Not Found

Find information on medical topics, symptoms, drugs, procedures, news and more, written in everyday language.

* This is the Consumer Version. *

Diabetes Mellitus (DM)

By Preeti Kishore, MD, Albert Einstein College of Medicine

1 iOS Android

Diabetes mellitus is a disorder in which blood sugar (glucose) levels are abnormally high because the body does not produce enough insulin to meet its needs.

  • Urination and thirst are increased, and people lose weight when they are not trying to.

  • Diabetes damages the nerves and causes problems with sensation.

  • Diabetes damages blood vessels and increases the risk of heart attack, stroke, kidney failure, and vision loss.

  • Doctors diagnose diabetes by measuring blood sugar levels.

  • People with diabetes need to follow a diet that is low in carbohydrates and fat, exercise, and usually take drugs to lower blood sugar levels.

Diabetes mellitus is a disorder in which the amount sugar in the blood is elevated. Doctors often use the full name diabetes mellitus, rather than diabetes alone, to distinguish this disorder from diabetes insipidus. Diabetes insipidus is a relatively rare disorder that does not affect blood glucose levels but, just like diabetes mellitus, also causes increased urination.

Blood sugar

There are many types of sugar. Some sugars are simple, and others are more complex. Table sugar (sucrose) is made of two simpler sugars called glucose and fructose. Milk sugar (lactose) is made of glucose and a simple sugar called galactose. The carbohydrates in bread, pasta, rice, and similar foods are long chains of different simple sugar molecules. Sucrose, lactose, carbohydrates, and other complex sugars must be broken down into their component simple sugars by enzymes in the digestive tract before the body can absorb them.

Once the body absorbs simple sugars, it usually converts them all into glucose, which is the main source of fuel for the body. Glucose is the sugar that is transported through the bloodstream and taken up by cells. Blood "sugar" really means blood glucose.

Did You Know...

  • Blood "sugar" really means blood glucose.


Insulin, a hormone released from the pancreas, controls the amount of glucose in the blood. Glucose in the bloodstream stimulates the pancreas to produce insulin. Insulin helps glucose to move from the blood into the cells. Once inside the cells, glucose is converted to energy, which is used immediately, or the glucose is stored as fat or glycogen until it is needed.

The levels of glucose in the blood vary normally throughout the day. They rise after a meal and return to premeal levels within about 2 hours after eating. Once the levels of glucose in the blood return to premeal levels, insulin production decreases. The variation in blood glucose levels is usually within a narrow range, about 70 to 110 milligrams per deciliter (mg/dL) of blood in healthy people. If people eat a large amount of carbohydrates, the levels may increase more. People older than 65 years tend to have slightly higher levels, especially after eating.

If the body does not produce enough insulin to move the glucose into the cells, or if the cells stop responding normally to insulin, the resulting high levels of glucose in the blood and the inadequate amount of glucose in the cells together produce the symptoms and complications of diabetes.

Types of Diabetes


Prediabetes is a condition in which blood glucose levels are too high to be considered normal but not high enough to be labeled diabetes. People have prediabetes if their fasting blood glucose level is between 101 mg/dL and 126 mg/dL or if their blood glucose level 2 hours after a glucose tolerance test is between 140 mg/dL and 200 mg/dL. Identifying people with prediabetes is important because the condition carries a higher risk of future diabetes as well as heart disease. Decreasing body weight by 5 to 10% through diet and exercise can significantly reduce the risk of developing future diabetes.

Type 1 diabetes

In type 1 diabetes (formerly called insulin-dependent diabetes or juvenile-onset diabetes), the body's immune system attacks the insulin-producing cells of the pancreas, and more than 90% of them are permanently destroyed. The pancreas, therefore, produces little or no insulin. Only about 10% of all people with diabetes have type 1 disease. Most people who have type 1 diabetes develop the disease before age 30, although it can develop later in life.

Scientists believe that an environmental factor—possibly a viral infection or a nutritional factor during childhood or early adulthood—causes the immune system to destroy the insulin-producing cells of the pancreas. A genetic predisposition may make some people more susceptible to the environmental factor.

