Type 2 diabetes mellitus is a common disease that interferes with the body's ability to store energy from food. The pancreas makes insulin, a substance that helps to store energy from food. In people with type 2 diabetes mellitus, the body makes plenty of insulin but cannot use it normally. The result is high blood sugar levels. Over time, high blood sugar levels can lead to blindness, kidney failure, nerve damage, and heart disease. Risk factors for type 2 diabetes mellitus include being overweight, lack of exercise, and family history of the disease. Because type 2 diabetes mellitus is common and has serious complications, it is important to understand factors associated with the disease. It is known that caffeine influences the way the body handles sugar. A recent study in the Netherlands showed that people who drank at least 7 cups of coffee a day were half as likely to develop type 2 diabetes mellitus as people who drank 2 cups or less a day. However, this study did not separate regular from decaffeinated coffee and did not ask the participants about other caffeine-containing drinks.