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Hypoglycemia

Glucose, a form of sugar, is the body's main fuel. Hypoglycemia, or low blood sugar, occurs when blood levels of glucose drop too low to fuel the body's activity.

Carbohydrates (sugars and starches) are the body's main dietary sources of glucose. During digestion, the glucose is absorbed into the blood stream (hence the term "blood sugar"), which carries it to every cell in the body. Unused glucose is stored in the liver as glycogen.

Hypoglycemia can occur as a complication of diabetes, as a condition in itself, or in association with other disorders.

The normal range for blood sugar is about 60 mg/dL (milligrams of glucose per deciliter of blood) to 120 mg/dL, depending on when a person last ate. In the fasting state, blood sugar can occasionally fall below 60 mg/dL and even to below 50 mg/dL and not indicate a serious abnormality or disease. This can be seen in healthy women, particularly after prolonged fasting. Blood sugar levels below 45 mg/dL are almost always associated with a serious abnormality.

How Does the Body Control Glucose?

The amount of glucose in the blood is controlled mainly by the hormones insulin and glucagon. Too much or too little of these hormones can cause blood sugar levels to fall too low (hypoglycemia) or rise too high (hyperglycemia). Other hormones that influence blood sugar levels are cortisol, growth hormone, and catecholamines (epinephrine and norepinephrine).

The pancreas, a gland in the upper abdomen, produces insulin and glucagon. The pancreas is dotted with hormone-producing tissue called the islets of Langerhans, which contain alpha and beta cells. When blood sugar rises after a meal, the beta cells release insulin. The insulin helps glucose enter body cells, lowering blood levels of glucose to the normal range. When blood sugar drops too low, the alpha cells secrete glucagon. This signals the liver to release stored glycogen and change it back to glucose, raising blood sugar levels to the normal range. Muscles also store glycogen that can be converted to glucose.

What Are the Symptoms of Hypoglycemia?

A person with hypoglycemia may feel weak, drowsy, confused, hungry, and dizzy. Paleness, headache, irritability, trembling, sweating, rapid heart beat, and a cold, clammy feeling are also signs of low blood sugar. In severe cases, a person can lose consciousness and even lapse into a coma.

The symptoms associated with hypoglycemia are sometimes mistaken for symptoms caused by conditions not related to blood sugar. For example, unusual stress and anxiety can cause excess production of catecholamines, resulting in symptoms similar to those caused by hypoglycemia but having no relation to blood sugar levels.

Hypoglycemia in people who do not have diabetes is far less common than once believed. However, it can occur in some people under certain conditions such as early pregnancy, prolonged fasting, and long periods of strenuous exercise. People on beta blocker medications who exercise are at higher risk of hypoglycemia, and aspirin can induce hypoglycemia in some children. Drinking alcohol can cause blood sugar to drop in some sensitive individuals, and hypoglycemia has been well documented in chronic alcoholics and binge drinkers. Eating unripe ackee fruit from Jamaica is a rare cause of low blood sugar.

References and Sources: Medline, Pubmed, National Institutes of Health

last update: December 2008


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