Caffeine could interfere with the body’s ability to handle blood sugar, thus worsening type 2 diabetes, U.S. researchers said on Monday.

The team at Duke University Medical Center in North Carolina found a strong correlation between caffeine intake at mealtime and increased glucose and insulin levels among people with type 2 diabetes.

The findings are significant enough that the researchers recommend people with diabetes consider reducing or eliminating caffeine from their diets.

“In a healthy person, glucose is metabolized within an hour or so after eating. Diabetics, however, do not metabolize glucose as efficiently,” said James Lane, a psychiatry professor who led the study. “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.”

Writing in the journal Diabetes Care, Lane and colleagues said they studied 14 habitual coffee drinkers with type 2 diabetes.

The researchers put the volunteers on a controlled diet. They took their medications, had their blood tested and then were given caffeine capsules. More blood was taken then and after giving the volunteers a liquid meal supplement.

Caffeine had little effect on glucose and insulin levels when the volunteers fasted, the researchers found. But after the liquid meal, those who were given caffeine had a 21 percent increase in their glucose level and insulin rose 48 percent.

“The goal of clinical treatment for diabetes is to keep the person’s blood glucose down,” Lane said in a statement. “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. 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.”