Coffee is one of the most popular beverages in the world (1). Ever wonder if there is any effect on your blood sugar levels after drinking a cup? A 2002 study (2) of 21 men who were not regular caffeine drinkers looked at the effect of caffeine on men with and without type 2 diabetes. Researchers found that, for both groups, taking a caffeine pill equivalent to 2-3 cups of coffee resulted in significant drops in glucose uptake, causing rises in blood glucose levels.

Another study, published in the August 2004 issue of Diabetes Care (3), looked at the affect of caffeine on a small sample of type 2 diabetics. Results showed that caffeine had minimal effect on glucose and insulin levels in between meals, but causes considerable surges after eating a meal. Those subjects receiving a 375-milligram dose of caffeine had a 21% bigger increase in glucose levels and a 48% larger insulin level increase in comparison with those taking a placebo during the two hours following their meals.

Yes, It Does

“In a healthy person, glucose is metabolized within an hour or so after eating. Diabetics, however, do not metabolize glucose as efficiently,” said researcher James D. Lane, PhD, associate research professor at Duke University “It appears that diabetics who consume caffeine are likely having a harder time regulating their insulin and glucose levels than those who don’t take caffeine.”

“It seems that caffeine, by further impairing the metabolism of meals, is something diabetics ought to consider avoiding. Some people already watch their diet and exercise regularly,” says Lane. “Avoiding caffeine might be another way to better manage their disease. In fact, it’s possible that staying away from caffeine could provide bigger benefits altogether.”

On the Other Hand

Conversely, a 2005 metastudy (4) concerning coffee consumption and risk of type 2 diabetes found that coffee consumption is associated with a significantly lower risk of type 2 diabetes. What goes on here?

Several potential explanations are put forward by the studys authors. One is that coffee has been shown to have antioxidant effects on the body, which would in turn reduce the kind of oxidative stress that is known to contribute to type 2 diabetes (5).

Another explanation is that coffee includes a significant amount of magnesium, which has been associated with improved insulin function (6). To make a long story short, there are ingredients in coffee other than caffeine which seem to have beneficial effects on diabetes risk.

So, in the short term, caffeine plays havoc with your insulin and glucose levels, but drinking coffee over a long period of time decreases your risk of developing diabetes type 2. Something seems wrong with the logic in that, doesnt it?


  1. Schaefer B. Coffee consumption and type 2 diabetes mellitus [letter]. Ann Intern Med. 2004;141:321

  2. Caffeine-Induced Impairment of Insulin Action but not Insulin Signaling in Human Skeletal Muscle Is Reduced by Exercise, by F.S. Thong and Colleagues. Diabetes 51:583-590, 2002

  3. Caffeine Impairs Glucose Metabolism in Type 2 Diabetes by Lane, J. Diabetes Care, August 2004; vol 27

  4. Coffee Consumption and Risk of Type 2 Diabetes by Rob M. van Dam, PhD; Frank B. Hu, MD, PhD JAMA. 2005;294:97-104

  5. Ceriello A, Motz E. Is oxidative stress the pathogenic mechanism underlying insulin resistance, diabetes, and cardiovascular disease? the common soil hypothesis revisited. Arterioscler Thromb Vasc Biol. 2004;24:816-823.

  6. de Valk HW. Magnesium in diabetes mellitus. Neth J Med. 1999;54:139-146

Coffee photo by Drab Makyo. Creative Commons license

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