People with diabetes need to control the abnormally high levels of glucose in their blood because over time that extra sugar can be profoundly harmful to tissues throughout the body. Many patients find that they eventually must treat one or more of the resulting complications, in addition to the underlying diabetes. According to the CDC, some of the most common complications include:

Heart disease, stroke and hypertension. Death rates from heart disease are two to four times higher among adults with diabetes than among their peers without it. The risk of stroke is similarly high. And more than 70 percent of people with diabetes develop a tendency for high blood pressure. Not surprisingly, then, whereas heart disease and stroke account for about 40 percent of all deaths, they kill about 65 percent of the diabetic population. But people with diabetes can reduce their risk for heart disease and stroke by controlling their cholesterol and blood pressure, taking aspirin and not smoking. Though not proved definitively, blood glucose control also probably reduces risk.

Blindness. Because it can damage the delicate blood vessels in the retina of the eye, diabetes is the leading cause of blindness with onset in adults—between 12,000 and 24,000 new cases every year. Fortunately, blindness can be prevented by controlling blood glucose and blood pressure. Annual eye exams, which can catch problems early, are a must for people with diabetes.

Kidney disease. Diabetes is the number one cause of kidney failure; it was responsible for 44 percent of all cases
in 2002. Again, control of glucose and blood pressure, along with annual screening tests, can reduce the risk.

Nervous system disorders. Between 60 and 70 percent of people with diabetes exhibit damage to their nervous systems that ranges from minor to severe. Almost 30 percent of those older than 40 lack at least some sensation in their toes or feet (a condition called peripheral neuropathy). Numbness or pain in the other limbs and sluggish digestion are also common.

Amputation. Partly because diabetic persons may not be aware of injuries or inflammation in numbed feet, they are at higher risk of severe infections that can lead to amputations. More than 60 percent of amputations involving toes, feet and legs (except those resulting from accidents) occur among people with diabetes. Most of those amputations could be prevented with glucose control and more attention to foot care.

Pregnancy problems. When diabetes is not well controlled before conception or in the first trimester, it can lead to spontaneous abortion in as many as 20 percent of pregnancies or to major birth defects. Poor control of diabetes later in the pregnancy can cause the baby to grow unusually large, which is risky to both mother and child.

Other complications. Almost a third of those with diabetes suffer gum disease severe enough to endanger teeth. Diabetic patients are also more likely to die of the flu or pneumonia. And when diabetes is very poorly controlled, people are at risk for developing disruptive biochemical imbalances, such as diabetic ketoacidosis, that can become life-threatening.

The lesson is simple: the more people do to control their diabetes, the better their chances for maintaining good health.