Epidemiological studies indicate an inverse association of coffee consumption with risk of type 2 diabetes mellitus. However, studies to determine the clinical effects of coffee consumption on the glucose metabolism biomarkers remain uncertain. The aim of this systematic review was to evaluate the effects of coffee consumption on glucose metabolism. A search of electronic databases (PubMed and Web of Science) was performed identifying studies published until September 2017. Eight clinical trials (n = 247 subjects) were identified for analyses. Participants and studies characteristics, main findings, and study quality (Jadad Score) were reported. Short-term (1-3 h) and long-term (2-16 weeks) studies were summarized separately. Short-term studies showed that consumption of caffeinated coffee may increase the area under the curve for glucose response, while for long-term studies, caffeinated coffee may improve the glycaemic metabolism by reducing the glucose curve and increasing the insulin response. The findings suggest that consumption of caffeinated coffee may lead to unfavourable acute effects; however, an improvement on glucose metabolism was found on long-term follow-up.
Keywords: AMPK, Adenosine monophosphate-activated protein kinase; AUC, Area under the curve; CGA, Chlorogenic acids; Coffee; Glucose; HOMA-IR, Homeostasis model assessment insulin resistance index; IL, Interleukin; ISI, Insulin Sensitivity Index; Insulin; Insulin sensitivity; OGTT, Oral glucose tolerance test; PRISMA, Preferred reporting items for systematic reviews and meta-analyses; RCT, Randomised controlled trial; T2DM, Type 2 diabetes mellitus; Type 2 diabetes mellitus.