Ask The Expert
Eating Well

I'll assume you are asking about caffeinated coffee and not decaffeinated, since decaf coffee is mainly associated only with heartburn.

Caffeine has been associated with heartburn, restlessness, insomnia, high blood pressure, high cholesterol, and heart disease-due to caffeine's effect of increasing epinephrine (adrenaline) levels in your body. Epinephrine is the hormone released in times of stress, which causes your heart to palpate, as well as to make you feel nervous and anxious.

Caffeine can raise blood glucose if ingesting over 500mg of caffeine:

One resource was from Diabetes Spectrum volume 4, #5, 1991, which stated that some studies have noted caffeine's potential to raise blood glucose because caffeine potentiates the effects of epinephrine and glucagon. Both of these hormones cause the liver to release stored glucose. The level at which this response was seen was approximately 500 mg of caffeine. According to this article, the average daily consumption of caffeine is about 200mg, and there are about 73 mg of caffeine per 100ml of percolated coffee, so this author concluded it was unlikely that caffeine would cause any significant rise in blood glucose. Needless to say, this article was written before the current coffee/espresso craze and the extra large coffee servings at stores. Another article stated that an 8-ounce cup of coffee contains about 150 mg caffeine. Although there are no official recommendations to limit caffeine consumption, you should be aware that if you consume significant amounts of coffee, or take caffeine-containing medications (and/or other caffeine containing beverages such as Coke, Dr. Pepper, Mountain Dew, or hot cocoa), especially in a short period of time, you could experience a rise in your blood glucose.

Caffeine can enhance the symptoms of low blood glucose:

Diabetes Care, volume 23, #4, April 2000, reported a study showing that ingesting 200mg of caffeine twice a day caused subjects to experience more episodes of hypoglycemia, and to have more intense warning symptoms of upcoming low blood sugar episodes.

Caffeine reduced the incidence of nocturnal (night time hypoglycemia):

Reported in Diabetes Care 2005; 28:1316-1320, researchers were unclear on the cause but speculated that it may be related to an alteration in non-REM sleep, another well known side-effect of coffee, and that this warrants further study.

Caffeine impairs glucose metabolism:

Researchers in Ontario reported in Diabetes Care 2005; 28:576-572 that caffeine (given in a pill form for this study) reduced insulin sensitivity, and it did not improve even after a 3-month exercise program (as exercise is generally known to increase insulin sensitivity). This study seemed at first to contradict a previous report suggesting that coffee might decrease the risk of type 2 diabetes. The conclusion was that more research is needed, since coffee contains several other substances that may affect sugar metabolism, such as antioxidants, potassium, and magnesium--i.e. it could have been the specific effect of caffeine in this study that impaired glucose metabolism, vs. the effect of coffee in other studies that seemed to decrease the risk of diabetes.

Conclusion:

The jury is still out, as coffee vs. caffeine intake can have very different biological effects. Most experts feel that moderate caffeine intake will not have any significant effect on your blood glucose, but naturally individual response may vary. Please check this out with your physician and diabetes educator.