Type 2 Diabetes Causes and Risk Factors

Medically Reviewed by Michael Dansinger, MD on May 16, 2021

Although not everyone with type 2 diabetes is overweight, obesity and an inactive lifestyle are two of the most common causes of type 2 diabetes. These things are responsible for about 90% to 95% of diabetes cases in the United States.

What Causes Type 2 Diabetes?

When you're healthy, your pancreas (an organ behind your stomach) releases insulin to help your body store and use sugar from the food you eat. Diabetes happens when one or more of the following occurs:

  • Your pancreas doesn't make any insulin.
  • Your pancreas makes very little insulin.
  • Your body doesn’t respond the way it should to insulin

Unlike people with type 1 diabetes, people with type 2 diabetes make insulin. But the insulin their pancreas releases isn’t enough, or their body can't recognize the insulin and use it properly. (Doctors call this insulin resistance.)

When there isn't enough insulin or the insulin isn't used as it should be, glucose (sugar) can't get into your cells. It builds up in your bloodstream instead. This can damage many areas of the body. Also, since cells aren't getting the glucose they need, they don't work the way they should.

Risk Factors for Type 2 Diabetes

Type 2 diabetes is believed to have a strong genetic link, meaning that it tends to run in families. If you have a parent, brother, or sister who has it, your chances rise. Several genes may be related to type 2 diabetes. Ask your doctor about a diabetes test if you have any of the following risk factors:

  • High blood pressure
  • High blood triglyceride (fat) levels. It's too high if it's over 150 milligrams per deciliter (mg/dL).
  • Low "good" cholesterol level. It's too low if it's less than 40 mg/dL.
  • Gestational diabetes or giving birth to a baby weighing more than 9 pounds
  • Prediabetes. That means your blood sugar level is above normal, but you don't have the disease yet.
  • Heart disease
  • High-fat and carbohydrate diet. This can sometimes be the result of food insecurity, when you don’t have access to enough healthy food.
  • High alcohol intake
  • Sedentary lifestyle
  • Obesity or being overweight
  • Polycystic ovary syndrome (PCOS)
  • Being of an ethnicity that’s at higher risk: African Americans, Native Americans, Hispanic Americans, and Asian Americans are more likely to get type 2 diabetes than non-Hispanic whites.
  • You're over 45 years of age. Older age is a significant risk factor for type 2 diabetes. The risk of type 2 diabetes begins to rise significantly around age 45 and rises considerably after age 65.
  • You’ve had an organ transplant. After an organ transplant, you need to take drugs for the rest of your life so your body doesn’t reject the donor organ. These drugs help organ transplants succeed, but many of them, such as tacrolimus (Astagraf, Prograf) or steroids, can cause diabetes or make it worse.

A proper diet and healthy lifestyle habits, along with medication, if you need it, can help you manage type 2 diabetes the same way you manage other areas of your life. Be sure to seek the latest information on this condition as you become your own health advocate.

The Role of Insulin in the Cause of Type 2 Diabetes

To understand why insulin is important, it helps to know more about how your body uses food for energy. Your body is made up of millions of cells. To make energy, these cells need food in a very simple form. When you eat or drink, much of the food is broken down into a simple sugar called glucose. It moves through your bloodstream to these cells, where it provides the energy your body needs for daily activities.

Insulin and other hormones control the amount of glucose in your bloodstream. Your pancreas is always releasing small amounts of insulin. When the amount of glucose in your blood rises to a certain level, the pancreas will release more insulin to push more glucose into the cells. This causes the glucose levels in the blood (blood glucose levels) to drop.

To keep blood glucose levels from getting too low (hypoglycemia, or low blood sugar), your body signals you to eat and releases some glucose from the stores kept in the liver. It also tells the body to release less insulin.

People with diabetes either don't make insulin or their body's cells can no longer use their insulin. This leads to high blood sugars. By definition, diabetes is:

  • A blood glucose level of greater than or equal to 126 milligrams per deciliter (mg/dL) of blood after an 8-hour fast (not eating anything)
  • A non-fasting glucose level greater than or equal to 200 mg/dL, along with symptoms of diabetes
  • A glucose level greater than or equal to 200 mg/dL on a 2-hour glucose tolerance test

A1c greater than or equal to 6.5%. Unless the person is having obvious symptoms of diabetes or is in a diabetic crisis, the diagnosis must be confirmed with a repeat test.

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