Skip Navigation

Diabetes Mellitus

Last Updated: Mar 1, 2019

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:

Symptoms and Complications

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

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.



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.

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

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.


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.


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.


Additional Resources

Home Health Testing Guides

Testing Company Reviews

Related Topics

Tina Shahian, PhD

Tina is a writer for Innerbody Research, where she has written a large body of informative guides about health conditions.


A communication specialist in life science and biotech subjects, Tina’s successful career is rooted in her ability to convey complex scientific topics to diverse audiences. Tina earned her PhD in Biochemistry from the University of California, San Francisco and her BS degree in Cell Biology from U.C. Davis. Tina Shahian’s Linkedin profile.


In her spare time, Tina enjoys drawing science-related cartoons.