Patient information: Diabetes mellitus type 2: Overview (Beyond the Basics)
- David K McCulloch, MD
David K McCulloch, MD
- Clinical Professor of Medicine
- University of Washington
Type 2 diabetes mellitus is a disorder that disrupts the way your body uses glucose (sugar).
All the cells in your body need sugar to work normally. Sugar gets into the cells with the help of a hormone called insulin. If there is not enough insulin, or if the body stops responding to insulin, sugar builds up in the blood. This is what happens to people with diabetes mellitus.
There are two different types of diabetes mellitus. In type 1 diabetes mellitus, the problem is that the pancreas (an organ in the abdomen) does not make enough insulin. In type 2 diabetes mellitus, the pancreas does not make enough insulin (figure 1), the body becomes resistant to normal or even high levels of insulin, or both. This causes high blood glucose (blood sugar) levels, which can cause problems if untreated. In the United States, Canada, and Europe, about 90 percent of all people with diabetes have type 2 diabetes.
Type 2 diabetes is a chronic medical condition that requires regular monitoring and treatment throughout your life. Treatment includes lifestyle changes, self-care measures, and sometimes medications. Fortunately, these treatments can keep blood sugar levels close to normal and minimize the risk of developing complications.
THE IMPACT OF DIABETES
Being diagnosed with type 2 diabetes can be a frightening and overwhelming experience, and you likely have questions about why it developed, what it means for your long-term health, and how it will affect your everyday life.
For most people, the first few months after being diagnosed are filled with emotional highs and lows. If you have just been diagnosed with diabetes, you and your family should use this time to learn as much as possible so that caring for your diabetes (including testing your blood sugar, going to medical appointments, and taking your medications) becomes a part of your daily routine. (See "Patient information: Self-blood glucose monitoring in diabetes mellitus (Beyond the Basics)".)
In addition, you should talk to your doctor or nurse about resources that are available for medical as well as psychological support. These may include group classes, meetings with a nutritionist, social worker, or nurse educator, and other educational resources such as books, web sites, or magazines. Several of these resources are listed below. (See 'Where to get more information' below.)
Despite the risks associated with type 2 diabetes, most people can lead active lives and continue to enjoy the foods and activities that they previously enjoyed. Diabetes does not mean an end to "special occasion" foods like birthday cake, and most people with diabetes can enjoy exercise in almost any form. (See "Patient information: Type 2 diabetes mellitus and diet (Beyond the Basics)" and "Patient information: Diabetes mellitus type 2: Alcohol, exercise, and medical care (Beyond the Basics)".)
CAUSES OF TYPE 2 DIABETES
Genetic causes — Many people with type 2 diabetes have a family member with either type 2 diabetes or other medical problems associated with diabetes, such as high cholesterol levels, high blood pressure, or obesity.
The lifetime risk of developing type 2 diabetes is 5 to 10 times higher in first-degree relatives (sister, brother, son, daughter) of a person with diabetes compared with a person with no family history of diabetes.
The likelihood of developing type 2 diabetes is greater in certain ethnic groups, such as people of Hispanic, African, and Asian descent.
Environmental conditions — Environmental factors such as what you eat and how active you are, combined with genetic causes, affect the risk of developing type 2 diabetes.
Pregnancy — A small number (about 3 to 5 percent) of pregnant women develop diabetes during pregnancy, called "gestational diabetes." Gestational diabetes is similar to type 2 diabetes, but usually resolves after the woman delivers her baby. Women who have gestational diabetes are at increased risk for developing type 2 diabetes later in life. (See "Patient information: Gestational diabetes mellitus (Beyond the Basics)".)
TYPE 2 DIABETES DIAGNOSIS
The diagnosis of diabetes is based upon your symptoms and the results of blood tests. (See "Clinical presentation and diagnosis of diabetes mellitus in adults".)
Symptoms — Before being diagnosed with type 2 diabetes, most people have no symptoms at all. In those who do have symptoms, the most common include:
●Needing to urinate frequently
Laboratory tests — Several blood tests are used to measure blood glucose levels, the primary test for diagnosing diabetes.
