Carbohydrate-induced memory impairment in adults with type 2 diabetes

The association between junk foods consumption and attention deficit hyperactivity disorder in children and adolescents: a systematic review and meta-analysis of observational studies

The adverse effects of junk foods on the risk of attention deficit hyperactivity disorder (ADHD) symptoms were reported in several studies. In this meta-analysis, the association between junk food consumption and the risk of ADHD was investigated in children and adolescents. A comprehensive systematic search was conducted to find all relevant literature via four databases, including PubMed, Web of Science, Scopus, and Google scholar, up to September 2022. Two independent authors screened all documents based on inclusion criteria. The overall effect sizes and related 95% confidence interval (CI) were pooled with the random effect approach. Subgroup analysis was done to measure potential sources of heterogeneity between studies. The quality of the included studies was evaluated with The Newcastle-Ottawa scale (NOS). Nine observational studies with 58,296 children /adolescents were eligible to be include in the meta-analysis. According to the random effect model, there was a positive relation between the consumption of junk foods and ADHD symptoms (odds ratio (OR): 1.24, 95%CI 1.15-1.34, P < 0.001, I2: 37.4%, P = 0.085). A similar significant positive association was shown in the subgroups analysis by different junk foods (sweetened beverages/soft drinks, sweets/candies, and other types of junk foods). This meta-analysis finding demonstrated that consuming junk foods, especially sweetened beverages/soft drinks, and sweets/candies is associated with ADHD symptoms.

Physical activity in a swimming pool attenuates memory impairment by reducing glutamate and inflammatory cytokines and increasing BDNF in the brain of mice with type 2 diabetes

Type 2 diabetes is a risk factor for the development of cognitive impairment. Increasing evidence suggests that regular exercise is beneficial for the treatment of clinical symptoms in diabetic patients. The current study aimed to evaluate whether increasing physical activity through swimming training can reduce memory impairment in an animal model of type 2 diabetes. Diabetes and non-diabetes mice underwent swimming training for four weeks, and then working, spatial, and recognition memory were evaluated using three behavioral tests. Body weight, glucose, and insulin resistance were monitored. We also measured inflammatory cytokines (interleukin (IL)- 6, IL-1β, and tumor-necrosis-factor (TNF)-α), an anti-inflammatory cytokine (IL-10), and brain-derived-neurotrophic-factor (BDNF), and glutamate levels in the hippocampus or prefrontal cortex of mice. The findings showed that diabetes increased body weight, glucose, and insulin resistance, impaired working, spatial and recognition memory, increased levels of IL-6, IL-1β, TNF-α, and glutamate levels, and decreased BDNF in the hippocampus of diabetic mice. While higher physical activity was associated with reduced body weight, glucose, and insulin resistance, attenuated memory impairment, IL-6, IL-1β, TNF-α, and glutamate, and increased BDNF levels in the hippocampus and prefrontal cortex of diabetic mice. This study shows that swimming training can normalize body weight and glucose-insulin axis and reduce inflammation and glutamate in the hippocampus and enhance the neurotrophic system in both the hippocampus and prefrontal cortex of diabetic mice. This study also suggests that higher physical activity through swimming training can improve cognitive impairment in a mouse model of type 2 diabetes.

Inside the diabetic brain: Insulin resistance and molecular mechanism associated with cognitive impairment and its possible therapeutic strategies

Type 2 diabetes mellitus (T2DM) the most prevalent metabolic disease that has evolved into a major public health issue. Concerning about its secondary complications, a growing body of evidence links T2DM to cognitive impairment and neurodegenerative disorders. The underlying pathology behind this secondary complication disease is yet to be fully known. Nonetheless, they are likely to be associated with poor insulin signaling as a result of insulin resistance. We have combed through a rising body of literature on insulin signaling in the normal and diabetic brains along with various factors like insulin resistance, hyperglycemia, obesity, oxidative stress, neuroinflammation and Aβ plaques which can act independently or synergistically to link T2DM with cognitive impairments. Finally, we explored several pharmacological and non-pharmacological methods in the hopes of accelerating the rational development of medications for cognitive impairment in T2DM by better understanding these shared pathways.

Metabolic Disturbances Induced by Sleep Restriction as Potential Triggers for Alzheimer's Disease

Sleep has a major role in learning, memory consolidation, and metabolic function. Although it is known that sleep restriction increases the accumulation of amyloid β peptide (Aβ) and the risk to develop Alzheimer's disease (AD), the mechanism behind these effects remains unknown. In this review, we discuss how chronic sleep restriction induces metabolic and cognitive impairments that could result in the development of AD in late life. Here, we integrate evidence regarding mechanisms whereby metabolic signaling becomes disturbed after short or chronic sleep restriction in the context of cognitive impairment, particularly in the accumulation of Aβ in the brain. We also discuss the role of the blood-brain barrier in sleep restriction with an emphasis on the transport of metabolic signals into the brain and Aβ clearance. This review presents the unexplored possibility that the alteration of peripheral metabolic signals induced by sleep restriction, especially insulin resistance, is responsible for cognitive deficit and, subsequently, implicated in AD development.

Is resveratrol a prospective therapeutic strategy in the co-association of glucose metabolism disorders and neurodegenerative diseases?

Objectives: The mechanism behind the progression of Mild Cognitive Impairment (MCI) to Alzheimer's disease (AD) remains poorly understood. However some evidence pointed out that the co-occurrence of metabolic conditions affecting glucose homeostasis, as type 2 diabetes mellitus (T2DM), may be an important catalyst in this context. Notably, candidate drugs which modulate common pathways in the development of MCI-to-AD mediated by T2DM may offer likely therapy for AD. Nonetheless, limited pharmacological alternatives that modulate common pathways in T2DM, MCI, and AD are available. In the recent decades, studies have shown that resveratrol may act as a neuroprotective compound, but little is known about its potential in improving cognitive and metabolic aspects associated with AD progression mediated by the co-association between TDM2-MCI.Methods: In this review, we discuss possible protective mechanisms of resveratrol on shared pathways associated with AD progression mediated by T2DM-MCI co-occurrence.Results: Some studies indicated that insulin resistance and hyperglycemia may be also a T2DM risk factor for the progression of MCI-to-AD, promoting alterations in metabolic pathways associated with neuronal plasticity, and increasing pro-inflammatory environment. Interestingly, basic research and clinical trials indicate that resveratrol may modulate those pathways, showing a potential neuroprotective effect of this polyphenol.Conclusion: Therefore, there is not enough clinical data supporting the translational therapeutic use of resveratrol in this scenario.

