Diabetes mellitus is a condition that results when the pancreas produces little or no insulin * , or when the cells of the body cannot use the insulin produced effectively. When insulin is absent or ineffective, the cells of the body cannot absorb glucose (sugar) from blood to provide the body with energy.

Melinda's Story

Melinda has just turned 12 and feels hungry all the time. Her stomach growls in class and her after-school snack no longer keeps her from feeling hungry until dinner. In addition, no matter how many trips she makes to the school water fountain to drink water, she is always thirsty. Even worse, she needs to go to the bathroom a lot. One of her teachers, after signing Melinda's seventh bathroom pass for the day, suggests that Melinda ask her parents to take her to the doctor. She thinks Melinda might have diabetes. It turns out the teacher was right.

The pancreas is one of the most important organs in the body. It has several functions as part of the endocrine (hormone-producing) system and the digestive system, including the production of insulin.

The pancreas is one of the most important organs in the body. It has several functions as part of the endocrine (hormone-producing) system and the digestive system, including the production of insulin.
Illustration by Frank Forney. © 2016 Cengage Learning®.

What Is Diabetes?

The term diabetes refers a condition in which the body does not properly process food to be used as energy. When people eat, food is turned into glucose (sugar) that the body uses for energy. The pancreas is an organ near the stomach that makes a hormone called insulin that helps get glucose into the body's cells. Diabetes occurs when the pancreas fails to produce sufficient insulin or any insulin at all. It can also be caused by the failure of the body's cells to properly use produced insulin.

The pancreas contains groups of cells that function like tiny factories, producing different hormones * at exactly the right time and in the right amount. These groups, or “islands,” of cells are called islet (EYE-let) cells. One type of islet cells, the beta (BAY-ta) cells, is responsible for producing the hormone insulin. The human body needs insulin to function, because insulin helps the body turn food into energy.

Greek Origin for Words: A Diabetes Dictionary

Many English words come from Greek, including many of the words used to describe diabetes, as well as the word diabetes itself:

Diabetes: Greek for “passing through,” because Greek doctors noticed how much liquid people with diabetes drank and how often they needed to urinate

Emia: Greek for “blood”

Glyk: Greek for “sugar”

Hyper: Greek for “above,” and thus “too much”

Hypo: Greek for “below,” and thus “too little”

Insulin: Greek for “island,” which refers to the groups of islet cells in the pancreas responsible for making insulin and other hormones that look like tiny islands when viewed with a microscope

Mellitus: Greek for “honey-like” or “sweet,” because it was noticed that the urine of people with diabetes tasted sweet because of its high sugar content

Insulin works like a key; it “unlocks” the door to cells. When insulin production stops or slows down in the beta cell factory, the body's cells cannot take in the glucose they need for energy. People with diabetes get glucose from their food, but no matter how much they eat, if the insulin “key” is absent or not working properly, their glucose fuel is “locked out” of the body's cells.

There are two principal types of diabetes. Melinda has type 1 diabetes mellitus. Type 1 diabetes is usually diagnosed before a person turns 19 years old and, at times, is referred to as juvenile diabetes. The pancreas of a person with type 1 diabetes makes little or no insulin on its own, so that person depends on injections of insulin to stay healthy. That person also needs to make lifestyle changes with regard to when and what he or she eats.

Type 2 diabetes mellitus occurs when the cells of the body do not respond to insulin the way they should. This type of diabetes typically affects people who are older than 40 years. Extra body fat contributes to this condition and, in many cases, weight loss can help remedy it. A person with type 2 diabetes is not necessarily dependent on insulin injections the way a person with type 1 diabetes is. People with type 2 diabetes can be treated with pills in addition to a change in diet.

Uncontrolled diabetes can cause serious health complications. People with diabetes can develop heart disease, blindness, or kidney failure, as well as complications that require the amputation of lower limbs. Diabetes can even cause death. According to the Centers for Disease Control and Prevention, diabetes is the seventh-leading cause of death in the United States.

Is Diabetes Contagious?

