Effect of glucose, glucose regulation, and word imagery value on human memory

Insulin resistance is associated with cognitive dysfunction in multiple sclerosis patients: A cross-sectional study

Multiple sclerosis (MS) is a progressive inflammatory neurodegenerative disease of the nervous system accompanied by demyelination. MS-associated cognitive impairments mainly involve recent memory, information processing speed, stable memory, and executive function. Moreover, MS is associated with impaired glucose and insulin metabolism, which can exacerbate cognitive decline. The present study aimed to compare the cognitive status of MS patients with and without insulin resistance. In this cross-sectional study, 74 relapsing-remitting multiple sclerosis diagnosed patients were enrolled. Indicators of insulin resistance, including fasting blood glucose, insulin level, and homeostatic model assessment of insulin resistance (HOMA-IR) index, were measured. They were then divided into two groups based on the results of the HOMA-IR index. Cognition status was evaluated by the minimal assessment of cognitive function in multiple sclerosis battery. The prevalence of insulin resistance was 37.8%, and the prevalence of cognitive decline was estimated to be 67.56%. Mean scores of the California verbal learning test (CVLT), CVLT delayed free recall, controlled oral word association test, and judgment of line orientation tests were significantly lower in MS patients with insulin resistance than without. In addition, a negative correlation was demonstrated between the results of the CVLT, CVLT delayed free recall, controlled oral word association test, judgment of line orientation tests, brief visuospatial memory test, and Delis-Kaplan executive function system sorting tests and fasting insulin levels. Greater verbal memory and spatial comprehension impairments were observed in MS patients with insulin resistance.

Extracellular levels of glucose in the hippocampus and striatum during maze training for food or water reward in male rats

Glucose potently enhances cognitive functions whether given systemically or directly to the brain. The present experiments examined changes in brain extracellular glucose levels while rats were trained to solve hippocampus-sensitive place or striatum-sensitive response learning tasks for food or water reward. Because there were no task-related differences in glucose responses, the glucose results were pooled across tasks to form combined trained groups. During the first 1-3 min of training for food reward, glucose levels in extracellular fluid (ECF) declined significantly in the hippocampus and striatum; the declines were not seen in untrained, rewarded rats. When trained for water reward, similar decreases were observed in both brain areas, but these findings were less consistent than those seen with food rewards. After the initial declines in ECF glucose levels, glucose increased in most groups, approaching asymptotic levels ∼15-30 min into training. Compared to untrained food controls, training with food reward resulted in significant glucose increases in the hippocampus but not striatum; striatal glucose levels exhibited large increases to food intake in both trained and untrained groups. In rats trained to find water, glucose levels increased significantly above the values seen in untrained rats in both hippocampus and striatum. The decreases in glucose early in training might reflect an increase in brain glucose consumption, perhaps triggering increased brain uptake of glucose from blood, as evident in the increases in glucose later in training. The increased brain uptake of glucose may provide additional neuronal metabolic substrate for metabolism or provide astrocytic substrate for production of glycogen and lactate.

A study of the association between cognitive abilities and dietary intake in young women

BACKGROUND

Cognitive abilities comprise activities that relate to receiving and responding to information from the environment, internal processing, making complex decisions, and then responding to this in the context of behavior.

AIM

The current study investigated the association between dietary intake and seven aspects of cognitive abilities among healthy young women.

METHODS

The study was carried out among 182 women aged 18-25 years. A valid and reliable food frequency questionnaire containing 65 food items was used to estimate dietary intake. Neuropsychological function and cognitive abilities of participants were determined using standard questionnaires.

RESULTS

Significant differences were found in depression, anxiety, stress, physical, and mental health-related quality of life as well as daytime sleepiness for the participants in different quartiles of cognitive abilities score (p<0.05). Participants in the fourth quartile of cognitive abilities score consumed significantly higher energy, carbohydrate, protein, calcium, iron, zinc, vitamin A, thiamin, and riboflavin compared to those in the lowest quartile (p<0.05). There were strong correlations between total cognitive abilities score and dietary sodium, calcium, phosphorus, and thiamin (p<0.05). Using stepwise multiple linear regression analysis, iron and thiamin were statistically significant factors for the prediction of cognitive abilities.

CONCLUSIONS

These findings demonstrate that neurocognitive function is related to dietary macro and micronutrients including energy, carbohydrate, protein, calcium, iron, zinc, vitamin A, thiamin, and riboflavin on cognitive performance among young women without memory deficit.

Non-nutritive Sweeteners and Glycaemic Control

PURPOSE OF REVIEW

The consumption of foods and beverages containing non-nutritive sweeteners (NNS) has increased worldwide over the last three decades. Consumers' choice of NNS rather than sugar or other nutritive sweeteners may be attributable to their potential to reduce weight gain.

RECENT FINDINGS

It is not clear what the effects of NNS consumption are on glycaemic control and the incidence of type 2 diabetes. This review aims to examine this question in epidemiological, human intervention and animal studies. It is not clear that NNS consumption has an effect on the incidence of type 2 diabetes or on glycaemic control even though there is some evidence for the modification of the microbiome and for interaction with sweet taste receptors in the oral cavity and the intestines' modification of secretion of glucagon-like peptide-1 (GLP-1), peptide YY (PYY), ghrelin and glucose-dependent insulinotropic polypeptide (GIP), which may affect glycaemia following consumption of NNS. In conclusion, long-term studies of NNS consumption are required to draw a firm conclusion about the role of NNS consumption on glycaemic control.

Glycemic impact of non-nutritive sweeteners: a systematic review and meta-analysis of randomized controlled trials

BACKGROUND/OBJECTIVES

Nonnutritive sweeteners (NNSs) are zero- or low-calorie alternatives to nutritive sweeteners, such as table sugars. A systematic review and meta-analysis of randomized controlled trials was conducted to quantitatively synthesize existing scientific evidence on the glycemic impact of NNSs.

SUBJECTS/METHODS

PubMed and Web of Science databases were searched. Two authors screened the titles and abstracts of candidate publications. The third author was consulted to resolve discrepancies. Twenty-nine randomized controlled trials, with a total of 741 participants, were included and their quality assessed. NNSs under examination included aspartame, saccharin, steviosides, and sucralose. The review followed the PRISMA guidelines.

