Each year, the words “you have diabetes” are spoken with greater frequency, often to unsuspecting individuals. Among Americans, the prevalence of diabetes has grown dramatically during the 20th century. Today, more than 16 million Americans have diabetes—90 percent of them are older than 40 years.

Interestingly, half of these adults do not even know they have the disease because symptoms develop gradually and, at first, are hard to identify. Early diagnosis is important, though, because the longer diabetes goes untreated, the greater your risk for serious complications.

Diabetes mellitus is a disorder of metabolism—the way the body uses digested food for energy and growth. The origin of the name “diabetes mellitus” is Greek, referring to sweetness or honey (mellitus) that passes through (diabetes). After a meal, food is broken down into simpler forms and absorbed by the body.

Simple sugars, amino acids, and fatty acids are used by the body or converted by the liver into sugar (glucose), the preferred fuel the body burns for energy. For cells to use this form of sugar, insulin—a hormone that is produced by the pancreas—must “unlock” the cells to allow glucose to enter.

The pancreas, a long, thin organ that is about the size of a hand, is located behind the stomach. Normally the pancreas produces the right amount of insulin to accommodate the amount of sugar that is in the blood. Diabetes is actually not a single condition but a group of diseases with one thing in common—a problem with insulin.

In a person with diabetes, the pancreas does not produce sufficient insulin to meet the body’s needs. This insufficiency may develop if the pancreas stops producing the right amount and quality of insulin, if the rest of the body’s cells do not respond properly to insulin, or a combination of both.

Insulin is required for glucose to be metabolized properly. If there is not enough insulin, excess glucose builds up in the blood, and the resulting condition is called hyperglycemia. Persistent hyperglycemia causes almost all the symptoms that may alert an individual to the development of diabetes.

These symptoms can include frequent urination, extreme thirst, blurred vision, fatigue, unexplained weight loss, recurrent infection, tingling or loss of feeling in the hands or feet, and hunger. With diabetes, the excess glucose spills into the urine, and the urine output increases.

Consequently, the person with diabetes becomes dehydrated and thirsty. Fatigue results when the supply of glucose to cells is not available, causing energy levels to decline. To compensate for the lost fuel, the body burns stored fat, and weight loss and hunger may occur.

Left untreated, persistent hyperglycemia is also responsible for most of the long-term complications of diabetes (see Long-Term Complications of Diabetes, this page). There are several types of diabetes—different disorders with different causes. The two most common types are described here.

Type 1 Diabetes

Type 1 diabetes occurs in 1 in 10 people with diabetes. In these individuals, the pancreas produces little or no insulin. To control blood sugar, insulin must be taken. Most people whose diabetes is diagnosed before age 30 have the insulindependent type. It used to be called insulin-dependent diabetes mellitus or juvenile-onset diabetes.

Type 1 diabetes affects both sexes equally. In most cases it is due to an autoimmune disease in which the body’s immune system attacks and destroys the insulin-producing beta cells in the pancreas. This type of diabetes commonly develops in childhood, but it can occur at any age.

It can develop unnoticed for several years and then suddenly become apparent, often after an illness. Some people—particularly children and teenagers—may first become aware of the disease when they develop ketoacidosis. This is a serious complication in which the blood becomes more acidic because of severe insulin deficiency.

Type 2 Diabetes

Type 2 diabetes accounts for about 85 to 90 percent of diabetes in people older than 30. It was previously called non-insulin-dependent or adult-onset diabetes. Most persons with type 2 diabetes are overweight or obese. For people with this type of diabetes, total absence of insulin is not the problem.

The problem is that the body does not make enough insulin to meet its needs and the insulin does not work normally to control glucose levels. This is termed “insulin resistance” and leads to hyperglycemia. Excess weight is by far the greatest risk factor for development of type 2 diabetes.

Most people who develop type 2 diabetes are overweight, a condition that appears to impair insulin action. Someone who is overweight and has diabetes may be able to achieve a normal blood sugar without medication simply by losing weight. Losing as little as 10 percent of body weight has been shown to lower blood glucose.