Cerebral Fructose Metabolism as a Potential Mechanism Driving Alzheimer's Disease

The loss of cognitive function in Alzheimer's disease is pathologically linked with neurofibrillary tangles, amyloid deposition, and loss of neuronal communication. Cerebral insulin resistance and mitochondrial dysfunction have emerged as important contributors to pathogenesis supporting our hypothesis that cerebral fructose metabolism is a key initiating pathway for Alzheimer's disease. Fructose is unique among nutrients because it activates a survival pathway to protect animals from starvation by lowering energy in cells in association with adenosine monophosphate degradation to uric acid. The fall in energy from fructose metabolism stimulates foraging and food intake while reducing energy and oxygen needs by decreasing mitochondrial function, stimulating glycolysis, and inducing insulin resistance. When fructose metabolism is overactivated systemically, such as from excessive fructose intake, this can lead to obesity and diabetes. Herein, we present evidence that Alzheimer's disease may be driven by overactivation of cerebral fructose metabolism, in which the source of fructose is largely from endogenous production in the brain. Thus, the reduction in mitochondrial energy production is hampered by neuronal glycolysis that is inadequate, resulting in progressive loss of cerebral energy levels required for neurons to remain functional and viable. In essence, we propose that Alzheimer's disease is a modern disease driven by changes in dietary lifestyle in which fructose can disrupt cerebral metabolism and neuronal function. Inhibition of intracerebral fructose metabolism could provide a novel way to prevent and treat this disease.

Iron-related dietary pattern increases the risk of poor cognition

INTRODUCTION

High iron intake has been shown to be associated with poor cognition. We aimed to examine the association between iron-related dietary pattern (IDP) and cognitive function in Chinese adults.

METHOD

Longitudinal study data from the China Health and Nutrition Survey (CHNS) during 1991-2006 were used (N = 4852, ≥55 years old). Dietary intake was obtained from a 3-day food record during home visits. Reduced rank regression was used to construct IDP with iron intake as a response variable. Cognitive function was assessed in 1997, 2000, 2004 and 2006. Multivariable mixed linear regression and logistic regression were used in the analyses.

RESULTS

IDP was characterised by high intake of fresh vegetable, wheat, legume, beverage, offal, rice and whole grain. High IDP intake was associated with poor cognition. In fully adjusted models, across the quartiles of IDP, the odds ratio (95% CI) for poor cognitive function were: 1.00, 1.06 (0.86-1.30), 1.24 (0.99-1.54), and 1.50 (1.17-1.93), respectively. There was a borderline significant interaction between IDP and meat intake (p interaction 0.085). The association between high IDP and poor cognition was only observed among those with no or low intake of meat. With the adjustment of carbohydrate or iron intake, the IDP and cognition association became non-significant. IDP was positively associated with lead intake. The association between IDP and poor cognition was partly mediated by lead intake.

CONCLUSIONS

Iron-related dietary pattern is associated with poor cognition in Chinese adults, partly due to high intake of carbohydrate, iron and lead.

The Effects of Carbohydrates, in Isolation and Combined with Caffeine, on Cognitive Performance and Mood-Current Evidence and Future Directions

This review examines the effects of carbohydrates, delivered individually and in combination with caffeine, on a range of cognitive domains and subjective mood. There is evidence for beneficial effects of glucose at a dose of 25 g on episodic memory, but exploration of dose effects has not been systematic and the effects on other cognitive domains is not known. Factors contributing to the differential sensitivity to glucose facilitation include age, task difficulty/demand, task domain, and glucoregulatory control. There is modest evidence to suggest modulating glycemic response may impact cognitive function. The evidence presented in this review identifies dose ranges of glucose and caffeine which improve cognition, but fails to find convincing consistent synergistic effects of combining caffeine and glucose. Whilst combining glucose and caffeine has been shown to facilitate cognitive performance and mood compared to placebo or glucose alone, the relative contribution of caffeine and glucose to the observed effects is difficult to ascertain, due to the paucity of studies that have appropriately compared the effects of these ingredients combined and in isolation. This review identifies a number of methodological challenges which need to be considered in the design of future hypothesis driven research in this area.

Metabolic and Cognitive Outcomes of Subchronic Once-Daily Intranasal Insulin Administration in Healthy Men

Insulin acts in the brain to limit food intake and improve memory function. We have previously shown that 8 weeks of intranasal insulin delivered in four daily doses of 40 IU decrease body weight and enhance word list recall. In the present study, we investigated the effect on body composition, endocrine parameters, and memory performance of 8 weeks of once-daily administration of 160 IU in healthy men. We assumed that intranasal insulin administered before nocturnal sleep, a period of relative metabolic inactivity that moreover benefits memory formation, would be superior to insulin delivery in the morning and placebo administration. After a 2-week baseline period, healthy male normal-weight subjects (mean age, 27.1 ± 0.9 years) received either placebo, 160 IU intranasal insulin in the morning, or 160 IU in the evening (n = 12 per group) for 8 consecutive weeks. Throughout the experiment, we measured body weight and body composition as well as circulating concentrations of glucose, insulin, adrenocorticotropin, cortisol, growth hormone, insulin-like growth-factor 1, adiponectin, and leptin. Declarative and procedural memory function was repeatedly assessed by means of, respectively, word list recall and word-stem priming. We found that neither morning nor evening insulin compared to placebo administration induced discernible changes in body weight and body composition. Delayed recall of words showed slight improvements by insulin administration in the evening, and serum cortisol concentrations were reduced after 2 weeks of insulin administration in the morning compared to the other groups. Results indicate that catabolic long-term effects of central nervous insulin delivery necessitate repetitive, presumably pre-meal delivery schedules. The observed memory improvements, although generally weaker than previously found effects, suggest that sleep after intranasal insulin administration may support its beneficial cognitive impact.

Persistent impairment in working memory following severe hyperglycemia in newly diagnosed type 2 diabetes

Acute hyperglycemia has been shown to cause cognitive impairments in animal models. There is growing appreciation of the numerous effects of hyperglycemia on neuronal function as well as blood–brain barrier function. In humans, hypoglycemia is well known to cause cognitive deficits acutely, but hyperglycemia has been less well studied. We present a case of selective neurocognitive deficits in the setting of acute hyperglycemia. A 60-year-old man was admitted to the hospital for an episode of acute hyperglycemia in the setting of newly diagnosed diabetes mellitus precipitated by steroid use. He was managed with insulin therapy and discharged home, and later, presented with complaints of memory impairment. Deficits included impairment in his declarative and working memory, to the point of significant impairment in his overall functioning. The patient had no structural lesions on MRI imaging of the brain or other systemic illnesses to explain his specific deficits. We suggest that his acute hyperglycemia may have caused neurological injury, and may be responsible for our patient’s memory complaints.

