What Are the Causes and Genetic Components of Type 2 Diabetes?

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By : dLife Editors

Reviewed by: Qin Yang, M.D., Ph.D. 4/18.

Type 2 diabetes—previously referred to as adult-onset or non-insulin dependent diabetes—accounts for 90 to 95 percent of all diabetes cases in the United States.

It’s characterized by the body’s inability to use insulin effectively. Insulin is a hormone produced by the pancreas that helps the body turn glucose into energy.

Unlike people with type 1 diabetes, who do not produce insulin at all, people with type 2 diabetes do make insulin.  In fact, they even produce more than people without diabetes.

However due to problems with insulin resistance, which means the body can’t use the insulin anymore to break down all the glucose.  Insulin therefore produced by the pancreas is not sufficient to overcome insulin resistance, leading to increased blood sugars.

Type 2 Diabetes Causes

The exact causes of type 2 diabetes aren’t completely understood, but it’s widely accepted that a combination of inherited genetic risk factors and environmental triggers is involved.

Risk factors include obesity, physical inactivity, poor diet, smoking, chronic stress, low birth weight, high blood pressure, a history of gestational diabetes, and high fasting blood glucose levels.

Individuals with a parent or sibling with type 2 diabetes have a higher chance of developing the disease than those with no family history.

African Americans, Hispanics/Latinos, Native Americans, some Asians, and Pacific Islanders are at greater risk for type 2 diabetes.

Risk increases with age, but it is important to note that rates of type 2 diabetes in children and adolescents have been on the rise recently.

Type 2 Diabetes Symptoms

Not everyone with type 2 diabetes has symptoms, particularly in the early stages of the disease. In fact, 8.1 million of the 29.1 million people with diabetes in America are unaware that they even have the disease. 8.9 percent of Americans have type 2 diabetes.

Type 2 diabetes symptoms may include one or more of the following:

  • Excessive thirst
  • Frequent urination
  • Extreme hunger
  • Unexplained weight loss
  • Fatigue, or a feeling of being “run down” and tired
  • Rapid breathing
  • Blurred vision
  • Dry, itchy skin
  • A headache
  • Tingling or burning pain in the feet, legs, hands, or other parts of the body
  • High blood pressure
  • Mood swings
  • Irritability, depression
  • Frequent or recurring infections, such as urinary tract infections, yeast infections, and skin infections
  • Slow healing of cuts and bruises

Unlike type 1 diabetes, which frequently has a sudden onset of symptoms and reaches a crisis point before a diagnosis is made, the signs of type 2 diabetes may be gradual and more insidious.

Often, the first symptoms that people with undiagnosed type 2 diabetes experience result from complications of the disease, such as blurry vision (retinopathy) or foot pain (neuropathy).

If you’re experiencing any type 2 diabetes symptoms, please contact your healthcare provider immediately for medical evaluation.

Type 2 Diabetes Diagnosis

The National Institutes of Health (NIH) and the American Diabetes Association (ADA) recommend screening for all people beginning at the age of forty-five, at baseline intervals of every three years. It is also recommended that testing is considered in adults of any age if they are overweight and have one or more additional risk factors for type 2 diabetes.  Those with additional diabetes risk factors may require more frequent testing.

Diagnostic Tests

Diabetes may be diagnosed using various combinations of the following tests. Please note that many of the blood tests described below require specific preparation for optimum performance. To get the most accurate results, be sure to closely follow the instructions of your healthcare provider. This list is not all-inclusive, and other blood tests may be prescribed based upon your specific medical history.

  • Fasting plasma glucose test: Measures blood glucose levels after a fast (no food for at least eight hours). Levels of 126 mg/dL (7 mmol/L) or higher indicate a need for a subsequent retest on a different day to confirm a diagnosis of diabetes.
  • Oral glucose tolerance test (OGTT): The patient is given an oral dose of glucose solution (75 grams of an extremely sweet drink), and glucose levels are checked multiple times over three hours. Glucose levels that quickly rise above normal levels (i.e., 200 mg/dL (11.11 mmol/L) or higher) and take longer to normalize usually indicate diabetes.
  • Two-hour postprandial glucose test: Measures ability to metabolize carbohydrates and produce insulin. Postprandial means after a meal and this test is administered following an oral glucose tolerance test (OGTT). Two-hour postprandial glucose values of 200 mg/dL (11.1 mmol/L) or higher indicate diabetes.
  • HbA1C (A1C): Measures the amount of glycated hemoglobin in the bloodstream over a 120-day period. A high percentage of glycated hemoglobin indicates problems with long-term blood sugar control. A1C results of 6.5 percent (48 mmol/mol) or greater indicate diabetes.
  • Random plasma glucose: Measures blood glucose levels with a small blood draw taken at any time of the day (hence the term “random.”) Levels of 200 mg/dL (11.1 mmol/L) or higher, along with the presence of symptoms of diabetes, indicate a diagnosis of diabetes.

Type 2 Diabetes Treatment

A long-term commitment to good nutrition, careful monitoring of carbohydrate intake, and regular physical activity are critical to successful type 2 diabetes treatment.

Medications for type 2 diabetes, including oral medications and injectables, are prescribed when diet and exercise alone aren’t enough to keep blood sugar levels within a safe range.

Some people with type 2 diabetes may eventually require regular insulin injections to keep their blood glucose levels under control.

The information provided by regular blood sugar testing helps your healthcare team assess the efficacy of your type 2 diabetes treatment plan, and provides data for making the necessary adjustments.

Qin Yang, M.D., Ph.D., is an Assistant Professor of Medicine, Physiology, and Biophysics at the Center for Diabetes Research in the Department of Medicine, Division of Endocrinology, at the UC Irvine School of Medicine.  He specializes in Endocrinology & Metabolism and Internal Medicine.


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