Systematic review of randomised controlled trials of the effects of caffeine or caffeinated drinks on blood glucose concentrations and insulin sensitivity in people with diabetes mellitus

Background Compounds other than macronutrients have been shown to influence blood glucose concentrations and insulin sensitivity in people with diabetes, with caffeine being one such substance. The present study systematically reviewed the evidence of the effects of caffeine on blood glucose concentrations and/or insulin sensitivity in people with diabetes. Methods Four databases, including MEDLINE and EMBASE, were searched up to 1 February 2012. Randomised controlled trials (RCTs) investigating the effects of caffeine on blood glucose and/or insulin sensitivity in humans, diagnosed with type I, type II or gestational diabetes mellitus (GDM), were included. Quality assessment and data extraction were conducted and agreed by both authors. Results Of 253 articles retrieved, nine trials (134 participants) were identified. Trials in people with type II diabetes demonstrated that the ingestion of caffeine (approximately 200–500 mg) significantly increased blood glucose concentrations by 16–28% of the area under the curve (AUC) and insulin concentrations by 19–48% of the AUC when taken prior to a glucose load, at the same time as decreasing insulin sensitivity by 14–37%. In type I diabetes, trials indicated enhanced recognition and a reduced duration of hypoglycaemic episodes following ingestion of 400–500 mg caffeine, without altering glycated haemoglobin. In GDM, a single trial demonstrated that approximately 200 mg of caffeine induced a decrease in insulin sensitivity by 18% and a subsequent increase in blood glucose concentrations by 19% of the AUC. Conclusions Evidence indicates a negative effect of caffeine intake on blood glucose control in individuals with type II diabetes, as replicated in a single trial in GDM. Larger‐scale RCTs of longer duration are needed to determine the effects of timing and dose. Early indications of a reduced duration and an improved awareness of hypoglycaemia in type I diabetes require further confirmation.