Hypoglycemia is a syndrome (group of related symptoms) caused by abnormally low levels of blood sugar. It is not a disease or disorder by itself. Although some doctors disagree about the exact cutoff point for measuring hypoglycemia, the usual standard is 60–70 milligrams per deciliter (mg/dL) of blood.
Hypoglycemia can be understood as the result of the body's difficulty in regulating blood sugar levels. It is normal for people's blood sugar levels
to rise and fall over the course of a normal day from about 70 mg/dL to 140 mg/dL, depending on whether they has just eaten, if they are digesting their meal, or if they have not eaten for some hours (as when sleeping). The body normally regulates the level of glucose in the blood by means of two hormones secreted by the pancreas, a small organ located near the liver.
When a person eats a meal, the carbohydrates in such foods as rice, potatoes, pasta, sugary foods, and bread are broken down into glucose, which is then absorbed into the bloodstream. As the glucose level in the blood rises, the pancreas secretes insulin, a hormone that helps the body's tissues make use of the glucose. If there is more glucose in the blood than is needed for the body's energy needs at the time, the extra glucose is stored in the liver in a form called glycogen. As the levels of glucose in the blood drop, the pancreas secretes another hormone called glucagon. Glucagon stimulates the liver to convert the stored glycogen back into glucose and release it into the blood. The additional glucose then raises the person's blood sugar level.
What happens in hypoglycemia is that the normal process of blood sugar regulation no longer works smoothly. This problem may develop as a complication of diabetes, a side effect of some medications, or the result of other diseases or tumors. When blood sugar levels drop below
about 70 mg/dL, a person with hypoglycemia may begin to experience the mental and physical symptoms of hypoglycemia.
It is difficult to tell with certainty how many people in the general American population suffer from hypoglycemia, because some people use the term loosely to refer to irritable feelings or mild anxiety associated with hunger even though they have not had a blood sugar test and may in fact have normal levels of blood glucose. Most doctors think that between 5 and 10 percent of Americans have true hypoglycemia. About 55 percent of patients with diabetes will have mild hypoglycemia at some point during treatment for the disease. Hypoglycemia caused by tumors that secrete insulin is very rare, affecting one or two persons per million.
As far as is known, hypoglycemia affects persons of all races and men and women equally. Reactive or fasting hypoglycemia is more common in adults over thirty-five than in adolescents or young adults. Hypoglycemia related to food allergies or overly low levels of growth hormone occurs mostly in children.
Hypoglycemia has a number of possible causes: In patients with diabetes, hypoglycemia is usually a side effect of the medications taken to control blood sugar levels. A person's blood sugar level can fall too low if he or she skips meals, exercises too long or too vigorously, takes too large a dose of their diabetes medication, or drinks alcohol.
Patients who do not have diabetes can develop reactive hypoglycemia. This is a condition in which a person's blood sugar drops suddenly between two and five hours after eating sugary foods. Reactive hypoglycemia is not caused by a disease.
Fasting hypoglycemia is a condition that develops in some people as a result of tumors that secrete insulin; certain types of hormone disorders; drinking alcohol; or taking certain medications (particularly sulfa drugs, quinine, and aspirin). It is most noticeable when a person wakes up in the morning.
The symptoms of hypoglycemia are related to the functioning of the central nervous system (CNS) and another part of the nervous system called the sympathetic nervous system. The reason why low blood sugar affects the nervous system before other parts of the body is that the brain
and the nerves have higher energy requirements than other tissues. If blood sugar levels drop too low, a hormone called epinephrine is released, which triggers both mental and physical symptoms related to the nervous system.
Mental symptoms that are caused by hypoglycemia include confusion, difficulty thinking clearly, and eventually loss of consciousness or seizures.
Physical symptoms typically include sweating or a clammy feeling, headaches, general weakness or dizziness, speeded-up heartbeat, trembling or shaking, and hunger.
Not everyone with hypoglycemia experiences the same symptoms or experiences them with the same degree of severity. It is possible for a person to have a blood sugar level below 60 mg/dL and have no noticeable symptoms.
Diagnosis of hypoglycemia is based in part on the patient's history and partly on the results of blood and other tests. If the patient does not have diabetes, the doctor will look for three signs known as Whipple's triad: 1) the patient has the symptoms of hypoglycemia; 2) when tested, the blood sugar level is below 45 mg/dL (in a woman) or 55 mg/dL (in a man); 3) the symptoms are relieved in a few minutes when the patient is given sugar or a sugary drink.
If the patient has diabetes, the doctor will review the patient's treatment history to see whether the dosage or specific drug needs to be adjusted. The doctor may also order laboratory tests to look for breakdown products of insulin in the patient's blood. If the person has an insulin-secreting tumor, their blood insulin levels will be high but the level of insulin breakdown products will be low.
