Diabetes Facts

January 7, 2025

This page was reviewed under our medical and editorial policy by Ping H. Wang, M.D., professor and chair, Department of Diabetes, Endocrinology & Metabolism, City of Hope^® Cancer Center Duarte

Diabetes is a chronic condition, with the number of people affected by it increasing every year in the United States and around the world. It affects how much sugar (glucose) is circulating in the blood, which may be harmful, and even life-threatening, if left untreated.

What Is Diabetes?

Diabetes is a chronic illness in which a person’s blood sugar (glucose) level is too high. Glucose is a source of energy that comes from food or is made by the body itself. The amount of glucose in the blood is managed by insulin, a key hormone made by the pancreas. With diabetes, however, the pancreas makes less insulin than the body requires or the body is unable to use insulin appropriately. In some cases, the body makes no insulin at all.

How Common Is Diabetes?

Rates of diabetes have been climbing worldwide and in the United States.

Worldwide, more than 400 million people have diabetes, and about 1.5 million people die from diabetes each year, according to the World Health Organization.

In 2021, about 12% of the U.S. population — more than 38 million people — had diabetes diagnosed by a health care provider, according to the U.S. Centers for Disease Control and Prevention (CDC). The CDC estimates that another 3.4% were unaware they met the criteria for a diabetes diagnosis or they did not report having it. And prevalence rises as people age. In all, 29% of Americans aged 65 years and older had diabetes in 2021.

What Causes Diabetes?

Diabetes is commonly classified as type 1, type 2 or gestational, and each of these most common diabetes types has a unique cause.

In type 1 diabetes, the immune system attacks and destroys cells in the pancreas that make insulin. This is known as an autoimmune disease. Type 1 diabetes is usually diagnosed in childhood or adolescence, but it may happen at any age. A person with type 1 diabetes must take insulin every day because their pancreas is unable to make it, or it doesn't make enough of it.

In type 2 diabetes, the pancreas makes insulin, but the body is unable to use it properly to regulate blood sugar levels. Type 2 diabetes may develop at any age, and it is often connected to certain risk factors such as excess weight and family history.

Sometimes, diabetes starts during pregnancy. This is known as gestational diabetes, and it typically improves after the mother gives birth. While the cause is unknown, it is thought that certain pregnancy hormones may block the action of insulin in the woman’s body (insulin resistance). People diagnosed with gestational diabetes may be more likely to develop type 2 diabetes later on.

Diabetes may also be caused by other factors, including:

• Certain genetic mutations
• Hormonal diseases, such as Cushing syndrome, in which the body releases too much cortisol; acromegaly, when it makes too much growth hormone; and certain thyroid problems
• Injury to or removal of the pancreas or pancreatic cancer
• Certain medications affecting insulin production or how insulin works

Diabetes Risk Factors

Researchers continue to learn more about the underpinnings of diabetes. Each type has its own risk factors, some of which a patient may be able to modify by making lifestyle changes.

The risk factors for type 1 diabetes include:

• Having a parent or sibling with type 1 diabetes
• Young age (being a child, teen or young adult)
• Being a white person

Studies are underway to determine what causes the immune system to attack pancreatic cells, the cause of type 1 diabetes. Scientists suspect certain environmental factors may interact with a person’s genetic background and lead to the onset of type 1 diabetes.

Type 2 diabetes may also have a genetic component. People who have a parent or sibling with type 2 diabetes may have an increased risk for the disease. Other risk factors for type 2 diabetes include:

• Being obese or overweight
• Getting too little exercise (fewer than three times a week)
• Having nonalcoholic fatty liver disease (NAFLD)
• Being age 45 years or older
• Having gestational diabetes or having a baby who weighed nine pounds or more at birth
• Being Hispanic or Latino, African American, Alaska Native, Pacific Islander or Asian American

Risk factors for developing gestational diabetes include a mix of changing hormone levels, genetics and lifestyle factors, such as the amount of weight gained during pregnancy.

Prediabetes and other less common types of diabetes — such as latent autoimmune diabetes in adults (LADA), steroid-induced diabetes, type 3c diabetes, maturity onset diabetes of the young (MODY) and others — have different causes and risk factors.

Is Diabetes Genetic?

Type 1 diabetes may run in families, and having a parent or sibling with type 2 diabetes may increase a person’s risk for developing it.

For patients with a family history of type 1 diabetes, health care providers may recommend a blood test to check levels of islet autoantibodies. Islets are the cells in the pancreas that make insulin. An autoantibody is an antibody that arises to fight substances formed by a person’s own body, and some are the cause of autoimmune diseases. If the islet autoantibody test result is positive, it does not necessarily mean a person has type 1 diabetes, but a doctor may recommend further testing and evaluation. If the test is negative, doctors may repeat it in the future.

Having a parent, brother or sister with type 2 diabetes may increase a person’s risk for developing it. Unlike type 1 diabetes, anyone with lifestyle risk factors such as excess weight or lack of exercise may have an increased risk for developing type 2 diabetes.