• Type 1 diabetes, the early-onset, or "juvenile," form of the disease, occurs when the body's immune system destroys the beta cells in the pancreas that produce insulin. Patients with type 1 diabetes require insulin injections.
• Type 2 diabetes, the more common, adult-onset, form of the disease, arises when a person becomes less responsive to insulin—often by gaining weight or reducing physical activity. The muscle and liver cells resist insulin's influence, and too much sugar stays in the blood. The beta cells of the pancreas compensate by expanding in number or size to produce extra insulin. When the pancreas can no longer keep up with the body's demand for more insulin, type 2 diabetes results. About one-third of patients require insulin treatment; the rest try to manage their sugar levels with diet, exercise and oral medications.
• Insulin resistance, a first step toward type 2 diabetes, can arise from a long list of defects along the multistep insulin-signaling pathway. Changes can occur, for example, in expression of genes or proteins that are targets of insulin action. Metabolic abnormalities, some brought on by aging, others by obesity, can cause the body to defy insulin's commands.
• The vast majority of people with diabetes—about 90 percent—have the type 2 form. More than 80 percent of people with type 2 diabetes are overweight.
• In a study of more than 3,200 people at high risk for developing type 2 diabetes—who had impaired glucose tolerance and were overweight—a low-fat diet and 30 minutes of daily exercise resulted in an average 15-pound weight loss and a 58 percent reduction in the risk of getting type 2 diabetes.
• Diabetes is the main cause of kidney failure, limb amputations and new-onset blindness and is a major cause of heart disease and stroke.

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Reprinted from the HHMI Bulletin,
December 2001, pages 16-21.
©2001 Howard Hughes Medical Institute