Type 2 diabetes

In type 2 diabetes (formerly called non–insulin-dependent diabetes or adult-onset diabetes), the pancreas continues to produce insulin, sometimes even at higher-than-normal levels. However, the body develops resistance to the effects of insulin, so there is not enough insulinto meet the body’s needs.

Type 2 diabetes was once rare in children and adolescents but has recently become more common. However, it usually begins in people older than 30 and becomes progressively more common with age. About 27% of people older than 65 have type 2 diabetes. People of certain racial and ethnic backgrounds are at increased risk of developing type 2 diabetes: blacks, Asian Americans, American Indians, and Hispanics who live in the United States have a twofold to threefold increased risk as compared with whites. Type 2 diabetes also tends to run in families.

Obesity is the chief risk factor for developing type 2 diabetes, and 80 to 90% of people with this disorder are overweight or obese. Because obesity causes insulin resistance, obese people need very large amounts of insulin to maintain normal blood glucose levels.

Certain disorders and drugs can affect the way the body uses insulinand can lead to type 2 diabetes. High levels of corticosteroids (due to Cushing disease or taking corticosteroid drugs) and pregnancy (gestational diabetes) are the most common causes of impaired insulin use. Diabetes also may occur in people with excess production of growth hormone (acromegaly) and in people with certain hormone-secreting tumors. Severe or recurring pancreatitis and other disorders that directly damage the pancreas can lead to diabetes.

Symptoms of Diabetes

The two types of diabetes have very similar symptoms.

The first symptoms of diabetes are related to the direct effects of high blood glucose levels and include

  • Increased thirst

  • Increased urination

  • Increased hunger

When the blood glucose level rises above 160 to 180 mg/dL, glucose spills into the urine. When the level of glucose in the urine rises even higher, the kidneys excrete additional water to dilute the large amount of glucose. Because the kidneys produce excessive urine, people with diabetes urinate large volumes frequently (polyuria). The excessive urination creates abnormal thirst (polydipsia). Because excessive calories are lost in the urine, people may lose weight. To compensate, people often feel excessively hungry.

Other symptoms of diabetes include

  • Blurred vision

  • Drowsiness

  • Nausea

  • Decreased endurance during exercise

Type 1 diabetes

In people with type 1 diabetes, the symptoms often begin abruptly and dramatically. A serious condition called diabetic ketoacidosis, a serious complication in which the body produces excess acid, may quickly develop. In addition to the usual diabetic symptoms of excessive thirst and urination, the initial symptoms of diabetic ketoacidosis also include nausea, vomiting, fatigue, and—particularly in children—abdominal pain. Breathing tends to become deep and rapid as the body attempts to correct the blood’s acidity (see Acidosis), and the breath smells fruity and like nail polish remover. Without treatment, diabetic ketoacidosis can progress to coma and death, sometimes very quickly.

After type 1 diabetes has begun, some people have a long but temporary phase of near-normal glucose levels (honeymoon phase) due to partial recovery of insulinsecretion.

Type 2 diabetes

People with type 2 diabetes may not have any symptoms for years or decades before they are diagnosed. Symptoms may be subtle. Increased urination and thirst are mild at first and gradually worsen over weeks or months. Eventually, people feel extremely fatigued, are likely to develop blurred vision, and may become dehydrated.

Sometimes during the early stages of diabetes, the blood glucose level is abnormally low at times, a condition called hypoglycemia.

Because people with type 2 diabetes produce some insulin, ketoacidosis does not usually develop even when type 2 diabetes is untreated for a long time. However, the blood glucose levels can become extremely high (often exceeding 1,000 mg/dL). Such high levels often happen as the result of some superimposed stress, such as an infection or drug use. When the blood glucose levels get very high, people may develop severe dehydration, which may lead to mental confusion, drowsiness, and seizures, a condition called nonketotic hyperglycemic-hyperosmolar syndrome. Currently, many people with type 2 diabetes are diagnosed by routine blood glucose testing before they develop such severely high blood glucose levels.