Diabetes is not contagious like a cold or chickenpox. People cannot catch it from one another. Instead, scientists believe that diabetes caused by a combination of genetic and environmental factors. Scientists suspect that people with type 1 diabetes are born with certain genes for the illness, just as they are born with genes that determine eye color. Genes are inherited from biological parents. Children who have close family members, such as a father, mother, or sibling, with type 1 diabetes are more likely to develop the disease than children who do not. In fact, if a one child in a family has type 1 diabetes, his or her siblings have a 1 in 10 chance of developing type 1 diabetes before age 50.

Scientists also believe that the environment also plays a role in who develops type 1 diabetes. A trigger such as a virus * can cause a person's immune system to attack and destroy the pancreas's beta cells, which destroys their ability to make insulin. An environmental trigger may work in conjunction with genes to determine who gets type 1 diabetes. This may explain why some people develop type 1 diabetes while others do not.

For type 2 diabetes, scientists believe that genes and obesity *

The hormone insulin is the key that unlocks the cell's glucose channel, allowing glucose (blood sugar) to enter the cell and refuel it. Without the insulin key, glucose is locked out of the cell and will remain in the bloodstream.

The hormone insulin is the key that unlocks the cell's glucose channel, allowing glucose (blood sugar) to enter the cell and refuel it. Without the insulin key, glucose is locked out of the cell and will remain in the bloodstream.
Illustration by Frank Forney. © 2016 Cengage Learning®.

How Common Is Diabetes?

According to the American Diabetes Association (ADA), in 2012 approximately 29.1 million Americans (9.3 percent of the U.S. population) had diabetes. Of this number, 8.1 million cases were undiagnosed. In addition, 1.4 million Americans were newly diagnosed with diabetes each year.

How Do People Know If They Have Diabetes?

People with diabetes may exhibit several symptoms, including frequent urination, excessive thirst, unexplained weight loss, and extreme hunger. People with diabetes may also experience sudden vision changes, numbness in their hands and feet, and fatigue. They may also have skin problems, such as dry skin or difficulty healing, and may experience more infections than usual.

How Do Doctors Diagnose and Treat Diabetes?

Sports Stars with Type 1 Diabetes

Some outstanding athletes were diagnosed with type 1 diabetes mellitus at an early age:

Jackie Robinson: Robinson was the baseball player who broke the color barrier in professional baseball in 1947. During his 10-year career with the Brooklyn Dodgers, Robinson was a batting champion, most valuable player (MVP), and a member of six championship teams. He was baseball's first rookie of the year. Robinson was elected to the Hall of Fame in 1962, his first year of eligibility.

Bobby Clarke: The tenacious leader of hockey's Philadelphia Flyers for 15 seasons (1969–1984), Clarke was first diagnosed with diabetes at the age of 15 years. Undeterred, he went on to win three Hart trophies as league MVP.

Jason Johnson: Johnson was an American Major League Baseball player, debuting for the Pittsburgh Pirates in 1997 and subsequently playing for 11 years with a number of teams including the Boston Red Sox, Cincinnati Reds, and a moderately successful run with the Baltimore Orioles. He was diagnosed at age 11 and became the first diabetic to use an insulin pump on the playing field.


The Greek physician Aretaeus (ar-uh-TE-us) of Cappadocia (c. 81–c. 138) described diabetes as a “melting down of the flesh and limbs into urine.” Throughout history, many people with the disease died at an early age by wasting away, although the disease was probably not as prevalent in ancient times as it is in modern times.

Treatments frequently involved dietary changes. Aretaeus recommended milks, cereals, and starches. In 1797 John Rollo recommended a meat diet high in proteins. These diets were not cures for diabetes, but they did allow people with diabetes to live longer than if they had remained on regular diets.

The first truly successful treatment for diabetes was finally made available during the 1920s, when Frederick Banting, Charles Best, and John James Macleod first isolated insulin for use through therapeutic injections.

Because people with type 2 diabetes continue to make insulin that is functioning to a certain extent, they may develop symptoms over a period of months or years without facing immediate danger. They may feel tired, worn out, or thirsty much of the time, without thinking that their symptoms could be indicative of diabetes. In many cases, type 2 diabetes is actually discovered by accident, during a routine physical exam or screening blood or urine test.


