Caffeine, helpful as it may be in the morning, isn't necessarily the most healthful drug around. A few studies have shown that it can decrease insulin sensitivity—an serious problem for diabetics. Researchers at Duke University tested some diabetic coffee drinkers to see how caffeine affected them.

What the researchers wanted to know: How does caffeine affect glucose and insulin levels?

What they did: Fourteen coffee drinkers who'd had Type II diabetes for at least six months were recruited for the study. For one week, they each kept track of all the caffeinated drinks imbibed. Then they came in twice for testing, once for caffeine and once for a placebo. Each patient first had blood taken for a baseline measurement, then took two pills of either caffeine or a placebo, had more blood taken, took another pill and drank a "liquid meal," and then had two more blood samples taken. The whole process took several hours both times, with waits for the caffeine (or placebo) and meal to be processed. Glucose and insulin levels were measured in the blood.

What they found: After taking caffeine, the patients didn't process glucose as well as they did after a placebo; they had both more glucose and more insulin circulating in their blood. Caffeine didn't affect fasting levels of glucose and insulin—the levels taken before the patients ate anything.

What the study means to you: Avoiding caffeine could improve your ability to use glucose; in this study, the patients' blood glucose was decreased by 21 percent, which is similar to the 30 percent glucose decrease seen with some drugs diabetics take to control glucose levels.

Caveats: This was a small experiment done in space of two weeks and may not apply to long-term use. Also, the patients got their caffeine straight; coffee or tea might contain healthful compounds that could offset the effects of caffeine. But the results are interesting enough to merit more research.

Find out more: James D. Lane, lead author on this study, has done several studies on caffeine.

Read the article: Lane, J.D. et al. "Caffeine Impairs Glucose Metabolism in Type II Diabetes." Diabetes Care. August 2004, Vol. 27, No. 8, pp. 2047–2048.

Abstract online: http://care.diabetesjournals.org