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Diabetes Mellitus

Last Updated: May 13, 2022

Overview: Types of Diabetes Mellitus

Diabetes mellitus (DM) is a common disease in which the blood sugar (glucose) is abnormally elevated. Normally, the body obtains glucose from food, and additional glucose is made in the liver. The pancreas produces insulin, which enables glucose to enter cells and serve as fuel for the body. In patients with diabetes, glucose accumulates in the blood instead of being properly transported into cells. Excess blood sugar is a serious problem that may damage the blood vessels, heart, kidneys, and other organs.

About 5-10% of patients with diabetes are diagnosed with type 1 diabetes mellitus, an autoimmune disorder in which the immune system mistakenly attacks the insulin-producing beta cells in the pancreas, causing the organ to no longer produce insulin. Type 1 DM most commonly occurs in children or young adults, and the incidence of new cases is increasing.

Healthy pancreas, where insulin is produced

Approximately 90-95% of people with diabetes have type 2 diabetes mellitus, which occurs when the body becomes unable to use the insulin produced by the pancreas. This condition is also called insulin resistance. The prevalence of type 2 DM is increasing dramatically worldwide. In the past, type 2 DM was associated with adulthood; however, it is rapidly increasing in children because of the rise in childhood obesity.

Gestational diabetes mellitus (GDM) occurs during pregnancy. This form of diabetes usually resolves after delivery, but patients with GDM have an increased risk of developing type 2 DM later in life.

Causes and Risk Factors

Type 1 DM is an autoimmune disorder and the exact cause is unknown. Causes may include genetic factors, environmental factors, and viruses.

For type 2 DM, the major risk factors include a family history of type 2 DM, increased age, obesity, and a sedentary lifestyle. Type 2 DM can develop in people who are not obese, but obesity is a major risk factor because excess body fat causes insulin resistance.

Gestational diabetes mellitus is caused by certain hormones associated with pregnancy that interfere with insulin’s function. GDM occurs more frequently in patients who are overweight, are older than 25, have close relatives with diabetes, or have given birth to a baby weighing more than 9 pounds.

Steroid medication may cause diabetes or exacerbate existing disease.

DM is also caused by:

  • Excess hormone production
  • Pancreatic diseases
  • Genetic factors—among them, hereditary hemochromatosis, one of the most common hereditary conditions; learn about DNA health testing to find out how you can test to discover your own risk.

Symptoms and Complications

People with type 1 DM usually experience a sudden onset of symptoms including:

  • Frequent urination
  • Extreme thirst
  • Weight loss
  • Abnormal hunger
  • Fatigue
  • Blurred vision.

The severity of symptoms depends on the blood sugar level. Individuals with type 2 DM usually have a much more gradual onset of symptoms, and many people with type 2 DM are asymptomatic for years.


  • Diabetic ketoacidosis (DKA) is a life-threatening condition associated with increased fat metabolism and production of harmful acids (ketones). Patients diagnosed with DKA develop very high blood sugar levels, abdominal pain, fruity-smelling breath, dehydration, severe weakness, lethargy, and coma.
  • Hyperglycemic hyperosmolar nonketotic syndrome is characterized by extremely high blood sugar levels, dehydration, fever, confusion, and coma.
  • Atherosclerosis causes the narrowing of arteries throughout the body. This problem increases the risk for coronary heart disease, heart attacks, cerebrovascular disease, stroke, and impaired circulation to the legs (peripheral artery disease).
  • Damage to nerves (neuropathy) in the arms and legs causes decreased sensation, numbness, and tingling. Neuropathy and poor blood circulation in the feet can cause non-healing wounds and infections that may necessitate lower extremity amputations.
  • Damage to blood vessels in the kidney ultimately impairs kidney function (nephropathy).
  • Impaired blood flow in the retina (diabetic retinopathy) can lead to blindness.


