Mohammad Reza Emami - Department of Clinical Nutrition, School of Nutritional Sciences and Dietetics, Tehran University of Medical Sciences (TUMS), Tehran, Iran

Background and Aim: Due to the inconsistent results of previous studies on the impact of acute coffee consumption on glycaemic indices, this meta-analysis was accomplished to evaluate the acute effects of caffeine and caffeinated coffee on insulin sensitivity index (ISI) and serum levels of glucose and insulin in healthy and diabetic subjects.Methods: PubMed and EMBASE were systematically searched for all English Randomized controlled Trial studies that published up to November 2017. Weighted mean differences (WMD) were reported with 95% confidence interval (CI) as a measure of caffeine effects on glycemic indices. Cochran’s Q test and I2 were applied to assess the between-study variance. Subgroup analysis was performed to assess possible sources of heterogeneity.Results: In total, 18 trials with a total of 252 subjects were enrolled in the meta-analysis. The pooled analysis revealed that acute caffeine supplementation, as pure caffeine or caffeinated coffee, increases glucose concentration (WMD=2.48, 95%CI: 0.75 to 4.20; P = 0.005) and decreases ISI (WMD= -0.46; 95% CI: -0.86 to-0.07 P-value = 0.003), while, no significant effect was found on insulin levels (WMD= 0.03, 95%CI: -0.84 to 0.89), with evidence of significant heterogeneity for analyses. In subgroup analysis, both caffeine and caffeinated coffee significantly increased serum glucose levels; however, this effect was significant for dose 250 mg of caffeine ingestion. For ISI, only pure caffeine was found to reduce ISI, not caffeinated coffee.Conclusion: Acute caffeine intake may increase glucose concentration and decrease insulin sensitivity index. Caffeine had no significant effect on insulin levels.

caffeine; coffee; insulin; glucose; insulin sensitivity; meta-analysis