A growing body of research suggests that caffeine disrupts glucose metabolism and may contribute to the development and poor control of type 2 diabetes, a major public health problem. A review article in the inaugural issue of Journal of Caffeine Research: The International Multidisciplinary Journal of Caffeine Science, a quarterly peer-reviewed journal from Mary Ann Liebert, Inc. publishers, examines the latest evidence, contradicting earlier studies suggesting a protective effect of caffeine.
James Lane, PhD, Duke University, describes numerous studies that have demonstrated caffeine's potential for increasing insulin resistance (impaired glucose tolerance) in adults that do not have diabetes, an effect that could make susceptible individuals more likely to develop the disease. In adults with type 2 diabetes, studies have shown that the increase in blood glucose levels that occurs after they eat carbohydrates is exaggerated if they also consume a caffeinated beverage such as coffee. This effect could contribute to higher glucose levels in people with diabetes and could compromise treatment aimed at controlling their blood glucose.
In a 2002 study published in Diabetes Care, a team of physicians from the Netherlands announced their findings: that caffeine decreased healthy test subjects' insulin sensitivity by 15%. The doctors who conducted this study concluded that the cellular receptor sites were not adversely changed with caffeine, but that the elevated levels of epinephrine in blood plasma were probably what caused the reduced absorption of insulin (and consequent elevated blood sugar levels).
A further study, published in 2007 in the Journal of Physiology looked specifically at the impact the elevated adrenaline levels might have on insulin resistance. The physicians in Copenhagen who completed this study concluded that adrenaline plays a role in insulin resistance, but it is not solely responsible for the physical symptoms.
Because adrenaline is also a stress-response hormone, it begs the question how many insulin resistant and pre-diabetic patients would get positive blood sugar benefits from stress-reduction activities such as meditation or yoga!
Exercise can Reduce the Negative Effects of Caffeine
For those patients with insulin resistance, pre-diabetes, and type 2 diabetes who cannot face giving up their morning cup of joe, there is one ray of hope: exercise.
A team of eight scientists from Canada, Belgium and Denmark published the findings of their study under the title "Caffeine-Induced Impairment of Insulin Action but Not Insulin Signaling in Human Skeletal Muscle Is Reduced by Exercise" in the March 2002 edition of the American Diabetes Association's magazine Diabetes.
This study focused mainly on "glucose disposal" - the process of getting the blood sugar out of the blood and into the muscles and organs for energy. One of the findings of this study included that "after an acute bout of exercise, whole-body glucose disposal is enhanced."
In the case of Type 2 Diabetes, the only way diet and exercise will help with the reversal of the disease is if the patient succeeds in losing weight. For the insulin resistant and pre-Diabetic patient, dietary adjustments and exercise can actually heal the body before lasting damage is done. For the pre-diabetic conditions, even if significant weight loss is not achieved, positive health effects can take place on a cellular level!
"More than 220 million people worldwide have diabetes, says Editor-in-Chief Jack E. James, PhD, School of Psychology, National University of Ireland, Galway, Ireland. "The links that have been revealed between diabetes and the consumption of caffeine beverages (especially coffee) are of monumental importance when it is acknowledged that more than 80% of the world's population consumes caffeine daily. Dr. Lane's review of the topic gives the clearest account to date of what we know, what we don't know, and what needs to be done -- urgently!"