Alternative names
Diabetes mellitus

Diabetes is a life-long disease marked by high levels of sugar in the blood. It can be caused by too little insulin (a hormone produced by the pancreas to regulate blood sugar), resistance to insulin, or both.

Causes, incidence, and risk factors
To understand diabetes, it is important to first understand the normal process of food metabolism. 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 glucose. This is because their pancreas does not make enough insulin or their muscle, fat, and liver cells do not respond to insulin normally, or both.

There are three major types of diabetes:

  • Type 1 Diabetes Mellitus is usually diagnosed in childhood. The body makes little or no insulin, and daily injections of insulin are required to sustain life. Without proper daily management, medical emergencies can arise.  
  • Type 2 diabetes is far more common than type 1 and makes up 90% or more of all cases of diabetes. It usually occurs in adulthood. Here, the pancreas does not make enough insulin to keep blood glucose levels normal, often because the body does not respond well to the 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 the growing number of older Americans, increasing obesity, and failure to exercise.  
  • Gestational diabetes is high blood glucose that develops at any time during pregnancy in a person who does not have diabetes.

Diabetes affects about 17 million Americans. There are many risk factors for diabetes, including:

  • A parent, brother, or sister with diabetes  
  • Obesity  
  • Age greater than 45 years  
  • Some ethnic groups (particularly African-Americans and Hispanic Americans)  
  • Gestational diabetes or delivering a baby weighing more than 9 pounds  
  • High blood pressure  
  • High blood levels of triglycerides (a type of fat molecule)  
  • High blood cholesterol level

The American Diabetes Association recommends that all adults be screened for diabetes at least every three years. A person at high risk should be screened more often.


High blood levels of glucose can cause several problems, including frequent urination, excessive thirst, hunger, fatigue, weight loss, and blurry vision. However, because type 2 diabetes develops slowly, some people with high blood sugar experience no symptoms at all.

Symptoms of type 1 diabetes:

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

Symptoms of type 2 diabetes:

  • Increased thirst  
  • Increased urination  
  • Increased appetite  
  • Fatigue  
  • Blurred vision  
  • Slow-healing infections  
  • Impotence in men

Signs and tests
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 glucose tests are used to diagnose diabetes:

Patients with Type 1 Diabetes usually develop symptoms over a short period of time, and the condition is often diagnosed in an emergency setting. In addition to having high glucose levels, acutely ill type 1 diabetics have high levels of ketones.

Ketones are produced by the breakdown of fat and muscle, and they are toxic at high levels. Ketones in the blood cause a condition called “acidosis” (low blood pH). Urine testing detects both glucose and ketones in the urine. Blood glucose levels are also high.


There is no cure for diabetes. The immediate goals are to stabilize your blood sugar and eliminate the symptoms of high blood sugar. The long-term goals of treatment are to prolong life, relieve symptoms, and prevent long-term complications such as heart disease and kidney failure.


Basic diabetes management skills will help prevent the need for emergency care. These skills include:

  • How to recognize and treat low blood sugar (hypoglycemia) and high blood sugar (hyperglycemia)  
  • What to eat and when  
  • How to take insulin or oral medication  
  • How to test and record blood glucose  
  • How to test urine for ketones (type 1 diabetes only)  
  • How to adjust insulin and/or food intake when changing exercise and eating habits  
  • How to handle sick days  
  • Where to buy diabetes supplies and how to store them

After you learn the basics of diabetes care, learn how the disease can cause long-term health problems and the best ways to prevent these problems. People with diabetes need to review and update their knowledge, because new research and improved ways to treat diabetes are constantly being developed.


You should work closely with your health care provider to learn how much fat, protein, and carbohydrates you need in your diet. Your specific meal plans need to be tailored to your food habits and preferences. People with type 1 diabetes should eat at about the same times each day and try to be consistent with the types of food they choose. This helps to prevent blood sugars from becoming extremely high or low. Type 2 diabetics should follow a well-balanced and low-fat diet.

A registered dietician can be very helpful in planning dietary needs.

Weight management is important to achieving control of diabetes. Some people with type 2 diabetes can stop medications after losing excess weight, although the diabetes is still present.


Medications to treat diabetes include insulin and glucose-lowering pills, called oral hypoglycemic agents. The bodies of people with type 1 diabetes cannot make their own insulin, so daily insulin injections are required. The bodies of people with type 2 diabetes make insulin but cannot use it effectively.

Insulin is not available in oral form. It is delivered by injections that are generally required one to four times per day. Some people use an insulin pump, which is worn at all times and delivers a steady flow of insulin throughout the day.

Insulin preparations differ in how quickly they start to work and how long they remain active. Sometimes different types of insulin are mixed together in a single injection. The types of insulin to use, the doses required, and the number of daily injections are chosen by a health care professional trained to provide diabetes care.

People who need insulin are taught to give themselves injections by their health care providers or diabetes educators.

Unlike type 1 diabetes, type 2 diabetes may respond to treatment with exercise, diet, and/or oral medications. There are several oral hypoglycemic agents that lower blood glucose in type 2 diabetes. They fall into one of three groups:

  • Medications that increase insulin production by the pancreas. These include Amaryl, Glucotrol, and Glucotrol XL, Micronase, Diabeta, Glynase, Prandin, and Starlix.  
  • Medications that increase sensitivity to insulin. These include Glucophage, Avandia, and Actos.  
  • Medications that delay absorption of glucose from the gut. These include Precose and Glyset.

