For most healthy adults, caffeine doesn't noticeably affect blood sugar. The medical term for blood sugar is glucose. Having up to 400 milligrams of caffeine a day seems to be safe for most people.
In the U.S., one of the most common sources of caffeine is coffee. The average U.S. adult drinks about two 8-ounce (240-milliliter) cups of coffee a day. A cup of coffee generally has about 120 to 180 milligrams of caffeine. But the amount of caffeine can vary quite a bit depending on the type of coffee. Other sources of caffeine include energy drinks, some soft drinks, black tea and chocolate.
Some studies suggest that drinking coffee — whether caffeinated or decaffeinated — may actually reduce the risk of developing type 2 diabetes.
If you have diabetes, caffeine might affect the way your body uses insulin. And that could lead to higher or lower blood sugar. For some people with diabetes, about 200 milligrams of caffeine can cause this change. For others, it may have no significant effect on blood sugar.
Caffeine affects each person differently. If you have diabetes or if you find it hard to control your blood sugar, limiting the amount of caffeine in your diet might be helpful. Talk to a member of your healthcare team if you have questions or concerns about caffeine.