Diseases & Conditions

Adult-Onset Diabetes Mellitus - Type 2 Diabetes Mellitus

Overview, Causes, & Risk Factors

Type 2 diabetes mellitus, more often known as type 2 diabetes, is the most common type of diabetes. Unlike in type 1 diabetes, people with type 2 diabetes may make healthy or even high levels of insulin. But, their body cells do not use insulin effectively. This resistance to insulin is often caused by obesity. Insulin is a hormone that helps control the level of glucose in the blood. Glucose is the main form of sugar in the body. When the body cannot control the level of glucose, it has a hard time converting food into the energy that the body needs to work. There are other forms of diabetes as well.

What is going on in the body?

The pancreas, a long, thin organ located behind the stomach, makes insulin. In healthy people, the pancreas makes extra insulin when a person eats. Insulin moves glucose from the bloodstream into the body cells. The cells use glucose as their main energy source.

In a person with type 2 diabetes, however, even though the pancreas may make enough insulin, the body cells are resistant to the effects of insulin. So they don't receive enough glucose and the blood glucose level rises too high. This causes a condition called hyperglycemia, and it can cause damage to the body, if left untreated.

What are the causes and risks of the disease?

Obesity is the main cause of type 2 diabetes in both adults and children. A recent study showed a 33% increase in the number of Americans with type 2 diabetes during the past 8 years. The increase was 70% in people who were 30 to 39 years of age.

Type 2 diabetes accounts for about 90% to 95% of the cases of diabetes in the US. Type 2 diabetes used to be rare in children, but is now diagnosed in 20% of the children who have diabetes. Of the children diagnosed with type 2 diabetes, 85% are obese. At this time, most children diagnosed with type 2 diabetes are 10 years of age or older. Researchers believe there will be an increase in type 2 diabetes in younger children who become obese.

Type 2 diabetes is more common in people with a family history of the disease. It's also more common among African Americans, Hispanic Americans, Pacific Islanders, Asian Americans, and Native Americans.

Other risk factors for the development of type 2 diabetes include:

  • age of 45 or older
  • an HDL, the so-called good cholesterol, level equal to or less than 35 mg/dL (milligrams per deciliter)
  • high blood pressure, defined as a reading of 140/90 mmHg or higher
  • a history of gestational diabetes or of having babies that weighed more than 9 pounds at birth
  • lack of physical activity
  • a triglyceride level equal to or more than 250 mg/dL
  • A recent study of 16,000 American women between the ages of 40 and 65 years showed that diabetes was listed as one of the top six diagnoses. A long-term study is under way to see if menopause and changes in hormone levels are factors in developing type 2 diabetes.

    Almost all people who develop type 2 diabetes have a condition called prediabetes first. This condition used to be known as impaired glucose tolerance or impaired fasting glucose, and the ADA estimates that almost 16 million people over the age of 40 have it. This condition occurs when blood glucose levels are higher than healthy levels but too low to be diagnosed as diabetes. Without lifestyle changes, most people who have prediabetes will progress to type 2 diabetes within 10 years.

    Symptoms & Signs

    What are the signs and symptoms of the disease?

    Symptoms of type 2 diabetes usually develop slowly over time. They are not as noticeable as in type 1 diabetes. Many people who have type 2 diabetes never have any symptoms at all. If they do develop symptoms, they are usually linked to high levels of glucose in the blood and can include:

  • excessive hunger
  • excessive thirst
  • fatigue and weakness
  • frequent urination and an increase in the amount of urine passed
  • infections of the skin, vagina, bladder, or other areas
  • nausea
  • vomiting
  • visual problems, such as blurred vision
  • weight loss in spite of increased appetite and thirst
  • Diabetic ketoacidosis sometimes occurs in people with type 2 diabetes. When the cells in the body don't get enough glucose, the body starts to burn fat for energy. This produces waste products known as ketones. High levels of ketones can result in too much acid in the body, called ketoacidosis. This condition requires medical attention right away to prevent coma and death. Symptoms it can cause include:

  • dehydration
  • dry lips
  • sunken eyes
  • labored breathing
  • vomiting
  • abdominal distress,
  • fruity-smelling breath

  • Diagnosis & Tests

    How is the disease diagnosed?

    A doctor may suspect diabetes after taking a person's health history and doing a physical exam. Based on those results, the doctor may want to check for a high glucose level in the blood. There are several types of blood tests doctors can use to diagnose diabetes, including:

  • fasting plasma glucose test, which is the most common method to diagnose most cases of diabetes. In this test, a person is asked to fast overnight for at least 8 hours. In the morning, the level of glucose in the blood is then checked. Healthy fasting plasma glucose levels are less than 110 milligrams per deciliter or mg/dL. A fasting plasma glucose level of more than 126 mg/dL usually suggests diabetes. Levels between 110 and 126 mg/dL are seen in prediabetes.
  • oral glucose tolerance test, which is the preferred way to diagnose gestational diabetes. It can also be used to diagnose type 2 diabetes and prediabetes. In this test, a person is asked to drink a sweet liquid. Blood samples are then drawn at timed intervals. If a person does not have diabetes, the glucose levels will rise and then fall quickly after drinking the sweet liquid. When a person has diabetes, glucose levels will rise higher and fail to come down as fast as those in a person without diabetes. If the blood glucose level is 140 to 199 mg/dL 2 hours after drinking the liquid, a diagnosis of prediabetes can be made.
  • plasma glucose test, which can be done without fasting and is used as a screening tool. A level of 200 mg/dL or higher suggests diabetes. If the level is above 200 mg/dL on two separate days, a fasting glucose test or oral glucose tolerance test can be done to confirm the diagnosis of diabetes.

