Sure enough, researchers at Duke University did a study of caffeine’s effect on blood sugar levels. They tested 14 people with type 2 diabetes and discovered that large doses of caffeine can cause blood sugar levels to climb:

The study showed that caffeine had little effect on glucose and insulin levels during the fasting period, but it caused significant surges after eating a meal. People who received the 375-milligram dose of caffeine experienced a 21% larger increase in glucose levels and a 48% larger increase in insulin levels compared with those who took the placebo during the two hours following their meals.

“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,” says Lane. “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.” […]

It’s not that caffeine creates blood sugar, but it seems to aggravate blood sugar levels when consumed with a high-carbohydrate meal. So, I may be out of the woods on this one — I generally have a mid-carb breakfast of diced apples with cottage cheese (+ cinnamon + Splenda) but I drink my tea about an hour after I eat breakfast. With any luck, most of my breakfast-based blood sugars would have been metabolized by then.