Although more research is needed to confirm these results, researchers say their findings show that people with diabetes who have problems with glucose and insulin control should consider cutting back on caffeine in their diets.
The study showed that after a large dose of caffeine, blood glucose and insulin levels surge in response after meals in people with type 2 diabetes. These patients can have high insulin levels because they inefficiently use the hormone to lower blood glucose.
"In a healthy person, glucose is metabolized within an hour or so after eating. Diabetics, however, do not metabolize glucose as efficiently," says researcher James D. Lane, PhD, associate research professor in the department of psychiatry and behavioral sciences at Duke University, in a news release. "It appears that diabetics who consume caffeine are likely having a harder time regulating their insulin and glucose levels than those who don't take caffeine."
"The goal of clinical treatment for diabetes is to keep the person's blood glucose down," says Lane.
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.