Effects of caffeine on glucose tolerance: A placebo-controlled study

Objective: The investigation was performed to study the effects of 200 mg oral caffeine on glucose tolerance. Design: Single-blind Latin square with active treatment (caffeine) and placebo. Setting: The University of Padova, Department of Internal Medicine. Subjects: 30 nonsmoking healthy subjects aged 26-32 years who abstained not only from coffee but also from tea, chocolate and cola for 4 weeks and who had given their informed consent. Interventions: A 75 g oral glucose tolerance test (OGTT) was performed after giving caffeine or placebo (highly decaffeinated coffee). Results: The glycaemic curve was normal in all subjects and was similar in the two groups until the second hour; in subjects taking caffeine a shift towards the right was detected at the 2nd, 3rd and 4th hours in comparison to those taking the placebo. Blood insulin levels were comparable after caffeine and after placebo along the entire OGTT. Conclusions: The data suggest that caffeine intake induces a rise in blood glucose levels that is insulin independent.