Caffeine, a component of many popular dietary sources such as coffee, tea, colas, and chocolate, decreases insulin sensitivity by 15 percent in people without diabetes, say researchers in the Netherlands.
The doctors, who conducted a small test group study, published their findings in the February 2002 issue of Diabetes Care.
Researchers from the University Medical Center in Nijmegen injected doses of caffeine equal to moderate consumption into 12 healthy individuals and doses of a placebo (inactive) substance into 10 individuals after all the subjects had abstained from caffeine for 72 hours.
The decrease in insulin sensitivity documented during the caffeine trial neared the magnitude of the increase in insulin sensitivity that can be achieved by taking oral insulin-sensitizing agents, researchers say. In addition, the caffeine group had higher blood levels of free fatty acids and increased levels of the hormone adrenaline, which causes the liver to release glucose and limits the release of insulin.
The increase of adrenaline may be causing the decrease in insulin sensitivity, the researchers speculate. They point out that further studies need to determine whether the decreased insulin sensitivity continues over time with chronic use of caffeine. Because tolerance may develop with long-term ingestion of caffeine, they add, it’s premature to advise caffeine restriction to manage insulin resistance.
On the other hand, a group of doctors from Canada, Belgium and Denmark, who reported their findings in the March 2002 issue of Diabetes, noted that exercise helps to reduce caffeine-induced insulin resistance.
These researchers tested seven men who, on two occasions, did one hour of one-legged knee extensor exercise three hours before receiving either caffeine or a placebo in a double-blinded trial. In the group that received the caffeine, whole-body glucose was reduced by 37.5 micromols, versus a 54.1-micromol reduction in those who received the placebo substance.
“Exercise reduces the detrimental effects of caffeine on insulin action in muscle,” the researchers write in Diabetes.