Chromium,Combination of Vitamin C & D ,Vitamin E is useful in preventing diabetes because it helps insulin work more effectively, thus lowering blood sugar.Foods such as grapefruit, whole wheat products, apples and tomatoes, all have the mineral chromium in them.
And i am not sure if this alone can cure diabetes.It will be good along with medicines.These are capable of neutralizing or inactivates free radicals stored in the body and build a strong immune system.