Diabetes is a chronic disease in which the body cannot regulate the amount of sugar in the blood.
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 stored or used as fuel.
People with diabetes have high blood sugar because their body cannot move sugar from the blood into muscle and fat cells to be burned or stored for energy, and because their liver makes too much glucose and releases it into the blood. This is because either:
Their pancreas does not make enough insulin
Their cells do not respond to insulin normally
Both of the above
There are two major types of diabetes. The causes and risk factors are different for each type:
Type 1 diabetes can occur at any age, but it is most often diagnosed in children, teens, or young adults. In this disease, the body makes little or no insulin. This is because the pancreas cells that make insulin stop working. Daily injections of insulin are needed. The exact cause is unknown.
Type 2 diabetes is much more common. It most often occurs in adulthood, but because of high obesity rates, teens and young adults are now being diagnosed with this disease. Some people with type 2 diabetes do not know they have it.
There are other causes of diabetes, and some patients cannot be classified as type 1 or type 2.
Gestational diabetes is high blood sugar that develops at any time during pregnancy in a woman who does not have diabetes.
If your parent, brother, or sister has diabetes, you may be more likely to develop the disease.
A high blood sugar level can cause several symptoms, including:
A urine analysis may show high blood sugar. But a urine test alone does not diagnose diabetes.
Your health care provider may suspect that you have diabetes if your blood sugar level is higher than 200 mg/dL. To confirm the diagnosis, one or more of the following tests must be done.
Fasting blood glucose level -- diabetes is diagnosed if the fasting glucose level is higher than 126 mg/dL on two different tests. Levels between 100 and 126 mg/dL are called impaired fasting glucose or pre-diabetes. These levels are risk factors for type 2 diabetes.
Oral glucose tolerance test -- diabetes is diagnosed if the glucose level is higher than 200 mg/dL 2 hours after drinking a sugar drink. (This test is used more often for type 2 diabetes.)
Screening for type 2 diabetes in people who have no symptoms is recommended for:
Overweight children who have other risk factors for diabetes, starting at age 10 and repeated every 3 years
Overweight adults (BMI of 25 or higher) who have other risk factors
Adults over age 45, repeated every 3 years
Type 2 diabetes may be reversed with lifestyle changes, especially losing weight with exercise and by eating healthier foods. Some cases of type 2 diabetes can also be improved with weight-loss surgery.
Getting better control over your blood sugar, cholesterol, and blood pressure levels helps reduce the risk of kidney disease, eye disease, nervous system disease, heart attack, and stroke.
To prevent diabetes complications, visit your health care provider at least two to four times a year. Talk about any problems you are having. Follow your health care provider's instructions on managing your diabetes.
Many resources can help you understand more about diabetes. If you have diabetes, you can also learn ways to manage your condition and prevent diabetes complications.
Keeping an ideal body weight and an active lifestyle may prevent or delay the start of type 2 diabetes.
Type 1 diabetes cannot be prevented.
American Diabetes Association. Standards of medical care in diabetes -- 2014. Diabetes Care. 2014; Jan;34 Suppl 1:S14-S80.
Buse JB, Polonsky KS, Burant CF. Type 2 diabetes mellitus. In: Kronenberg HM, Melmed S, Polonsky KS, Larsen PR. Williams Textbook of Endocrinology. 12th ed. Philadelphia, PA: Saunders Elsevier; 2011:chap 31.
Eisenbarth GS, Buse JB. Type 1 diabetes mellitus. In: Kronenberg HM, Melmed S, Polonsky KS, Larsen PR. Williams Textbook of Endocrinology. 12th ed. Philadelphia, PA: Saunders Elsevier; 2011:chap 32.
Brent Wisse, MD, Associate Professor of Medicine, Division of Metabolism, Endocrinology & Nutrition, University of Washington School of Medicine, Seattle, WA. Also reviewed by David Zieve, MD, MHA, Isla Ogilvie, PhD, and the A.D.A.M. Editorial team.