What Is Diabetes Mellitus?

<p>PrathanChorruangsak / Getty Images</p>

PrathanChorruangsak / Getty Images

Medically reviewed by Anju Goel, MD, MPH

Diabetes mellitus—more commonly known as diabetes—is a chronic disease that occurs when you have higher than normal levels of blood glucose (or, blood sugar). Glucose is the body’s main source of energy. Too much glucose can lead to symptoms such as fatigue, feeling thirsty, and blurry vision.

Research estimates that 11% of the U.S. population has some form of diabetes. Fortunately, there are several treatments that can help you manage diabetes, such as lifestyle changes and medications. Learning more about diabetes and understanding how to manage your condition can help prevent long-term complications and improve your quality of life.

Types of Diabetes

There are several different types of diabetes. While the symptoms, diagnostic process, and treatment options have some overlap, each type of diabetes is specific. These types include:

  • Type 1 diabetes (T1D): About 5% to 10% of people with diabetes have this form. Historically, people sometimes called type 1 diabetes “juvenile diabetes” or “insulin-dependent diabetes.” This is because type 1 diabetes often starts during childhood and early adolescence—though anyone can develop T1D at any age.

  • Type 2 diabetes (T2D): About 90% to 95% of people with diabetes have what is called type 2 diabetes. Oftentimes, this type develops in adulthood, but some children can also have T2D.

  • Type 3c diabetes: Roughly 4% to 5% of people with diabetes this type. Researchers believe that some sort of physical damage to the pancreas can lead to type 3c diabetes. It's worth noting that this type is sometimes misdiagnosed as type 2 diabetes.

  • Gestational diabetes: Due to physical and hormonal changes during pregnancy, some people develop diabetes when they're expecting. This type of diabetes usually goes away after the baby is born. However, people who have had gestational diabetes have a higher risk of eventually developing type 2 diabetes in the future.


Generally, there is overlap between the symptoms of the different types of diabetes. However, each type can present some unique symptoms that you should know. Here's how to recognize the differences.

Type 1 Diabetes Symptoms

Symptoms of T1D often develop quickly, in a matter of just a few weeks. It's also common to experience more severe symptoms if you have this type. Some hallmark characteristics of T1D include:

People with type 1 diabetes may also eventually notice symptoms of a diabetes complication called diabetic ketoacidosis, or DKA. This complication can cause vomiting, stomach pain, rapid breathing, and fruity-smelling breath.

Type 2 Diabetes Symptoms

With T2D, it can be common to not experience symptoms at first. When symptoms do gradually begin, they may be a result of elevated blood sugar levels or from damage to the organs that diabetes can cause. If you suspect you may have type 2 diabetes, here are some symptoms to keep in mind:

  • Extreme fatigue

  • Repeated infections or sores and cuts that heal slowly

  • Dry mouth

  • Feeling thirsty

  • Urinating frequently

  • Tingling, numbness, or pain in the hands and feet

  • Dark patches on the skin

  • Blurry vision

  • Irritability or other mood changes

Type 3c Diabetes Symptoms

Most people with type 3c diabetes also experience some symptoms of type 1 and type 2 diabetes. But, those with type 3c diabetes can also have symptoms that appear as a result of damage to the pancreas. These include:

  • Fatty stools (poops)

  • Stomach pain

  • Diarrhea

Gestational Diabetes Symptoms

Gestational diabetes usually doesn’t cause any symptoms. If you do develop this condition while pregnant, you may however notice symptoms such as being thirstier than normal or needing to urinate more frequently. 


Your pancreas makes a hormone called insulin. This hormone plays an important role in signaling cells to allow glucose from your blood to enter the cells in your muscles, fat, and liver. Your muscles, fat, and liver can then use glucose as energy for your body. You get glucose from the food you eat. After eating a meal, your blood sugar naturally rises. When this happens, your pancreas creates insulin and releases it into your blood to lower your blood sugar and keep it in a normal range.

When something interferes with your pancreas' ability to produce insulin, your blood sugar levels can stay elevated, increasing your risk of having too much glucose in your blood. Excess blood sugar can lead to the onset of diabetes symptoms. All types of diabetes occur as a result of a problem with your pancreas. What exactly leads to issues with your pancreas and your body's ability to produce insulin depends on the type of diabetes you have.

