What is it?

Type 2 diabetes, once known as adult-onset or noninsulin-dependent diabetes, is a chronic condition that affects the way your body metabolizes sugar (glucose), your body's main source of fuel.

When you have type 2 diabetes, your body is resistant to the effects of insulin — a hormone that regulates the movement of sugar into your cells — or your body doesn't produce enough insulin to maintain a normal glucose level. Untreated, the consequences of type 2 diabetes can be life-threatening.

There's no cure for type 2 diabetes, but you can manage — or even prevent — the condition. Start by eating healthy foods, exercising and maintaining a healthy weight. If diet and exercise aren't enough, you may need diabetes medications or insulin therapy to manage your blood sugar.

Symptoms

Type 2 diabetes symptoms may develop very slowly. In fact, you can have type 2 diabetes for years and not even know it. Look for:

• Increased thirst and frequent urination. As excess sugar builds up in your bloodstream, fluid is pulled from the tissues. This may leave you thirsty. As a result, you may drink — and urinate — more than usual.
• Increased hunger. Without enough insulin to move sugar into your cells, your muscles and organs become depleted for energy. This triggers intense hunger.
• Weight loss. Despite eating more than usual to relieve hunger, you may lose weight. Without the ability to use glucose, the body uses alternative fuels stored in muscle and fat. Calories are lost as excess glucose is released in the urine.
• Fatigue. If your cells are deprived of sugar, you may become tired and irritable.
• Blurred vision. If your blood sugar is too high, fluid may be pulled from the lenses of your eyes. This may affect your ability to focus clearly.
• Slow-healing sores or frequent infections. Type 2 diabetes affects your ability to heal and resist infections.
• Areas of darkened skin. Some people with type 2 diabetes have patches of dark, velvety skin in the folds and creases of their bodies — usually in the armpits and neck. This condition, called acanthosis nigricans, may be a sign of insulin resistance.

Causes

Type 2 diabetes develops when the body becomes resistant to insulin or when the pancreas stops producing enough insulin. Exactly why this happens is unknown, although excess weight and inactivity seem to be important factors.

Insulin is a hormone that comes from the pancreas, a gland located just behind the stomach. When you eat, the pancreas secretes insulin into the bloodstream. As insulin circulates, it acts like a key by unlocking microscopic doors that allow sugar to enter your cells. Insulin lowers the amount of sugar in your bloodstream. As your blood sugar level drops, so does the secretion of insulin from your pancreas.

Glucose — sugar — is a main source of energy for the cells that make up muscles and other tissues. Glucose comes from two major sources: the food you eat and your liver. After intestinal digestion and absorption, sugar is absorbed into the bloodstream. Normally, sugar then enters cells with the help of insulin.

The liver acts as a glucose storage and manufacturing center. When your insulin levels are low — when you haven't eaten in a while, for example — the liver metabolizes stored glycogen into glucose to keep your glucose level within a normal range.

In type 2 diabetes, this process works improperly. Instead of moving into your cells, sugar builds up in your bloodstream. This occurs when your pancreas doesn't make enough insulin or your cells become resistant to the action of insulin.

In type 1 diabetes, which is much less common, the pancreas produces little or no insulin.

Risk factors

Researchers don't fully understand why some people develop type 2 diabetes and others don't. It's clear that certain factors increase the risk, however, including:

• Weight. Being overweight is a primary risk factor for type 2 diabetes. The more fatty tissue you have, the more resistant your cells become to insulin.
• Inactivity. The less active you are, the greater your risk of type 2 diabetes. Physical activity helps you control your weight, uses up glucose as energy and makes your cells more sensitive to insulin.
• Family history. The risk of type 2 diabetes increases if a parent or sibling has type 2 diabetes.
• Race. Although it's unclear why, people of certain races — including blacks, Hispanics, American Indians and Asian-Americans — are more likely to develop type 2 diabetes.
• Age. The risk of type 2 diabetes increases as you get older, especially after age 45. That's probably because people tend to exercise less, lose muscle mass and gain weight as they age. But type 2 diabetes is also increasing dramatically among children, adolescents and younger adults.
• Prediabetes. Prediabetes is a condition in which your blood sugar level is higher than normal, but not high enough to be classified as type 2 diabetes. Left untreated, prediabetes often progresses to type 2 diabetes.
• Gestational diabetes. If you developed gestational diabetes when you were pregnant, your risk of developing type 2 diabetes later increases. If you gave birth to a baby weighing more than 9 pounds (4.1 kilograms), you're also at risk of type 2 diabetes.

Complications

Type 2 diabetes can be easy to ignore, especially in the early stages when you're feeling fine. But diabetes affects many major organs, including your heart, blood vessels, nerves, eyes and kidneys. Controlling your blood sugar levels can help prevent these complications.

