Caffeine May Affect Blood Glucose Levels

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A small study conducted at Duke University has suggested that caffeine may hurt blood glucose control in people with Type 2 diabetes. The study’s authors have suggested that people with diabetes may want to avoid caffeinated beverages based on these findings; however, not all medical experts agree that total avoidance is necessary.

The study, which was published in the February issue of the journal Diabetes Care, looked at 10 people with Type 2 diabetes, average age 63. These people were all regular coffee drinkers before the study started and treated their diabetes with diet, exercise, and oral medicines, but not insulin.

The researchers gave the study participants identical packets of pills to take with breakfast and lunch for two days. One day’s pills contained the amount of caffeine present in four cups of coffee, while the other day’s pills were placebos (inactive pills). The participants did not know which pills they were taking on which days and did not consume any other caffeine during the study.

The researchers used continuous glucose monitors to track the participants’ glucose levels during the study. They found that the participants’ average daily glucose levels were about 8% higher on the days that they took the caffeine pills than on the days when they took the placebos. Their post-meal glucose levels were also significantly higher on the days when they consumed caffeine.

These results were consistent with the findings of two previous small studies of caffeine’s effect on people with Type 2 diabetes. The new study was also small, but it was well-designed in that it was double-blind (the participants did not know if they were getting the caffeine pill or the placebo) and featured a crossover (all participants received the caffeine pill and the placebo at different times). However, its results are puzzling in light of some large observational studies, which have found that people who drink coffee appear to have a reduced risk of developing Type 2 diabetes. However, this effect may be due to the presence of compounds in coffee other than caffeine, such as antioxidants.

Some possible explanations for why caffeine may raise blood glucose levels are that it may interfere with the process that transports glucose from the blood into the body’s cells and that it may trigger the release of hormones that raise blood glucose levels.

The Duke researchers indicated that more studies are needed to fully understand caffeine’s effect on blood glucose. However, James Lane, Ph.D., the medical psychologist who led the Duke study, stated of people with Type 2 diabetes that “They may find that it’s easier for them to keep their glucose down if they avoid caffeine.” Writing on the subject in the January/February 2008 issue of Diabetes Self-Management magazine, though, Lynn Grieger, R.D., C.D.E, C.P.T., suggests that “Until more studies are conducted, it is probably best to limit coffee intake to moderate levels.” She also points out that a “cup” of coffee from a café or fast-food restaurant often contains more than 8 fluid ounces, so people looking to limit their caffeine intake should pay attention to portion sizes.

What have your experiences been with caffeine? Do you think it affects your blood glucose control? Bloggers Eric Lagergren and Andy Stuckey—both of whom have Type 1 diabetes, which wasn’t looked at in this study—have blogged about their suspicions that caffeine may have raised their blood glucose levels. (Check out Eric’s entry “In Praise of the Diabetes Contact List” and Andy’s entry “You’re Always On My Mind: Questions and Thoughts About Diabetes” for more.)

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