Health A-Z

Medical Content Created by the Faculty of the
Harvard Medical School

Hypoglycemia

What Is It?

Hypoglycemia is an abnormally low level of blood sugar (blood glucose). Because the brain depends on blood sugar as its primary source of energy, hypoglycemia interferes with the brain's ability to function properly. This can cause dizziness, headache, blurred vision, difficulty concentrating and other neurological symptoms. Hypoglycemia also triggers the release of body hormones, such as epinephrine and norepinephrine. Your brain relies on these hormones to raise blood sugar levels. The release of these hormones causes additional symptoms of tremor, sweating, rapid heartbeat, anxiety and hunger.

Hypoglycemia is most common in people with diabetes. For a person with diabetes, hypoglycemia occurs because of too high a dose of diabetic medication, especially insulin, or a change in diet or exercise. Insulin and exercise both lower blood sugar and food raises it. Hypoglycemia is common in people who are taking insulin or oral medications that lower blood glucose, especially drugs in the sulfonylurea group (Glyburide and others).

True hypoglycemia with laboratory reports of low blood sugar rarely occurs in people who do not have diabetes. When it does occur outside of diabetes, hypoglycemia can be caused by many different medical problems. A partial list includes:

• Gastrointestinal surgery, usually involving removal of some part of the stomach. Surgery that removes part of the stomach can alter the normal relationships between digestion and insulin release

• The antibiotics gatifloxacin (Tequin, which was recently removed from the market in the U.S.), levofloxacin (Levoquin), and related drugs

• A pancreatic tumor, called an insulinoma, that secretes insulin

• A deficiency of growth hormone from the pituitary gland or of cortisol from the adrenal glands. Both of these hormones help to keep blood sugars normal

• Alcohol

• Overdose of aspirin

• Severe liver disease

• Use of insulin by someone who does not have diabetes

• Cancers, such as cancer of the liver

• Rarely, an enzyme defect. Examples of enzymes that help keep blood sugar normal are glucose-6-phosphatase, liver phosphorylase, and pyruvate carboxylase,