RESULTS

Meta-analysis was performed to estimate and track the trajectory of blood glucose concentrations over time after NNS consumption, and to test differential effects by type of NNS and participants' age, weight, and disease status. In comparison with the baseline, NNS consumption was not found to increase blood glucose level, and its concentration gradually declined over the course of observation following NNS consumption. The glycemic impact of NNS consumption did not differ by type of NNS but to some extent varied by participants' age, body weight, and diabetic status.

CONCLUSIONS

NNS consumption was not found to elevate blood glucose level. Future studies are warranted to assess the health implications of frequent and chronic NNS consumption and elucidate the underlying biological mechanisms.

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.

The impact of diet-based glycaemic response and glucose regulation on cognition: evidence across the lifespan

The brain has a high metabolic rate and its metabolism is almost entirely restricted to oxidative utilisation of glucose. These factors emphasise the extreme dependence of neural tissue on a stable and adequate supply of glucose. Whereas initially it was thought that only glucose deprivation (i.e. under hypoglycaemic conditions) can affect brain function, it has become apparent that low-level fluctuations in central availability can affect neural and consequently, cognitive performance. In the present paper the impact of diet-based glycaemic response and glucose regulation on cognitive processes across the lifespan will be reviewed. The data suggest that although an acute rise in blood glucose levels has some short-term improvements of cognitive function, a more stable blood glucose profile, which avoids greater peaks and troughs in circulating glucose is associated with better cognitive function and a lower risk of cognitive impairments in the longer term. Therefore, a habitual diet that secures optimal glucose delivery to the brain in the fed and fasting states should be most advantageous for the maintenance of cognitive function. Although the evidence to date is promising, it is insufficient to allow firm and evidence-based nutritional recommendations. The rise in obesity, diabetes and metabolic syndrome in recent years highlights the need for targeted dietary and lifestyle strategies to promote healthy lifestyle and brain function across the lifespan and for future generations. Consequently, there is an urgent need for hypothesis-driven, randomised controlled trials that evaluate the role of different glycaemic manipulations on cognition.

Effects of Systemic Metabolic Fuels on Glucose and Lactate Levels in the Brain Extracellular Compartment of the Mouse

Classic neuroenergetic research has emphasized the role of glucose, its transport and its metabolism in sustaining normal neural function leading to the textbook statement that it is the necessary and sole metabolic fuel of the mammalian brain. New evidence, including the Astrocyte-to-Neuron Lactate Shuttle hypothesis, suggests that the brain can use other metabolic substrates. To further study that possibility, we examined the effect of intraperitoneally administered metabolic fuels (glucose, fructose, lactate, pyruvate, ß-hydroxybutyrate, and galactose), and insulin, on blood, and extracellular brain levels of glucose and lactate in the adult male CD1 mouse. Primary motor cortex extracellular levels of glucose and lactate were monitored in freely moving mice with the use of electrochemical electrodes. Blood concentration of these same metabolites were obtained by tail vein sampling and measured with glucose and lactate meters. Blood and extracellular fluctuations of glucose and lactate were monitored for a 2-h period. We found that the systemic injections of glucose, fructose, lactate, pyruvate, and ß-hydroxybutyrate increased blood lactate levels. Apart for a small transitory rise in brain extracellular lactate levels, the main effect of the systemic injection of glucose, fructose, lactate, pyruvate, and ß-hydroxybutyrate was an increase in brain extracellular glucose levels. Systemic galactose injections produced a small rise in blood glucose and lactate but almost no change in brain extracellular lactate and glucose. Systemic insulin injections led to a decrease in blood glucose and a small rise in blood lactate; however brain extracellular glucose and lactate monotonically decreased at the same rate. Our results support the concept that the brain is able to use alternative fuels and the current experiments suggest some of the mechanisms involved.

Training-induced elevations in extracellular lactate in hippocampus and striatum: Dissociations by cognitive strategy and type of reward

Recent evidence suggests that astrocytes convert glucose to lactate, which is released from the astrocytes and supports learning and memory. This report takes a multiple memory perspective to test the role of astrocytes in cognition using real-time lactate measurements during learning and memory. Extracellular lactate levels in the hippocampus or striatum were determined with lactate biosensors while rats were learning place (hippocampus-sensitive) or response (striatum-sensitive) versions of T-mazes. In the first experiment, rats were trained on the place and response tasks to locate a food reward. Extracellular lactate levels in the hippocampus increased beyond those of feeding controls during place training but not during response training. However, striatal lactate levels did not increase beyond those of controls when rats were trained on either the place or the response version of the maze. Because food ingestion itself increased blood glucose and brain lactate levels, the contribution of feeding may have confounded the brain lactate measures. Therefore, we conducted a second similar experiment using water as the reward. A very different pattern of lactate responses to training emerged when water was used as the task reward. First, provision of water itself did not result in large increases in either brain or blood lactate levels. Moreover, extracellular lactate levels increased in the striatum during response but not place learning, whereas extracellular lactate levels in the hippocampus did not differ across tasks. The findings from the two experiments suggest that the relative engagement of the hippocampus and striatum dissociates not only by task but also by reward type. The divergent lactate responses of the hippocampus and striatum in place and response tasks under different reward conditions may reflect ethological constraints tied to foraging for food and water.

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.

Development of new UV-vis spectroscopic microwave-assisted method for determination of glucose in pharmaceutical samples

A new UV-Visible spectroscopic method assisted with microwave for the determination of glucose in pharmaceutical formulations was developed. In this study glucose solutions were oxidized by ammonium molybdate in the presence of microwave energy and reacted with aniline to produce a colored solution. Optimum conditions of the reaction including wavelength, temperature, and pH of the medium and relative concentration ratio of the reactants were investigated. It was found that the optimal wavelength for the reaction is 610 nm, the optimal reaction time is 80s, the optimal reaction temperature is 160°C, the optimal reaction pH is 4, and the optimal concentration ratio aniline/ammonium molybdate solution was found to be 1:1. The limits of detection and quantification of the method are 0.82 and 2.75 ppm for glucose solution, respectively. The use of microwaves improved the speed of the method while the use of aniline improved the sensitivity of the method by shifting the wavelength.

Impaired glucose regulation is associated with poorer performance on the Stroop Task

BACKGROUND

Type 2 diabetes is a risk factor for development of cognitive dysfunction. Impairments in glucose regulation have been associated with poorer performance on tests of executive function and information processing speed.