Although long-term complications of diabetes develop gradually, they can eventually be disabling or even life-threatening. Some of the potential complications of diabetes include:

• Heart and blood vessel disease. Diabetes dramatically increases the risk of various cardiovascular problems, including coronary artery disease with chest pain (angina), heart attack, stroke, narrowing of the arteries (atherosclerosis) and high blood pressure. In fact, according to a 2007 study, the risk of stroke more than doubles within the first five years of being treated for type 2 diabetes. About 75 percent of people who have diabetes die of some type of heart or blood vessel disease.
• Nerve damage (neuropathy). Excess sugar can injure the walls of the tiny blood vessels (capillaries) that nourish your nerves, especially in the legs. This can cause tingling, numbness, burning or pain that usually begins at the tips of the toes or fingers and gradually spreads upward. Poorly controlled blood sugar can eventually cause you to lose all sense of feeling in the affected limbs. Damage to the nerves that control digestion can cause problems with nausea, vomiting, diarrhea or constipation. For men, erectile dysfunction may be an issue.
• Kidney damage (nephropathy). The kidneys contain millions of tiny blood vessel clusters that filter waste from your blood. Diabetes can damage this delicate filtering system. Severe damage can lead to kidney failure or irreversible end-stage kidney disease, requiring dialysis or a kidney transplant.
• Eye damage. Diabetes can damage the blood vessels of the retina (diabetic retinopathy), potentially leading to blindness. Diabetes also increases the risk of other serious vision conditions, such as cataracts and glaucoma.
• Foot damage. Nerve damage in the feet or poor blood flow to the feet increases the risk of various foot complications. Left untreated, cuts and blisters can become serious infections. Severe damage might require toe, foot or even leg amputation.
• Skin and mouth conditions. Diabetes may leave you more susceptible to skin problems, including bacterial and fungal infections. Gum infections also may be a concern, especially if you have a history of poor dental hygiene.
• Osteoporosis. Diabetes may lead to lower than normal bone mineral density, increasing your risk of osteoporosis.
• Alzheimer's disease. Type 2 diabetes may increase the risk of Alzheimer's disease and vascular dementia. The poorer your blood sugar control, the greater the risk appears to be. So what connects the two conditions? One theory is that cardiovascular problems caused by diabetes could contribute to dementia by blocking blood flow to the brain or causing strokes. Other possibilities are that too much insulin in the blood leads to brain-damaging inflammation, or lack of insulin in the brain deprives brain cells of glucose.
• Hearing problems. Diabetes can also lead to hearing impairment.

Diagnosis

In June 2009, an international committee composed of experts from the American Diabetes Association, the European Association for the Study of Diabetes and the International Diabetes Federation recommended that type 2 diabetes testing include the:

• Glycated hemoglobin (A1C) test. This blood test indicates your average blood sugar level for the past two to three months. It works by measuring the percentage of blood sugar attached to hemoglobin, the oxygen-carrying protein in red blood cells. The higher your blood sugar levels, the more hemoglobin you'll have with sugar attached. An A1C level of 6.5 percent or higher on two separate tests indicates you have diabetes. A result between 6 and 6.5 percent is considered prediabetes, which indicates a high risk of developing diabetes.

If the A1C test isn't available, or if you have certain conditions that can make the A1C test inaccurate — such as if you're pregnant or have an uncommon form of hemoglobin (known as a hemoglobin variant) — your doctor may use the following tests to diagnose diabetes:

• Random blood sugar test. A blood sample will be taken at a random time. Regardless of when you last ate, a random blood sugar level of 200 milligrams per deciliter (mg/dL) or higher suggests diabetes.
• Fasting blood sugar test. A blood sample will be taken after an overnight fast. A fasting blood sugar level less than 100 mg/dL is normal. A fasting blood sugar level from 100 to 125 mg/dL is considered prediabetes. If it's 126 mg/dL or higher on two separate tests, you'll be diagnosed with diabetes.

An oral glucose tolerance test may also be performed. For this test, you fast overnight, and the fasting blood sugar level is measured. Then, you drink a sugary liquid, and blood sugar levels are tested periodically for the next several hours. A reading of more than 200 mg/dL after two hours indicates diabetes. A reading between 140 and 199 mg/dL indicates prediabetes.

The American Diabetes Association recommends routine screening for type 2 diabetes beginning at age 45, especially if you're overweight. If the results are normal, repeat the test every three years. If the results are borderline, ask your doctor when to come back for another test. Screening is also recommended for people who are under 45 and overweight if there are other heart disease or diabetes risk factors present, such as a sedentary lifestyle, a family history of type 2 diabetes, a personal history of gestational diabetes or blood pressure above 135/80 millimeters of mercury (mm Hg).

If you're diagnosed with diabetes, the doctor may do other tests to distinguish between type 1 and type 2 diabetes — which often require different treatment strategies because in type 1 diabetes, the pancreas no longer makes insulin.

After the diagnosis

A1C levels need to be checked between two and four times a year. Your target A1C goal may vary depending on your age and various other factors. However, for most people, the American Diabetes Association recommends an A1C level below 7 percent. Ask your doctor what your A1C target is.

The American Diabetes Association has recently introduced a formula that translates the A1C into what's known as an estimated average glucose (eAG). The eAG more closely correlates with daily blood sugar readings. An A1C of 7 percent translates to an eAG of 154 mg/dL. That would mean that your average blood sugar levels are around 150 mg/dL.

Compared with repeated daily blood sugar tests, A1C testing better indicates how well your diabetes treatment plan is working. An elevated A1C level may signal the need for a change in your medication or meal plan.

In addition to the A1C test, the doctor will also take blood and urine samples periodically to check your cholesterol levels, thyroid function, liver function and kidney function. The doctor will assess your blood pressure. Regular eye and foot exams also are important.