Type 1 diabetes is believed to be an autoimmune disease. An autoimmune disease occurs when the body's system for fighting infection -- the immune system -- turns against a part of the body. In type 1 diabetes, the immune system attacks the cells in the pancreas that produce insulin and destroys them. The pancreas then produces little or no insulin.

Scientists do not know exactly what causes the body's immune system to attack the cells in the pancreas, but they believe that both genetic factors and environmental factors, such as viruses, are involved.

While type 2 diabetes is believed to have a strong genetic link, a wide variety of risk factors are believed to greatly increase the likelihood of a person developing type 2 diabetes.

These include:

• Obesity or being overweight;
• High blood pressure;
• High blood triglyceride (fat) levels;
• A high-fat diet;
• High-alcoholic intake;
• A sedentary lifestyle;
• Aging (risk begins to rise significantly at about age 45 years);
• Ethnicity (certain groups, such as African Americans, Native Americans, Hispanic Americans, and Japanese Americans, have a greater risk of developing type 2 diabetes);
• Gestational diabetes or giving birth to a baby weighing more than 9 pounds.