What is Diabetes?

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

How diabetes develops

When your digestive system breaks down food, your blood sugar level rises. The body’s cells absorb 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 it efficiently, sugar levels rise in the bloodstream. As a result:

  1. Right away, the body’s cells may be starved for energy.
  2. The levels of fatty substances in the blood rise, resulting in atherosclerosis and decreased blood flow in the larger blood vessels.
  3. Over time, high blood glucose levels may damage the eyes, kidneys, nerves or heart.  

What is Diabetes? (PDF)

Types of diabetes

Type 1 diabetes

This type of diabetes is also called insulin-dependent diabetes. People with Type 1 diabetes must take insulin and also may take other medications daily. This makes up for the insulin not being produced by 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 condition can develop at a later age. People with a family history of Type 1 diabetes have a greater risk of developing it. 

Type 1 diabetes develops when the body’s immune system attacks and destroys cells in the pancreas that make insulin.

Once these cells are destroyed, the pancreas produces little or no insulin, so glucose stays in the blood. When there’s too much glucose in the blood, especially for prolonged periods, 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. Type 2 diabetes has historically been diagnosed primarily in adults. But adolescents and young adults are developing Type 2 diabetes at an alarming rate because of family history and higher rates of obesity and physical inactivity.

This type of diabetes can occur when the body develops “insulin resistance” and can’t efficiently use the insulin it makes. As Type 2 diabetes progresses, the insulin producing ability of the pancreas decreases.

Diabetes can develop gradually without symptoms and 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.

With the exception of gestational diabetes, diabetes that happens for the first time during pregnancy, once a body becomes diabetic, diet and health management will be a life-long process.

If you’ve been diagnosed with diabetes, it’s important to follow your health care professional’s recommendations and take all medications as directed. It’s also important to commit to making healthy diet and lifestyle changes that can help manage your condition and slow its progression.
Learn more about the risk factors and what you can do to live your longest and healthiest life.

Precursors to diabetes

Insulin resistance

Insulin resistance occurs when the body makes insulin but can’t use it efficiently. This causes glucose to build up in the bloodstream instead of being used by cells.

To reduce 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 result, blood sugar levels begin to rise.

When a fasting person has too much glucose in the blood (hyperglycemia) or too much insulin in the blood (hyperinsulinemia), they 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.

People with insulin resistance are more likely to have a history of being obese and physically inactive. They are also likely to have other cardiovascular risk factors such as high cholesterol and high blood pressure.

Additional risk factors for insulin resistance include:

  • Age 45 or older
  • Family members with diabetes
  • History of gestational diabetes, heart disease or stroke
  • Polycystic ovary syndrome
  • Black American, Alaska Native, American Indian, Asian American, Hispanic/Latino, Native Hawaiian, or Pacific Islander American

Other factors that contribute to insulin resistance include metabolic syndrome, certain medications and hormonal and sleep disorders.

That’s why it’s important to be aware of diabetes risk factors and take steps to prevent diabetes.


Prediabetes means the body is having trouble getting your blood sugar down to a healthy range, but it hasn’t yet reached the level of Type 2 diabetes.

If you’ve been told that you have prediabetes, you can reduce your risk of developing Type 2 diabetes by improving your diet, increasing your physical activity and losing weight if you are overweight.

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.