Most of the food we eat is broken down into glucose, a form of sugar that provides the main source of fuel for the body. After digestion, glucose passes into the bloodstream. Insulin, a hormone produced by the pancreas, helps glucose get into cells and converts glucose to energy. Without insulin, glucose builds up in the blood, and the body loses its main source of fuel.

In type 1 diabetes, the immune system destroys the insulin-producing beta cells of the pancreas. This form of diabetes usually strikes children and young adults, who require daily or more frequent insulin injections or using an insulin pump for the rest of their lives. Insulin treatment, however, is not a cure, nor can it reliably prevent the long-term complications of the disease. Although scientists do not know what causes the immune system to attack the cells, they believe that both genetic factors and environmental factors are involved.

Type 1 diabetes accounts for about 5 to 10 percent of diagnosed diabetes in the United States, occurs equally in males and females, and is more common in Caucasians. Symptoms include increased thirst and urination, constant hunger, weight loss, blurred vision, and extreme fatigue. If not treated with insulin, a person can lapse into a life-threatening coma.

Type 2 diabetes, which accounts for about 90 percent of diabetes cases in the United States, is most common in adults over age 40. Affecting about 6 percent of the U.S. population, this form of diabetes is strongly linked with obesity (more than 80 percent of people with type 2 diabetes are overweight), inactivity, and a family history of diabetes. It is more common in African Americans, Hispanic Americans, American Indians, and Asian and Pacific Islander Americans. With the aging of Americans and the alarming increase in obesity in all ages and ethnic groups, the incidence of type 2 diabetes has also been rising nationwide.

Type 2 diabetes is often part of a metabolic syndrome that includes obesity, high blood pressure, and high levels of blood lipids. People with type 2 diabetes first develop insulin resistance, a disorder in which muscle, fat, and liver cells do not use insulin properly. At first, the pancreas produces more insulin, but gradually its capacity to secrete insulin falters, and the timing of insulin secretion becomes abnormal. After diabetes develops, insulin production continues to decline.

Symptoms include fatigue, nausea, frequent urination or infections, unusual thirst, weight loss, blurred vision, and slow healing of wounds or sores. Some people have no symptoms at all. Researchers estimate that about one-third of people with type 2 diabetes don't know they have it.

Many people with type 2 diabetes can control their blood glucose by following a careful diet and exercise program, losing excess weight, and taking oral medication. However, the longer a person has type 2 diabetes, the more likely he or she will need insulin injections, either alone or together with oral medications.

Gestational diabetes develops during pregnancy. Like type 2 diabetes, it occurs more often in African Americans, American Indians, Hispanic Americans, and people with a family history of diabetes. Though it usually disappears after delivery, the mother is at increased risk of getting type 2 diabetes later in life.