Surprisingly, persons who are not overweight by traditional criteria also may be at risk for diabetes. Excess body fat distributed mostly in the abdomen increases the chance for development of type 2 diabetes. Other risk factors include age, race, heredity, and lack of physical activity.

Type 2 diabetes may go undetected for many years, because hyperglycemia develops slowly and the disease may not immediately produce the classic symptoms of diabetes. Unfortunately, even without symptoms, there are hidden dangers, including damage to major organs such as the heart and kidneys.

Because the disease usually develops after age 40, and the incidence increases more steeply after age 55, it is important that people in middle age be screened for the disease and see their physician if symptoms develop.

Type 2 diabetes is more common among Native Americans, Hispanics, African-Americans, and westernized Asians than among people of European ancestry.

Long-Term Complications of Diabetes Numerous studies have shown that keeping the blood glucose level close to normal delays the onset and prevents the progression of eye, kidney, and nerve diseases caused by diabetes.

Even if blood glucose has not been controlled in the past, any improvement in diabetes control may help to avoid or delay complications of diabetes and their progression. Treatment of high blood lipid values and high blood pressure, which are commonly associated with diabetes, is also important.

• Eye disease—In the absence of good glucose control, eye disease develops in nearly everyone with diabetes. Diabetic retinopathy occurs because high blood sugar (especially coupled with high blood pressure) can damage the small blood vessels in the retina (the light-sensitive area within the eye).

Diabetes also can lead to cataracts, damage the macula (the area in the eye where the optic nerve is located), and increase the risk of glaucoma.

In addition to keeping your glucose levels under control, it is important to have regular eye examinations with an ophthalmologist, who dilates the eyes and does a thorough examination of them. A non-dilated eye test is not adequate for screening.

• Kidney failure—In the absence of good glucose control, a person with diabetes is 20 times more likely to develop kidney failure than someone who does not have the disease. Kidney disease results when chronic high blood sugar damages the small vessels in the kidneys which are responsible for filtering waste from the blood.

Ultimately, kidney failure may occur, requiring dialysis or a kidney transplant. People with diabetes should have the function of their kidneys evaluated routinely.

• Nerve damage—Also called neuropathy, nerve damage occurs in 30 to 40 percent of people with diabetes. Nerve damage can cause numbness and tingling, pain, insensitivity to pain and temperature, and extreme sensitivity to touch. Experts think the damage results from the effect of chronic high blood sugar on blood vessels that supply nerve cells. The feet are especially vulnerable to neuropathy.

• Cardiovascular disease—Chronic high blood sugar is associated with narrowing of the arteries (atherosclerosis), high blood pressure, heart attack, and stroke. It is also associated with increased blood levels of triglycerides (a type of blood fat) and decreased levels of HDL (“good”) cholesterol.

Unless appropriately treated, an individual with diabetes is 5 times more likely to have a stroke and 2 to 4 times more likely to have coronary artery disease. Also, smoking dramatically accelerates the development of these cardiovascular complications. Anyone with diabetes should stop smoking.

• Infections—High blood sugar impairs the function of immune cells and increases the risk of infections. The mouth, gums, lungs, skin, feet, bladder, and genital area are common sites of infection. Nerve damage in the legs and feet can make someone with diabetes less aware of injuries or infection, increasing the risk of amputation. With proper care of the feet, foot complications can be minimized or avoided.

Although an area of active research, there is currently no proven means of preventing type 1 diabetes. However, these lifestyle changes minimize the risk of, and may actually prevent, type 2 diabetes: Maintain a healthful weight—Most people who develop type 2 diabetes are overweight.

Aggressive efforts aimed at achieving and maintaining a healthful weight may be beneficial, especially in combination with exercise.

Eat a balanced diet—A diet low in saturated fat and sugar and high in complex carbohydrates and dietary fiber also has been linked to a reduced risk of diabetes. Exercise—People who exercise regularly have a significantly lower incidence of type 2 diabetes.