A person who has been diagnosed with type 1 diabetes needs to take several steps in order to function well. These include taking insulin, eating healthful foods, exercising and maintaining a healthy weight, and monitoring blood glucose levels. All of these measures contribute toward achieving the major goal: keeping the amount of glucose in the blood as close to normal as possible, so the person with diabetes can stay healthy and feel good.


People with type 1 diabetes need lifelong insulin therapy to keep their blood sugar levels close to normal. Insulin cannot be taken in pill form because stomach enzymes interfere with insulin's action. Therefore, insulin comes in liquid form (dissolved in water) in a bottle or preloaded pen and must be injected into the body.

Most people take insulin by using a needle or a preloaded pen to inject it into the layer of fat beneath the skin. The most common places where people inject insulin are in the arms, legs, stomach, and hips—all places where people have some fat. The injection does not hurt much because the needle is very thin. Usually a person needs to inject insulin this way two or more times a day, on a set schedule, coordinated with meals.

Some people with type 1 diabetes use an insulin pump, which is about the same size as a flip cell phone, with a small container filled with insulin. The insulin is pumped automatically into the person's body through a small tube attached to a needle inserted under the skin. The insulin is pumped in at a slow rate all the time, with an extra “boost” pumped in before meals to prepare the body for the incoming sugar.

For people with type 1 diabetes taking insulin, one factor stays constant: they must take insulin every single day to allow the body's cells to take in and use glucose properly. They cannot take a break or decide to stop taking it or they will become ill.

For people with type 2 diabetes, insulin may not be necessary. Instead, people who have type 2 diabetes are often able to manage their diabetes with dietary changes and a weight control program. In some cases, people with type 2 diabetes are given pills to help the body make more insulin or respond to insulin more normally. In some severe cases, they may need to take insulin injections.

Young man using a blood glucose meter at home. To measure sugar level, you prick your finger with a lancet to get a drop of blood. Then place the blood on a disposable “test strip” that is inserted in the meter.

Young man using a blood glucose meter at home. To measure sugar level, you prick your finger with a lancet to get a drop of blood. Then place the blood on a disposable “test strip” that is inserted in the meter. The meter reports results in milligrams of glucose per deciliter of blood, or mg/dl.

Proper nutrition is a very important part of staying healthy for everyone but especially for a person with diabetes. Because food affects how much glucose is in the blood, people with diabetes must pay careful attention to the food they eat, how much they eat, and when they eat it. In particular, because carbohydrates are the body's main source of glucose, many people with diabetes estimate the amount of carbohydrates in each meal to determine whether they are getting the correct amount of sugar. This does not mean that the eating habits of someone with diabetes are very different from other people. The food itself can be the same as that eaten by most people; but, in most cases, their meal must be eaten on some sort of schedule, must include snacks, and must limit sweets because of the large amount of sugar they contain.


Just like healthy eating, exercise is important for everyone, especially for people with diabetes. At one point in history, it was believed that people with diabetes should not exercise, but that opinion has changed. Exercise helps insulin work better to control the level of glucose in the blood. Exercise also helps keep all people with diabetes at the proper weight, and it helps maintain a healthy heart and blood vessels. In addition, exercise helps people feel good about themselves.

When diabetics exercise, they use glucose at a rate that is faster than normal, so they must pay special attention to ensure their blood glucose level does not drop too low. To ensure the proper level, they may need less insulin and more food before exercise, or snacks during and after exercise.

Diabetes: The United States and the World

According to the American Diabetes Association, diabetes remains the seventh-leading cause of death in the United States. According to the World Health Organization, about 350 million people worldwide have the illness, a number likely to more than double by 2035.

Type 2 diabetes mellitus has increasingly been reported in children and adolescents, so much so that, in some parts of the world, type 2 has become the main type of diabetes in children. The global increase in childhood obesity and physical inactivity is widely believed to play a crucial role.

More than 80 percent of deaths caused by diabetes occur in low- and middle-income countries. Healthy diet, regular physical activity, maintaining a normal body weight, and avoiding tobacco use can prevent or delay the onset of type 2 diabetes mellitus.