A high-glycemic diet is associated with cerebral amyloid burden in cognitively normal older adults

Background: Little is known about the relation between dietary intake and cerebral amyloid accumulation in aging.Objective: We assessed the association of dietary glycemic measures with cerebral amyloid burden and cognitive performance in cognitively normal older adults.Design: We performed cross-sectional analyses relating dietary glycemic measures [adherence to a high-glycemic-load diet (HGLDiet) pattern, intakes of sugar and carbohydrates, and glycemic load] with cerebral amyloid burden (measured by florbetapir F-18 positron emission tomography) and cognitive performance in 128 cognitively normal older adults who provided eligibility screening data for the University of Kansas's Alzheimer's Prevention through Exercise (APEX) Study. The study began in November 2013 and is currently ongoing.Results: Amyloid was elevated in 26% (n = 33) of participants. HGLDiet pattern adherence (P = 0.01), sugar intake (P = 0.03), and carbohydrate intake (P = 0.05) were significantly higher in participants with elevated amyloid burden. The HGLDiet pattern was positively associated with amyloid burden both globally and in all regions of interest independently of age, sex, and education (all P ≤ 0.001). Individual dietary glycemic measures (sugar intake, carbohydrate intake, and glycemic load) were also positively associated with global amyloid load and nearly all regions of interest independently of age, sex, and educational level (P ≤ 0.05). Cognitive performance was associated only with daily sugar intake, with higher sugar consumption associated with poorer global cognitive performance (global composite measure and Mini-Mental State Examination) and performance on subtests of Digit Symbol, Trail Making Test B, and Block Design, controlling for age, sex, and education.Conclusion: A high-glycemic diet was associated with greater cerebral amyloid burden, which suggests diet as a potential modifiable behavior for cerebral amyloid accumulation and subsequent Alzheimer disease risk. This trial was registered at clinicaltrials.gov as NCT02000583.

Mild cognitive impairment in type 2 diabetes mellitus and related risk factors: a review

Type 2 diabetes mellitus (T2DM) is a global epidemic disease and has become a significant health problem. Many studies have raised concern about the mild cognitive impairment (MCI) with T2DM and even the Alzheimer’s disease patients with T2DM. The incidence of MCI is higher in individuals with T2DM than those without diabetes. Cognitive changes might affect everyday activities depending on the work and situation. Although the exact pathophysiology of MCI in T2DM is unclear, many studies suggest that the alterations in pathoglycemia, diabetic complications, related end products, and physical/psychological status are significant risk factors. In this article, we systematically overview the studies to illustrate the related risk factors of cognitive impairment in patients with T2DM. Further high quality studies and treatment need to be initiated and it will become incumbent on clinicians to identify and cure the earliest signs of clinical impairment.

A four-day Western-style dietary intervention causes reductions in hippocampal-dependent learning and memory and interoceptive sensitivity

In animals, a Western style diet-high in saturated fat and added sugar-causes impairments in hippocampal-dependent learning and memory (HDLM) and perception of internal bodily state (interoception). In humans, while there is correlational support for a link between Western-style diet, HDLM, and interoception, there is as yet no causal data. Here, healthy individuals were randomly assigned to consume either a breakfast high in saturated fat and added sugar (Experimental condition) or a healthier breakfast (Control condition), over four consecutive days. Tests of HDLM, interoception and biological measures were administered before and after breakfast on the days one and four, and participants completed food diaries before and during the study. At the end of the study, the Experimental condition showed significant reductions in HDLM and reduced interoceptive sensitivity to hunger and fullness, relative to the Control condition. The Experimental condition also showed a markedly different blood glucose and triglyceride responses to their breakfast, relative to Controls, with larger changes in blood glucose across breakfast being associated with greater reductions in HDLM. The Experimental condition compensated for their energy-dense breakfast by reducing carbohydrate intake, while saturated fat intake remained consistently higher than Controls. This is the first experimental study in humans to demonstrate that a Western-style diet impacts HDLM following a relatively short exposure-just as in animals. The link between diet-induced HDLM changes and blood glucose suggests one pathway by which diet impacts HDLM in humans.

The effect of Cinnamomum zeylanicum bark water extract on memory performance in alloxan-induced diabetic mice

Cinnamomum zeylanicum (cinnamon) has a wide range of beneficial effects including mild glucose lowering activity. The aim of the present study was to investigate whether cinnamon bark extract has the potential to improve memory performance and glucose profiles in diabetic mice. Memory was assessed by the novel object recognition task in male Balb/c mice. In this method, the difference between exploration time of a familiar object and a novel object was considered as an index of memory performance (recognition index, RI). The water extract was prepared by boiling cinnamon bark for 15 min. Alloxan induced diabetes in animals (serum glucose levels were 322 ± 7.5 mg/dL), and also impaired memory performance (RI= -3.3% ± 3.3) which differed significantly from control animals (RI = 32% ± 6.5). Although treatment with cinnamon only reduced fasting blood glucose level moderately but it improved memory performance remarkably (RI = 25.5% ± 5.6). Oxidative stress following administration of cinnamon extract was lower in diabetic mice. It was concluded that cinnamon water extract could be a useful alternative medicine in diabetic patients’ daily regimen which not only reduces blood glucose levels but also improves memory performance and lipid peroxidation level.

The Effects of Breakfast and Breakfast Composition on Cognition in Adults

Extensive literature has addressed the acute cognitive effects of breaking a fast. Recent reviews in this line of work have synthesized available research on the cognitive consequences of fasting compared with nutrient intake and the cognitive effects of macronutrient consumption. These largely have been inconclusive, possibly in part because of selection criteria limiting the scope of studies covered. The purpose of the current review is to integrate the results of the literature examining the cognitive effects of breakfast and breakfast composition in adults with the use of a flexible definition of breakfast, specifically, any caloric intake after a fasting period of ≥8 h. This review includes 38 studies that examine the acute cognitive impact of breakfast and 16 studies that examine the effects of breakfast composition. Results suggest that healthy adults show a small but robust advantage for memory (particularly delayed recall) from consuming breakfast. Largely equivocal results emerge for attention and motor and executive function; there were no effects from breakfast on language. Regarding breakfast composition, a smaller number of studies and widely disparate methodology addressing this question preclude definitive conclusions about the effects of cognition. A subset of this literature examines these questions in the context of glucoregulation; the findings emphasize the importance of considering differences in glucoregulation in research designs, even among healthy cohorts. The limitations of this literature include methodologic differences, such as the use of different tests to measure cognitive constructs, as well as the effects of timing in test administration.

Severe hypoglycemia is associated with antidiabetic oral treatment compared with insulin analogs in nursing home patients with type 2 diabetes and dementia: results from the DIMORA study

OBJECTIVES

Severe hypoglycemia is associated with cognitive decline and dementia in older persons with type 2 diabetes. The role of antidiabetic treatments on severe hypoglycemia is unknown in dementia. The aims were to determine the prevalence of severe hypoglycemic events and investigate associations among severe hypoglycemic and specific antidiabetic treatments (classes of oral agents and types of insulin analogs) in a large sample of nursing home patients with diabetes according to dementia status.

DESIGN

Cross-sectional observational study.

SETTING

A total of 150 nursing homes across Italy.

