Patient Basics: Type 2 Diabetes Mellitus

Originally published by Harvard Health.

What Is It?

Type 2 diabetes is a chronic disease. It is characterized by high levels of sugar in the blood. Type 2 diabetes is also called type 2 diabetes mellitus and adult-onset diabetes. However, more and more children and teens are developing this condition. Since type 2 diabetes is much more common than type 1 diabetes, it often is just called “diabetes”.

During digestion, food is broken down into basic components. Carbohydrates are broken down into simple sugars, primarily glucose. Glucose is a critically important source of energy for the body’s cells. To provide energy to the cells, glucose needs to leave the blood and get inside the cells.

Insulin traveling in the blood signals the cells to take up glucose.  Insulin is a hormone produced by the pancreas. When levels of glucose in the blood rise (for example, after a meal), the pancreas produces more insulin.

Type 2 diabetes occurs when your body’s cells do not react efficiently to insulin. This condition is called insulin resistance. The cells do not accept as much glucose from the blood as they should. The cells resist the effects of insulin. As a result, glucose starts to build up in the blood.

In people with insulin resistance, the pancreas “sees” the blood glucose level rising. The pancreas responds by making extra insulin to maintain a normal blood sugar. Over time, the body’s insulin resistance gets worse. In response the pancreas makes more and more insulin. Finally, the pancreas gets “exhausted”.  It cannot keep up with the demand for more and more insulin. As a result, blood glucose levels stay high.

Type 2 Diabetes Mellitus

Type 2 diabetes runs in families. It most often affects people who are older than 40. But type 2 diabetes is now being seen in more and more young people. Obesity greatly increases the risk of diabetes.


The symptoms of diabetes are related to high blood glucose levels. They include:

  • Excessive urination, thirst and hunger
  • Weight loss
  • Increased susceptibility to infections, especially yeast or fungal infections

Extremely high blood sugar levels also can lead to a dangerous complication called hyperosmolar syndrome. This is a life-threatening form of dehydration. In some cases, hyperosmolar syndrome is the first sign that a person has type 2 diabetes. It causes confused thinking, weakness, nausea and even seizure and coma.

The treatment of type 2 diabetes also can produce symptoms, when it leads to the complication of low blood sugar (called hypoglycemia). People with type 2 diabetes take medications to reduce blood sugar. But these medications may cause sugar levels to drop below normal, particularly if someone has eaten less than usual. Symptoms of hypoglycemia include:

  • Sweating
  • Trembling
  • Dizziness
  • Hunger
  • Confusion
  • Seizures and loss of consciousness (if hypoglycemia is not recognized and corrected)

You can correct hypoglycemia by eating or drinking something that has carbohydrates. This raises your blood sugar level.

Type 2 diabetes affects all parts of the body. It can cause serious, potentially life-threatening complications. These include:

  • Atherosclerosis — Atherosclerosis is fat buildup in the artery walls. This can impair blood flow to the all the organs. The heart, brain and legs are most often affected.
  • Retinopathy — Tiny blood vessels at the back of the eye become damaged by high blood sugar. Caught early, retinopathy damage can be minimized by tightly controlling blood sugar and using laser therapy. Untreated retinopathy can lead to blindness.
  • Neuropathy — This is nerve damage. The most common type is peripheral neuropathy. The nerves to the legs are damaged first, causing pain and numbness in the feet. This can advance to cause symptoms in the legs and hands. Damage to the nerves that control digestion, sexual function and urination can also occur.
  • Foot problems — Sores and blisters on the feet occur for two reasons:
    • If peripheral neuropathy causes numbness, the person will not feel irritation in the foot. The skin can break down and form an ulcer.
    • Blood circulation can be poor, leading to slow healing. Left untreated, a simple sore can become infected and very large.
  • Nephropathy — Damage to the kidneys. This is more likely if blood sugars remain elevated and high blood pressure is not treated aggressively.


Diabetes is diagnosed by testing the blood for sugar levels. Blood is tested in the morning after you have fasted overnight.

Typically, the body keeps blood sugar levels between 70 and 100 milligrams per deciliter (mg/dL), even after fasting. If a blood sugar level after fasting is greater than 125 mg/dL, diabetes is diagnosed.

Your doctor will examine you to look for signs of diabetes complications. These include:

  • Obesity, especially abdominal obesity.
  • High blood pressure
  • Deposits of blood, or puffy yellow spots in the retina of your eyes
  • Decreased sensation in the legs
  • Weak pulses in the feet
  • Abnormal pulses in the abdomen
  • Blisters, ulcers or infections of the feet

Laboratory tests are also used routinely to evaluate diabetes. These include:

  • Fasting glucose. A test of your blood sugar level after you have not eaten for several hours.
  • Hemoglobin A1C (HbA1c). Indicates how close to average your blood glucose has been during the previous two months.
  • Blood creatinine and urine microalbumin. Tests for evidence of kidney disease.
  • Lipid profile. Measures levels of triglycerides and total, HDL, and LDL cholesterol. This evaluates the risk of atherosclerosis.

Expected Duration

Diabetes is a lifelong illness.

Aging and episodic illness can cause the body’s insulin resistance to increase. As a result, additional treatment typically is required over time.


