Consumption of glucose drinks slows sensorimotor processing: double-blind placebo-controlled studies with the Eriksen flanker task

The Impact of Free and Added Sugars on Cognitive Function: A Systematic Review and Meta-Analysis

A relationship between excessive sugar consumption and cognitive function has been described in animal models, but the specific effects of sugars in humans remains unclear. This systematic review and meta-analysis aimed to evaluate the current knowledge, research characteristics, and quality of evidence of studies investigating the impacts of free and added sugars on human cognition in healthy participants. The review identified 77 studies (65 experimental trials, n = 3831; 9 cross-sectional studies, n = 11,456; and 3 cohort studies, n = 2059). All cohort studies and eight of the nine cross-sectional studies found significant positive correlations between added sugar consumption and risk of cognitive impairment. Four studies identified reduced risk of cognitive impairment associated with natural fructose-containing foods. The majority of randomised control trials assessed short-term glucose facilitation effects on cognitive outcomes. The results from these studies suggest the need for a tightly regulated blood glucose level, dependent on individualised physiological factors, for optimal cognitive function. A meta-analysis of a subset of studies that assessed the impact of glucose on recall found improvements in immediate free recall compared to controls (p = 0.002). The findings highlight the potentially detrimental effect of excessive, long-term, or prenatal added sugar consumption on cognitive function. Further research is needed to examine the specific effects of free and added sugars on cognitive function.

Comparing the effects of dietary sugars on cognitive performance and reaction time: A randomized, placebo- controlled and double-blind experimental trial

The aim of the study was to compare the effects of acute intake dietary sugars on cognitive performance and reaction time. This study was, randomized, placebo-controlled, double-blind experimental design, conducted with 75 healthy adults. At the beginning of the study, the participants (36 male, 39 female; 21.6 ± 1.3 years of age; body mass index: 21.59 ± 1.94 kg/m²) were randomly divided into equal five groups (n:15) (glucose (10 g), fructose (10 g), sucrose (10 g), saccharin (0.24 g), placebo), and received dietary sugars dissolved in 200 mL of water. Cognitive performance was determined with Cancelation Test, and the Simple Response Time and Ruler Drop Tests were used in order to response and reaction time of participants, respectively. General score of cognitive performance (0.93 ± 0.1), reaction (295 ± 20 ms), and response (204 ms) were highest in glucose and lowest in placebo (0.63 ± 0.1; 368 ± 22 ms; 251 ms, respectively) (p < .001). Saccharin groups had a higher reaction (312 ± 22 ms) and response (216 ms) time score compared to consumed fructose (316 ± 39; 227 ms), sucrose (354 ± 26; 246 ms), and placebo (368 ± 22; 251 ms) groups, respectively (p < .001). These findings show that differences in the absorption pattern and sweetness levels of sugar types may have different effects on cognitive performance and reaction time.

The Impact of Free Sugar on Human Health-A Narrative Review

The importance of nutrition in human health has been understood for over a century. However, debate is ongoing regarding the role of added and free sugars in physiological and neurological health. In this narrative review, we have addressed several key issues around this debate and the major health conditions previously associated with sugar. We aim to determine the current evidence regarding the role of free sugars in human health, specifically obesity, diabetes, cardiovascular diseases, cognition, and mood. We also present some predominant theories on mechanisms of action. The findings suggest a negative effect of excessive added sugar consumption on human health and wellbeing. Specific class and source of carbohydrate appears to greatly influence the impact of these macronutrients on health. Further research into individual effects of carbohydrate forms in diverse populations is needed to understand the complex relationship between sugar and health.

Cognitive glucose sensitivity-proposing a link between cognitive performance and reliance on external glucose uptake

Existing evidence on the effects of glucose supplementation on cognitive performance appears inconclusive. Metabolic switching offers an approach to explain such incoherent findings based on differences in cognitive functioning after fasting. We propose a new construct, cognitive glucose sensitivity (CGS), which quantifies individual performance gain due to glucose supplementation. We tested the hypothesis that the effects of glucose ingestion depend on CGS, cognitive task domain, and sex. In addition, the relationship between CGS and body mass index (BMI) was examined. Seventy-one participants (48 female) were tested in two conditions each (deprivation baseline vs. glucose supplementation), performing tasks from different cognitive domains (memory and executive functioning). We found significant evidence for a correlation of deprivation baseline performance and CGS across domains (Corsi-Block-Tapping Task: r = -0.57, p < 0.001; Go-No-Go Task: r = 0.39, p = 0.001; word list recall: r = -0.50, p < 0.001). Moreover, individual CGS differed significantly between tasks (p = 0.018). Only in men, BMI was significantly related to CGS in a word recall paradigm (r = 0.49, p = 0.017). Our findings support the notion that the effects of glucose depend on CGS, task domain, and sex. The effort to reduce performance impairment (short-term) might sacrifice independence from external glucose (long term), possibly via declining blood glucose regulation. Therefore, CGS could be regarded as a candidate to enhance our understanding of the etiology of unhealthy eating.

Effect of glucose and sucrose on cognition in healthy humans: a systematic review and meta-analysis of interventional studies

CONTEXT

Evidence suggests that plasma glucose levels may influence cognitive performance, but this has not been systematically reviewed and quantified.

OBJECTIVE

The aim of this review was to investigate the potential effects of glucose and sucrose, compared with placebo, on cognition in healthy humans.

DATA SOURCES

The electronic databases PubMed and Web of Science were searched up to December 2019. Reference lists of selected articles were checked manually.

STUDY SELECTION

Randomized controlled trials or crossover trials that compared glucose or sucrose with placebo for effects on cognition were eligible.

DATA EXTRACTION

Potentially eligible articles were selected independently by 2 authors. Risk of bias was assessed through the Cochrane Collaboration tool. Standardized mean differences (SMDs) were obtained from random-effects meta-analyses for a subsample of studies that reported the same outcomes.

RESULTS

Thirty-seven trials were identified, of which 35 investigated the effect of glucose consumption compared with placebo on cognition. Two studies found no effect of glucose on cognition, while the others found mixed results. Only 3 of the 37 studies investigated the effects of sucrose intake, reporting mixed results. Meta-analyses revealed a significantly positive effect of glucose compared with control, but only when a verbal performance test (immediate word recall) was used in parallel-design studies (SMD = 0.61; 95%CI, 0.20-1.02; I2 = 0%). Twenty-four studies were classified as having high risk of bias for the selection procedure.

CONCLUSIONS

A limited body of evidence shows a beneficial effect of glucose in individuals performing immediate verbal tasks. High-quality trials with standardized cognitive measurements are needed to better establish the effect of glucose or sucrose on cognition.

SYSTEMATIC REVIEW REGISTRATION

PROSPERO registration number CRD42019122939.