copied from: https://www.mercola.com/2002/mar/6/caffeine_diabetes.htm

Caffeine Linked to Diabetes

Preliminary findings from a small study suggest that drinking moderate amounts of coffee may put healthy individuals at risk for decreased insulin sensitivity, or an inability to process blood sugar efficiently. Decreased insulin sensitivity is a precursor to diabetes.

The finding may have serious health implications, especially when superimposed on already-disturbed glucose tolerance or established type 2 diabetes.

Caffeine reduced insulin sensitivity by 15%. The decrease in insulin sensitivity was comparable to the increase in sensitivity produced by taking diabetes drugs.

The caffeine group also had higher blood levels of free fatty acids than their peers in the comparison group, the report indicates.

Caffeine's ability to decrease insulin sensitivity could occur because the drug boosts levels of free fatty acids, as well as the hormone epinephrine. The caffeine group exhibited a five-fold increase in blood levels of the hormone.

Diabetes Care February 2002;25:364-369