Type 1 diabetes is not the most common type of diabetes; type 2 is much more common and accounts for about 95% of all cases of diabetes. In type 1 diabetes, the pancreas stops making insulin, which the body requires to move glucose (sugar) into cells. People with type 2 diabetes have plenty of insulin, at least early on in the disease. The problem is something doctor's call insulin resistance. The body's cells don't respond to insulin, so sugar does not enter the cells, which causes blood sugar levels to rise. Later in type 2 diabetes, the pancreas tires out and insulin secretion falls, so the amount of treatment that is needed for type 2 diabetes can increase over time.

Of the estimated 21 million Americans with diabetes, approximately 6 million — nearly one-third — do not know they have it. Type 2 diabetes, particularly, can be present without obvious symptoms.

More than 1.5 million new cases of diabetes are diagnosed annually in adults, according to the U.S. Centers for Disease Control and Prevention (CDC). The number of Americans with diabetes more than doubled between 1980 and 2003. Part of this increase can be explained by changes to the way diabetes is diagnosed. Unfortunately, though, much of the increase was caused by obesity. (CDC National Diabetes Surveillance System)

It's the other way around. If you have diabetes, the disease itself causes elevated sugar levels in the blood.

A stunning 10 million Americans could vastly reduce their odds of developing type 2 diabetes through changes in lifestyle, researchers believe. They base those beliefs on the outcome of a large-scale clinical trial, the Diabetes Prevention Program, conducted by Harvard's Joslin Diabetes Center and 26 other major centers. The goal of the study was to determine whether type 2 diabetes might be forestalled through weight loss and physical activity. Study participants aimed for a weight loss of 7%, and at least 150 minutes of moderate activity, such as walking, weekly. Exercise and diet changes reduced the risk of diabetes among people at high risk by nearly 60% during the three years of this study.

Diligent lifestyle changes are more effective than medication. According to findings from the Diabetes Prevention Program, people at high risk of developing type 2 diabetes were shown to reduce their risk by 58% by improving diet and exercise habits. A diabetes drug called metformin (Glucophage) also reduced risk, but less dramatically than did exercise and diet control.

Research strongly suggests that aggressively lowering blood glucose through diet and exercise may prevent, delay, or minimize your need to take medication after you are diagnosed with diabetes. Good blood-sugar control after you are diagnosed helps to reduce the risk of diabetes complications, including kidney, eye and nerve disease.

African-Americans develop type 2 diabetes at a rate that is as much as 2.3 times higher than whites. In Hispanics, the prevalence of diabetes is 1.8 times higher than in whites.

In addition to ethnicity, family history is a prominent risk factor. But there are other important risk factors, including: physical inactivity, being overweight, a diagnosis of polycystic ovary syndrome, a history of gestational diabetes (a type of diabetes associated with pregnancy), and mild elevations in blood sugar (a condition regarded as a precursor to development of type 2 diabetes).

A fasting blood sugar test can be ordered by your doctor's office. If you are over 45, especially if you have a family history of type 2 diabetes, you should be tested periodically.