People who develop type 2 diabetes usually experience two preliminary stages: insulin resistance and impaired glucose tolerance. Insulin resistance is a condition in which the pancreas manages to pump enough insulin to bring down blood sugar levels, but with levels of insulin much higher than normal.

Over time, a person with insulin resistance secretes more and more insulin to move the same amount of glucose into the cells, where it is needed for energy. In many people, this ability to compensate eventually breaks down. When this happens, blood sugar levels begin to climb, despite the high levels of insulin produced by the pancreas.

Many times, despite having higher–than–normal blood sugar levels, people with impaired glucose tolerance are not aware of their condition. Symptoms can be mild, such as slightly increased thirst or more frequent urination, or not present at all. However, higher–than–normal blood sugar levels can begin to cause damage in many organs, such as the kidneys, eyes, and blood vessels.

Health care providers and diabetes experts recommend that everyone older than age 45 be tested for diabetes. People with the following risk factors should be tested earlier:

• People with a Body Mass Index (BMI) greater than 25
• Women who had a baby weighing 9 pounds or more at birth
• People who have a parent, sister, and/or brother with diabetes
• Anyone who is sedentary
• People of certain races, including Hispanics, African Americans, and Native Americans