Most type 2 diabetics will require more than one medication for good blood sugar control within three years of starting their first medication. Different groups of oral medications may be combined, or insulin and oral medications may be used together.

Some people with type 2 diabetes find they no longer need medication if they lose weight and increase activity, because when their ideal weight is reached, their own insulin and a careful diet can control their blood glucose levels.

Oral hypoglycemic agents are not known to be safe for use in pregnancy; women who have type 2 diabetes and take these medications may be switched to insulin during pregnancy and while breast-feeding.

Gestational diabetes is treated with diet and insulin.


Self-monitoring of blood glucose is done by checking the glucose content of a drop of blood. Regular testing tells you how well diet, medication, and exercise are working together to control your diabetes.

The results of the test can be used to adjust meals, activity, or medications to keep blood sugar levels in an appropriate range. Testing provides valuable information for the health care provider and identifies high and low blood sugar levels before serious problems develop.

The American Diabetes Association recommends that premeal blood sugar levels fall in the range of 80 to 120 mg/dL and bedtime blood levels fall in the range of 100 to 140 mg/dL. Your doctor may adjust this depending on your circumstances.

You should also ask your doctor how often to check your hemoglobin A1c (HbA1c) level. The HbA1c is a measure of average blood glucose during the previous two to three months. It is a very helpful way to monitor a patient’s overall response to diabetes treatment over time. A person without diabetes has an HbA1c around 5%. People with diabetes should try to keep it below 7%.

Ketone testing is another test that is used in type 1 diabetes. Ketones build up in the blood when there is not enough insulin in people with type 1diabetes, eventually “spilling over” into the urine. The ketone test is done on a urine sample. High levels of blood ketones may result in a serious condition called ketoacidosis. Ketone testing is usually done at the following times:

  • When the blood sugar is higher than 240 mg/dL  
  • During acute illness (for example, pneumonia, heart attack, or stroke)  
  • When nausea or vomiting occur  
  • During pregnancy


Regular exercise is especially important for people with diabetes. It helps with blood sugar control, weight loss, and high blood pressure. People with diabetes who exercise are less likely to experience a heart attack or stroke than diabetics who do not exercise regularly. You should be evaluated by your physician before starting an exercise program.

Here are some exercise considerations:

  • Choose an enjoyable physical activity that is appropriate for your current fitness level.  
  • Exercise every day, and at the same time of day, if possible.  
  • Monitor blood glucose levels before and after exercise.  
  • Carry food that contains a fast-acting carbohydrate in case you become hypoglycemic during or after exercise.  
  • Carry a diabetes identification card and a mobile phone or change for a payphone in case of emergency.  
  • Drink extra fluids that do not contain sugar before, during, and after exercise.

Changes in exercise intensity or duration may require changes in diet or medication dose to keep blood sugar levels from going too high or low.


People with diabetes are prone to foot problems because of the likelihood of damage to blood vessels and nerves and a decreased ability to fight infection. Problems with blood flow and damage to nerves may cause an injury to the foot to go unnoticed until infection develops. Death of skin and other tissue can occur.

If left untreated, the affected foot may need to be amputated. Diabetes is the most common condition leading to amputations.

To prevent injury to the feet, people with diabetes should adopt a daily routine of checking and caring for the feet as follows:

  • Check your feet every day, and report sores or changes and signs of infection.  
  • Wash your feet every day with lukewarm water and mild soap, and dry them thoroughly.  
  • Soften dry skin with lotion or petroleum jelly.  
  • Protect feet with comfortable, well-fitting shoes.  
  • Exercise daily to promote good circulation.  
  • See a podiatrist for foot problems or to have corns or calluses removed.  
  • Remove shoes and socks during a visit to your health care provider and remind him or her to examine your feet.  
  • Stop smoking, which hinders blood flow to the feet.

Support Groups

For additional information, see diabetes resources.

Expectations (prognosis)

The risks of long-term complications from diabetes can be reduced.

The Diabetes Control and Complications Trial (DCCT) studied the effects of tight blood sugar control on complications in type 1 diabetes. Patients treated for tight blood glucose control had an average HbA1c of approximately 7%, while patients treated less aggressively had an average HbA1c of about 9%. At the end of the study, the tight blood glucose group had dramatically fewer cases of kidney disease, eye disease, and nervous system disease than the less-aggressively treated patients.

In the United Kingdom Prospective Diabetes Study (UKPDS), researchers followed nearly 4,000 people with type 2 diabetes for 10 years. The study monitored how tight control of blood glucose (HbA1c of 7% or less) and blood pressure (less than 144 over less than 82) could protect a person from the long-term complications of diabetes.

This study found dramatically lower rates of kidney, eye, and nervous system complications in patients with tight control of blood glucose. In addition, there was a significant drop in all diabetes-related deaths, including lower risks of heart attack and stroke. Tight control of blood pressure was also found to lower the risks of heart disease and stroke.

The results of the DCCT and the UKPDS dramatically demonstrate that good blood glucose and blood pressure control, many of the complications of diabetes can be prevented.


Emergency complications include diabetic hyperglycemic hyperosmolar coma.

Long-term complications include:

Calling your health care provider

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

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

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

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

Maintaining an ideal body weight and an active lifestyle may prevent the onset of type 2 diabetes. Currently there is no way to prevent type 1 diabetes.

Johns Hopkins patient information

Last revised: December 7, 2012
by Sharon M. Smith, M.D.

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