Complications of diabetes

Diabetes damages blood vessels, causing them to narrow and therefore restricting blood flow. Because blood vessels throughout the body are affected, people may have many complications of diabetes. Many organs can be affected, particularly the following:

Diagnosis of Diabetes

  • Measuring the level of glucose in the blood

The diagnosis of diabetes is made when people have abnormally high levels of glucose in the blood. Doctors do screening tests on people who are at risk for diabetes but have no symptoms.

Did You Know...

  • Many people have type 2 diabetes and are not aware of it.

Blood glucose measurement

Doctors check blood glucose levels in people who have symptoms of diabetes such as increased thirst, urination, or hunger. Additionally, doctors may check blood glucose levels in people who have disorders that can be complications of diabetes, such as frequent infections, foot ulcers, and yeast infections.

To measure blood glucose levels, a blood sample is usually taken after people have fasted overnight. However, it is possible to take blood samples after people have eaten. Some elevation of blood glucose levels after eating is normal, but even after a meal the levels should not be very high. Fasting blood glucose levels should never be higher than 126 mg/dL. Even after eating, blood glucose levels should not be higher than 200 mg/dL.

Hemoglobin A 1c

Doctors can also measure the level of a protein, hemoglobin A1C (also called glycosylated or glycolated hemoglobin), in the blood. Hemoglobin is the red, oxygen-carrying substance in red blood cells. When blood is exposed to high blood glucose levels over a period of time, glucose attaches to the hemoglobin and forms glycosylated hemoglobin. The hemoglobin A1C level (reported as the percentage of hemoglobin that is A1C) reflects long-term trends in blood glucose levels rather than rapid changes.

Measurements of hemoglobin A1C can be used to diagnose diabetes when testing is done by a certified laboratory (not by instruments used at home or in a doctor's office). People with a hemoglobin A1C level of 6.5% or more have diabetes. If the level is between 5.7 and 6.4, they have prediabetes.

Oral glucose tolerance test

Another kind of blood test, an oral glucose tolerance test, may be done in certain situations, such as screening pregnant women for gestational diabetes or testing older people who have symptoms of diabetes but normal glucose levels when fasting. However, it is not routinely used for testing for diabetes, including in pregnant women at very low risk, because the test can be very cumbersome.

In this test, people fast, have a blood sample taken to determine the fasting blood glucose level, and then drink a special solution containing a large, standard amount of glucose. More blood samples are then taken over the next 2 to 3 hours and are tested to determine whether the glucose in the blood rises to abnormally high levels.

Screening for diabetes

Blood glucose levels are often checked during a routine physical examination. Checking the levels of glucose in the blood annually is particularly important in older people, because diabetes is so common in later life. People may have diabetes, particularly type 2 diabetes, and not know it.

There are no routine tests to screen for type 1 diabetes, but it is particularly important to do screening tests in people at risk of type 2 diabetes, including those who

  • Are over 45 yr old

  • Are overweight

  • Have high blood pressure and/or a lipid disorder such as high cholesterol

  • Have a family history of diabetes

  • Have had diabetes during pregnancy or had a baby who weighed over 9 pounds at birth

  • Are of African American, Hispanic, Asian American, or American Indian ethnicity

People with these factors should be screened for diabetes at least once every three years. Diabetes risk can be estimated using online risk calculators. Doctors may measure fasting blood glucose levels and hemoglobin A1C level, or do an oral glucose tolerance test. If the test results are on the border between normal and abnormal, doctors do the screening tests more often, at least once a year.

Treatment of Diabetes

  • Diet

  • Exercise

  • Education

  • In type 1 diabetes, insulin injections

  • In type 2 diabetes, often drugs by mouth and sometimes insulin injections

Diet, exercise, and education are the cornerstones of treatment of diabetes and often the first recommendations for people with mild diabetes. People who have very high blood glucose levels and people with type 1 diabetes (no matter their blood glucose levels) also require drugs.

Because complications are less likely to develop if people with diabetes strictly control their blood glucose levels, the goal of diabetes treatment is to keep blood glucose levels within the normal range as much as possible.

