A small controlled study published in Diabetes Care (February 2008) examined the short-term effects of caffeine consumption on blood glucose control in individuals with type 2 diabetes.
The study included 10 adults with type 2 diabetes who were managing their condition through diet alone and were not taking glucose-lowering medications. Participants were monitored continuously over a three-day period using devices that measured blood glucose levels throughout the day. On one of the study days, subjects were given caffeine capsules equivalent to approximately four cups of coffee; on the other days, they received placebo capsules.
Participants were provided with a standardized nutrient drink for breakfast and were allowed to select their own meals for lunch and dinner. Blood glucose responses following meals were compared between the caffeine and placebo days.
On the day caffeine was consumed, post-meal blood glucose levels were higher following each meal. Average increases in glucose levels were approximately 9% after breakfast, 15% after lunch, and 26% after dinner compared with placebo days. Overall, average daily blood glucose levels were about 8% higher on the caffeine day.
The authors concluded that acute caffeine intake was associated with impaired glucose control in this small group of individuals with type 2 diabetes, suggesting that caffeine consumption may influence post-meal glucose responses in some patients.
