What Is Diabetes Mellitus?

Diabetes mellitus, also called diabetes, is a group of conditions that affect the body's ability to control blood sugar, or glucose. It is characterized by issues making insulin, the body's ability to use it properly, or both.

Types of diabetes mellitus include

The word "diabetes" originates from AD Greek physician Aretus the Cappadocian and translates to mean "a passer through, a siphon." Aretus is responsible for labeling the condition associated with polyuria or excessive urination. People with diabetes were known to pass water like a siphon.

Although diabetes mellitus and diabetes insipidus share the same "diabetes" Latin name, they are not the same. In Latin, the term "insipidus" means tasteless.

Insulin is a hormone made by an organ called the pancreas. It influences how much sugar in your blood. Blood sugar is either used for energy or stored for later use.

Boy checking his blood sugar.

 Fatcamera / Getty Images

What Are the Types of Diabetes Mellitus?

According to the American Diabetes Association (ADA), "Classification is important for determining therapy, but some individuals cannot be clearly classified as having type 1 or type 2 diabetes at the time of diagnosis."

The American Diabetes Association classifies diabetes into the following general categories:

  • Type 1 diabetes: Due to autoimmune β-cell destruction, usually leading to absolute insulin deficiency
  • Type 2 diabetes: Due to a progressive loss of adequate β-cell insulin secretion frequently on the background of insulin resistance
  • Gestational diabetes mellitus: Diabetes diagnosed in the second or third trimester of pregnancy that was not clearly overt diabetes prior to gestation
  • Specific types of diabetes due to other causes: Monogenic diabetes syndromes, diseases of the exocrine pancreas (such as cystic fibrosis and pancreatitis), and drug- or chemical-induced diabetes (such as with glucocorticoid use, in the treatment of HIV/AIDS, or after organ transplantation)

Prediabetes is a condition that is also described as impaired glucose tolerance (IGT) or impaired fasting glucose (IFG). While not necessarily classified as a type of diabetes mellitus, it's an important part of the conversation since it is considered a precursor to type 2 diabetes.


While prediabetes is not necessarily classified as a type of diabetes, it's important to know about it because approximately 96 million American adults—more than 1 in 3—have prediabetes. Of those with prediabetes, more than 80% don’t know they have it.

Prediabetes, a condition that is also described as impaired glucose tolerance (IGT) or impaired fasting glucose (IFG), is considered a precursor of type 2 diabetes. Prediabetes does not typically cause symptoms, but without intervention, it can progress to type 2 diabetes.

If you have prediabetes, you probably make enough insulin, but the cells of your body are resistant to insulin and its effects. Insulin is the hormone that takes sugar from the blood to the cells for energy.

When your cells are resistant to insulin, glucose (sugar) remains in the blood, as opposed to being taken to the cells. This results in a slightly elevated blood glucose level, as well as decreased energy. In addition, the body may actually begin to make more insulin, which overworks the pancreas and exacerbates the situation, causing high insulin levels.

Dietary management, weight loss, and exercise are often effective for treating prediabetes—but sometimes medication is needed. The goal for people with prediabetes should be to avoid developing type 2 diabetes.

Type 1 Diabetes

Type 1 diabetes is an autoimmune disease that affects the pancreas and accounts for approximately 4.9% to 6.4% of those with diabetes. It occurs when the body’s immune system attacks the insulin-producing beta cells in the pancreas and destroys them.

People with type 1 diabetes do not make insulin and need to take insulin via injection or infusion so that they can maintain blood sugar control and utilize carbohydrates for energy. Elevated blood sugar resulting in weight loss, excessive hunger, excessive thirst, and bed-wetting in children are signs of type 1 diabetes.

To validate a diagnosis, physicians will test for antibodies, proteins that help the body protect itself from “foreign” substances such as bacteria or viruses. People with type 1 diabetes usually have antibodies that destroy the body’s insulin-making beta cells.

This disease typically affects younger people and was once called juvenile diabetes, but can occur also occur in adulthood. The rate at which the beta cells die typically occurs more rapidly in children than adults.