PARTICIPANTS

A total of 2258 patients with type 2 diabetes (dementia = 1138, no dementia = 1120).

MEASUREMENTS

Diagnosis of dementia before nursing home admission. Data were collected regarding functional status, glycemic control, antidiabetic treatments, comorbidities, and biochemical and clinical measurements. Logistic regression models with severe hypoglycemia as the dependent variable were used to test associations with antidiabetic agents.

RESULTS

Patients had a mean age (SD) of 82 (8) years, body mass index (BMI) of 25.4 (4.8), fasting plasma glucose (FPG) of 7.5 (3.0) mmol/L, postprandial glucose (PPG) of 10.3 (3.6) mmol/L, HbA1c of 7.1% (54 mmol/L), and impairments in activities of daily living (ADLs) of 3.7 (2.1). Severe hypoglycemia was more prevalent in patients with dementia (18%) compared with patients without dementia (8%). Patients with dementia were older, showed greater ADL impairments, greater number of comorbidities, lower FPG, and higher PPG compared with those without dementia. Adjusted logistic regression models in patients with dementia showed that rapid- and long-acting insulin analogs were associated with reduced odds ratio (OR) (OR 0.333; 95% confidence interval [CI] 0.184-0.602; OR 0.248, 95% CI 0.070-0.882, respectively), whereas sulphonylureas and combined metformin + sulphonylurea were associated with increased ORs (OR 8.805, 95% CI 4.260-18.201; OR 6.639; 95% CI 3.273-14.710, respectively) of experiencing severe hypoglycemia. No correlations were found in patients without dementia.

CONCLUSION

In older nursing home patients with type 2 diabetes, severe hypoglycemia was significantly higher in dementia. Our findings suggest that sulphonylureas should be used with caution, whereas rapid- and long-acting insulin analogs seem safer.

Blood glucose, diet-based glycemic load and cognitive aging among dementia-free older adults

BACKGROUND

Although evidence indicates that Type II Diabetes is related to abnormal brain aging, the influence of elevated blood glucose on long-term cognitive change is unclear. In addition, the relationship between diet-based glycemic load and cognitive aging has not been extensively studied. The focus of this study was to investigate the influence of diet-based glycemic load and blood glucose on cognitive aging in older adults followed for up to 16 years.

METHODS

Eight-hundred and thirty-eight cognitively healthy adults aged ≥50 years (M = 63.1, SD = 8.3) from the Swedish Adoption/Twin Study of Aging were studied. Mixed effects growth models were utilized to assess overall performance and change in general cognitive functioning, perceptual speed, memory, verbal ability, and spatial ability as a function of baseline blood glucose and diet-based glycemic load.

RESULTS

High blood glucose was related to poorer overall performance on perceptual speed as well as greater rates of decline in general cognitive ability, perceptual speed, verbal ability, and spatial ability. Diet-based glycemic load was related to poorer overall performance in perceptual speed and spatial ability.

CONCLUSION

Diet-based glycemic load and, in particular, elevated blood glucose appear important for cognitive performance/cognitive aging. Blood glucose control (perhaps through low glycemic load diets) may be an important target in the detection and prevention of age-related cognitive decline.

Dietary glycaemic load associated with cognitive performance in elderly subjects

PURPOSE

Ageing is associated with loss of cognitive function and an increased risk of dementia which is expected to place growing demands on health and long-term care providers. Among multiple causative factors, evidence suggests that cognitive impairment in older subjects may be influenced by diet. The objective of this study was to examine the association between dietary patterns, dietary glycaemic load (GL) and cognition in older Irish adults.

METHODS

Community-dwelling subjects (n 208; 94 males and 114 females; aged 64-93 years) were analysed. Dietary intake was assessed using a validated semi-quantitative food frequency questionnaire. Cognitive capacity was tested using the Mini-Mental State Examination (MMSE). The data were clustered to derive patterns of dietary intake. Multivariable-adjusted logistic and Poisson regression models were used to examine the relationship between dietary GL and MMSE score.

RESULTS

Elderly subjects consuming 'prudent' dietary patterns (high in fruit, vegetables, fish, low-fat dairy and salad dressings and low in red meat and white bread) had higher MMSE scores (better cognitive function) than those consuming 'Western' dietary pattern (high in red meat and white bread and low in fruit and vegetables; P < 0.05). Logistic and Poisson regression analyses both indicated that the MMSE score was inversely associated with the GL of the diet (P < 0.05) even after adjusting for age, gender, diabetes, hypertension, healthy food diversity, nutritional status, residential property price, cardiovascular medications and energy intake.

CONCLUSION

In this community-dwelling elderly Irish cohort, consumption of a high glycaemic diet is associated with poorer cognitive performance as assessed by the MMSE.

Is Alzheimer's disease a systemic disease?

Although Alzheimer's disease (AD) is the most common neurodegenerative disease, the etiology of AD is not well understood. In some cases, genetic factors explain AD risk, but a high percentage of late-onset AD is unexplained. The fact that AD is associated with a number of physical and systemic manifestations suggests that AD is a multifactorial disease that affects both the CNS and periphery. Interestingly, a common feature of many systemic processes linked to AD is involvement in energy metabolism. The goals of this review are to 1) explore the evidence that peripheral processes contribute to AD risk, 2) explore ways that AD modulates whole-body changes, and 3) discuss the role of genetics, mitochondria, and vascular mechanisms as underlying factors that could mediate both central and peripheral manifestations of AD. Despite efforts to strictly define AD as a homogeneous CNS disease, there may be no single etiologic pathway leading to the syndrome of AD dementia. Rather, the neurodegenerative process may involve some degree of baseline genetic risk that is modified by external risk factors. Continued research into the diverse but related processes linked to AD risk is necessary for successful development of disease-modifying therapies.

Animal protein intake is associated with higher-level functional capacity in elderly adults: the Ohasama study

OBJECTIVES

To determine the association between protein intake and risk of higher-level functional decline in older community-dwelling adults.

DESIGN

Prospective.

SETTING

Ohasama Town, Japan.

PARTICIPANTS

Residents (N = 1,007; mean age 67.4 ± 5.5) free of functional decline at baseline; follow-up was conducted for 7 years.

MEASUREMENTS

Nutrient and food intakes were determined using a validated 141-item food frequency questionnaire. Participants were divided into quartiles according to intake levels of total, animal, and plant protein. Subscales of the Tokyo Metropolitan Institute of Gerontology Index of Competence subscales were used to assess higher-level functional decline. Logistic regression analysis was used to examine the future risk of higher-level functional decline in relation to protein intake, with lowest protein intake as reference.