METHODS

We administered the Stroop Color Word Task, where higher interference scores are indicative of decreased selective attention, to 98 non-diabetic volunteers (64 m; %fat=37 ± 12; age=36 ± 9 yrs, race=41 NA/30 C/13 H/14 AA) on our inpatient unit. After 3d on a weight maintaining diet, % body fat was measured by DXA and a 75 g oral glucose tolerance test (OGTT) was administered. Impaired glucose regulation (IGR) was defined as: fasting plasma glucose ≥ 100 and ≤ 125 mg/dL and/or 2h plasma glucose between ≥ 140 and ≤ 199 mg/dL (IGR; n=48; NGR; n=50). Total and incremental area under the curve (AUC) for insulin and glucose were calculated.

RESULTS

Stroop interference scores were not significantly associated with any measure of adiposity or insulin concentrations. Individuals with IGR had significantly higher interference scores than those with normal glucose regulation (NGR; p=0.003). Higher interference scores were significantly correlated with fasting plasma glucose concentrations (r=0.26, p=0.007) and total glucose AUC (r=0.30, p=0.02) and only trending so for iAUC and 2h plasma glucose (r=0.18, p=0.08; r=0.17, p=0.09 respectively). In separate multivariate linear models, fasting plasma glucose (p=0.002) and total glucose AUC (p=0.0005) remained significant predictors of Stroop interference scores, even after adjustment for age, sex, race, education and %fat.

CONCLUSIONS

Individuals with IGR had decreased performance on a test of selective attention. Fasting plasma glucose was more strongly associated with lower performance scores than 2h plasma glucose. Our results indicate that even mild hyperglycemia in the non-diabetic range is associated with attentional processing difficulties in a sample of younger adults. Whether these impairments precede or are induced by impaired glucose regulation is not clear.

The Influence of Fat Co-administration on the Glucose Memory Facilitation Effect

Memory for a list of 20 words can be enhanced when learning is preceded by consumption of 25 g of glucose, compared with consumption of an equally sweet aspartame solution. The present study examined whether memory performance is also enhanced when glucose is administered in conjunction with another food constituent, in particular fat. Four groups of healthy young participants were tested under one of four conditions: (a) glucose + full-fat yoghurt; (b) glucose + fat-free yoghurt; (c) aspartame + full-fat yoghurt; (d) aspartame + fat-free yoghurt. The groups were compared on measures of blood glucose and cognitive performance. Participants receiving a glucose drink in conjunction with a fat-free yoghurt displayed higher blood glucose levels (BGL) and better performance on short- and long-delay recall of the word list compared with (a) individuals who consumed the glucose drink in conjunction with a full-fat yoghurt and (b) individuals who consumed the aspartame drink. The glycaemic data indicated that the presence of fat slows down glucose absorption. The findings suggest that only foods with a relatively fast glucose absorption rate are able to significantly enhance the encoding and long-term retention of novel memory materials in healthy young adults.

Glucose and memory: the influence of drink, expectancy, and beliefs

RATIONALE

An increasing number of studies suggest that glucose can enhance aspects of memory and the central methodology is the use of the glucose-placebo design. One critical issue therefore is separating the pharmacological effects of glucose from the expectancies created by consuming a drink that might contain glucose.

OBJECTIVE

A modified balanced placebo design examined the role that expectancy and belief about the drink consumed has on the pharmacological changes observed following glucose consumption.

METHOD

Ninety-three participants, allocated according to a drink (glucose, placebo) × message (told glucose, told nothing, told placebo) unrelated design, were administered tasks assessing immediate and delayed verbal free recall, spatial recognition and semantic verification. Each task has some evidence for hippocampus involvement, and variations in task difficulty were used to assess the idea that glucose effects are sensitive to task difficulty.

RESULTS

While the messages biased drink judgements in the expected direction, judgements of drink content were at chance and glucose only enhanced delayed free recall. The subtle effects of the messages did not modify the glucose enhancement. However, believing glucose had been consumed showed an independent improvement in delayed free recall. There was no evidence that task complexity enhanced the glucose effect.

CONCLUSIONS

The findings indicate that expectancy effects are unlikely to be confused with glucose enhancements, but beliefs about consuming glucose can augment performance on delayed free recall. The discussion considers the hippocampus and complexity hypotheses of glucose's mode of action and proposes the routine collection of drink beliefs in future studies.

Response variability to glucose facilitation of cognitive enhancement

Glucose facilitation of cognitive function has been widely reported in previous studies (including our own). However, several studies have also failed to detect glucose facilitation. There is sparsity of research examining the factors that modify the effect of glucose on cognition. The aims of the present study were to (1) demonstrate the previously observed enhancement of cognition through glucose administration and (2) investigate some of the factors that may exert moderating roles on the behavioural response to glucose, including glucose regulation, body composition (BC) and hypothalamic–pituitary–adrenal axis response. A total of twenty-four participants took part in a double-blind, placebo-controlled, randomised, repeated-measures study, which examined the effect of 25 and 60 g glucose compared with placebo on cognitive function. At 1 week before the study commencement, all participants underwent an oral glucose tolerance test. Glucose facilitated performance on tasks of numeric and spatial working memory, verbal declarative memory and speed of recognition. Moderating variables were examined using several indices of glucoregulation and BC. Poorer glucoregulation predicted improved immediate word recall accuracy following the administration of 25 g glucose compared with placebo. Those with better glucoregulation showed performance decrements on word recall accuracy following the administration of 25 g glucose compared with placebo. These findings are in line with accumulating evidence that glucose load may preferentially enhance cognition in those with poorer glucoregulation. Furthermore, the finding that individuals with better glucoregulation may suffer impaired performance following a glucose load is novel and requires further substantiation.