Sometimes children will get diagnosed with type 1 diabetes and have a honeymoon period, otherwise known as a remission, in which the pancreas may still secrete some insulin. This time can last weeks, months, or even up to year in some instances. However, over time the pancreas stops working altogether and insulin needs increase.

Type 2 Diabetes

Type 2 diabetes is a chronic disease in which the body is unable to adequately control the levels of glucose in the blood, which can lead to dangerously high blood glucose (hyperglycemia). It accounts for approximately 90.4% to 92.1% of those with diabetes.

According to the Centers for Disease Control and Prevention (CDC), type 2 diabetes develops most often in people over the age of 45, however rates are rising among children, teens, and young adults. The disease is marked by an increase in blood sugar levels and a heightened resistance to the insulin.

Type 2 diabetes is a highly prevalent condition with numerous risk factors. The risk of developing this form of diabetes increases with age, weight gain, and lack of physical activity. People who have had gestational diabetes or those with high blood pressure (hypertension), cholesterol or triglycerides (dyslipidemia) are also at increased risk.

Type 2 diabetes has a stronger genetic predisposition than type 1 diabetes, but the genetics are complex and not currently fully defined.

The CDC notes that, among adults diagnosed with diabetes, 90% are overweight. Most of the time, weight loss and lifestyle modification can improve blood glucose levels by decreasing insulin resistance. Depending on how high blood glucose levels are at diagnosis, medication may be needed. But, through diet changes and weight loss, it may be possible to reach and hold normal blood sugar levels without medication.

Gestational Diabetes

Gestational diabetes develops during pregnancy when the pancreas cannot accommodate for insulin resistance, which is common during pregnancy due to placental secretion of hormones. In the United States, about 6% to 9% of people who are pregnant develop gestational diabetes.

When the cells are resistant to insulin, sugar (glucose) accumulates in the blood. People who are diagnosed with gestational diabetes do not have diabetes before they become pregnant.

If a person has gestational diabetes for one pregnancy they may have it again for other births. This type of diabetes usually shows up in the middle of pregnancy and people are usually screened for it between 24 and 28 weeks.

The ADA advises that women who are planning a pregnancy get screened for diabetes if they have risk factors and recommends testing all pregnancy-planners for undiagnosed diabetes. Further, the ADA advises testing pregnant women before 15 weeks if they have risk factors and recommends testing for undiagnosed diabetes at the first prenatal visit, if they have not been screened preconception.  

People who are overweight before pregnancy or those with diabetes in the family tend to be more prone to gestational diabetes, but this isn't always the case. In addition, it is more common in people who are Native American, Alaskan Native, Hispanic, Asian, and Black, but is also found in those who are White.

It is important to treat gestational diabetes as soon as it is diagnosed. Keeping blood sugars within normal range will help to prevent any complications, such as having a cesarean delivery, a baby born too large, and developing obesity or type 2 diabetes later in life.

Treatment usually includes changes to diet, specifically following a carbohydrate-controlled diet. Carbohydrates are the nutrients that impact blood sugars the most. Careful blood glucose monitoring will also help people with gestational diabetes to keep their blood sugar in tight control and track glycemic patterns to improve management.

Movement or some form of exercise can help to utilize insulin by reducing insulin resistance. Sometimes, a person who cannot control their blood sugar with diet alone will need medication, such as insulin, to get their blood sugar to a healthy range.

Most cases of gestational diabetes resolve with delivery. However, the ADA recommend being tested for diabetes at 4–12 weeks postpartum to assess status. And, women with a history of gestational diabetes mellitus should have lifelong screening for the development of type 2 diabetes or prediabetes every 1–3 years.

Latent Autoimmune Diabetes in Adults (LADA)

Latent autoimmune diabetes in adults, otherwise referred to as LADA or diabetes 1.5, is very similar to type 1 diabetes with the exception that it usually occurs later in life. People with LADA have the presence of islet antibodies at diagnosis, but the progression of beta cell (β-cell) failure (when the cells of the pancreas stop making insulin) is slow.

