Chromium is a mineral derived from food. Since it can be used up when we eat a lot of simple carbohydrates, this is the link between high sugar consumption and type 2 diabetes. As chromium levels fall the insulin receptors close off and the insulin becomes unable to carry the glucose out of the blood.
Because we tend to eat a lot of simple carbohydrates, and chromium is found in trace amounts in most foods it is a good idea to supplement. The average healthy person I recommend 200mcg daily. Type 2 diabetics I recommend 200mcg 3 to 4 times daily.