What Causes Type 1 Diabetes?

Scientists believe that type 1 diabetes occurs because of an abnormal autoimmune response, which causes your immune system to attack your pancreas by mistake. This immune system response specifically destroys healthy cells in the pancreas that are responsible for making insulin. Once these cells become damaged, your pancreas can't process insulin normally which can increase your risk of having high blood sugar levels and developing diabetes symptoms.

What Causes Type 2 Diabetes?

With type 2 diabetes, the cells in your body stop responding normally to insulin. As a result, they become what's called "insulin resistant." Your pancreas may initially make more insulin to try to help keep your blood sugar levels low. But eventually, your pancreas isn't able to make the insulin your body needs and the amount of glucose in your blood rises.

It's not completely clear what can cause insulin resistance. However, researchers believe that having a family history of diabetes, carrying higher amounts of adipose tissue (or, body fat around your waist), and living a sedentary lifestyle can increase your likelihood of becoming insulin resistant. When this happens, your body can't use glucose normally—which leads to elevated levels of blood sugar and boosts your risk of developing T2D symptoms.

What Causes Type 3c Diabetes?

Type 3c diabetes occurs as a result of broader damage to your pancreas. Your pancreas can become damaged for several reasons including chronic pancreatitis, cystic fibrosis, and pancreatic cancer. These conditions can lower your pancreas' ability to function normally and cause problems with producing insulin.


If you suspect you have symptoms of diabetes or have a family history of the condition, it's good practice to see your healthcare provider for proper testing. Your provider will ask you about your personal and family medical history, learn about your symptoms and lifestyle habits, and perform a physical exam to assess whether they should order additional tests.

The two most common diagnostic tests for diabetes include:

  • Fasting glucose test: Measures the glucose in your blood to see if it is elevated after at least 8 hours without food. Over 126 milligrams of glucose per deciliter of blood (mg/dL) may indicate that you have diabetes. It's worth noting that 100 to 125 mg/dL is a sign of having prediabetes.

  • Hemoglobin A1C test: Estimates how elevated your blood glucose has been over the last three months. A normal A1C level is under 5.7%. Receiving a result of 5.7% to 6.4% means that you have prediabetes—which occurs when you have higher than average blood sugar, but not high enough where you have diabetes. An A1C level of 6.5% or more can result in a diabetes diagnosis.

Your healthcare provider may also use the following tests:

  • Random plasma glucose test: While not as helpful or reliable of a test for a diabetes diagnosis, your healthcare provider may use this test if you haven't fasted.

  • Glucose challenge test: A test that providers more commonly use to check for gestational diabetes. This test involves measuring the amount of glucose in your blood after you drink something very sweet.

If your healthcare provider suspects you have T1D, they may order additional testing, such as a blood test that checks if your body is producing antibodies against the cells in your pancreas. These antibodies can help diagnose T1D, but are not found in your body if you have T2D.


If you receive a diagnosis for a type of diabetes, your healthcare provider can help you understand your treatment options and support you as you learn to manage your condition. There is no cure for diabetes, but the goal of treatment is to keep your blood sugar within a normal range.

Making small, healthy changes to your diet and increasing your movement or physical activity can have positive effects on lowering your insulin resistance. In fact, some people with T2D specifically can manage their condition with these lifestyle changes without the need to take medications.

Your healthcare provider will often discuss a comprehensive treatment plan which includes a combination of both lifestyle changes and medical treatments, such as non-insulin medications and insulin treatments.

Non-Insulin Medications

If lifestyle changes aren't giving you the results you're aiming for, medication can help you manage your diabetes. Non-insulin medications are a common treatment for people with T2D. There are currently several medications on the market to help you keep your blood sugar levels in a normal range. The most common drug healthcare providers prescribe first is called Glucophage (metformin)—mostly because of its low cost, minimal side effects, and ability to promote weight loss.

If treatment with Glucophage and lifestyle changes aren’t enough, The American Academy of Family Physicians recommends adding one of the following classes of oral medications to your treatment plan if you have T2D. Examples of these medications include:

  • Diabeta (glyburide)

  • Avandia (rosiglitazone)

  • Invokana (canagliflozin)

  • Januvia (sitagliptin)

However, other options are available, including some injectable medications such as Ozempic or Wegovy (semaglutide). If you are interested in trying injectable treatments, ask your healthcare provider if this is a good option for you.