●Random blood sugar test – For a random blood sugar test, you can have blood drawn at any time throughout the day, regardless of when you last ate. If your blood sugar is 200 mg/dL (11.1 mmol/L) or higher and you have symptoms of high blood sugar (see 'Symptoms' above), it is likely that you have diabetes.
●Fasting blood sugar test – A fasting blood sugar test is a blood test done after not eating or drinking for 8 to 12 hours (usually overnight). A normal fasting blood sugar level is less than 100 mg/dL (5.55 mmol/L).
●Hemoglobin A1C test – The "A1C" blood test measures your average blood sugar level over the past two to three months. Normal values for A1C are 4 to 5.6 percent. The A1C test can be done at any time of day (before or after eating).
●Oral glucose tolerance test – Oral glucose tolerance testing (OGTT) is a test that involves drinking a special glucose solution (usually orange or cola flavored). Your blood sugar level is tested before you drink the solution, and then again one and two hours after drinking it.
Criteria for diagnosis — The following criteria are used to classify your blood sugar levels as normal, increased risk (blood sugar levels that are higher than normal and indicate a risk of future diabetes), or diabetes.
Normal — Fasting blood sugar less than 100 mg/dL (5.55 mmol/L).
Categories of increased risk
●Impaired fasting glucose is defined as a fasting blood sugar level between 100 and 125 mg/dL (5.6 to 6.9 mmol/L).
●Impaired glucose tolerance is defined as a blood sugar level of 140 to 199 mg/dL two hours after an oral glucose tolerance test.
●A1C – persons with 5.7 to 6.4 percent are at highest risk, although there is a continuum of increasing risk across the entire spectrum of subdiabetic A1C levels.
At least 50 percent of people with impaired glucose tolerance eventually develop type 2 diabetes. Even if they don't develop diabetes, these people are at increased risk of heart disease. Impaired glucose tolerance is very common; about 11 percent of all people between the ages of 20 and 74 have impaired glucose tolerance.
Diabetes mellitus — A person is considered to be diabetic if he or she has one or more of the following:
●Symptoms of diabetes (see 'Symptoms' above) and a random blood sugar of 200 mg/dL (11.1 mmol/L) or higher
●A fasting blood sugar level of 126 mg/dL (7.0 mmol/L) or higher
●A blood sugar of 200 mg/dL (11.1 mmol/L) or higher two hours after an oral glucose tolerance test
●An A1C of 6.5 percent or higher
The blood tests must be repeated on another day to confirm the diagnosis of diabetes.
Type 1 versus type 2 diabetes — Doctors can usually tell whether a person has type 1 or type 2, but there are situations when the diagnosis is difficult to determine. In such cases, doctors often run additional blood tests.
TYPE 2 DIABETES TREATMENT
A full discussion of the treatment for type 2 diabetes is available separately. (See "Patient information: Diabetes mellitus type 2: Treatment (Beyond the Basics)" and "Patient information: Diabetes mellitus type 2: Insulin treatment (Beyond the Basics)" and "Patient information: Hypoglycemia (low blood sugar) in diabetes mellitus (Beyond the Basics)".)
TYPE 2 DIABETES COMPLICATIONS
Complications of type 2 diabetes can be related to the disease itself or to the treatments used to manage diabetes. (See "Patient information: Preventing complications in diabetes mellitus (Beyond the Basics)".)
PREGNANCY AND DIABETES
Women with type 2 diabetes are usually able to become pregnant and have a healthy baby. A full discussion of diabetes in pregnancy is available separately. (See "Patient information: Care during pregnancy for women with type 1 or 2 diabetes mellitus (Beyond the Basics)".)
WHERE TO GET MORE INFORMATION
Your healthcare provider is the best source of information for questions and concerns related to your medical problem.
This article will be updated as needed on our web site (www.uptodate.com/patients). Related topics for patients, as well as selected articles written for healthcare professionals, are also available. Some of the most relevant are listed below.