Relative intake of macronutrients impacts risk of mild cognitive impairment or dementia

High caloric intake has been associated with an increased risk of cognitive impairment. Total caloric intake is determined by the calories derived from macronutrients. The objective of the study was to investigate the association between percent of daily energy (calories) from macronutrients and incident mild cognitive impairment (MCI) or dementia. Participants were a population-based prospective cohort of elderly persons who were followed over a median 3.7 years (interquartile range, 2.5-3.9) of follow-up. At baseline and every 15 months, participants (median age, 79.5 years) were evaluated using the Clinical Dementia Rating scale, a neurological evaluation, and neuropsychological testing for a diagnosis of MCI, normal cognition, or dementia. Participants also completed a 128-item food-frequency questionnaire at baseline; total daily caloric and macronutrient intakes were calculated using an established database. The percent of total daily energy from protein (% protein), carbohydrate (% carbohydrate), and total fat (% fat) was computed. Among 937 subjects who were cognitively normal at baseline, 200 developed incident MCI or dementia. The risk of MCI or dementia (hazard ratio, [95% confidence interval]) was elevated in subjects with high % carbohydrate (upper quartile: 1.89 [1.17-3.06]; p for trend = 0.004), but was reduced in subjects with high % fat (upper quartile: 0.56 [0.34-0.91]; p for trend = 0.03), and high % protein (upper quartile 0.79 [0.52-1.20]; p for trend = 0.03) in the fully adjusted models. A dietary pattern with relatively high caloric intake from carbohydrates and low caloric intake from fat and proteins may increase the risk of MCI or dementia in elderly persons.

Chromium picolinate modulates serotonergic properties and carbohydrate metabolism in a rat model of diabetes

Chromium picolinate (CrPic) has shown both antidepressant and antidiabetic properties. In this study, the effects of CrPic on serotonergic properties and carbohydrate metabolism in diabetic rats were evaluated. Sixty male Sprague-Dawley rats were divided into four groups. (1) The control group received only standard diet (8 % fat). (2) The CrPic group was fed standard diet and CrPic (80 μg CrPic per kilogram body mass (b.m.)/day), for 10 weeks (microgram/kilogram b.m./day). (3) The HFD/STZ group fed a high-fat diet (HFD, 40 % fat) for 2 weeks and then received streptozotocin (STZ, 40 mg/kg, i.p.) (i.v.) HFD-STZ-CrPic group treated as the previous group and then were administered CrPic. CrPic administration to HFD/STZ-treated rats increased brain chromium levels and improved all measurements of carbohydrate metabolism and serotonergic properties (P<0.001). CrPic also significantly increased levels of insulin, tryptophan, and serotonin (P<0.001) in the serum and brain, and decreased cortisol levels in the serum (P<0.01). Except chromium levels, no significant effect of CrPic supplementation was detected on the overall measured parameters in the control group. CrPic administration was well tolerated without any adverse events. The results support the use of CrPic supplementation which improves serotonergic properties of brain in diabetes.

Dairy constituents and neurocognitive health in ageing

Age-related cognitive decline (ARCD) and dementia are of increasing concern to an ageing population. In recent years, there has been considerable research focused on effective dietary interventions that may prevent or ameliorate ARCD and dementia. While a number of studies have considered the impact that dairy products may have on physiological health, particularly with regard to the metabolic syndrome and cardiovascular health, further research is currently needed in order to establish the impact that dairy products have in the promotion of healthy brain function during ageing. The present review considers the available evidence for the positive effects of dairy products on the metabolic syndrome and glucose regulation, with consideration of the implications for neurocognitive health. A literature search of current (September 2010) meta-analyses/reviews and original research regarding dairy products and cognition was conducted through SCOPUS using the following search terms for dairy consituents: dairy, milk, cheese, yoghurt, probiotics, whey protein, alpha lactalbumin, calcium, B-12, bioactive peptides and colostrinin (CLN). These search terms for dairy products were combined with the following search terms related to cognition and health: cognition, cognitive decline, dementia, Alzheimer's disease, metabolic syndrome, diabetes, insulin resistance and glucose regulation. Concerns regarding SFA and other fatty acids found in dairy products are also reviewed in relation to different forms of dairy products. The review also considers recent evidence for positive neurocognitive effects associated with bioactive peptides, CLN and proline-rich polypeptides, α-lactalbumin, vitamin B12, calcium and probiotics. Future directions for the extraction and purification of beneficial constituents are also discussed. It is concluded that low-fat dairy products, when consumed regularly as part of a balanced diet, may have a number of beneficial outcomes for neurocognitive health during ageing.

The effect of glucose dose and fasting interval on cognitive function: a double-blind, placebo-controlled, six-way crossover study

RATIONALE

Previous research has identified a number of factors that appear to moderate the behavioural response to glucose administration. These include physiological state, dose, types of cognitive tasks used and level of cognitive demand. Another potential moderating factor is the length of the fasting interval prior to a glucose load.

OBJECTIVES

Therefore, we aimed to examine the effect of glucose dose and fasting interval on mood and cognitive function.

METHODS

The current study utilised a double-blind, placebo-controlled, balanced, six period crossover design to examine potential interactions between length of fasting interval (2 versus 12 hours) and optimal dose for cognition enhancement.

RESULTS

Results demonstrated that the higher dose (60 g) increased working memory performance following an overnight fast, whereas the lower dose (25 g) enhanced working memory performance following a 2-h fast.

CONCLUSIONS

The data suggest that optimal glucose dosage may differ under different conditions of depleted blood glucose resources. In addition, glucoregulation was observed to be a moderating factor. However, further research is needed to develop a model of the moderating and mediating factors under which glucose facilitation is best achieved.

Dose-response investigation into glucose facilitation of memory performance and mood in healthy young adults

It has been suggested that the memory enhancing effect of glucose follows an inverted U-shaped curve, with 25 g resulting in optimal facilitation in healthy young adults. The aim of this study was to further investigate the dose dependency of the glucose facilitation effect in this population across different memory domains and to assess moderation by interindividual differences in glucose regulation and weight. Following a double-blind, repeated measures design, 30 participants were administered drinks containing five different doses of glucose (0 g, 15 g, 25 g, 50 g, and 60 g) and were tested across a range of memory tasks. Glycaemic response and changes in mood state were assessed following drink administration. Analysis of the data showed that glucose administration did not affect mood, but significant glucose facilitation of several memory tasks was observed. However, dose-response curves differed depending on the memory task with only performance on the long-term memory tasks adhering largely to the previously observed inverted U-shaped dose-response curve. Moderation of the response profiles by interindividual differences in glucose regulation and weight was observed. The current data suggest that dose-response function and optimal dose might depend on cognitive domain and are moderated by interindividual differences in glucose regulation and weight.