Treatment of high blood pressure and high cholesterol levels, which can contribute to circulation problems, can help prevent some of the complications of diabetes as well. A low dose of aspirin taken daily is also helpful to reduce the risk of heart attacks.

It is helpful for people with diabetes to carry or wear medical identification (such as a bracelet or tag) to alert health care practitioners to the presence of diabetes. This information allows health care practitioners to start life-saving treatment quickly, especially in the case of injury or change in mental status.

Diabetic ketoacidosis and nonketotic hyperglycemic-hyperosmolar syndrome are medical emergencies because they can cause coma and death. Treatment is similar for both and centers around giving intravenous fluids and insulin.

Diabetes treatment goals

Experts recommend that people keep their blood glucose levels

  • Between 70 and 130 mg/dL fasting (before meals)

  • Less than 180 mg/dL 2 hours after meals

Hemoglobin A1c levels should be less than 7%.

Because aggressive treatment to reach these goals increases the risk that blood glucose might go too low (hypoglycemia), these goals are adjusted for some people in whom hypoglycemia is not desirable, such as older people.

Some other goals are keeping systolic blood pressure less than 140 mm Hg and diastolic blood pressure less than 80 mm Hg. The level of low-density lipoprotein (LDL) cholesterol (the "bad" cholesterol) in the blood should be kept below 100 mg/dL.

General treatment of diabetes

People with diabetes benefit greatly from learning about the disorder, understanding how diet and exercise affect their blood glucose levels, and knowing how to avoid complications. A nurse trained in diabetes education can provide information about managing diet, exercising, monitoring blood glucose levels, and taking drugs.

People with diabetes should stop smoking and consume only moderate amounts of alcohol (up to one drink per day for women and two for men).

Diet for people with diabetes

Diet management is very important in people with both types of diabetes mellitus. Doctors recommend a healthy, balanced diet and efforts to maintain a healthy weight. People with diabetes can benefit from meeting with a dietitian or a diabetes educator to develop an optimal eating plan. Such a plan includes avoiding simple sugars, increasing dietary fiber, limiting portions of carbohydrate-rich and fatty foods (especially saturated fats), and avoiding long periods between meals to prevent hypoglycemia, particularly when the person is taking insulin. The American Diabetes Association has many helpful tips on diet, including recipes. Even when people follow the proper diet, drugs may often be needed to help control the level of cholesterol in the blood.

People with type 1 diabetes who are able to maintain a healthy weight may be able to avoid the need for large doses of insulin. People with type 2 diabetes may be able to avoid the need for all drugs by achieving and maintaining a healthy weight. Some people who have been unsuccessful in losing weight through diet and exercise may take drugs to help them lose weight or may even undergo stomach reduction (bariatric) surgery.

Exercise for people with diabetes

Exercise, in appropriate amounts, can also help people control their weight and maintain blood glucose levels within the normal range. Because blood glucose levels go down during exercise, people must be alert for symptoms of hypoglycemia. Some people need to eat a small snack during prolonged exercise, decrease their insulin dose, or both. People with diabetes should stop smoking and consume only moderate amounts of alcohol (up to one drink per day for women and two for men).

Drug treatment of diabetes

There are many drugs used to treat diabetes. People with type 1 diabetes require insulin injections to lower blood glucose levels. Most people with type 2 diabetes require drugs by mouth to lower blood glucose levels but some also require insulin.

Monitoring diabetes treatment

Monitoring blood glucose levels is an essential part of diabetes care. People with diabetes must adjust their diet, exercise, and take drugs to control blood glucose levels. Monitoring blood glucose levels provides the information needed to make those adjustments. Waiting until symptoms of low or high blood glucose levels develop is a recipe for disaster.

Many things cause blood glucose levels to change:

  • Diet

  • Exercise

  • Stress

  • Illness

  • Drugs

  • Time of day

The blood glucose levels may jump after people eat foods they did not realize were high in carbohydrates. Emotional stress, an infection, and many drugs tend to increase blood glucose levels. Blood glucose levels increase in many people in the early morning hours because of the normal release of hormones (growth hormone and corticosteroids), a reaction called the dawn phenomenon. And blood glucose may shoot too high if the body releases certain hormones in response to low blood glucose levels (Somogyi effect). Exercise may cause the levels of glucose in the blood to fall low, requiring that additional carbohydrates be consumed.

