Does Caffeine Increase Blood Sugar Levels?

Does Caffeine Increase Blood Sugar Levels?

Researchers at Duke University have been taking aim at caffeine for some years now, and they think that people with type 2 diabetes should avoid coffee. According to the results of two small but significant studies, Dr. James Lane believes that caffeine affects the way that diabetics metabolize carbohydrates and leads to increased blood sugar levels.

Back in 2004, Dr. James Lane and fellow researchers tested the effects of caffeine in 14 people with type 2 diabetes. They tested the fasting blood sugar levels of each person, then gave them two caffeine pills and tested blood sugar levels an hour later. Each person then drank a high-carb meal replacement drink with a third caffeine pill, and blood sugar levels were tested one hour and two hours after their ‘meal’. Each person was tested on two different days. On one of those days, half the group got real caffeine and the other half took a placebo. On the second day, those who got a placebo on day one got the real deal, and those who got caffeine the first study day took a placebo. Neither researchers nor subjects knew which was which.

Even though fasting blood sugar levels weren’t affected by the caffeine, the blood sugar levels of those who took the caffeine pills showed significantly higher levels of blood sugar after meals than those who did not. The researchers concluded that caffeine has some effect on the interaction between glucose and insulin, though the study could not determine exactly what the mechanism was. They did advise, based on the results of the study, that people with diabetes might do better to avoid coffee or drink decaf.

In January 2008, the same group of researchers released the results of a second study. In this study, which included ten participants with type 2 diabetes, researchers implanted a small glucose monitoring device under the skin to measure blood sugar levels throughout the course of the day. That allowed researchers to track the effects of the caffeine on blood sugar levels over the course of 72 hours while participants carried on with their lives.


The patients were each given a caffeine pill on one day and a placebo on another day. Researchers found that on the days that they took caffeine pills, their blood sugar levels averaged 8% higher over the entire course of the day than on the days that they took a placebo. The effect was especially marked after meals. Blood sugar levels after breakfast were an average of 9% higher, 15% higher after lunch and 26% higher after dinner.

Researchers not sure why caffeine raises blood sugar levels
Lane says that there are two possible reasons for the increases in blood sugar levels on the days that patients received caffeine pills. Caffeine may interfere with the process that moves glucose from the blood into muscle and other cells in the body, breaking into the chain of metabolism in some way. Caffeine may also trigger adrenaline, which boosts blood sugar levels. Other researchers have speculated that caffeine makes the body less sensitive to insulin levels in the blood. Lane plans further research to determine whether cutting caffeine from the diet will help diabetics better control blood sugar levels.

“My advice would be, if patients are having trouble controlling their blood glucose and they are coffee drinkers, particularly heavy coffee drinkers, they might want to give it a try to see if it makes a difference to them,” he said. He believes that it may make a big difference to some, while others will see little difference at all.

A care advisor at Diabetes UK said that the research is “interesting”, but the sample is very small, so it proves very little. She said, “More research is needed before we ask people with diabetes to stop drinking coffee. The best way to control glucose levels is through healthy eating and exercise.”

Other critics of the study’s recommendation pointed out that the researchers used caffeine pills, not brewed coffee which may contain other components that negate the effect of caffeine. Other studies have shown that drinking coffee reduces the risk of developing diabetes.