Glucose enhancement of memory is modulated by trait anxiety in healthy adolescent males

Glucose administration is associated with memory enhancement in healthy young individuals under conditions of divided attention at encoding. While the specific neurocognitive mechanisms underlying this 'glucose memory facilitation effect' are currently uncertain, it is thought that individual differences in glucoregulatory efficiency may alter an individual's sensitivity to the glucose memory facilitation effect. In the present study, we sought to investigate whether basal hypothalamic-pituitary-adrenal axis function (itself a modulator of glucoregulatory efficiency), baseline self-reported stress and trait anxiety influence the glucose memory facilitation effect. Adolescent males (age range = 14-17 years) were administered glucose and placebo prior to completing a verbal episodic memory task on two separate testing days in a counter-balanced, within-subjects design. Glucose ingestion improved verbal episodic memory performance when memory recall was tested (i) within an hour of glucose ingestion and encoding, and (ii) one week subsequent to glucose ingestion and encoding. Basal hypothalamic-pituitary-adrenal axis function did not appear to influence the glucose memory facilitation effect; however, glucose ingestion only improved memory in participants reporting relatively higher trait anxiety. These findings suggest that the glucose memory facilitation effect may be mediated by biological mechanisms associated with trait anxiety.

Do specific dietary constituents and supplements affect mental energy? Review of the evidence

The numbers of marketing claims and food, beverage, and drug products claiming to increase mental energy have risen rapidly, thus increasing the need for scientific specificity in marketing and food label claims. Mental energy is a three-dimensional construct consisting of mood (transient feelings about the presence of fatigue or energy), motivation (determination and enthusiasm), and cognition (sustained attention and vigilance). The present review focuses on four dietary constituents/supplements (Ginkgo biloba, ginseng, glucose, and omega-3 polyunsaturated fatty acids) to illustrate the current state of the literature on dietary constituents and mental energy. The strongest evidence suggests effects of Ginkgo biloba on certain aspects of mood and on attention in healthy subjects, as well as associations between omega-3 polyunsaturated fatty acids and reduced risk of age-related cognitive decline. Limitations of the current data and challenges for future research are discussed.

Intersection between metabolic dysfunction, high fat diet consumption, and brain aging

Deleterious neurochemical, structural, and behavioral alterations are a seemingly unavoidable aspect of brain aging. However, the basis for these alterations, as well as the basis for the tremendous variability in regards to the degree to which these aspects are altered in aging individuals, remains to be elucidated. An increasing number of individuals regularly consume a diet high in fat, with high-fat diet consumption known to be sufficient to promote metabolic dysfunction, although the links between high-fat diet consumption and aging are only now beginning to be elucidated. In this review we discuss the potential role for age-related metabolic disturbances serving as an important basis for deleterious perturbations in the aging brain. These data not only have important implications for understanding the basis of brain aging, but also may be important to the development of therapeutic interventions which promote successful brain aging.

Effect of age and glucoregulation on cognitive performance

Type 2 diabetes has been associated with a number of physiological consequences including neuropathy, retinopathy, and incidence of vascular disease. Less is known about the effect on cognition of prediabetes, a period when glucose regulation is abnormal. It is not clear which aspect of impaired glucoregulation is most predictive of cognitive deterioration. In the present experiment, we measured cognitive function in 93 healthy male and female nondiabetic older participants who ranged in age from 55 to 88 years. Various biological measures were obtained including a glucose tolerance test during which glucose and insulin were measured. Participants were evaluated twice, once after drinking a saccharin solution and on another occasion after drinking a glucose solution (50 g). The analysis of the correlations between the biological measures and the results of the cognitive tasks revealed that evoked glucose measures such as peak glucose and glucose at 1 hour were most often correlated with cognitive performance. We observed that progressively worse glucose regulation predicted poorer performance on measures of working memory and executive function-that is, on the Arithmetic, Digit Span Backward, Letter-Number Sequencing, Spatial Span Forward, Spatial Span Backward (trend), and Modified Brown-Peterson tasks. Although, there was no significant facilitative effect of glucose on cognitive performance, it reduced the association between glucose regulation and cognition, apparently by slightly improving performance. These results suggest that cognitive functions may be impaired before glucoregulatory impairment reaches levels consistent with a type 2 diabetes diagnosis.

Glucoregulatory and order effects on verbal episodic memory in healthy adolescents after oral glucose administration

The ingestion of oral glucose has been observed to facilitate memory performance in both elderly individuals and in young adults. However, fewer studies have investigated the effect of glucose on memory in children or adolescents. In the present study, the ingestion of a glucose laden drink was observed to enhance verbal episodic memory performance in healthy adolescents under conditions of divided attention, relative to a placebo drink. Further analyses found that this glucose memory facilitation effect was observed only in adolescents exhibiting better glucoregulatory efficiency. These findings demonstrate that the glucose memory facilitation effect can be generalised to younger individuals. The importance of controlling for treatment order in within-subjects designs investigating the glucose memory enhancement effect is also discussed.

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.

Type 2 diabetes and risk of cognitive impairment and dementia

Diabetes is a major public health burden. Even a modest effect of diabetes on cognitive function has significant public health implications. Several lines of mechanistic evidence implicate a role of insulin and glucose metabolism on risk of developing dementia, including Alzheimer's disease. Population-based studies have shown that those with type 2 diabetes mellitus have an increased risk of cognitive impairment, dementia, and neurodegeneration. There are many mechanisms through which diabetes could increase risk of dementia, including glycemia, insulin resistance, oxidative stress, advanced glycation endproducts, inflammatory cytokines, and microvascular and macrovascular disease. This paper presents a review of the evidence on diabetes and increased risk of dementia and cognitive impairment, a discussion of different possible mechanisms, and remaining gaps in our knowledge.

The influence of the glycaemic load of breakfast on the behaviour of children in school

The impact of breakfasts of different glycaemic loads on the performance of nineteen children, aged six to seven years, was explored. Over a four week period, children attended a school breakfast club each day and ate one of three meals. Each meal offered a similar amount of energy but differed in their glycaemic load. When working individually, the behaviour of a child was rated in the classroom every ten seconds for 30 min to produce a measure of time spent on task. Memory was assessed by asking for the recall of a series of objects. The ability to sustain attention was measured by asking for a response after various delays. The incidence of negative behaviour was recorded when playing a video game that was too difficult to allow success. Two to three hours after a low glycaemic load breakfast had been consumed, performance on the tests of memory and the ability to sustain attention were better, fewer signs of frustration were displayed and initially more time was spent on task when working individually in class. The importance of the results was discussed in the context of the wide range of factors that influence behaviour in school.