Patients with type 1 DM often develop pronounced symptoms of diabetes, so the disease is usually readily diagnosed. Conversely, people with type 2 DM may experience no symptoms. Screening tests are important for high risk groups, such as pregnant women, people with a family history of diabetes, and people older than 45.

Prediabetes is a condition of mildly elevated blood glucose levels found in people at risk for developing type 2 DM. Prediabetes is often diagnosed upon routine screening of otherwise asymptomatic individuals. With early lifestyle changes, prediabetes is reversible.

Tests for Diabetes

Fasting blood glucose is measured after an 8 hour fast.

  • Normal: less than 100 mg/dl
  • Prediabetes: 100-125 mg/dl
  • Diabetes: 126 mg/dl or higher

Oral glucose tolerance test (OGTT) is performed after consumption of a high-glucose solution.

  • Normal: less than 140 mg/dl
  • Prediabetes: 140-199 mg/dl
  • Diabetes: 200 mg/dl or higher

Random blood glucose of 200 mg/dl or higher indicates diabetes.

Glycated hemoglobin (A1C) is an indicator of a person’s average blood sugar for the past 2 or 3 months. The test measures the percent of hemoglobin adherent to glucose molecules.

  • Normal: less that 5.7%
  • Prediabetes: 5.7-6.4%
  • Diabetes: 6.5% or higher


Lifestyle Changes

Patients with diabetes are advised to reduce their consumption of refined carbohydrates and adhere to a high-fiber, low-fat, and low-calorie diet. Daily aerobic exercise is recommended because exercise naturally lowers blood sugars and helps control the disease.


  • Insulin therapy is absolutely essential for most patients with type 1 DM, and insulin is also required in some cases of type 2 DM. Insulin is administered by injections or an insulin pump.
  • Oral glucose-lowering medications work to lower blood sugar by either stimulating the pancreas to produce more insulin; inhibiting glucose production by the liver; enhancing the body’s response to insulin; or blocking digestive enzymes involved in the metabolism of carbohydrates.
  • Pancreas transplants may be performed in patients when treatment with medications fails.

Self-Monitoring of Blood Sugar

All patients with diabetes must monitor their blood glucose levels to verify that the diabetes is under control. The frequency of monitoring depends on the type of medication a patient uses. Low blood sugar (hypoglycemia) is a serious adverse effect of diabetic medications and may cause sweating, shakiness, dizziness, confusion, loss of consciousness, or seizures.


Type 2 DM is considered a preventable disease, and people with prediabetes can prevent a progression to diabetes by losing weight, eating a healthy diet, and exercising. A combination of daily aerobic exercise and resistance training (twice a week) is very beneficial for maintaining blood sugar control.


  • Powers AC. Chapter 344. Diabetes Mellitus In: Longo DL, Fauci AS, Kasper DL, Hauser SL, Jameson J, Loscalzo J. eds. Harrison’s Principles of Internal Medicine, 18e. New York: McGraw-Hill; 2012.
  • Diabetes Overview. National Diabetes Information Clearinghouse (NDIC), A service of the National Institute of Diabetes and Digestive and Kidney Diseases (NIDDK), National Institutes of Health (NIH) website. Accessed June 4, 2014.
  • Diabetes. Mayo Clinic website. Accessed June 5, 2014.

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Carla Hightower, MD

Carla Hightower, MD is a physician and wellness coach who has written informative articles about diseases and health conditions for Innerbody.


Dr. Hightower’s 20+ years of experience as a practicing physician and her passion for healthy eating and living have made her a compelling presence in media appearances and speaking engagements. Through her business, Living Health Works, Dr. Hightower offers wellness workshops and online courses to individuals, private groups, and corporations.


Dr. Hightower earned her Doctor of Medicine degree from Northwestern University, where she subsequently completed her anesthesiology residency and obtained her MBA. She holds certifications in integrative health coaching and plant-based nutrition from Duke University and Cornell University, respectively.