Often people with LADA are mistakenly diagnosed with type 2 diabetes. LADA can also resemble type 1 diabetes due to beta cell dysfunction and testing will be done to distinguish between the two.

The prevalence of LADA is around 10% among incident case subjects of diabetes aged 40–75 years. Among people younger than 35 with type 2 diabetes, the frequency of LADA is higher.

At initial diagnosis, most people with LADA do not require insulin because their pancreas is still making some. However, within six years, β-cell function is severely impaired, leading to insulin dependency in most LADA patients.

Monogenic Diabetes

Monogenic diabetes is a rare form of diabetes that occurs when there are mutations or defects in one (mono) gene. According to the National Institute of Diabetes and Digestive and Kidney Disease (NIDDK), monogenic forms of diabetes account for about 1% to 4% of all cases of diabetes in the United States.

It appears in several forms and is most common in people 25 years and younger. It is characterized by a defect in beta cell function, the cells that make insulin. Therefore, the body is less able to make insulin but the cells are not necessarily resistant to it, as is the case in type 2 diabetes.

We are going to cover two forms of monogenic diabetes: Neonatal (or congenital) diabetes mellitus (NDM) and maturity-onset diabetes of the young (MODY).

Neonatal Diabetes Mellitus (NDM)

Neonatal diabetes (NDM), also known as congenital diabetes, is typically diagnosed in the first 6-to-12 months of life. It can either be transient or permanent. It occurs in approximately 1 in 90,000 to 160,000 live births and there are over 20 known genetic causes for neonatal diabetes mellitus.

Infants with NDM do not produce enough insulin, leading to an increase in blood glucose. NDM is often mistaken for type 1 diabetes, but type 1 diabetes is very rarely seen before 6 months of age.

In infants with hyperglycemia (high blood sugar) who are being treated with insulin, but still have persistent elevated blood sugars for more than one week, a neonatal diabetes diagnosis should be investigated as well as prompt genetic testing.

Signs and symptoms may include frequent urination, rapid breathing, or dehydration. Infants with NDM may also be smaller in size and have difficulty gaining weight and growing.

Sometimes treatment can be successful with oral glucose-lowering medications called sulfonylureas; in this case, early treatment may improve neurological outcomes. In addition, proper treatment can normalize growth and development.

Maturity-Onset Diabetes of the Young (MODY)

Maturity-onset diabetes of the young (MODY) accounts for about 2% of people with diabetes and is diagnosed during adolescence or early adulthood. A number of gene mutations have been known to cause MODY.

Sometimes people with MODY have no symptoms at all and may only have slightly elevated blood sugars that are recognized during routine blood work. Other types of gene mutations will cause higher blood sugar levels and require medical intervention by the form of insulin or oral diabetes medicines.

People with MODY typically have a family history of diabetes—you may see a parent, grandparent and child with it. Genetic testing is needed to diagnose MODY and other monogenic forms of diabetes. It is recommended to test for these forms of diabetes if:

  • Diabetes is diagnosed within the first 6 months of age
  • Diabetes is diagnosed in children and young adults, particularly those with a strong family history of diabetes, who do not have typical features of type 1 or type 2 diabetes, such as the presence of diabetes-related autoantibodies, obesity, and other metabolic features
  • A person has stable, mild fasting hyperglycemia, especially if obesity is not present

Diabetes Mellitus Symptoms

Although there are many forms of diabetes, most of the symptoms are the same. The pace in which they appear can be different. For example, in people with type 2 diabetes, symptoms often develop over several years and can be missed altogether or go on for a long time before being noticed. That's why it's important to know the risk factors for diabetes.

In opposition, people with type 1 diabetes can develop symptoms in just a few weeks or months and symptoms can be severe. In addition to the most common symptoms, people with type 1 diabetes, may also have stomach pain, nausea, fruity breath or a very serious acute consequence of elevated blood sugar, diabetic ketoacidosis.