Gastric emptying, diabetes, and aging

Gastric emptying is mildly slowed in healthy aging, although generally remains within the normal range for young people. The significance of this is unclear, but may potentially influence the absorption of certain drugs, especially when a rapid effect is desired. Type 2 diabetes is common in the elderly, but there is little data regarding its natural history, prognosis, and management. This article focuses on the interactions between gastric emptying and diabetes, how each is influenced by the process of aging, and the implications for patient management.

The effect of glucose administration on the recollection and familiarity components of recognition memory

Previous research has demonstrated that glucose administration facilitates long-term memory performance. The aim of the present research was to evaluate the effect of glucose administration on different components of long-term recognition memory. Fifty-six healthy young individuals received (a) a drink containing 25 g of glucose or (b) an inert placebo drink. Recollection and familiarity components of recognition memory were measured using the 'remember-know' paradigm. The results revealed that glucose administration led to significantly increased proportion of recognition responses based on recollection, but had no effect on the proportion of recognition responses made through participants' detection of stimulus familiarity. Consequently, the data suggest that glucose administration appears to facilitate recognition memory that is accompanied by recollection of contextual details and episodic richness. The findings also suggest that memory tasks that result in high levels of hippocampal activity may be more likely to be enhanced by glucose administration than tasks that are less reliant on medial temporal lobe structures.

Glucose enhances newborn memory for spoken words

The effect of a 2 g/kg glucose feed was compared with a water feed on retention of a spoken word in 2-4 days old infants in a between group randomized trial. Infants heard a word in 30-s trials until they demonstrated orientation (head turns towards the sound) and habituation. After a 100 s delay, infants who received glucose turned toward the word less often than infants receiving water (means 31.8 vs. 57.7%, t = 2.8, p < 0.01) implying that they remembered the word better. There were no differences between groups in measures of attention to or rate of learning of the word. Only infants who subsequently oriented towards a different word, indicating that they remained alert, were used in the data analysis. The results suggest that glucose enhanced memory for a spoken word in neonates.

The effect of the interaction between glucose tolerance and breakfasts varying in carbohydrate and fibre on mood and cognition

As a glucose containing drink has been reported to improve memory, and missing breakfast has been reported to adversely influence memory late in the morning, meals designed to differ in their ability to release glucose into the blood stream were contrasted. Using a factorial design, breakfasts containing 15, 30 or 50 g of carbohydrate and 1.5, 6 or 13 g of fibre were compared. The glucose tolerance of participants proved to be an important factor. Those with better tolerance reported better mood. Those eating breakfasts containing greater amounts of carbohydrate reported feeling tired rather than energetic. The amount of carbohydrate did not negatively affect memory in those with better glucose tolerance, however, the consumption of more carbohydrate resulted in more forgetting in those with poorer glucose tolerance. The effect with reactions times differed from memory in that a greater intake of carbohydrate resulted in faster responses later in the morning.

Longitudinal study of the effects of a high-fat diet on glucose regulation, hippocampal function, and cerebral insulin sensitivity in C57BL/6 mice

Although the increasing rate of obesity has stimulated interest in the effects of diet composition on peripheral systems, comparatively little work has been done to examine effects upon the brain. A diet high in fat is one of many factors that can promote obesity, and previous research has shown that such a diet can produce learning and memory impairment in rodents. In the present study, C57BL/6 mice were placed on either a high-fat (45% kcal fat) or regular (5% kcal fat) diet, and examined at different points during the subsequent year. The high-fat diet led to increased weight gain, significant impairment in glucoregulation, and altered insulin-mediated signaling within the hippocampus, an area of the brain believed to be important for the acquisition of memory. Following ten months on either diet, synaptic function in ex vivo hippocampal slices was examined, and neither stimulus-response curves nor electrically induced long-term potentiation were found to be different. As well, performance in the Morris water maze, a hippocampal-dependent test of spatial memory, was not influenced by diet. However, mice consuming a high-fat diet failed to perform an operant bar-pressing task, indicating a significant impairment to procedural learning and consolidation processes. Despite causing broad peripheral changes in C57BL/6 mice, consuming a large proportion of calories from saturated fat had only a limited effect upon learning and memory, which suggests that certain aspects of brain function are selectively vulnerable to the influences of diet.

Insulin resistance, inflammation, and cognition in Alzheimer's Disease: Lessons for multiple sclerosis

Insulin resistance (reduced ability of insulin to stimulate glucose utilization) is common in North American and Europe, where as many as one third of all older adults suffer from prodromal or clinical type 2 diabetes mellitus. It has long been known that insulin-resistant conditions adversely affect general health status. A growing body of findings suggests that insulin contributes to normal brain functioning and that peripheral insulin abnormalities increase the risk for memory loss and neurodegenerative disorders such as Alzheimer's disease. Potential mechanisms for these effects include insulin's role in cerebral glucose metabolism, peptide regulation, modulation of neurotransmitter levels, and modulation of many aspects of the inflammatory network. An intriguing question is whether insulin abnormalities also influence the pathophysiology of multiple sclerosis (MS), an autoimmune disorder characterized by elevated inflammatory biomarkers, central nervous system white matter lesions, axonal degeneration, and cognitive impairment. MS increases the risk for type 1 diabetes mellitus. Furthermore, the lack of association between MS and type 2 diabetes may suggest that insulin resistance affects patients with MS and the general population at the same alarming rate. Therefore, insulin resistance may exacerbate phenomena that are common to MS and insulin-resistant conditions, such as cognitive impairments and elevated inflammatory responses. Interestingly, the thiazolidinediones, which are used to treat patients with type 2 diabetes, have been proposed as potential therapeutic agents for both Alzheimer's disease and MS. The agents improve insulin sensitivity, reduce hyperinsulinemia, and exert anti-inflammatory actions. Ongoing studies will determine whether thiazolidinediones improve cognitive functioning for patients with type 2 diabetes or Alzheimer's disease. Future studies are needed to examine the effects of thiazolidinediones on patients with MS.

