Diabetes Mellitus: An Overview

Overview

What is diabetes mellitus?

Diabetes mellitus is a disease that prevents your body from properly using the energy from the food you eat. Diabetes occurs in one of the following situations:

  • The pancreas (an organ behind your stomach) produces little insulin or no insulin at all. Insulin is a naturally occurring hormone, produced by the beta cells of the pancreas, which helps the body use sugar for energy.

-Or-

  • The pancreas makes insulin, but the insulin made doesn't work as it should. This condition is called insulin resistance.

To better understand diabetes, it helps to know more about how the body uses food for energy (a process called metabolism).

Your body is made up of millions of cells. To make energy, the cells need food in a very simple form. When you eat or drink, much of your food is broken down into a simple sugar called glucose. Glucose provides the energy your body needs for daily activities.

The blood vessels and blood are the highways that transport sugar from where it is either taken in (the stomach) or manufactured (in the liver) to the cells where it is used (muscles) or where it is stored (fat). Sugar isn't able to go into the cells by itself. The pancreas releases insulin into the blood, which serves as the helper, or the "key," that lets sugar into the cells for use as energy.

When sugar leaves the bloodstream and enters the cells, the blood sugar level is lowered. Without insulin, or the "key," sugar can't get into the body's cells for use as energy. This causes sugar to rise. Too much sugar in the blood is called "hyperglycemia" (high blood sugar).

What are the types of diabetes?

There are two main types of diabetes: Type 1 and Type 2:

  • Type 1 diabetes occurs because the insulin-producing cells of the pancreas (beta cells) are damaged. In Type 1 diabetes, the pancreas makes little or no insulin, so sugar can;t get into the body's cells for use as energy. People with Type 1 diabetes must use insulin injections to control their blood glucose. Type 1 is the most common form of diabetes in people who are under age 30, but it can occur at any age. Ten percent of people with diabetes are diagnosed with Type 1.
  • In Type 2 diabetes (adult onset diabetes), the pancreas makes insulin, but it either doesn't produce enough, or the insulin doesn't work properly. Nine out of 10 people with diabetes have Type 2. This type occurs most often in people who are over 40 years old but can occur even in childhood if there are risk factors present. Type 2 diabetes may sometimes be controlled with a combination of diet, weight management and exercise. However, treatment also may include oral glucose-lowering medications (taken by mouth) or insulin injections (shots).

Other types of diabetes might result from pregnancy (gestational diabetes), surgery, use of certain medicines, various illnesses and other specific causes.

What is gestational diabetes?

Gestational diabetes occurs when there is a high blood glucose level during pregnancy. As pregnancy progresses, the developing baby has a greater need for glucose. Hormone changes during pregnancy also affect the action of insulin, which brings about high blood glucose levels.

Pregnant women who have a greater risk of developing gestational diabetes include those who:

Blood glucose levels usually return to normal after childbirth. However, women who have had gestational diabetes have an increased risk of developing Type 2 diabetes later in life.

Symptoms and Causes

What causes diabetes?

The causes of diabetes are not known. The following risk factors may increase your chance of getting diabetes:

  • Family history of diabetes or a personal history of gestational diabetes.
  • African-American, Hispanic, Native American, or Asian-American race, Pacific Islander or ethnic background.
  • Injury to the pancreas (such as infection, tumor, surgery or accident).
  • Autoimmune disease.
  • Age (risk increases with age).
  • Physical stress (such as surgery or illness).

There are risk factors that you might have more control over, including:

  • High blood pressure.
  • Abnormal blood cholesterol or triglyceride levels.
  • Smoking.
  • Being overweight.
  • Use of certain medications, including steroids

It is important to note that sugar itself doesn't cause diabetes. Eating a lot of sugar can lead to tooth decay, but it doesn't cause diabetes.

What are the symptoms of diabetes?

The symptoms of diabetes include:

  • Increased thirst.
  • Increased hunger (especially after eating).
  • Dry mouth.
  • Frequent urination.
  • Unexplained weight loss (even though you are eating and feel hungry).

Other symptoms include:

What are the symptoms of low blood sugar?

Most people have symptoms of low blood sugar (hypoglycemia) when their blood sugar is less than 70 mg/dl. (Your healthcare provider will tell you how to test your blood sugar level.)

When your blood sugar is low, your body gives out signs that you need food. Different people have different symptoms. You will learn to know your symptoms.

Common early symptoms of low blood sugar include the following:

  • Feeling weak or dizzy, including trembling and feeling shaky.
  • Feeling hungry.
  • Sweating.
  • Pounding heart.
  • Pale skin.
  • Feeling frightened or anxious.

Late symptoms of low blood sugar include:

  • Feeling confused or being able to keep your mind on one subject.
  • Headache.
  • Poor coordination.
  • Bad dreams or nightmares.
  • Feeling cranky.
  • Numbness in your mouth and tongue.
  • Passing out.

Diagnosis and Tests

How is diabetes diagnosed?

Diabetes is diagnosed with fasting sugar blood tests or with A1c blood tests, also known as glycated hemoglobin tests. A fasting blood sugar test is performed after you have had nothing to eat or drink for at least eight hours. Normal fasting blood sugar is less than 100 mg/dl (5.6 mmol/l). You do not have to be fasting for an A1c blood test. Diabetes is diagnosed by one of the following (see chart):

  • Your blood sugar level is equal to or greater than 126 mg/dl (7 mmol/l).
  • You have two random blood sugar tests over 200 mg/dl (11.1 mmol/l) with symptoms.
  • You have an oral glucose tolerance test with results over 200 mg/dl (11.1 mmol/l).
  • Your A1c test is greater than 6.5 percent on two separate days.