The most common symptoms of elevated blood sugar include:

  • Polyuria: excessive urination, often at night
  • Polydipsia: excessive thirst or thirst that can not be quenched
  • Polyphagia: excessive hunger, often paired with weight loss
  • Weight loss
  • Numbness and tingling in the hands and feet
  • Feeling very tired or fatigued
  • Dry skin
  • Sores that heal slowly
  • Having more infections than usual

Another very rare symptom of very elevated blood sugar in people with type 2 diabetes is nonketotic hyperosmolar syndrome.


Most forms of diabetes are chronic; therefore, proper management of blood sugars will be a critical part in preventing short and long term complications. When diabetes is not managed well for extended periods of time, it can lead to a variety of micro (small) and macro (large) vascular issues.


Neuropathy is disease of the nervous system that is often characterized by numbness, tingling, and burning. The three major forms in people with diabetes are peripheral neuropathy, autonomic neuropathy, and mononeuropathy.

The most common form is peripheral neuropathy, which affects mainly the legs and feet. This can increase the risk of foot ulcers, amputations, and Charcot joints.

Autonomic neuropathy is a group of symptoms that occur when there is damage to the nerves that manage everyday bodily functions, including blood pressure, heart rate, temperature control, bladder function, digestion, and sexual function.

Mononeuropathy is damage to a single nerve, which can result in pain, impaired mobility, and/or numbness. Carpal tunnel syndrome is one of the best-known forms of mononeuropathy.

Other complications of diabetes mellitus include:

What Are the Main Causes and Risk Factors of Diabetes Mellitus?

The causes of diabetes will differ depending on the type of diabetes you have. For example, diabetes that affects the body's ability to make insulin, as in type 1 diabetes, has multiple genetic predispositions and is also related to environmental factors that are still poorly defined. People with this type of diabetes are rarely obese.

These types of diabetes are also associated with other autoimmune diseases, such as Graves' disease, Hashimoto's thyroiditis, Addison's disease, vitiligo, celiac sprue, autoimmune hepatitis, myasthenia gravis, and pernicious anemia.

Type 2 diabetes is largely a disease related to lifestyle, however, it appears that people who have family members who have been diagnosed with type 2 diabetes are at a greater risk for developing it themselves.

In addition, people of African-American, Hispanic, Pacific-Island, or Native-American descent also have a higher-than-normal rate of type 2 diabetes. Studies show more than 120 gene variants have been identified as linked to causing type 2 diabetes. However, having a genetic disposition towards type 2 is not a guarantee of diagnosis.

Lifestyle plays an important part in determining who gets type 2 diabetes. Some potential causes include poor diet, sedentary lifestyle and low activity level, aging, elevated cholesterol or lipid levels, obesity, history of metabolic syndrome (characterized by high cholesterol and triglycerides, high waist-to-hip ratio, high blood pressure), and a history of gestational diabetes.

Diabetes Mellitus Diagnosis

A diagnoses of diabetes usually involves a blood test. In most forms of diabetes, assessing hemoglobin A1C (a three month average of blood sugar), confirms diagnosis.

This type of test is used more commonly to diagnose diabetes in individuals with risk factors, but can also identify those with prediabetes who are at higher risk of developing diabetes in the future.

However, not all types of diabetes are straightforward and therefore some people may need additional blood work, genetic testing, or an oral glucose tolerance test to confirm a diagnosis.

If your medical team is using another means to diagnose type 2 diabetes, such as a fasting plasma glucose or a random blood sugar test, they will need to confirm elevated levels on two separate occasions.

Diabetes Mellitus Treatment

All treatment plans for people with diabetes should be individualized. Consideration of past medical history, blood sugar control, culture, diet preferences, and goals will be important in formulating a plan. Depending on the type of diabetes you have and your blood sugar status at diagnosis, your treatment plan will look different.

For example, a person diagnosed with prediabetes can start treatment with lifestyle changes—a small amount of weight loss, reducing intake of processed foods and simple sugars, exercise, and smoking cessation.

