Feb. 6, 2002 -- Caffeine is one of the most widely used "drugs" in the world. And now researchers have found that caffeine affects how well insulin -- the hormone that regulates blood sugar -- works in the body.
Caffeine is able to enter the brain and directly increase blood pressure and stimulate the release of stress hormones. These hormones are known to affect insulin and blood sugar in the body. So the researchers investigated whether caffeine has any harmful effects on blood sugar metabolism.
Lead researcher Gerben B. Keijzers, MD, and colleagues gave either caffeine or a placebo -- through a vein in the arm -- to 12 healthy volunteers. They then measured blood levels of insulin and stress hormones.
The caffeine was given at a dose of 3 mg per kilogram. For a 120 pound woman, that's equal to 160 mg of caffeine. For a 170 pound man, that's 230 mg.
The researchers then calculated insulin sensitivity. This is a measure of how well the body is using insulin. When insulin sensitivity goes down, this indicates that your body is less able to take blood sugar into the cells to be used for energy.
Caffeine decreased insulin sensitivity by 15%, a significant decline compared to placebo. Plus, stress hormone levels in the blood increased with caffeine. Blood pressure increased to a small degree as well.
A brewed 7 oz. cup of coffee has about 100 mg of caffeine. A 12 oz. cup of iced tea has 70 mg. Here are some examples of caffeine amounts in various soft drinks:
Mountain Dew 55 mg
Coca-Cola 46 mg
Mr. Pibb 41 mg
Dr. Pepper 40 mg
Pepsi-Cola 37 mg
It's important to keep in mind that these were healthy people. The question of whether caffeine might decrease insulin sensitivity and thus raise blood sugar in someone with diabetes is still unanswered. The results of this study suggest that it might.