Like cancer, diabetes mellitus—diabetes for short—is a group of diseases with a common biochemical characteristic. In diabetes, the common feature is abnormal metabolism of carbo¬hydrates, particularly glucose.

This can lead, over many years, to kidney disease, atherosclerosis, heart attack, stroke, gan¬grene, and other complications including blindness. In fact, diabetes is the third leading cause of blindness in the United States.

All types of diabetes have something to do with insu¬lin, a hormone produced by special cells in the pancreas, called islets of Langerhans. Insulin is one of several compounds the body uses to control the levels of glucose in the blood. With¬out insulin, blood sugar levels rise dangerously high. The same thing can happen if the body loses its ability to respond to insulin.

Noninsulin-dependent diabetes usually appears in middle or old age, particularly in people who are overweight. As many as 9 percent of people 65 and older may have this disease.

Genetic, environmental, and lifestyle fac¬tors can place a person at increased risk for developing noninsulin-dependent diabetes.

The most important risk factors are in¬creasing age, family history of diabetes, and obesity—especially fat carried in the abdomen.

Researchers have found that fast¬ing blood sugar levels tend to increase as body weight in¬creases, but exactly how these risk factors contribute to the development of noninsulin-dependent diabetes is still the subject of research.