RESULTS

During the study period, 24.4% of eligible participants reported declines in higher-level functional capacity. After adjustment for putative confounding factors, men in the highest quartile of animal protein intake had significantly lower risk of higher-level functional decline than those in the lowest quartile (odds ratio (OR) = 0.41, 95% confidence interval (CI) = 0.20-0.83; P for trend .01). These associations were not seen in women (OR = 0.76, 95% CI = 0.41-1.34; P for trend .37). No consistent association was observed between plant protein intake and future higher-level functional decline in either sex.

CONCLUSION

Higher protein, particularly animal protein, was associated with lower risk of decline in higher-level functional capacity in older men. Animal protein intake may be a modifiable indicator for early detection and prevention of higher-level functional decline in elderly adults.

Cognitive functions in type 1 and type 2 diabetes. Metaanalysis

Introduction: Diabetes has been repeatedly associated with a wide variety of cognitive impairments. Aim: To clarify the differences in cognitive dysfunctions between the two types of diabetes. Method: Metaanalysis was performed using databases of Medline, PubMed and ScienceDirect (3 studies with type 1 and 6 with type 2 diabetes). Results: Adults with type 1 diabetes showed lower performance than control subjects in all fields. The effect size had the highest value in psychomotor activity (D = –0.69). The effect size was small for delayed verbal memory (D = –0.48), attention (D = –0.47), language (D = –0.44), visual processing (D = –0.35), immediate verbal memory (D = –0.30), working memory (D = –0.27) and executive functions (D = –0.26). Adults with type 2 diabetes showed lower performance than control subjects in all cognitive domains, except for working memory (D = +0.03). The effect size had the highest value in immediate verbal memory (D = –1.12), psychomotor activity (D = –0.82) and delayed verbal memory (D = –0.81). The effect size was moderate for general intellectual abilities (D = –0.68) and small for general memory (D = –0.37), attention (D = –0.35), language (D = –0.35), visual processing (D = –0.33) and executive functions (D = –0.33). Conclusion: Both types of diabetes are associated with reduced performance in numerous cognitive domains. Orv. Hetil., 2013, 154, 694–699.

Neurocognitive impairment and comorbid depression in patients of diabetes mellitus

This study was conducted to find out the association of diabetes mellitus with cognitive functioning and depressive features. We included 50 diabetic and 30 control subjects who were screened on the basis of various inclusion and exclusion criteria. Then, a history of variables under study was taken and respective laboratory investigations were noted. First, the Becks Depression Inventory (BDI) was administrated to the patients. The cognitive function was then assessed using the digit span test, stroop Test, controlled oral word association test, visual target cancellation test, digit symbol substitution test, and visuospatial working memory matrix. The composite score on all tests was used to make cognitive index. The data was compiled and appropriate statistical methods were used. We found that 48% of elderly diabetic patients showed cognitive impairment. Poor metabolic control (hyperglycemia) was associated significantly and negatively with cognitive index in diabetic patients. Hyperglycemia was significantly and negatively correlated with immediate memory and attention, verbal memory, psychomotor functioning (DSST), and visuospatial memory. In conclusion, genesis of cognitive deficits in diabetic patients is complex. However, it appears from the study that such deficits do exist and may be associated with chronically poorly controlled diabetes.

Western diet consumption and cognitive impairment: links to hippocampal dysfunction and obesity

Intake of saturated fats and simple carbohydrates, two of the primary components of a modern Western diet, is linked with the development of obesity and Alzheimer's Disease. The present paper summarizes research showing that Western diet intake is associated with cognitive impairment, with a specific emphasis on learning and memory functions that are dependent on the integrity of the hippocampus. The paper then considers evidence that saturated fat and simple carbohydrate intake is correlated with neurobiological changes in the hippocampus that may be related to the ability of these dietary components to impair cognitive function. Finally, a model is described proposing that Western diet consumption contributes to the development of excessive food intake and obesity, in part, by interfering with a type of hippocampal-dependent memory inhibition that is critical in the ability of animals to refrain from responding to environmental cues associated with food, and ultimately from consuming energy intake in excess of that driven solely by caloric need.

Insulin resistance, diabetes and cognitive function: consequences for preventative strategies

Cognitive decline and dementia both place a heavy burden on patients and their relatives, and any means of preventing such age-related changes are worthy of consideration. Those who have the metabolic syndrome with or without diabetes suffer more often from dysexecutive problems and slower psychomotor speed than do other patients. In epidemiological studies, diabetes has appeared to be a risk factor for all types of dementia, including vascular dementia, although the role of the metabolic syndrome in the risk of Alzheimer's disease is still a matter of debate. The possible mechanisms of cognitive alterations are multiple, and may differ according to age group and duration of diabetes or the metabolic syndrome. Drug interventional trials addressing the prevention of cognitive decline through action on the metabolic syndrome are disappointing-albeit scarce at this time. Lifestyle interventions in middle-aged or younger-elderly subjects should also be implemented in the general population.

The influence of carbohydrate on cognitive performance: a critical evaluation from the perspective of glycaemic load

Links between nutrition and cognition are widely acknowledged. Within the context of short-term cognitive performance, carbohydrate has been the dietary component most commonly investigated. The majority of studies investigating the influence of carbohydrate on cognitive performance have employed oral glucose drink interventions followed by measures of performance on cognitive tests. More recently, studies have investigated the effect of different carbohydrates on cognitive performance rather than just pure glucose drinks. To date, studies have not been evaluated based on a standardised measure of glycaemic response, such as glycaemic load. The present review provides a critical evaluation of eight studies that have explored the relationships between food carbohydrate and cognitive performance and allow glycaemic load to be used as a basis for comparison. The key finding is that these provide insufficient evidence to support a consistent effect of glycaemic load on short-term cognitive performance. Future studies should employ consistent test methodologies and describe food interventions in more detail to facilitate meaningful comparisons and interpretations of results.

Antioxidant vitamins reduce acute meal-induced memory deficits in adults with type 2 diabetes

Memory impairment is observed in adults with type 2 diabetes mellitus (T2DM), with further acute deficits after meal ingestion. This study explored whether postprandial oxidative stress was a contributor to these meal-induced memory deficits. Sixteen adults with T2DM (mean age, 63.5 +/- 2.1 years) who were not regularly taking high-dose antioxidant supplements were fed a high-fat meal, the same test meal with vitamins C (1000 mg) and E (800 IU) tablets, or water on 3 separate occasions. After meal ingestion, a battery of cognitive tests were administered, which included measures of delayed verbal memory, assessed at 60 and 105 minutes after meal ingestion. Relative to water consumption, the high-fat meal resulted in poorer performance at 105 minutes postingestion on measures of delayed verbal recall (word list and paragraph recall) and working memory (Digit-Span Forward). Coconsumption of antioxidant vitamins and high-fat meal prevented this meal-induced deficit such that performance on these tasks was indistinguishable from that after water intake. At the same time point, a small but significant improvement on the word-naming and color-naming components of Stroop was observed after meal ingestion, relative to water, irrespective of whether antioxidants were consumed, demonstrating the specificity of meal-induced impairments to memory function. Executive function, assessed by Trails Parts A and B, was not influenced by meal or antioxidant ingestion. In adults with T2DM, coconsumption of antioxidant vitamins minimizes meal-induced memory impairment, implicating oxidative stress as a potential contributor to these decrements.