  • Prevention & Expectations

    What can be done to prevent the disease?

    The best way to prevent type 2 diabetes is through modest lifestyle changes. These changes can be helpful to almost any person's health, but if a person has been diagnosed with prediabetes, lifestyle changes are essential. The key is to:

  • maintain a healthy body weight
  • eat a healthy diet for diabetes
  • exercise 30 minutes a day at least 5 days a week
  • The Disease Prevention Program, a federally funded study, demonstrated the effect of lifestyle changes on a person's risk factors for type 2 diabetes. Participants in the study exercised moderately for 150 minutes a week. Most of them chose to walk briskly for 30 minutes, 5 days a week. They also ate a reduced-fat diet with large amounts of vegetables. The weight loss goal was 7%, or 14 pounds for a person weighing 200 pounds. With these changes, the individuals lowered their risk of developing type 2 diabetes by 58%.

    What are the long-term effects of the disease?

    Over time, high blood sugar levels damage blood vessels, nerves, and other internal structures. Long-term effects of diabetes may include:

  • Retinopathy, a disease in the retina of the eye that can cause blindness. Diabetes is the number one cause of blindness in adults who are younger than age 40.
  • Diabetic nephropathy, which is a disease of the kidneys. This disease can progress to a form of kidney failure known as chronic renal failure. Diabetes is the leading cause of chronic renal failure.
  • Atherosclerosis, also known as hardening of the arteries. Atherosclerosis can lead to heart attacks and strokes. It can also cause poor circulation in the legs and feet.
  • Diabetic neuropathy, which means damage to nerves in the arms and legs. This damage can cause numbness and pain in the hands and feet. When combined with poor circulation, neuropathy can result in diabetic foot ulcers and leg infections that may require amputation.
  • Autonomic neuropathy, which is a disorder that affects certain nerves. It may cause problems with digestion, diarrhea, erectile dysfunction, a rapid heartbeat, and low blood pressure.
  • Coma or death may occur as a result of diabetic ketoacidosis. In addition, smoking greatly increases the risk of getting many of these long-term effects. People with diabetes who smoke are a much higher risk for heart attacks, strokes, infections, and problems with circulation.

    What are the risks to others?

    Type 2 diabetes is not catching and poses no risk to others. It does tend to run in families.

    Treatment & Monitoring

    What are the treatments for the disease?

    The most effective treatment for type 2 diabetes is a change in lifestyle, including the following:

  • Weight loss. Loss of as little as 10 to 15 pounds can help keep blood glucose levels under control.
  • Healthy eating. A healthy diet can help with weight loss. And that can prevent the need for medicine.
  • Regular exercise. Walking only 30 minutes a day can lead to better glucose control.
  • A person with type 2 diabetes may also be treated with oral medicines and/or insulin shots. Diabetes pills can work in four ways.

  • They can stimulate the pancreas to make more insulin.
  • They can help the cells in the body use insulin and glucose better.
  • They can keep the starches that are eaten from being broken down into glucose in your intestines.
  • They can reduce the amount of glucose that is released from the liver.
  • Careful monitoring and management help keep diabetes under control and reduce the risk of long-term effects. A person with diabetes should:

  • monitor his or her blood glucose levels at home
  • take medicines as prescribed by the doctor
  • know how to recognize and treat hypoglycemia, which is low blood glucose
  • get regular eye checkups that include an examination of the retina after the pupil of the eye has been dilated with eye drops
  • do thorough foot care on a daily basis
  • follow a plan to monitor and treat changing blood glucose levels when sick or under stress
  • follow a healthy diet
  • have regular checkups with the doctor
  • get a pneumonia shot
  • get a flu shot each fall
  • Treating the complications of diabetes may involve many different specialists. For example, a person with diabetes may need to see eye, heart, foot, hormone, and circulation specialists. Dieticians also help people with diabetes by designing a healthy eating plan. Dieticians can also suggest healthy calorie intake levels and types of foods to eat.

    What are the side effects of the treatments?

    The oral medicines used for type 2 diabetes may cause weight gain, diarrhea, gas, allergic reactions, or liver damage. Some may also cause blood glucose levels to go too low. This condition is known as hypoglycemia. It can cause:

  • nervousness
  • shakiness
  • confusion
  • hunger
  • sweating
  • nausea
  • If this condition goes untreated, a person can pass out. The usual treatment for low blood glucose is to drink a sweet beverage or eat a sweet food. If low blood glucose goes untreated, a person may pass out or have seizures. Emergency medical care is crucial in this situation.

    What happens after treatment for the disease?

    Although type 2 diabetes cannot be cured, it can be controlled with careful management. The person will need lifelong monitoring and treatment to help prevent serious complications.

    How is the disease monitored?

    A person with diabetes should keep all of appointments with his or her primary doctor, as well as other scheduled specialists. Physical exams, blood tests, urine tests, foot and skin care, routine eye exams, and routine dental care are all part of basic care for a person with diabetes. The main goal of treatment is to keep blood glucose levels as close to a healthy range as is safely possible. In general, ideal ranges of blood glucose levels are 80 to 120 milligrams per deciliter (mg/dL) before meals and 100 to 140 mg/dL at bedtime. Any new or worsening symptoms should be reported to the doctor.


    Author:Eileen McLaughlin, RN, BSN
    Date Written:
    Editor:Crist, Gayle P., MS, BA
    Edit Date:09/30/02
    Reviewer:Kathleen A. MacNaughton, RN, BSN
    Date Reviewed:09/30/02




    The Merck Manual of Medical Information, 1997