Living with diabetes can be overwhelming, especially in the beginning. Luckily, many people who have been diagnosed with diabetes may have an entire diabetes treatment team to help them. This team usually includes a doctor, a diabetes nurse, a dietician, a psychologist, and a social worker. Ideally, the entire team partners with the patient and the patient's family, so that they can maintain as normal a life as possible.


Both type 1 and type 2 diabetes can have negative long-term effects on a person's health. These effects tend to develop very slowly. Because a person with diabetes may not process fat properly, there can be damage to the blood vessels in the body, which increases the chances for high blood pressure, heart attack, and stroke. Diabetes can also have long-term effects on the eyes, because tiny blood vessels in the retina * become weakened. If these blood vessels burst, they can cause bleeding and scarring in the eye, or even blindness. The chance of nerve damage and of developing kidney disease is also increased in a person with diabetes. Also, foot health can become an issue for people with diabetes. Because the condition can affect circulation to the feet, small cuts or wounds can turn into serious infections without proper care. When such infections occur, they may lead to death of cells and tissue (called gangrene). When this happens, the affected foot may need to be amputated (surgically removed) to prevent further spread of infection or tissue death.

Sometimes, even with insulin, proper nutrition, and exercise, it can be difficult to control diabetes completely. Blood glucose levels can become either too high or too low in some cases, and blood levels of ketones can rise to toxic levels.


Hypoglycemia (hy-po-gly-SEE-mee-uh) occurs when the level of glucose in the blood is too low. This can happen when a person takes too much insulin, misses a meal or snack, or exercises too hard without taking special precautions. In its beginning stages, hypoglycemia can make a person weak, shaky, dizzy, and sweaty. People with diabetes learn to be aware of these warning signs and almost always take action immediately by drinking some juice or taking glucose tablets to quickly raise their blood glucose level. If left untreated, hypoglycemia can cause a person to become disoriented, sleepy, or have a hard time talking. Eventually, the person may become very confused and uncoordinated and, in extreme cases, go into a coma * . The treatment for an extreme case of hypoglycemia is to give the person sugar as soon as possible, by intravenous * injection, if necessary.


In 1889 Oskar Minkowski (1858–1931) and Joseph von Mering (1849–1908) were among early researchers to discover that removing the pancreas of dogs rendered them diabetic. Shortly thereafter, Edward Sharpey-Schafer (1850–1935) discovered the active principle in the islets of Langerhans, and he named it insulin.

Canadian surgeon Frederick Banting (1891–1941) and physician Charles Best (1899–1978), using the laboratory of John James Macleod (1876–1935) at the University of Toronto, also conducted research on dogs that led to a better understanding of the medical uses for insulin.

In 1923 Banting and Macleod were awarded the Nobel Prize in Physiology or Medicine for the discovery of insulin. Banting shared his half of the prize money with Best.


Ketoacidosis (keet-o-as-uh-DOE-sis) occurs in uncontrolled diabetes when the blood becomes too acidic as a result of high levels of ketones. Ketones are acids that form when the body uses fat for energy instead of carbohydrates. People with ketoacidosis may be nauseated or vomiting and breathing deeply. If they do not get treated, they can become dehydrated and go into a coma. Emergency treatment involves insulin and lots of intravenous fluids. Fortunately, ketoacidosis is almost always preventable in people whose diabetes has been diagnosed early and is well-managed.

Can Diabetes Be Prevented?

A major study of people at high risk for diabetes (the Diabetes Prevention Program, the findings of which were published in 2002) showed that people can delay and possibly prevent the disease by losing a small amount of weight (5 to 7 percent of total body weight) through 150 minutes of physical activity a week and healthier eating.

For people with diabetes, controlling blood sugar is the key to preventing and lessening complications from the disease. It is very important for people with diabetes to have regular physical checkups, at which doctors can monitor blood pressure and foot health, check fat levels in the blood, and look for problems with the kidneys. In addition, annual trips to the eye doctor are crucial. If an ophthalmologist * discovers problems with the blood vessels in the retina, vision problems often can be prevented or lessened with laser surgery. People with diabetes should avoid smoking and tobacco use.