Reactive hypoglycemia is diagnosed by measuring the person's blood glucose in the doctor's office while he or she is having symptoms and then measuring the blood glucose again after the patient eats or drinks. If the patient's blood glucose level was below 70 mg/dL while he or she was having symptoms and the symptoms were relieved by food, the person is diagnosed as having reactive hypoglycemia.
Fasting hypoglycemia is diagnosed by a blood sample that shows a blood glucose level of less than 50 mg/dL after an extended supervised fast (usually seventy-two hours in an adult). A healthy person can usually maintain a blood glucose level above 50 mg/dL for seventy-two hours.
Treatment for hypoglycemia depends in part on its cause. Diabetics are usually asked to monitor their lifestyle habits, particularly eating and exercise patterns, as well as paying close attention to the proper use of their medications.
Patients with reactive hypoglycemia are cautioned to avoid sugary foods; have starches, high-protein, and high-fiber foods instead; and eat small meals or snacks every three to four hours rather than three large but widely spaced meals.
Fasting hypoglycemia is usually treated by evaluating the patient's medications and adjusting dosages as necessary; and recommending avoidance of alcohol. Fasting hypoglycemia caused by tumors is treated by surgical removal of the tumor.
Most people recover completely from an episode of hypoglycemia within minutes of taking some form of glucose. In a few cases, people who have fallen into comas before they were treated suffer long-term brain damage. In a very few cases, people may die from hypoglycemia if not treated.
Preventive measures vary somewhat for diabetics and for nondiabetics with hypoglycemia. Patients with diabetes should take the following steps to prevent hypoglycemia:
- Take medications exactly as prescribed; measure doses carefully.
- Do not skip meals or eat less than the amount of food prescribed for the insulin dosage.
- Keep alcohol consumption to a minimum.
- Exercise in moderation and check the blood glucose level before exercising.
- Check the blood glucose level with a home meter if early symptoms of hypoglycemia appear. If the level is below 70 mg/dL, take some glucose in the form of five or six pieces of hard candy, 1–2 teaspoons of honey or table sugar, two or three glucose tablets, or one-half cup of fruit juice.
- Measure the blood sugar again in fifteen minutes. If it is still below 70, take another dose of sugar or a sugary food or beverage. Always carry one of these foods or drinks in case of need.
- Wear a medical identification tag or bracelet if you have ever lost consciousness as a result of hypoglycemia.
- Ask the doctor about having a glucagon kit at home or work. People with a history of severe hypoglycemia may need to have a friend or relative inject them with the glucagon if they lose consciousness.
- Never drive a car without checking to see that the blood glucose level is above 70 mg/dL.
- People with reactive hypoglycemia should consult a registered dietitian to help them plan a personalized diet that will lower their risk of hypoglycemic episodes while still allowing them to eat foods they enjoy.
- Follow-up visits to the doctor to evaluate any further symptoms are also an important part of preventive care.
Research is focusing on a better understanding of the causes of reactive hypoglycemia. Researchers are also studying whether new devices for monitoring blood glucose levels frequently at home will help reduce the risk of hypoglycemic episodes.
WORDS TO KNOW
Fasting hypoglycemia: A type of hypoglycemia in people without diabetes that is caused by hormone deficiencies, medication side effects, or tumors rather than by reaction to a sugar-rich meal.
Glucagon: A hormone secreted by the pancreas that raises blood sugar levels by signaling the liver to convert glycogen to glucose.
Glycogen: A form of glucose that is stored in the liver as an energy reserve.
Insulin: A hormone secreted by the pancreas that lowers blood sugar levels by allowing body tissues to absorb and make use of the glucose.
Reactive hypoglycemia: A condition in which a person develops hypoglycemia between two and five hours after eating foods containing high levels of glucose.
Whipple triad: A group of three factors used to diagnose hypoglycemia: symptoms; blood sugar measuring below 45 mg/dL for a woman and 55 mg/dL for a man; and rapid recovery following a dose of sugar.
SEE ALSO Diabetes
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Fairview Health Services. Taking Charge of Your Diabetes. Minneapolis, MN: Fairview Press, 2006.
Kolata, Gina. “Study Undercuts Diabetes Theory.” New York Times, February 7, 2008. Available online at http://query.nytimes.com/gst/fullpage.html?res=9501E3D8163EF934A35751C0A96E9C8B63&sec=&spon=&page-wanted=all (accessed May 28, 2008). This is a news item about controversial findings from a diabetes study that suggest that trying to lower blood sugar levels to nearly normal in diabetic patients is harmful rather than helpful.
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