Scientists at the University of Guelph, Canada, report that there is an association between consumption of caffienated-coffee and impaired acute blood glucose management and insulin sensitivity, factors thaty may lead to diabetes type II, in healthy men.

Caffeine is a common ingriedient in numerous types of beverages and it is estimated that 80% of Americans consume caffeine every day. North Americans get 60 - 70% of their caffeine from coffee.

Impairement of blood glucose level management and insulin sensitvity are precursors to diabetes type II and heart disease, among others. High glycemic index diet, a diet with carbohydrates that release glucose very rapidly to the bloodstream, are among the causes for impaired blood glucose management and insuline senstivity, and consequently that may lead to diabetes type II.

The researchers investigated whether caffeine intake had any role on impairment of blood glucose management on people consuming foods typical of a Western diet. They evaluated the effect of caffeinated-coffee and decaffeinated-coffee on glucose and insulin responses on the same experimental subjects who consumed high and low glycemic index cereal meals.

Previous studies reviewed by the scientists have reported that the ingestion of caffeine (5 mg/kg body weight) and a 75-g oral glucose load has been shown to elicit an acute insulin–insensitive environment in healthy and obese individuals and in those with type 2 diabetes.

The current study was conducted on ten healthy men, between 18 and 50 years, non-smoking,  and with no known diabetes and glucose tolerance problems.  They were subjected to the following treatments in random order. They ingested caffeinated coffee (5 mg of caffeine per a kg of body weight) or the same volume of decaffeinated coffee followed 1 h later by either a high or low glycemic index (GI) cereal (providing 75 g of carbohydrate) mixed meal tolerance test.

They found out that caffeinated-coffee combined with the high glycemic index meal, compared to decaffeinated-coffee with high glycemic index meal, resulted in 147%, 29%, and 40% greater blood glucose, insulin (NS), and C-peptide concentrations, respectively. Further more, caffeinated-coffee combined with the low glycemic index meal, compared to decaffeinated-coffee with low glycemic index meal,  resulted in  216%, 44%, and 36% greater blood glucose, insulin, and C-peptide concentrations, respectively.

The effect of caffeinated-coffee intake, compared with the decaffeinated-coffee, on insulin sensitivity was greater when combined with the high glycemic index treatment (40% insulin sensitivty decrease) than when combined to the low glycemic index treatment (29% insulin sensitivity decrease).

The researchers concluded that consumption of caffeinated-coffee in combination with either a high or low glycemic index meal significantly impairs acute blood glucose management and insulin sensitivity compared with ingestion of decaffeinated coffee. They however recommended that further  research is needed to determine whether caffeinated-coffee is a risk factor for insulin resistance.

Their study was published in the May 2008 issue of the American Journal of Clinical Nutrition.

Source: Moisey, L. L., kacker, S., Bickerton, A. C., Robinson, L. E., and Graham, T. E. 2008. Caffeinated coffee consumption impairs blood glucose homeostasis in response to high and low glycemic index meals in healthy men. American Journal of Clinical Nutrition, 87(5): 1254-1261.