Monitoring blood glucose levels

Blood glucose levels can be measured easily at home or anywhere. Most blood glucose monitoring devices (glucose meters) use a drop of blood obtained by pricking the tip of the finger with a small lancet. The lancet holds a tiny needle that can be jabbed into the finger or placed in a spring-loaded device that easily and quickly pierces the skin. Most people find that the pricking causes only minimal discomfort. Then, a drop of blood is placed on a reagent strip. In response to glucose, the reagent strip undergoes some chemical changes.

A machine reads the changes in the test strip and reports the result on a digital display. Most of these machines time the reaction and read the result automatically. Some devices allow the blood sample to be obtained from other sites, such as the palm, forearm, upper arm, thigh, or calf. The machines are smaller than a deck of cards.

Continuous glucose monitoring (CGM) systems use a small glucose sensor placed under the skin. The sensor measures blood glucose levels every few minutes and displays the results on the screen of a small belt monitor worn like a cell phone. It also records results for the doctor to review. Alarms on the CGM system can be set to sound when blood glucose levels drop too low or climb too high, so the device can help people quickly identify worrisome changes in blood glucose. Disadvantages of this device are that it must be calibrated several times a day with the results from a fingerstick blood glucose meter, it may irritate the skin, and it is somewhat large. Additionally, because the results are not reliable enough to guide treatment, a fingerstick glucose measurement must still be done before the person takes insulin.

CGM systems have not been shown to be better than fingerstick glucose meters used alone, Moreover, since fingerstick glucose measurements are still required, this device is not useful for most people with diabetes. However, CGM systems are helpful in certain circumstances, such as in people with type 1 diabetes who have frequent, rapid changes in blood glucose (particularly when the glucose levels sometimes go very low), which are difficult to identify with fingerstick testing.

Most people with diabetes should keep a record of their blood glucose levels and report them to their doctor or nurse for advice in adjusting the dose of insulinor the oral antihyperglycemic drug. Many people can learn to adjust the insulin dose on their own as necessary.

Although urine can also be tested for the presence of glucose, checking urine is not a good way to monitor treatment or adjust therapy. Urine testing can be misleading because the amount of glucose in the urine may not reflect the current level of glucose in the blood. Blood glucose levels can get very low or reasonably high without any change in the glucose levels in the urine.

Hemoglobin A 1C

Doctors can monitor treatment using a blood test called hemoglobin A1C. When the blood glucose levels are high, changes occur in hemoglobin, the protein that carries oxygen in the blood. These changes are in direct proportion to the blood glucose levels over an extended period. The higher the hemoglobin A1C level, the higher the person's glucose levels have been. Thus, unlike the blood glucose measurement, which reveals the level at a particular moment, the hemoglobin A1Cmeasurement demonstrates whether the blood glucose levels have been controlled over the previous few months.

People with diabetes aim for a hemoglobin A1C level of less than 7%. Achieving this level is difficult, but the lower the hemoglobin A1C level, the less likely people are to have complications. Levels above 9% show poor control, and levels above 12% show very poor control. Most doctors who specialize in diabetes care recommend that hemoglobin A1C be measured every 3 to 6 months. Fructosamine, an amino acid that has bonded with glucose, is also useful for measuring blood glucose control over a period of a few weeks and is generally used when hemoglobin A1C results are not reliable, such as in people who have abnormal forms of hemoglobin.

Experimental diabetes treatments

Experimental treatments are also showing promise for the treatment of type 1 diabetes. In one such treatment, insulin-producing cells are transplanted into body organs. This procedure is not yet routinely done, however, because immunosuppressant drugs must be given to prevent the body from rejecting the transplanted cells. Newer techniques may make suppression of the immune system unnecessary.

More Information

Resources In This Article

Drugs Mentioned In This Article

  • Generic Name
    Select Brand Names
  • No US brand name

* This is the Consumer Version. *