Abstract
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.
