What is Diabetes?

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Diabetes, also called diabetes mellitus, is a condition that causes blood sugar to rise. A fasting blood glucose (sugar) level of 126 milligrams per deciliter (mg/dL) or higher is dangerous.

How diabetes develops

When your digestive system breaks down food, your blood sugar level rises. The body’s cells take up the sugar (glucose) in the bloodstream and use it for energy. The cells do this using a hormone called insulin, which is produced by the pancreas (an organ near the stomach).

When your body doesn’t produce enough insulin and/or doesn’t efficiently use the insulin it produces, sugar levels rise in the bloodstream. As a result:

  1. Right away, the body’s cells may be starved for energy.
  2. Over time, high blood glucose levels may damage the eyes, kidneys, nerves or heart.

Types of diabetes

Type 1 diabetes

This type of diabetes is also referred to as insulin-dependent diabetes. Those with Type 1 diabetes must take insulin or other medications daily. This compensates for insufficient amounts of insulin, a hormone required to translate blood glucose into energy for the body.

Type 1 diabetes was previously known as juvenile diabetes because it’s usually diagnosed in children and young adults. However, this chronic, lifelong disease can strike at any age. Those with a family history of Type 1 diabetes have a greater risk.

Health risks for Type 1 diabetes

During the development of Type 1 diabetes, the body’s immune system attacks certain cells (called beta cells) in the pancreas.

Although the reasons this occurs are still unknown, the effects are clear: Once these cells are destroyed, the pancreas produces little or no insulin, so glucose stays in the blood. And when there’s too much glucose in the blood, especially for prolonged periods, all the organ systems in the body suffer long-term damage.

Learn more about the health consequences of diabetes and how to treat it.

Type 2 diabetes

Type 2 diabetes is the most common form of diabetes. Historically, Type 2 diabetes has been diagnosed primarily in adults.

But adolescents and young adults are developing Type 2 diabetes at an alarming rate because of higher rates of obesity and physical inactivity — risk factors for Type 2 diabetes.

This type of diabetes can occur when:

  • The body develops “insulin resistance” and can’t efficiently use the insulin it makes.
  • The pancreas gradually loses its capacity to produce insulin.

In a mild form, this type of diabetes can go undiagnosed for many years. That’s cause for concern, since untreated diabetes can lead to many serious medical problems, including cardiovascular disease.

Type 2 diabetes may be delayed or controlled with diet and exercise.

Precursors to diabetes

Insulin resistance

Insulin resistance is a condition that affects more than 60 million Americans. It occurs when the body makes insulin but does not use it efficiently. This means that glucose builds up in the bloodstream instead of being used by cells.

To compensate for the high blood sugar levels, the insulin-producing cells in the pancreas release more and more insulin to try to keep blood sugar levels normal. Gradually, these cells fail to keep up with the body’s need for insulin. As a consequence, blood sugar levels begin to rise.

When a fasting individual has too much glucose in the blood (hyperglycemia) or too much insulin in the blood (hyperinsulinemia), that person may have insulin resistance.

Health risks of insulin resistance

People with insulin resistance are at greater risk of developing prediabetes, Type 2 diabetes and cardiovascular disease.

Those with insulin resistance are also more likely to have a history of being obese and physically inactive, and likely to have other cardiovascular risk factors such as dyslipidemia (too much LDL cholesterol), not enough HDL (good) cholesterol, high triglycerides and high blood pressure.

Untreated diabetes can lead to many serious medical problems, including heart disease and stroke. That’s why it’s important to be aware of diabetes symptoms and risk factors. Take whatever steps you can to prevent and treat insulin resistance and diabetes.


Prediabetes means that your blood sugar levels are higher than normal, but not yet crossing the threshold of a diabetes diagnosis.

If you’ve been told by your doctor that you have prediabetes, without making some healthy changes, you have a higher risk of developing Type 2 diabetes.

Learn more about prediabetes.

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Living with Type 2 diabetes?

Get monthly science-based diabetes and heart-healthy tips in your inbox. Know Diabetes by Heart raises awareness that living with Type 2 diabetes increases risk for heart disease and stroke – and that people should talk with their doctor at their next appointment about ways to reduce risk.