Glycemic index and glycemic load are not associated with brain lesions in the elderly

OBJECTIVE

The goal of this study was to determine if brain lesion volume was correlated with dietary glycemic index and glycemic load in elderly individuals.

DESIGN AND SETTING

This cross-sectional study was performed at an academic medical center as part of a clinical study of late-life depression.

PARTICIPANTS

Subjects (n=137) were age 60 or over, and were participating as non-depressed comparison subjects.

MEASUREMENTS

Food intake was assessed using the Block 1998 food frequency questionnaire. Glycemic index and glycemic load measures were derived from reported food intake. Brain lesion volumes were calculated from magnetic resonance imaging (MRI).

RESULTS

No significant associations were found between glycemic index or glycemic load, and brain lesion volume.

CONCLUSION

Dietary glycemic measures may be unrelated to brain lesions or may be related to brain lesions only in individuals with impaired glycemic control or other vascular risk factors. Further studies are needed to confirm this finding and to determine if glycemic control moderates this association.

Toward a model of memory enhancement in schizophrenia: glucose administration and hippocampal function

Recognition of the need to treat cognitive deficits in schizophrenia is compelling and well established, with empirical findings and conceptual arguments related to cognitive enhancement appearing regularly in the literature. Cognitive enhancement itself, however, remains at an early stage. Biological approaches have centered on the development of antipsychotic medications that also improve cognition, but the results have so far remained modest. As a way to facilitate the development of cognitive enhancers in schizophrenia, this article focuses on adjunctive pharmacological approaches to antipsychotic medications and highlights the need for systematic explorations of relevant brain mechanisms. While numerous conceptual criteria might be employed to guide the search, we will focus on 4 points that are especially likely to be useful and which have not yet been considered together. First, the discussion will focus on deficits in a particular cognitive domain, verbal declarative memory. Second, we will review the current status of preclinical and clinical efforts to improve declarative memory using antipsychotic medications, which is the main, existing mode of treatment. Third, we will examine an example of an adjunctive intervention-glucose administration-that improves memory in animals and humans, modulates function in brain regions related to verbal declarative memory, and is highly amenable to translational research. Finally, a heuristic model will be outlined to explore how the intervention maps on to the underlying neurobiology of schizophrenia. More generally, the discussion underlines the promise of cognitive improvement in schizophrenia and the need to approach the issue in a programmatic manner.

Acute effects of macronutrient manipulations on cognitive test performance in healthy young adults: A systematic research review

The potential for foods to exert effects on behaviour is increasingly recognised. Previous studies have incorporated both well-known and lesser-known cognitive tests in the evaluation of relationships between macronutrient interventions and mental performance. Systematic review methodology was used to identify studies of macronutrient effects on cognition, limited to acute effects in young, fasted, healthy adults. Thirty-one studies met the inclusion criteria, yielding a total of 134 outcome measures. The studies reviewed displayed a predominance of soluble glucose manipulations, and a paucity of complex carbohydrate, protein or fat manipulations. Memory performance was most commonly measured, but verbal fluency, attention, reaction time, psychomotor skill and problem solving were also assessed. Significant differences in performance tended to occur under circumstances of more intense cognitive demand and after delays. Memory emerged as the most sensitive cognitive modality to macronutrient manipulations. Tasks identified as sensitive included Serial Sevens, Free Word Recall and Cued Word Recall, with tentative support for the Word Recognition Task. Findings also suggested that visuo-spatial memory may be influenced by macronutrient manipulations.

Obese men respond to cognitive but not to catabolic brain insulin signaling

CONTEXT AND OBJECTIVE

Insulin acts in the brain to reduce food intake and body weight and is considered a major adiposity signal in energy homeostasis. In normal-weight men, intranasal insulin administration reduces body fat and improves declarative memory. The present experiments aimed to generalize these findings to obese patients, with a view to evaluate the therapeutic potential of the compound.

DESIGN, SUBJECTS AND MEASUREMENTS

Insulin and placebo, respectively, were intranasally administered four times a day (amounting to 160 IU day(-1)) over 8 weeks to two groups of 15 obese men each.

RESULTS

Contrasting with the catabolic effects in normal-weight men, insulin treatment did not induce any significant reduction of body weight (P>0.50) and body fat (P>0.44) in the obese subjects. However, in accordance with the effects in normal-weight men, declarative memory and mood were improved (P<0.05) and hypothalamic-pituitary-adrenal axis activity as assessed by circulating ACTH (P<0.01) and cortisol levels (P<0.04) was reduced.

CONCLUSIONS

Our results indicate that in obese men, intranasal insulin is functionally active in the central nervous system but fails to affect the neuronal networks critically involved in body weight regulation. We conclude that obesity in men is associated with central nervous resistance to the adiposity signal insulin. This defect likely contributes to the persistence of obesity in spite of elevated levels of circulating insulin in obese patients.

The effects of energy-rich diets on discrimination reversal learning and on BDNF in the hippocampus and prefrontal cortex of the rat

Male rats received normal chow or high-fat diets rich in dextrose (HFD) or sucrose (HFS). Half of the rats received 90-day unrestricted access to their diet prior to training, whereas the other half were food restricted throughout the study. We evaluated the effects of these dietary manipulations on discrimination and reversal performance and on post-training levels of brain-derived neurotrophic factor (BDNF) in the prefrontal cortex and the ventral and dorsal hippocampus. Neither diet nor restriction condition affected discrimination acquisition. However, prior unrestricted access to the HFD diet impaired discrimination reversal learning and reduced BDNF in the prefrontal cortex and ventral hippocampus. Also, rats given the HFD diet responded more than controls to the previously rewarded cue at the outset of discrimination reversal. The results suggest that consumption of the HFD diet may have had enduring effects on learning processes, some of which may contribute to the control of intake regulation.

Cognitive performance is associated with macronutrient intake in healthy young and middle-aged adults

PRIMARY OBJECTIVE

The objective was to examine whether dietary intakes of macronutrients are associated with neuropsychological performance.

RESEARCH DESIGN AND METHOD

Study participants were 3960 adults aged 20-59 years, who completed three neuropsychological tests and a 24-hour dietary recall as a part of the Third National Health and Nutrition Examination Survey, 1988-1994. Poor performance was defined as the test score below gender-specific 15th percentile.

