The average U.S. adult consumes about two 8-ounce cups (474 milliliters) of coffee a day, which can contain around 280 milligrams of caffeine. For most young, healthy adults, caffeine doesn't appear to noticeably affect blood sugar (glucose) levels, and consumption up to 400 milligrams a day appears to be safe.

Some studies suggest that drinking coffee, caffeinated and decaffeinated, may actually reduce your risk of developing diabetes.

If you already have diabetes, however, the impact of caffeine on insulin action may be associated with higher or lower blood sugar levels. For some people with diabetes, about 200 milligrams of caffeine — or the equivalent of one to two 8-ounce cups (237 to 474 milliliters) of plain, brewed coffee — may cause this effect.

Caffeine affects every person differently. If you have diabetes or you're struggling to control your blood sugar levels, limiting the amount of caffeine in your diet may provide a benefit.

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Feb. 20, 2018 See more Expert Answers