Caffeine, Exercise, and Glucose

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Lee SJ, Hudson R, Kilpatrick K, et al.: Caffeine Ingestion Is Associated With Reductions in Glucose Uptake Independent of Obesity and Type 2 Diabetes Before and After Exercise Training. Diabetes Care 28:566–572, 2005.

What is the problem and what is known about it so far?

We all have glucose in our blood because the body uses glucose for energy. Normally, the body breaks food down into glucose and sends it into the bloodstream.

Insulin, a hormone made by the pancreas, helps get the glucose from the blood into the cells to be used for energy. This is known as "glucose uptake." In people with type 2 diabetes, the pancreas doesn't make enough insulin or the insulin doesn’t work very well. As a result, blood glucose rises, and high blood glucose can result in long-term diabetes complications, such as heart disease, stroke, nerve damage, and kidney or eye problems.

Eating (Eating what?) and drinking caffeine have been linked to an increase in blood glucose. Although exercise can lower blood glucose levels, it is unknown whether it reverses the harmful effects of caffeine on blood glucose levels.

Why did the researchers do this particular study?

The researchers wanted to study the effect of caffeine on lean and obese men with and without type 2 diabetes. They also wanted to study whether exercise changed the way caffeine affected blood glucose.

Who was studied?

Eight lean men, 7 obese men with type 2 diabetes, and 8 obese men without type 2 diabetes from Kingston, Ontario, Canada. All were white nonsmokers who did not exercise regularly and whose weight had not changed for 6 months before the study. None of the subjects regularly drank much caffeine.

How was the study done?

Researchers studied the participants for 4 weeks without exercise and then during a 13-week exercise program. Researchers studied their body weight, body fat, and glucose levels during both periods. Before and after the exercise program, researchers measured the subjects' glucose levels after they were given either caffeine or a placebo (a "fake" pill).

What did the researchers find?

The researchers found that, in all groups, taking a pill with the same amount of caffeine as 2-3 cups of coffee resulted in a significant decrease in glucose uptake, which caused a rise in blood glucose levels. After exercise, glucose uptake was slightly better, but eating or drinking caffeine was still linked with a significant decline in glucose uptake.

What were the limitations of the study?

The researchers studied a small group of white, middle-aged men with similar lifestyles. Because the subjects were similar, it is difficult to apply the study's findings to other people.

What are the implications of the study?

Caffeine is linked with a decline in the body's ability to turn glucose into energy, regardless of exercise, obesity, or type 2 diabetes.

In this study, caffeine was taken in a pill. The results of this study do not apply to coffee, which contains many other substances (potassium, antioxidants, and magnesium) that seem to help people with type 2 diabetes. More studies are needed to look at the long-term effects of caffeine, taken in any form, on the body's use of glucose and blood glucose levels.

FOR MORE INFORMATION

Managing Your Blood Glucose

A Field Guide to Type 2 Diabetes: The Essential Resource from the Diabetes Experts ( Alexandria , VA , ADA , 2004)

Caffeine-Induced Impairment of Insulin Action but not Insulin Signaling in Human Skeletal Muscle Is Reduced by Exercise, by F.S. Thong and Colleagues. Diabetes 51:583-590, 2002