MAIN OUTCOMES AND RESULTS

While holding the energy percentages from different macronutrients, additional 100 kcal intake of energy was associated with a reduced odds of poor performance on serial digital learning test (OR = 0.98, 95% CI = 0.96, 0.99) and symbol digital substitution test (OR = 0.97, 95% CI = 0.96, 0.99). Compared with equivalent energy from carbohydrates, each 5% of energy from poly-unsaturated fatty acids (PUFA) or total fat was associated with a reduced OR of poor performance on simple reaction time test (PUFA: OR = 0.77, 95% CI = 0.63-0.95 and total fat: OR = 0.93, 95% CI = 0.87, 0.99). Poor global cognition was associated with an additional intake of 100 mg cholesterol (OR = 1.14, 95% CI = 1.05, 1.23). These associations were more salient in men.

CONCLUSION

Habitual intake of macronutrients is weakly but significantly associated with cognitive functioning. These relationships are more evident in men.

Adiposity indices and dementia

Indicators of adiposity, such as body-mass index (BMI), may be markers for changes in energy metabolism that influence dementia risk, progression, and ultimately death. Cross-sectional studies show that people with dementia have a lower BMI than those without dementia, which is potentially due to a greater rate of BMI decline occurring during the years immediately preceding dementia onset. However, a high BMI can also increase the risk for dementia when measured before clinical dementia onset, which might be due to vascular disorders or bioactive hormonal compounds that are secreted by adipose tissue. In this personal view, I consider how dementia is associated with BMI by looking at the role of BMI and obesity syndromes, mechanisms associated with adiposity, and the potential for hypothalamic dysregulation during the life course. Understanding the life course of adiposity by use of common surrogate measures, such as BMI, among those who do and do not develop dementia is relevant for understanding the causes of dementia and for shaping possible treatment options.

Acute effects of hyperglycaemia in children with type 1 diabetes mellitus: the patient's perspective

INTRODUCTION

This study presents the results of a systematic examination of how parents and patients perceive the effects of acute hyperglycaemia on mood and on intellectual and fine-motor performance.

METHODS

A random sample of parents and children with type 1 diabetes mellitus (n = 380) were asked via questionnaire about their perception of the effects of hyperglycaemia.

RESULTS

Answers were received from 368 children and parents (97%); mean age was 12.5 years (range 3.7 to 19.8 years). Blood glucose levels between 15-18 mmol/l were reported by 68% to affect thinking performance, by 75% to affect mood and emotions and by 53% to affect coordination. The symptoms most commonly associated with hyperglycaemia were (in decreasing order): irritable (64%), short-tempered (60%), moody (56%), unreasonable (43%), aggressive (37%), hyperactive (31%), sad/depressed (27%) confused (23%), clumsy (18%). Homework was thought to be affected by hyperglycaemia in 36%, sport in 25%, play activity in 32%. Higher mean HbA1c since diagnosis was associated with higher reporting of effects on feeling/mood (p <0.001). Parents were especially concerned about the effects of hyperglycaemia on school and social interaction.

CONCLUSIONS

The effects of hyperglycaemia on immediate performance are of concern to children and parents. Hyperglycaemia (15-18 mmol/l) is reported to influence emotion and behaviour more than intellectual and fine-motor performance. This may contribute to the adverse psychological consequences of type 1 diabetes mellitus in children.

A low-carbohydrate diet may prevent end-stage renal failure in type 2 diabetes. A case report

An obese patient with type 2 diabetes whose diet was changed from the recommended high-carbohydrate, low-fat type to a low-carbohydrate diet showed a significant reduction in bodyweight, improved glycemic control and a reversal of a six year long decline of renal function. The reversal of the renal function was likely caused by both improved glycemic control and elimination of the patient's obesity. Insulin treatment in type 2 diabetes patients usually leads to weight increase which may cause further injury to the kidney. Although other unknown metabolic mechanisms cannot be excluded, it is likely that the obesity caused by the combination of high-carbohydrate diet and insulin in this case contributed to the patient's deteriorating kidney function. In such patients, where control of bodyweight and hyperglycemia is vital, a trial with a low-carbohydrate diet may be appropriate to avoid the risk of adding obesity-associated renal failure to already failing kidneys.

Better cognitive performance following a low-glycaemic-index compared with a high-glycaemic-index carbohydrate meal in adults with type 2 diabetes

AIMS/HYPOTHESIS

Transient hyperglycaemia, consistent with that observed with normal meal ingestion, may be detrimental to cognitive performance in adults with type 2 diabetes. This study determined whether minimising the postprandial increase in blood glucose through the ingestion of low- rather than high-glycaemic-index (GI) carbohydrate meals differentially affected cognitive performance in the postprandial period.

SUBJECTS AND METHODS

Using a within-individual design, 21 free-living subjects (65+/-7.29 years) with type 2 diabetes consumed 50 g carbohydrate as a meal with either a low GI (pasta) or a high GI (white bread), or water on three separate mornings following an overnight fast. Neuropsychological tests were administered and plasma glucose concentrations measured.

RESULTS

Higher postprandial blood glucose AUC (gAUC) was associated with poorer verbal memory (paragraph recall, p=0.01; word list recall, p=0.012). Both the GI of the carbohydrate meal and individual differences in response to meal ingestion contributed to the variation in gAUC and consequent memory recall. Bread consumption, relative to pasta, resulted in both a higher gAUC (p<0.05) and worse delayed verbal memory performance (paragraph recall, p=0.042; wordlist recall, p=0.035). Additionally, performance following bread consumption was poorer than that following pasta on measures of working memory, executive function and auditory selective attention, while sustained attention showed no sensitivity to type of carbohydrate food consumed.

CONCLUSIONS/INTERPRETATION

Consuming 50 g of a low-GI carbohydrate meal, relative to a high-GI carbohydrate meal, generally results in better cognitive performance in the postprandial period in adults with type 2 diabetes, particularly in those individuals who experience the greatest food-induced elevations in blood glucose levels.

High-fat diets, insulin resistance and declining cognitive function

Results from our work in rats and others findings from human epidemiologic studies demonstrate deficits in cognitive performance following chronic ingestion of high fat, high saturated fat, diets. Yet, the precise physiologic mechanism underlying these deficits is not well understood. We report that older adults with insulin resistance show remarkably similar deficits in cognitive function and respond to glucose ingestion in a comparable manner to rodents fed a high-fat diet, suggesting that insulin resistance is a probable mediator of these diet-induced deficits. As insulin resistance worsens to overt type 2 diabetes, profound deficits in cognitive functions, especially those dependent on the medial temporal lobes, are apparent in both obese Zucker rats and humans with type 2 diabetes. Unlike the older adult with insulin resistance, glucose ingestion further impairs medial temporal lobe function in adults with type 2 diabetes. Collectively, the human and rodent data point to a role of diet-induced endocrine abnormalities, including the development of insulin resistance, as mediating the cognitive deficits associated with high fat consumption.

