Once it develops, diabetes is a lifelong condition that affects an estimated 23.6 million people in the United States—that’s almost 8 percent of the population. It’s considered a disorder of the metabolism, meaning that diabetes affects how the body uses food for growth and energy.

Glucose, Insulin, and Diabetes

In people with diabetes, the body is not able to use glucose normally and blood glucose levels are above normal. Glucose is important because it’s the body’s main source of fuel. Glucose is a form of sugar in the blood; when food is eaten, it’s broken down into glucose and passes into the bloodstream, where it provides energy.

Insulin, a hormone produced by the pancreas, is essential for the body’s process of using fuel, or glucose: blood cells need insulin to take up glucose. In people with diabetes, however, the pancreas produces too little or no insulin or their blood cells do not respond effectively to insulin.

As a result of insufficient insulin production or ineffective use, glucose builds up in the blood and, instead of being used as fuel, is passed out of the body in urine. In other words, the body loses its main source of fuel.

Types of Diabetes

There are three main types of diabetes:

  • Type 1 diabetes
  • Type 2 diabetes
  • Gestational diabetes

What Is Type 1 Diabetes?

Type 1 diabetes is an autoimmune disease. It’s also known as insulin-dependent diabetes. Five to 10 percent of diagnosed diabetes in the United States is type 1.

In autoimmune diseases, the body’s immune system (which normally fights infection) functions abnormally and attacks a part of the body. In type 1 diabetes, the immune system attacks the cells in the pancreas (beta cells) that produce insulin. As a result, a person with type 1 diabetes produces little or no insulin. He or she must take insulin daily to live.

Causes of Type 1 Diabetes
The exact causes of type 1 diabetes are still not known. Researchers suspect that causes include autoimmune, genetic, and environmental factors; viruses may also be involved. Though type 1 diabetes can develop at any age, it most often appears in children and young adults.

Risks for Type 1 Diabetes
Men and women have equal incidence of type 1 diabetes. It can occur at any age, though it most often develops in children. The disease is more common among Whites than among other races.

These risk factors increase the likelihood of developing both type 1 and type 2 diabetes:

  • Overweight or obesity
  • A parent, brother, or sister with diabetes
  • High blood pressure of 140/90 or higher
  • Abnormal cholesterol (HDL, or “good” cholesterol, 35 or lower; triglyceride level of 250 or higher)
  • Physical inactivity (less than three days per week of exercise)

What Is Type 2 Diabetes?

Type 2 diabetes is the more-common form of the disease; among people with diabetes, nine out of 10 have type 2. In type 2 diabetes, the pancreas makes insulin for some time, but the body can’t use it effectively. Insulin production eventually decreases, at which time glucose builds up in the blood and the body cannot use it for fuel.

Causes of Type 2 Diabetes
Type 2 diabetes most often affects people who are overweight, older, have a family history of diabetes, are physically inactive, or have had gestational diabetes. Certain ethnicities—such as African American, Mexican American, and Pacific Islander—also have a high incidence of type 2 diabetes.

Risks for Type 2 Diabetes
Pre-diabetes. Pre-diabetes refers to a condition where people have blood glucose levels that are higher than normal but not high enough to be considered diabetes. Pre-diabetes can still be a health concern—it raises the risk of developing type 2 diabetes, heart disease, and stroke. Without prevention, a person with pre-diabetes is likely to develop type 2 diabetes within 10 years. Preventive steps include weight loss of 5 to 7 percent through healthy diet and increased physical activity.

Type 2 diabetes is more common among older people, and many who develop it are overweight; in fact, being overweight or obese is the leading risk factor for type 2 diabetes because excess weight can keep the body from using insulin properly. African Americans, American Indians, Native Hawaiians and other Pacific Islanders and Hispanics have a higher incidence than Whites. Older age, impaired glucose tolerance, physical inactivity, a family history of diabetes or a personal history of gestational diabetes are risk factors for type 2 diabetes.

Diabetes Testing and Diagnosis

Diabetes is most often diagnosed in children and adults using a fasting blood glucose test. This test is performed when the patient hasn’t eaten for eight hours (in other words, after “fasting”) and measures levels of glucose in the blood. Diabetes may be diagnosed with a fasting blood glucose level of 126 milligrams per deciliter (mg/dL) or higher.

Other tests for diabetes include: 1) the oral glucose tolerance test, where blood glucose levels are measured two hours after drinking 75 grams of glucose dissolved in water; a blood glucose level of 200 me/dL indicates diabetes and 2) a blood glucose level of 200 mg/dL or higher taken at any time of day when other symptoms of diabetes are present.

Who should get tested? People who may want to consider testing include those over 45 years of age, especially if they are overweight, and people younger than 45 who are overweight and have one or more additional risk factors. Find a list of risk factors under “Risks.”