You can help to prevent type 2 diabetes by:

  • Maintaining your ideal body weight. This is especially true if you have a family history of diabetes.
  • Exercising regularly—like a brisk walk of 1-2 miles in 30 minutes—at least five times a week, even if that does not result in you achieving an ideal weight. That’s because regular exercise reduces insulin resistance.
  • Eating a healthy diet.
  • Taking medication. The medication metformin (Glucophage) offers some additional protection for people with pre-diabetes. Pre-diabetes is defined as blood glucose levels between 100 and 125 mg/dL.

If you already have type 2 diabetes, you can still delay or prevent complications:

  • Keep tight control of your blood sugar. This reduces the risk of most complications.
  • Lower your risk of heart-related complications by:
    • Taking a daily aspirin.
    • Aggressively managing other risk factors for atherosclerosis, such as:
      • High blood pressure
      • High cholesterol and triglycerides
      • Cigarette smoking
      • Obesity
  • Visit an eye doctor and a foot specialist every year to reduce eye and foot complications.


Diet and Exercise

In most cases, type 2 diabetes treatment begins with weight reduction through diet and exercise. A healthy diet for a person with diabetes is:

  • Low in saturated fats and cholesterol
  • Without any trans fats
  • Low in total calories
  • Nutritionally balanced with abundant amounts of:
    • Whole-grain foods
    • Monounsaturated oils
    • Fruits and vegetables

A daily multivitamin is recommended for most people with diabetes.

For some people, type 2 diabetes can be controlled just with diet and exercise.  Even if medications are required, diet and exercise remain important for controlling diabetes.

Medications: Pills

The medications used for type 2 diabetes include pills and injections.  The pills work in many different ways. They include medications that:

  • Reduce insulin resistance in the muscles and liver.
  • Increase the amount of insulin made and released by the pancreas.
  • Cause a burst of insulin release with each meal.
  • Delay the absorption of sugars from the intestine.
  • Slow your digestion.
  • Reduce your appetite for large meals.
  • Decrease the conversion of fat to glucose. These medications are called thiazolidinediones. One medication in this group has recently been linked to heart disease. As a result, drugs from this group are not recommended as a first choice in treatment.


Because type 2 diabetes develops when the pancreas cannot make enough insulin to overcome insulin resistance, about one of three people with this disease take some form of insulin injection.

In advanced type 2 diabetes, or for people who want to tightly control glucose levels, insulin may be needed more than once per day and in higher doses.

Treatment plans that include both very long-acting insulin and very short-acting insulin are frequently the most successful for controlling blood sugar. Very short-acting insulin is used with meals, to help control the spike in blood sugar levels that occur with a meal. If a person does not eat on a regular schedule, very short-acting insulin can be particularly helpful.

Treatment Side Effects

Medications used to treat type 2 diabetes can have side effects. These vary by medication. Side effects may include:

  • Low blood sugar levels (hypoglycemia)
  • Weight gain
  • Nausea
  • Diarrhea
  • Life-threatening buildup of lactic acid in the blood (in people with kidney failure)
  • Leg swelling
  • Worsening of heart failure
  • Liver inflammation
  • Increased risk of heart attack (with one of the thiazolidinediones medicines)
  • Excessive gas and bloating

Fortunately, these side effects are uncommon, so the benefits of treatment far outweigh the risks.

In addition to medicines that help control the level of blood sugar, people with type 2 diabetes often take other medicines that reduce the risk or to slow the onset of the complications of diabetes. These include medications that:

  • Slow the worsening of kidney disease.
  • Lower cholesterol. All diabetics should consider taking medication to lower their cholesterol.
  • Lower blood pressure. Diabetics should use medication to control high blood pressure if it can’t be improved by lifestyle changes.
  • Protect against heart attacks. Most people with diabetes benefit from a daily aspirin.

When To Call a Professional

If you have diabetes, see your doctor regularly.

People with high blood sugar levels have a higher risk of dehydration. Contact your doctor immediately if you develop vomiting or diarrhea and are not able to drink enough fluids.

Monitor your blood sugar as advised by your health care team. Report any significant deviations in blood sugar levels.


Your treatment plan is likely to require adjustment over time. Insulin resistance increases with age. And the insulin-producing cells in the pancreas may wear out as the pancreas tries to keep up with the body’s extra insulin needs.

After the first few years, the majority of people with type 2 diabetes require more than one medicine to keep their blood sugar controlled.

The prognosis in people with type 2 diabetes varies. It depends on how well an individual modifies his or her risk of complications. Heart attack, stroke and kidney disease can result in premature death. Disability due to blindness, amputation, heart disease, stroke and nerve damage may occur. Some people with type 2 diabetes become dependent on dialysis treatments because of kidney failure.

Additional Info

American Diabetes Association
ATTN: National Call Center
1701 N. Beauregard St.
Alexandria, VA 22311
Toll-Free: 1-800-342-2383

American Dietetic Association
120 South Riverside Plaza
Suite 2000
Chicago, IL 60606-6995
Toll-Free: 1-800-877-1600

National Diabetes Information Clearinghouse
1 Information Way
Bethesda, MD 20892-3560
Phone: 301-654-3327
Toll-Free: 1-800-860-8747
Fax: 301-907-8906

National Institute of Diabetes & Digestive & Kidney Disorders
Office of Communications and Public Liaison
Building 31, Room 9A04
31 Center Drive, MSC 2560
Bethesda, MD 20892-2560
Phone: 301-496-4000

Weight-Control Information Network
1 Win Way
Bethesda, MD 20892-3665
Phone: 202-828-1025
Toll-Free: 1-877-946-4627
Fax: 202-828-1028