[The role of nutritional factors on the structure and function of the brain: an update on dietary requirements]

The brain is an organ elaborated and functioning from substances present in the diet. Dietary regulation of blood glucose level (via ingestion of food with a low glycemic index ensuring a low insulin level) improves the quality and duration of intellectual performance, if only because at rest the adult brain consumes 50 p. 100 of dietary carbohydrates, 80 p. 100 of them for energy purposes. The nature of the amino acid composition of dietary proteins contributes to good cerebral function; tryptophan plays a special role. Many indispensable amino acids present in dietary proteins help to elaborate neurotransmitters and neuromodulators. Omega-3 fatty acids provided the first coherent experimental demonstration of the effect of dietary nutrients on the structure and function of the brain. First it was shown that the differentiation and functioning of cultured brain cells requires omega-3 fatty acids. It was then demonstrated that alpha-linolenic acid (ALA) deficiency alters the course of brain development, perturbs the composition and physicochemical properties of brain cell membranes, neurones, oligodendrocytes, and astrocytes (ALA). This leads to physicochemical modifications, induces biochemical and physiological perturbations, and results in neurosensory and behavioral upset. Consequently, the nature of polyunsaturated fatty acids (in particular omega-3) present in formula milks for infants (premature and term) conditions the visual and cerebral abilities, including intellectual abilities. Moreover, dietary omega-3 fatty acids are certainly involved in the prevention of some aspects of cardiovascular disease (including at the level of cerebral vascularization), and in some neuropsychiatric disorders, particularly depression, as well as in dementia, notably Alzheimer's disease. Their deficiency can prevent the satisfactory renewal of membranes and thus accelerate cerebral aging. Iron is necessary to ensure oxygenation, to produce energy in the cerebral parenchyma, and for the synthesis of neurotransmitters. The iodine provided by the thyroid hormone ensures the energy metabolism of the cerebral cells. The absence of iodine during pregnancy induces severe cerebral dysfunction, leading to cretinism. Manganese, copper, and zinc participate in enzymatic mechanisms that protect against free radicals, toxic derivatives of oxygen. The use of glucose by nervous tissue implies the presence of vitamin B1. Vitamin B9 preserves memory during aging, and with vitamin B12 delays the onset of signs of dementia, provided it is administered in a precise clinical window, at the onset of the first symptoms. Vitamins B6 and B12, among others, are directly involved in the synthesis of neurotransmitters. Nerve endings contain the highest concentrations of vitamin C in the human body. Among various vitamin E components, only alpha-tocopherol is involved in nervous membranes. The objective of this update is to give an overview of the effects of dietary nutrients on the structure and certain functions of the brain.

The relationship between type 2 diabetes and cognitive dysfunction: longitudinal studies and their methodological limitations

Type 2 diabetes and dementia in the elderly are major public health problems. Cross-sectional studies have suggested that these two conditions may be inter-related, but the nature of this association is uncertain. Causation can only be established through studies with a longitudinal design, taking into account the many potential confounding factors in any study of cognition. A literature search has identified 10 studies (nine population-based and one of case-controlled design) that included a definable diabetic population and assessments of cognitive function at baseline and at follow-up. These 10 studies utilised a combination of domain-specific cognitive assessments and a clinical diagnosis of dementia in the assessment of cognitive function. Diabetes was associated with either an accelerated cognitive decline or an increased incidence of dementia in eight of nine of the population-based studies. One study demonstrated a relationship between diabetes and vascular cognitive impairment, but not with other types of dementia. No association between type 2 diabetes and cognitive decline was demonstrated in the case-controlled study. These studies provide compelling evidence to support the view that people with type 2 diabetes are at increased risk of developing cognitive impairment in comparison with the general population.

Glucose improvement of memory: a review

The memory-improving action of glucose has now been studied for almost 20 years and the study of this phenomenon has led to a number of important developments in the understanding of memory, brain physiology and pathological consequences of impaired glucose tolerance. Glucose improvement of memory appears to involve two optimal doses in animals (100 mg/kg and 2 g/kg) that may correspond to two physiological mechanisms underlying glucose effects on memory. In humans, there have been few dose-response studies so the existence of more than one effective dose in humans is uncertain. Many tasks are facilitated by glucose in humans but tasks that are difficult to master or involve divided attention are improved more readily that easier tasks. There are a number of hypotheses about the physiological bases of the memory-improving action of glucose. Peripheral glucose injections could alleviate localized deficits in extracellular glucose in the hippocampus. These localized deficits may be due to changes in glucose transporters in that structure. Because certain neurotransmitters such as acetylcholine are directly dependent on the glucose supply for their synthesis, glucose is thought to facilitate neurotransmitter synthesis under certain circumstances. However, these hypotheses cannot account for the specificity of the dose-response effect of glucose. A number of peripheral mechanisms have been proposed, including the possibility that glucose-sensitive neurons in the brain or in the periphery may serve as glucose sensors and eventually produce neural changes that would facilitate memory processing. These latter results could be of importance because the mechanisms they suggest appear to be dose-dependent, a crucial characteristic to explain the dose-dependent effects of glucose. There may be an advantage to develop hypotheses that include both peripheral and central actions of glucose. There is evidence that impaired glucose regulation is associated with impaired cognition, particularly episodic memory. This impairment is minimal in young people but increases in older people (65 years and over) where it may compound other aging processes leading to reduced brain function. A small number of studies showed that glucose improvement of memory is associated with poor glucose regulation although this may not be the case for diabetic patients. Results of a few studies also suggest that drug treatments that improve glucose regulation also produce cognitive improvement in diabetic patients.

Acute hyperglycemia alters mood state and impairs cognitive performance in people with type 2 diabetes

OBJECTIVE

To examine the effects of acute hyperglycemia on cognitive function and mood in people with type 2 diabetes.

RESEARCH DESIGN AND METHODS

Twenty subjects with type 2 diabetes, median age 61.5 years (range 53.1-72.0), known duration of diabetes 5.9 years (range 2.8-11.2), BMI 29.8 kg/m2 (range 22.0-34.6), and HbA1c 7.5% (range 6.7-8.4) were studied. Treatment modalities varied from antidiabetic medications to insulin. A hyperinsulinemic glucose clamp was used to maintain arterialized blood glucose at either 4.5 (euglycemia) or 16.5 mmol/l (hyperglycemia) on two occasions in a randomized and counterbalanced fashion. Tests of information processing, immediate and delayed memory, working memory, and attention were administered, along with a mood questionnaire, during each experimental condition.

RESULTS

Speed of information processing, working memory, and some aspects of attention were impaired during acute hyperglycemia. Subjects were significantly more dysphoric during hyperglycemia, with reduced energetic arousal and increased sadness and anxiety.

CONCLUSIONS

During acute hyperglycemia, cognitive function was impaired and mood state deteriorated in a group of people with type 2 diabetes. These findings are of practical importance because intermittent or chronic hyperglycemia is common in people with type 2 diabetes and may interfere with many daily activities through adverse effects on cognitive function and mood.