Insulin Treatments

Insulin treatment is the standard treatment option for people with T1D. You can receive insulin treatments via a needle and syringe, an insulin pen, or a pump. It's worth noting that insulin treatments are not available in the form of a pill. Eventually, many people with type 2 diabetes may also need some type of insulin to manage their condition, especially if their diabetes progresses.

Different types of insulin are available. Your healthcare provider can help you figure out what type of insulin treatments you need and how often you should take them. If you are on insulin treatment, your healthcare provider will recommend doing regular check-ins to ensure that your blood sugar levels are staying close to your target goal.

How to Prevent Diabetes

There is no known way to prevent type 1 diabetes—mostly because researchers don't know what triggers type 1 diabetes. However, healthcare providers recommend incorporating dietary changes and increasing your physical activity to prevent type 2 diabetes. This is especially important if you have a family history of the condition, carry excess adipose tissue around the waist, or have prediabetes.

Any type of physical exercise that you can do regularly can help you reduce your risk. This may include options such as strength training, aerobic activity (e.g., swimming), walking, sports, or even completing household chores. The most important thing is to find ways to move your body more frequently and in ways that you enjoy.

Dietary changes are also important to prevent the onset of T2D symptoms. Some recommendations from the American Diabetes Association include:

  • Eating more whole grains and high-fiber foods

  • Reducing your intake of foods high in carbohydrates and increasing your protein intake

  • Avoiding sugar-sweetened beverages and foods high in sugar

It's important to note that weight isn’t the only indicator of your overall health. However, for some people, losing a bit of weight (if needed) can help their body become less resistant to insulin. One study found that for every kilogram (about 2.2 lbs) that people lost, they reduced their risk of diabetes by about 16%.


Diabetes can lead to several different complications. That's why it's essential to manage your condition and work with your healthcare provider to find the treatment options that are right for you. Some of these complications include:

  • Diabetic ketoacidosis (DKA): Diabetic ketoacidosis is a potentially life-threatening complication that is more common in type 1 diabetes than in type 2 diabetes. The condition can happen when your body doesn't have enough insulin and has to use fat for energy instead. This causes ketones (or, chemicals that your liver produces when it breaks down fat) to develop and build up in your body. The production of ketones may happen if you become sick or miss an insulin shot. Unfortunately, if your condition isn't well-managed, DKA can sometimes lead to diabetic coma or death.

  • Hypoglycemia: Living with diabetes can also cause you to develop hypoglycemia—a condition that occurs when you have very low blood sugar. It may sound counterintuitive to diabetes, but this condition may occur if you took too much insulin or drank an excessive amount of alcohol. If this condition becomes severe, you might develop serious symptoms such as a seizure.

  • Organ damage: In the long-term, elevated blood sugar from any type of diabetes damages multiple organ systems, especially if you aren't managing your condition well or following your treatment plan. As a result, diabetes can cause damage to your kidneys, eyes, nerves, blood vessels, and heart—while also increasing your risk of having a heart attack or stroke.

Living With Diabetes

Getting a diabetes diagnosis can feel discouraging and difficult. This condition often requires a lot of management and lifestyle changes. You’ll want to be proactive about your choices to prevent short-term and long-term complications. It can seem overwhelming when you are first diagnosed—and that's OK. Your healthcare team can help you understand diabetes and support you in managing your condition.

Living a full life with diabetes is possible. The following tips may help as you navigate your diagnosis:

  • Follow your healthcare provider’s instructions on medications and blood sugar monitoring

  • Check your feet regularly for signs of damage or infection

  • Get regular eye exams to check for eye complications

  • Move your body for 150 minutes or more per week, if possible

  • Make small, but important changes to your diet, such as eating fewer foods high in sugar and more foods high in protein

  • Work with your healthcare provider to manage any underlying health conditions (e.g., high blood pressure) that may be increasing your risk of diabetes-related complications

  • Talk to your loved ones, join a support group, or meet with a mental health professional to learn how to navigate your condition, receive support, and take care of your emotional well-being

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