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Diabetes is a chronic (lifelong) disease marked by high levels of sugar in the blood.

See also:

• Gestational diabetes
• Type 1 diabetes
• Type 2 diabetes
• Metabolic syndrome

Insulin is a hormone produced by the pancreas to control blood sugar. Diabetes can be caused by too little insulin, resistance to insulin, or both.

To understand diabetes, it is important to first understand the normal process by which food is broken down and used by the body for energy. Several things happen when food is digested:

• A sugar called glucose enters the bloodstream. Glucose is a source of fuel for the body.
• An organ called the pancreas makes insulin. The role of insulin is to move glucose from the bloodstream into muscle, fat, and liver cells, where it can be used as fuel.

People with diabetes have high blood sugar. This is because:

• Their pancreas does not make enough insulin
• Their muscle, fat, and liver cells do not respond to insulin normally
• Both of the above

There are three major types of diabetes:

• Type 1 diabetes is usually diagnosed in childhood. Many patients are diagnosed when they are older than age 20. In this disease, the body makes little or no insulin. Daily injections of insulin are needed. The exact cause is unknown. Genetics, viruses, and autoimmune problems may play a role.
• Type 2 diabetes is far more common than type 1. It makes up most of diabetes cases. It usually occurs in adulthood, but young people are increasingly being diagnosed with this disease. The pancreas does not make enough insulin to keep blood glucose levels normal, often because the body does not respond well to insulin. Many people with type 2 diabetes do not know they have it, although it is a serious condition. Type 2 diabetes is becoming more common due to increasing obesity and failure to exercise.
• Gestational diabetes is high blood glucose that develops at any time during pregnancy in a woman who does not have diabetes. Women who have gestational diabetes are at high risk of type 2 diabetes and cardiovascular disease later in life.

Diabetes affects more than 20 million Americans. Over 40 million Americans have prediabetes (early type 2 diabetes).

There are many risk factors for type 2 diabetes, including:

• Age over 45 years
• A parent, brother, or sister with diabetes
• Gestational diabetes or delivering a baby weighing more than 9 pounds
• Heart disease
• High blood cholesterol level
• Obesity
• Not getting enough exercise
• Polycystic ovary disease (in women)
• Previous impaired glucose tolerance
• Some ethnic groups (particularly African Americans, Native Americans, Asians, Pacific Islanders, and Hispanic Americans)

High blood levels of glucose can cause several problems, including:

• Blurry vision
• Excessive thirst
• Fatigue
• Frequent urination
• Hunger
• Weight loss

However, because type 2 diabetes develops slowly, some people with high blood sugar experience no symptoms at all.

Symptoms of type 1 diabetes:

• Fatigue
• Increased thirst
• Increased urination
• Nausea
• Vomiting
• Weight loss in spite of increased appetite

Patients with type 1 diabetes usually develop symptoms over a short period of time. The condition is often diagnosed in an emergency setting.

Symptoms of type 2 diabetes:

• Blurred vision
• Fatigue
• Increased appetite
• Increased thirst
• Increased urination

A urine analysis may be used to look for glucose and ketones from the breakdown of fat. However, a urine test alone does not diagnose diabetes.

The following blood tests are used to diagnose diabetes:

• Fasting blood glucose level -- diabetes is diagnosed if higher than 126 mg/dL on two occasions. Levels between 100 and 126 mg/dL are referred to as impaired fasting glucose or prediabetes. These levels are considered to be risk factors for type 2 diabetes and its complications.
• Oral glucose tolerance test -- diabetes is diagnosed if glucose level is higher than 200 mg/dL after 2 hours. (This test is used more for type 2 diabetes.)
• Random (non-fasting) blood glucose level -- diabetes is suspected if higher than 200 mg/dL and accompanied by the classic diabetes symptoms of increased thirst, urination, and fatigue. (This test must be confirmed with a fasting blood glucose test.)

Persons with diabetes need to have their hemoglobin A1c (HbA1c) level checked every 3 - 6 months. The HbA1c is a measure of average blood glucose during the previous 2 - 3 months. It is a very helpful way to determine how well treatment is working.

For additional information, see diabetes resources.

With good blood glucose and blood pressure control, many of the complications of diabetes can be prevented.

Studies have shown that strict control of blood sugar, cholesterol, and blood pressure levels in persons with diabetes helps reduce the risk of kidney disease, eye disease, nervous system disease, heart attack, and stroke.

Emergency complications include:

• Diabetic hyperglycemic hyperosmolar coma
• Diabetic ketoacidosis

Long-term complications include:

• Atherosclerosis
• Coronary artery disease
• Diabetic nephropathy
• Diabetic neuropathy
• Diabetic retinopathy
• Erection problems
• Hyperlipidemia
• Hypertension
• Infections of the skin, female urinary tract, and urinary tract
• Peripheral vascular disease
• Stroke

Go to the emergency room or call the local emergency number (such as 911) if you have symptoms of ketoacidosis:

• Abdominal pain
• Deep and rapid breathing
• Increased thirst and urination
• Loss of consciousness
• Nausea
• Sweet-smelling breath

Go to the emergency room or call the local emergency number (such as 911) if you have symptoms of extremely low blood sugar (hypoglycemic coma or severe insulin reaction):

• Confusion
• Convulsions or unconsciousness
• Dizziness
• Double vision
• Drowsiness
• Headache
• Lack of coordination
• Weakness

Maintaining an ideal body weight and an active lifestyle may prevent type 2 diabetes.

Currently there is no way to prevent type 1 diabetes.

There is no effective screening test for type 1 diabetes in people who don't have symptoms.

Screening for type 2 diabetes and people with no symptoms is recommended for:

• Overweight children who have other risk factors for diabetes starting at age 10 and repeating every 2 years
• Overweight adults (BMI greater than 25) who have other risk factors
• Adults over 45, repeated every 3 years

To prevent complications of diabetes, visit your health care provider or diabetes educator at least four times a year. Talk about any problems you are having.

Regularly have the following tests:

• Have your blood pressure checked every year (blood pressure goals should be 130/80 mm/Hg or lower).
• Have your glycosylated hemoglobin (HbA1c) checked every 6 months if your diabetes is well controlled, otherwise every 3 months.
• Have your cholesterol and triglyceride levels checked yearly (aim for LDL levels below 100 mg/dL).
• Get yearly tests to make sure your kidneys are working well (microalbuminuria and serum creatinine).
• Visit your ophthalmologist (preferably one who specializes in diabetic retinopathy) at least once a year, or more often if you have signs of diabetic retinopathy.
• See the dentist every 6 months for a thorough dental cleaning and exam. Make sure your dentist and hygienist know that you have diabetes.
• Make sure your health care provider inspects your feet at each visit.

Stay up-to-date with all of your vaccinations and get a flu shot every year in the fall.

Alemzadeh R, Wyatt DT. Diabetes Mellitus. In: Kliegman RM, ed. Kliegman: Nelson Textbook of Pediatrics. 18th ed. Philadelphia, Pa: Saunders;2007:chap 590.

American Diabetes Association. Standards of medical care in diabetes -- 2008. Diabetes Care. 2009; 32:S13-S61, 2009.

Eisenbarth GS, Polonsky KS, Buse JB. Type 1 Diabetes Mellitus. In: Kronenberg HM, Melmed S, Polonsky KS, Larsen PR. Kronenberg: Williams Textbook of Endocrinology. 11th ed. Philadelphia, Pa: Saunders Elsevier; 2008:chap 31.

Standards of medical care in diabetes--2007. Diabetes Care. Jan 2007;30 Suppl 1:S4-S41.