Objective: To test whether caffeine administered in coffee increases postprandial hyperglycemia in patients with type 2 diabetes who are habitual coffee drinkers.
Methods: The study used a within-subject, double-blind, placebo-controlled experimental design. Twenty adult coffee drinkers (11 women and 9 men) with type 2 diabetes treated with diet, exercise, orally administered antidiabetic agents, or some combination of these factors completed two mixed-meal tolerance tests (MMTT) after an overnight fast. Before the MMTT, each study participant received 250 mg of caffeine in 16 oz (475 mL) of decaffeinated coffee or decaffeinated coffee alone, with the treatment order counterbalanced in the group. Fasting and 1-hour and 2-hour postprandial blood samples were collected for measurement of plasma glucose and insulin concentrations.
Results: Glucose and insulin responses to the MMTT were quantified by the incremental areas under the 2-hour concentration-time curves (AUC2h). Administration of caffeine in decaffeinated coffee increased postprandial glucose and insulin responses (both P = 0.02). The mean plasma glucose AUC2h was 28% larger and the mean plasma insulin AUC2h was 19% larger after administration of caffeine than after administration of placebo.
Conclusion: Other constituents in coffee did not prevent the exaggeration of postprandial hyperglycemia by caffeine in these patients with type 2 diabetes, who were habitual coffee drinkers. Repeated on a daily basis, such effects could impair long-term glucose control in those patients with type 2 diabetes who habitually drink coffee or other caffeinated beverages.