Bottom line: Sprinkling a 1⁄2 teaspoon of cinnamon on your oatmeal in the morning can’t hurt, it’s tasty and it just may, over time, help ward off diabetes. But don’t go overboard. Animal studies suggest that a compound in cinnamon called coumarin may be toxic in high doses (although humans may not be as susceptible). Cinnamon oils are particularly concentrated, so steer clear. And if you have diabetes, don’t try cinnamon supplements without talking with your doctor: combining them with a prescription medication may be dangerous.