Scientists speculate that the caffeine lowers the body's sensitivity to insulin, meaning the hormone is not as effective as it once was. The cells don't absorb as much sugar from the blood after eating or drinking. To compensate, the body creates more insulin, which raises its level after your meals.
It's a double whammy because the body already uses insulin poorly, and blood sugar rises higher than it should. Caffeine might make this worse and make it hard to reduce blood sugar to healthy levels.
In time, the complications of diabetes, like heart disease or nerve damage, could become worse from the higher blood sugar induced by caffeine consumption.