The effect of glucose administration on the emotional enhancement effect in recognition memory

Previous research has demonstrated that glucose administration improves memory performance. However few studies have addressed the effects of glucose on emotional material that by nature already enjoys a memory advantage. The aim of the present research was therefore to investigate whether the memory facilitation effect associated with glucose would emerge for emotional words. Experiment 1 demonstrated that negative words were better recognized and remembered than positive and neutral words. Experiment 2 further explored these effects under conditions of glucose administration and an aspartame control. The results revealed that both the aspartame and glucose groups replicated the results from Experiment 1. The present research therefore demonstrated that the glucose facilitation effect did not emerge for material that already benefits from a memory advantage. These results also raise the question of whether the dose response relationship previously associated with glucose administration is applicable when the information being processed is of an emotional nature.

Impact of impaired glucose tolerance and type 2 diabetes on cognitive aging

Type 2 diabetes is becoming increasingly common in most Westernized countries and it now occurs at a younger age. There are pathologies associated with diabetes, mostly systemic ones. However, a growing number of studies is also showing that diabetes is associated with impaired cognitive processes in older adults and hasten the progression to dementia. The most common cognitive deficits are decreases in processing speed and verbal memory; these may extend to other aspects of cognition with increasing age. The link between diabetes and cognitive decline is obscured by depression, hypertension, as well as cardio- and cerebrovascular diseases, all of which occur to varying degrees in diabetic patients. A few studies indicate that controlling blood glucose with anti-diabetic treatments may help prevent the cognitive decline in diabetic patients before they are 70 years old. After that age, diabetes appears to produce faster cognitive decline and may increase the occurrence of pathological changes associated with vascular dementia or Alzheimer's disease.

[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.

Breakfasts that release glucose at different speeds interact with previous alcohol intake to influence cognition and mood before and after lunch

Alcohol consumption and the glycemic load (GL) of a meal interact to influence both mood and memory. The authors compared the effects of eating a high GL lunch on mood and memory after consumption of a breakfast high in either rapidly (RAG) or slowly (SAG) available glucose. When less than 4.5 g of alcohol had been drunk the previous evening, the eating of a high RAG meal was associated with better memory later in the morning. In contrast, after more than 4.5 g of alcohol had been drunk the previous evening, the SAG meal resulted in better memory. After lunch, if more than 4.5 g alcohol had been drunk the previous evening, the RAG breakfast, but neither the SAG meal nor fasting, resulted in a more confused feeling.

The relationship between impaired glucose tolerance, type 2 diabetes, and cognitive function

The present review integrates findings of published studies that have evaluated the cognitive function of treated and untreated type 2 diabetic patients and provides a detailed overview of the neuropsychological assessments conducted. Cognitive deficits are observed in older people with glucose intolerance or untreated diabetes but these deficits appear to be attenuated by treatments that improve glycemic control. Cognitive decrements in treated type 2 diabetic patients are most consistently observed on measures of verbal memory (35% of the measures) and processing speed (45% of the measures) while preserved function is observed on measures of visuospatial, attention, semantic and language function. Some studies suggest that deficits in cognitive functions are associated with poorer glycemic control. A number of other factors, such as depression, cardiovascular and cerebrovascular disease, increase these deficits. We conclude that, in diabetic patients who achieve and maintain good glycemic control, type 2 diabetes only has a small impact on cognitive functions before the age of 70 years. However, early onset of type 2 diabetes, poor glycemic control and the presence of micro- and macrovascular disease may interact to produce early cognitive deficits. In older adults (70 years and over), diabetes likely interacts with other dementing processes such as vascular disease and Alzheimer's disease to hasten cognitive decline.

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.

Modulation of memory by insulin and glucose: neuropsychological observations in Alzheimer's disease

Converging evidence has identified a potential association among Alzheimer's disease, glucose metabolism, insulin activity, and memory. Notably, type 2 diabetes, which is characterized by insulin resistance, may modulate the risk of Alzheimer's disease, and patients with Alzheimer's disease may have a greater risk for glucoregulatory impairments than do healthy older adults. In animal studies, it has been shown that raising blood glucose levels acutely can facilitate memory, in part, by increasing cholinergic activity, which is greatly diminished in patients with Alzheimer's disease. Other studies have confirmed that glucose administration can facilitate memory in healthy humans and in patients with Alzheimer's disease. Interestingly, glucose effects on memory appear to be modulated by insulin sensitivity (efficiency of insulin-mediated glucose disposal). Of course, the acute effects of glucose administration should be distinguished from the effects of chronic hyperglycemia (diabetes), which has been associated with cognitive impairments, at least in older adults. The relationship of insulin and memory has been more difficult to characterize. In animals, systemic insulin administration has been associated with memory deficits, likely due, in part, to hypoglycemia that occurs when exogenous insulin is not supplemented with glucose to maintain euglycemia. In healthy adults and patients with Alzheimer's disease, raising plasma insulin levels while maintaining euglycemia can improve memory; however, raising plasma glucose while suppressing endogenous insulin secretion may not improve memory, suggesting that adequate levels of insulin and glucose are necessary for memory facilitation. Clinical studies have corroborated findings that patients with Alzheimer's disease are more likely than healthy older adults to have reduced insulin sensitivity, and further suggest that apolipoprotein E genotype may modulate the effects of insulin on glucose disposal, memory facilitation, and amyloid precursor protein processing. Collectively, these findings support an association among Alzheimer's disease, impaired glucose metabolism, and reduced insulin sensitivity.