An A1c test should be performed in a laboratory using a method that is certified by the National Glycohemoglobin Standardization Program (NGSP) and standardized to the Diabetes Control and Complications Trial (DCCT) assay.

Type of testNormal
(mg/dL)
Pre-diabetes
(mg/dL)
Diabetes
(mg/dL)
Fasting
glucose test

Less than 100

100-125126 or higher
Random (anytime)
glucose test

Less than 140

140-199200 or higher
A1c test

Less than 5.7%

5.7 - 6.4%6.5% or higher
Oral glucose
tolerance test
Less than 140140-199200 or higher

Management and Treatment

How is diabetes managed?

There is no cure for diabetes, but it can be treated and controlled. The goals of managing diabetes are to:

  • Keep your blood glucose levels as near to normal as possible by balancing food intake with medication and activity.
  • Maintain your blood cholesterol and triglyceride (lipid) levels as near the normal ranges as possible.
  • Control your blood pressure. Your blood pressure should not go over 140/90.
  • Decrease or possibly prevent the development of diabetes-related health problems.

You hold the keys to managing your diabetes by:

  • Planning what you eat and following a balanced meal plan.
  • Exercising regularly.
  • Taking medication, if prescribed, and closely following the guidelines on how and when to take it.
  • Monitoring your blood glucose and blood pressure levels at home.
  • Keeping your appointments with your healthcare providers and having laboratory tests completed as ordered by your doctor.

What you do at home every day affects your blood glucose more than what your doctor can do every few months during your check-up.

What are insulin pumps?

Insulin pumps are small, computerized devices, about the size of a small cell phone that you wear on your belt, in your pocket, or under your clothes. They deliver rapid-acting insulin 24 hours a day through a small flexible tube called a cannula. The cannula is inserted under the skin using a needle. The needle is then removed leaving only the flexible tube under the skin. The pump user replaces the cannula every two to three days.

Insulin pump

An insulin pump can deliver insulin 24 hours a day.

It is important for pump users to frequently monitor their glucose levels either with a continuous glucose monitor or a fingerstick monitor. The pump delivers a continuous flow of insulin that can be adjusted if needed for things like exercise and stress. A pump user regularly enters information about their food intake and blood sugar levels into the pump so it can help them calculate insulin doses for food intake and high blood sugar levels.

Benefits of an insulin pump include fewer insulin injections, a more flexible lifestyle, and a more consistent and adjustable delivery of insulin.

Can I take both pills and insulin to control my blood sugar?

Yes. The combination of insulin and an oral medication, when taken as directed by your healthcare provider, is very safe and effective in controlling blood sugar. A typical combination therapy consists of taking an oral medication during the day and insulin at night.

Once you begin taking insulin, you will need to monitor your blood sugar more often to reduce the risk of low blood sugar reactions. Combination therapies are often helpful for people who have Type 2 diabetes. If you have been taking an oral medication, your doctor may change your treatment plan to include insulin injections. This change is often made to help people with Type 2 diabetes gain better control of their blood sugar.

Prevention

Can Type 2 diabetes be prevented?

Although diabetes risk factors like family history cannot be changed, there are other risk factors that you do have some control over. Implementing some of the healthy lifestyle habits below can improve these modifiable risk factors and help to decrease your chances of getting Type 2 diabetes:

Living With

What are some of the long-term complications of high blood sugar levels?

  • Retinopathy (eye disease): All patients with diabetes should see an ophthalmologist (eye specialist) every year for a dilated eye examination. Patients with known eye disease or symptoms of blurred vision in one eye or who have blind spots may need to see their ophthalmologist more often.
  • Nephropathy (kidney disease): Urine testing should be performed every year. Regular blood pressure checks are also important because management of high blood pressure is essential in slowing kidney disease. Have your blood pressure checked at every visit with your healthcare provider. The American Diabetes Association recommends keeping blood pressure below 140/90 for most adults. Persistent swelling in the leg or feet also may be a symptom of kidney disease and should be reported to your doctor.
  • Neuropathy (nerve disease): Numbness or tingling in your feet should be reported to your doctor at your regular visits. Check your feet every day for redness, calluses, cracks or breakdown in the skin tissue. If you notice these symptoms before your scheduled visits, notify your doctor immediately.

Other long-term complications may include:

  • Other eye problems, including glaucoma and cataracts.
  • Dental problems.
  • High blood pressure.
  • Heart attacks and strokes.
  • Sexual health problems.

Last reviewed by a Cleveland Clinic medical professional on 10/02/2018.

References

  • American Diabetes Association. Diabetes Basics. Accessed 6/8/2020.
  • The National Institute of Diabetes and Digestive and Kidney Diseases. What is Diabetes? Accessed 6/08/20.
  • American Diabetes Association. A1C and eAG. Accessed 6/8/2020.

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Cleveland Clinic is a non-profit academic medical center. Advertising on our site helps support our mission. We do not endorse non-Cleveland Clinic products or services. Policy

Cleveland Clinic is a non-profit academic medical center. Advertising on our site helps support our mission. We do not endorse non-Cleveland Clinic products or services. Policy