Whereas, someone with type 2 diabetes who has a very high hemoglobin A1C may need to start medication such as, oral glucose-lowering medication, an injectable medication such as a GLP-1 agonist, or a combination of both, in addition to lifestyle changes.

Each individual's diabetes treatment will be different, so try not to compare yourself to others.

People with type 1 diabetes or other immune-mediated types of diabetes will likely need to start insulin therapy via multiple daily injections or infusion. An endocrinologist (often referred to as a diabetes doctor) can be an important part of the treatment team, particularly for those people with type 1 diabetes.

People with prediabetes and type 2 diabetes can often receive treatment from their primary physician, but if their treatment plan appears to be too complicated, they can also benefit from seeing an endocrinologist.

In addition to lifestyle modifications (weight loss, healthy eating plan, exercise, smoking cessation), people with diabetes may need to see other specialists.

For example, people newly diagnosed with type 2 diabetes should receive a dilated eye exam at the time of their diagnosis. Those diagnosed with type 1 diabetes should receive this exam within five years of diagnosis. Following an initial examination, all people with diabetes should have their eyes checked every year thereafter.

If you are experiencing issues with your lower extremities, such as numbness and tingling in your feet, you may need to see a podiatrist or a vascular doctor.

If you have elevated cholesterol, type 2 diabetes, hypertension, and a family history of diabetes, you may need to see a cardiologist.


Diabetes is a disease that needs to be managed daily. Blood sugar testing, carbohydrate counting, exercise, adherence to medication, and specialist appointments are just some of the things that must be controlled.

Managing diabetes can become tiresome, confusing, and overwhelming, especially if a person is not thoroughly educated about their condition and treatment plan. The good news is that all people with diabetes can receive ongoing education and support.

The American Diabetes Association recommends that all people with diabetes receive diabetes self-management education (DSME) at the time of diagnosis and as needed thereafter.

Diabetes self-management education may lower the risk of diabetes complications as well as decrease treatment costs. It does this by reducing or eliminating medications and emergency room visits, and by helping people access cost-savings programs.

In addition, DSME has been shown to reduce the onset and/or advance of diabetes complications, improve quality of life, and encourage healthy lifestyle behaviors such as healthful eating and regular physical activity.

Certified Diabetes Care and Education Specialists (CDCES) deliver DSME and specialize in all things related to diabetes. They can be considered your "diabetes cheerleader"—offering a wealth of resources, information, and support.

Research demonstrates that working with a diabetes educator can improve outcomes for people with diabetes and prediabetes. If you don't have a CDCES, it's a great idea to add them to your healthcare team.


A Word From Verywell

There are many forms of diabetes which require different types of care and treatment regimes. For those people who have a family history of heart disease or type 2 diabetes, it's important to modify your lifestyle in an effort to reduce your risk of developing diabetes and its complications. Weight loss, a healthy diet, exercise, and smoking cessation are important steps to take.

If you are experiencing symptoms and suspect that you may have diabetes, seeking medical attention is critical.

Treatment and management of diabetes will vary based on type. However, all people with diabetes can benefit from the guidance provided by a diabetes care and education specialist. These specialists can help lessen the burden of this disease by providing support and expert instruction.

Although long-term complications are possible, people with diabetes can live long, healthy lives by keeping their diabetes in good control.

Frequently Asked Questions

  • What is the difference between diabetes and diabetes mellitus?

    Diabetes is a common way to refer to diabetes mellitus.

  • What are three signs of diabetes mellitus?

    Three signs of diabetes include peeing more often, increased hunger, and increased thirst.

  • What does mellitus mean in diabetes?

    The word "mellitus" means "honey, sweet" in Latin and was coined by Thomas Willis in 1675 as a reference to the sweetness of urine and blood of individuals with diabetes. This sweetness was first noted in ancient India.

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By Barbie Cervoni MS, RD, CDCES, CDN
Barbie Cervoni MS, RD, CDCES, CDN, is a New York-based registered dietitian and certified diabetes care and education specialist.