. Post-hoc analyses of 796 female patients entering PATH Medical Clinic, between January 4, 2009 and February 24, 2013, were performed as part of the "Menopause Analytical Hormonal Correlate Outcome Study" (MAHCOS). Patient age range was 39-76 years (46.7 ± 0.2). P300 latency and amplitude correlated with a number of hormones: follicle stimulating hormone (FSH), luteinizing hormone (LH), estradiol, estrone, estriol, DHEA, pregnenolone, progesterone, free and total testosterone, thyroid stimulating hormone (TSH), Vitamins D 1.25 and D 25OH, leptin, and insulin-like growth factor-binding protein 3 (IGF-BP3). Corrected statistics did not reveal significant associations with P300 latency or amplitude for these hormones except for leptin plasma levels. However, factor analysis showed that FSH and LH clustered together with Vitamin D1.25 and Vitamin D25OH, P300 latency (not amplitude), and log leptin were found to be associated in the same cluster. Utilizing regression analysis, once age adjusted, leptin was the only significant predictor for latency or speed (p = 0.03) with an effect size of 0.23. Higher plasma leptin levels were associated with abnormal P300 speed (OR = 0.98). Our findings show a significant relationship of higher plasma leptin levels, potentially due to leptin resistance, and prolonged P300 latency. This suggests leptin resistance may delay electrophysiological processing of memory and attention, which appears to be the first of such an association.

A systematic review of the evidence that brain structure is related to muscle structure and their relationship to brain and muscle function in humans over the lifecourse

BACKGROUND

An association between cognition and physical function has been shown to exist but the roles of muscle and brain structure in this relationship are not fully understood. A greater understanding of these relationships may lead to identification of the underlying mechanisms in this important area of research. This systematic review examines the evidence for whether: a) brain structure is related to muscle structure; b) brain structure is related to muscle function; and c) brain function is related to muscle structure in healthy children and adults.

METHODS

Medline, Embase, CINAHL and PsycINFO were searched on March 6th 2014. A grey literature search was performed using Google and Google Scholar. Hand searching through citations and references of relevant articles was also undertaken.

RESULTS

53 articles were included in the review; mean age of the subjects ranged from 8.8 to 85.5 years old. There is evidence of a positive association between both whole brain volume and white matter (WM) volume and muscle size. Total grey matter (GM) volume was not associated with muscle size but some areas of regional GM volume were associated with muscle size (right temporal pole and bilateral ventromedial prefrontal cortex). No evidence was found of a relationship between grip strength and whole brain volume however there was some evidence of a positive association with WM volume. Conversely, there is evidence that gait speed is positively associated with whole brain volume; this relationship may be driven by total WM volume or regional GM volumes, specifically the hippocampus. Markers of brain ageing, that is brain atrophy and greater accumulation of white matter hyperintensities (WMH), were associated with grip strength and gait speed. The location of WMH is important for gait speed; periventricular hyperintensities and brainstem WMH are associated with gait speed but subcortical WMH play less of a role. Cognitive function does not appear to be associated with muscle size.

CONCLUSION

There is evidence that brain structure is associated with muscle structure and function. Future studies need to follow these interactions longitudinally to understand potential causal relationships.