Patient level information — UpToDate offers two types of patient education materials.
The Basics — The Basics patient education pieces answer the four or five key questions a patient might have about a given condition. These articles are best for patients who want a general overview and who prefer short, easy-to-read materials.
Patient information: Type 2 diabetes (The Basics)
Patient information: Polycystic ovary syndrome (The Basics)
Patient information: Hemochromatosis (The Basics)
Patient information: Hemoglobin A1C tests (The Basics)
Patient information: Nonalcoholic fatty liver disease, including nonalcoholic steatohepatitis (NASH) (The Basics)
Patient information: Preparing for pregnancy when you have diabetes (The Basics)
Patient information: Acromegaly (The Basics)
Patient information: Preventing type 2 diabetes (The Basics)
Patient information: Diabetic ketoacidosis (The Basics)
Patient information: Hyperosmolar nonketotic coma (The Basics)
Patient information: Diabetes and infections (The Basics)
Patient information: Health risks of obesity (The Basics)
Beyond the Basics — Beyond the Basics patient education pieces are longer, more sophisticated, and more detailed. These articles are best for patients who want in-depth information and are comfortable with some medical jargon.
Patient information: Diabetes mellitus type 2: Alcohol, exercise, and medical care (Beyond the Basics)
Patient information: Foot care in diabetes mellitus (Beyond the Basics)
Patient information: Hypoglycemia (low blood sugar) in diabetes mellitus (Beyond the Basics)
Patient information: Preventing complications in diabetes mellitus (Beyond the Basics)
Patient information: Self-blood glucose monitoring in diabetes mellitus (Beyond the Basics)
Patient information: Type 2 diabetes mellitus and diet (Beyond the Basics)
Patient information: Gestational diabetes mellitus (Beyond the Basics)
Patient information: Diabetes mellitus type 2: Treatment (Beyond the Basics)
Patient information: Diabetes mellitus type 2: Insulin treatment (Beyond the Basics)
Patient information: Care during pregnancy for women with type 1 or 2 diabetes mellitus (Beyond the Basics)
Professional level information — Professional level articles are designed to keep doctors and other health professionals up-to-date on the latest medical findings. These articles are thorough, long, and complex, and they contain multiple references to the research on which they are based. Professional level articles are best for people who are comfortable with a lot of medical terminology and who want to read the same materials their doctors are reading.
Blood glucose self-monitoring in management of adults with diabetes mellitus
Classification of diabetes mellitus and genetic diabetic syndromes
Clinical presentation and diagnosis of diabetes mellitus in adults
Effects of exercise in diabetes mellitus in adults
Estimation of blood glucose control in diabetes mellitus
Glycemic control and vascular complications in type 2 diabetes mellitus
Insulin therapy in type 2 diabetes mellitus
Management of hypoglycemia during treatment of diabetes mellitus
Management of persistent hyperglycemia in type 2 diabetes mellitus
Nutritional considerations in type 1 diabetes mellitus
Nutritional considerations in type 2 diabetes mellitus
Prevention of type 2 diabetes mellitus
Screening for type 2 diabetes mellitus
The metabolic syndrome (insulin resistance syndrome or syndrome X)
Treatment of type 2 diabetes mellitus in the older patient
Pathogenesis of type 2 diabetes mellitus
The following organizations also provide reliable health information.
●National Library of Medicine
●National Institute of Diabetes and Digestive and Kidney Diseases
●American Diabetes Association (ADA)
●Hormone Health Network
- Knowler WC, Barrett-Connor E, Fowler SE, et al. Reduction in the incidence of type 2 diabetes with lifestyle intervention or metformin. N Engl J Med 2002; 346:393.
- Intensive blood-glucose control with sulphonylureas or insulin compared with conventional treatment and risk of complications in patients with type 2 diabetes (UKPDS 33). UK Prospective Diabetes Study (UKPDS) Group. Lancet 1998; 352:837.
All topics are updated as new information becomes available. Our peer review process typically takes one to six weeks depending on the issue.