Caffeine May Interfere With Glucose Control

In the study, published in the August issue of Diabetes Care, researchers looked at the effects of caffeine on glucose and insulin levels in 14 people with type 2 diabetes who regularly drank coffee. None of the participants required insulin therapy as part of their diabetes treatment. The participants were observed on two different mornings after an overnight fast and abstinence from caffeine.

On the observation days, the participants took their prescribed diabetes medications and provided a blood sample 30 minutes later. While still fasting they were then given two 125-milligram capsules of caffeine or a placebo. A cup of coffee contains from 80 milligrams to 175 milligrams of caffeine. A second set of blood tests were then analyzed an hour after the taking the pills. Participants were then fed a liquid meal containing 75 grams of carbohydrates and another 125-milligram caffeine capsule or placebo. Additional blood samples were taken an hour and two hours following the meal.

The study showed that caffeine had little effect on glucose and insulin levels during the fasting period, but it caused significant surges after eating a meal. People who received the 375-milligram dose of caffeine experienced a 21% larger increase in glucose levels and a 48% larger increase in insulin levels compared with those who took the placebo during the two hours following their meals. "It seems that caffeine, by further impairing the metabolism of meals, is something diabetics ought to consider avoiding. Some people already watch their diet and exercise regularly," says Lane. "Avoiding caffeine might be another way to better manage their disease. In fact, it's possible that staying away from caffeine could provide bigger benefits altogether." The researchers say that blood sugars after meals correspond more closely to overall blood glucose control and may more accurately predict heart disease risk.