Evidence for linkage between regulatory enzymes in glycolysis and schizophrenia in a multiplex sample

Observations of impaired glucose regulation in schizophrenia are long-standing, although their pathological and etiological significance is uncertain. One approach to the issue that minimizes environmental variables (e.g., medication and diet) is to determine whether genes related to glucose regulation show genetic linkage to schizophrenia. We examined the potential role of glucose metabolism in schizophrenia through a genome scan of affection status in schizophrenia and an empirical method for deriving P-values. Data were utilized from the NIMH Genetics Initiative for Schizophrenia dataset, which comprises a total sample consisting of 71 pedigrees containing 218 nuclear families and 987 individuals. A genome scan with 459 markers spaced at an average of 10 cM intervals was conducted using the linkage analysis program Genehunter separately for European- and African-American groups. Enzymes that regulate glycolysis were identified and the genes regulating these enzymes were located through the Online Mendelian Inheritance in Man (OMIM) website. The focus in this study was on genes located near previously reported schizophrenia susceptibility regions. The genome-wide significance of these genes to schizophrenia was assessed using permutation testing. When results were adjusted for multiple testing within and across ethnic groups, 6-phosphofructo-2-kinase/fructose-2,6-bisphosphatase 2 (PFKFB2; chromosome 1q32.2) achieved genome-wide significance (P = 0.04). In addition, hexokinase 3 (HK3; chromosome 5q35.3) was also suggestive of linkage (P = 0.09). For the European-American sample, PFKFB2 (1q32.2), hexokinase 3 (HK3; 5q35.3), and pyruvate kinase 3 (PK3; chromosome 15q23) achieved significance at the 0.05 level. None of the genes showed significance in the African-American sample. Our results provide further support for the view that genes that regulate glucose metabolism may also influence susceptibility to schizophrenia. More generally, they support the view that relationships between glucose dysregulation and schizophrenia are inherent to the disorder, and are not merely epiphenomena related to medication or other treatment factors.

Effect of age and glucoregulation on cognitive performance

Non-insulin dependent diabetes mellitus (NIDDM) has been associated with a number of physiological consequences including neuropathy, retinopathy and incidence of vascular disease. Recently, several authors reviewed studies that suggested that NIDDM is associated with cognitive impairments leading to a higher incidence of dementia. In the present experiment, we measured cognitive function in 57 healthy male and female non-diabetic older participants who ranged in age from 55 to 84. Various biological measures were obtained including a glucose tolerance test during which glucose and insulin were measured. Participants were separated into better and poorer glucoregulatory groups on the basis of their blood glucose levels during the tolerance test. Participants were evaluated twice, once after drinking a saccharin solution and on another occasion after drinking a glucose solution (50 g). Older participants (72 years and over) with poorer glucoregulation had the worse performance in tests evaluating working memory, verbal declarative memory and executive functions. Glucose administration appeared to only attenuate the decrements observed in the saccharin condition in the older participants for some of the tests. These results suggest that cognitive functions may be impaired before glucoregulatory impairment reaches levels consistent with a type II diabetes diagnosis.

Glucose effects on cognition in schizophrenia

Clozapine has been shown to improve verbal declarative memory and other cognitive functions in chronic schizophrenia. This raises the possibility that additional adjunctive manipulations might improve memory further. In this study, we hypothesized that glucose, which improves memory in a variety of conditions, including schizophrenia, would improve memory more than saccharin in a group of patients stabilized on clozapine. Twelve outpatients with schizophrenia who received treatment with clozapine participated in a double-blind, counterbalanced, crossover study. Subjects received beverages containing either glucose or saccharin on one occasion, and then the other beverage about a week later. Fifteen minutes after ingesting the beverage, subjects received a brief battery of neuropsychological tests to assess verbal declarative memory, attention, and executive functions. Blood glucose levels were assessed at baseline, and at 15 and 50 min after beverage ingestion. The main findings were that retention of a list of words was improved in the glucose condition, while performance on a complex test of sustained vigilance declined after glucose ingestion. These findings provide evidence that glucose improves declarative memory in patients with schizophrenia who were treated with clozapine, and underscore the possibility of developing effective protocols to reduce cognitive dysfunctions in the disorder. They also highlight the need to explore the extent to which glucose modulates nonmemory cognitive functions such as attention, and to understand more generally how glucose availability and regulation influence cognition.

Carbohydrate-induced memory impairment in adults with type 2 diabetes

OBJECTIVE

Memory impairment is observed in adults with type 2 diabetes. The focus of this study was to determine whether acute carbohydrate consumption contributes to or exacerbates memory dysfunction.

RESEARCH DESIGN AND METHODS

The impact of consuming 50 g of rapidly absorbed carbohydrate (one half bagel and white grape juice) at breakfast was examined in 19 adults with type 2 diabetes. Subjects (mean age 63 +/- 9 years, mean BMI 26.1 +/- 4.5 kg/m(2)) were tested, under fed and fasted conditions, on verbal declarative memory using both word list and paragraph recall tests (immediate and delayed [7-min] recall), Trails Test Part B as a measure of general brain function, and mood (subjectively monitoring global vigor and affect).

RESULTS

Under baseline (fasting) conditions, elevated blood HbA(1c) was negatively associated with immediate and delayed paragraph recall performance (R(2) = 0.30; P = 0.024) and higher fasting blood glucose trended toward poorer word list recall (R(2) = 0.09; P = 0.102). Carbohydrate ingestion influenced measures of delayed, but not immediate, recall in a time-dependent fashion (time x food) (word list, P = 0.046; paragraph, P = 0.044) such that delayed recall was improved at 15 min postingestion but was impaired at 30 min. Neither Trails Test scores (P = 0.17) nor mood (affect, P = 0.68 and vigor, P = 0.45) were influenced by food ingestion.

CONCLUSIONS

In adults with type 2 diabetes, poorer glycemic control is associated with lower performance on tests of declarative memory. Acute ingestion of high glycemic index carbohydrate foods further contributes to the underlying memory impairment.

Glucose effects on a continuous performance test of attention in adults

Increases in plasma blood glucose levels modulate memory, mood, and, to some extent, attention in adults. Participants in the present study were administered glucose (10, 100, and 500 mg/kg, or 50 g) or placebo (23.7 mg saccharin) shortly prior to completing the test of variables of attention (TOVA), a continuous performance test (CPT) commonly used to assess attention for diagnostic purposes. There were significant increases in blood glucose levels for the 500 mg/kg and 50 g groups, but only the 100 mg/kg group showed significant changes in behavior in comparison to the saccharin group. Specifically, the 100 mg/kg group performed worse on measures of commission errors, post-commission responses, and post-commission response time variability. There were no differences among the groups on other major variables of attention, including omission errors, response time, and response time variability. The results of this study demonstrate that large doses of glucose which increase blood glucose levels do not influence attention, but that a moderate dose (100 mg/kg) selectively impairs measures of impulsivity or disinhibition. Practitioners and researchers should maintain an awareness of dietary effects on attention and continue to examine micronutrients as potential confounds on diagnostic tests of cognition and behavior.