Drinking coffee, tea or caffeinated soft drinks every day can make it hard for people with type 2 diabetes to control their disease, research shows.
The findings suggest that eliminating caffeine from the diet might be a good way of managing blood sugar levels.
Blood sugar levels in patients who drank at least two cups of coffee every day increased by 8%. Caffeine also exaggerated the rise in blood glucose after a meal.
"We're not sure what it is about caffeine that drives glucose levels up, but we have a couple of theories," says lead author James Lane.
He suggests that caffeine may interfere with the process that moves glucose from the blood and into the muscles, it may also trigger the release of adrenaline that can boost sugar levels.
No current guidelines make suggest curbing caffeine intake for diabetics.
"Coffee is such a common drink in our society that we forget that tit contains a very powerful drug – caffeine," says Lane.
"Our study suggests that one way to lower blood sugar is to simply quit drinking coffee, or any other caffeinated beverages. It may not be easy, but it doesn't cost a dime, and there are no side effects."