Diabetes Research

Clinical trials are research projects undertaken by scientists, pharmaceutical companies, and government researchers to determine whether medications and treatment plans are safe and effective. To evaluate the effectiveness of careful self-management in reducing the long-term complications of diabetes, in 1983 the U.S. National Institute of Diabetes and Digestive and Kidney Diseases began a 10-year study, called the Diabetes Control and Complications Trial (or DCCT).

People with diabetes took part in the DCCT and followed instructions for testing their blood glucose three or four times a day, administering more frequent insulin injections or using an insulin pump, and following a specific diet. The test results showed that the people who maintained near-normal blood glucose levels had fewer longterm complications, such as problems with their heart, eyes, or kidneys. It proved that, for a person with diabetes, paying close attention to small symptoms on a daily basis has a big payoff later on.

Medic Alert Tags

People with diabetes often wear metal tags or bracelets imprinted or inscribed with important medical information. In the event of an accident or diabetic coma, the information on the tag can alert medical personnel about the patient's condition. Some companies offer medical alert tags that have an identification number unique to the individual so that a doctor who does not know the person can retrieve the patient's medical history in the event of emergency.

Diabetes research is ongoing; much of the scientific work is concerned with insulin—how to get it into the body or how to get the body to produce it on its own. Because insulin cannot be swallowed, researchers have investigated other ways to get it into the bloodstream without an injection, such as eye drops, nasal sprays, and inhalers. For example, clinical trials of inhaled and oral spray forms of insulin were being conducted in 2015. Scientists have also experimented with pancreas transplantation, as well as transplantation of the islet cells that make insulin. Until there is a cure for diabetes, people must live with it and control it by using the information and equipment available to them.

See also Genetic Diseases: Overview • Hypoglycemia • Kidney Disease • Obesity


Books and Articles

American Diabetes Association. American Diabetes Association Complete Guide to Diabetes. 5th ed. New York: Bantam, 2011.


Centers for Disease Control and Prevention. “Diabetes Home.” http://www.cdc.gov/diabetes/home/index.html (accessed March 30, 2016).

World Health Organization. “Diabetes.” http://www.who.int/mediacentre/factsheets/fs312/en/ (accessed March 30, 2016).


American Diabetes Association. 1701 N. Beauregard St., Alexandria, VA 22311. Toll-free: 800-342-2383. Website: http://www.diabetes.org (accessed March 30, 2016).

Centers for Disease Control and Prevention. 1600 Clifton Rd., Atlanta, GA 30329-4027. Toll-free: 800-232-4636. Website: http://www.cdc.gov (accessed March 30, 2016).

Children's Diabetes Foundation. 4380 S Syracuse St., Suite 430, Denver, CO 80237. Telephone: 303-863-1200. Website: http://www.childrensdiabetesfoundation.org (accessed March 30, 2016).

Juvenile Diabetes Research Foundation. 26 Broadway, New York, NY 10004. Toll-free: 800-533-2873. Website: http://www.jdrf.org (accessed March 30, 2016).

* insulin is a hormone, or chemical produced in the body, which is crucial in controlling the level of glucose (sugar) in the blood and in helping the body use glucose to produce energy.

* hormones are chemical substances produced by various glands and sent into the bloodstream to carry messages that have certain effects on other parts of the body.

* virus (VY-rus) is a tiny infectious agent that can cause infectious diseases. A virus can only reproduce within the cells it infects.

* obesity (o-BEE-suh-tee) is an excess of body fat. People are considered obese if they weigh more than 30 percent over what is healthy for their height.

* retina (REH-tuh-na) is the tissue that forms the inner surface of the back of the eyeballs; it receives the light that enters the eye and transmits it through the optic nerves to the brain to produce visual images.

* coma (KO-ma) is an unconscious state, like a very deep sleep. A person in a coma cannot be awakened, and cannot move, see, speak, or hear.

* intravenous (in-tra-VEE-nus), or IV, means within or through a vein. For example, medications, fluid, or other substances can be given through a needle or soft tube inserted through the skin's surface directly into a vein.

* ophthalmologist (off-thal-mä-l∂- jist) is a medical doctor who specializes in treating diseases of the eye.

Disclaimer:   This information is not a tool for self-diagnosis or a substitute for professional care.

(MLA 8th Edition)