What is hypoglycemia?
Hypoglycemia is a medical term referring to a pathologic state produced and usually defined by a lower than normal amount of sugar (glucose) in the blood. The term hypoglycemia literally means low blood sugar. Hypoglycemia can produce a variety of symptoms and effects but the principal problems arise from an inadequate supply of glucose as fuel to the brain,
resulting in impairment of function (neuroglycopenia). Derangements of function can range from vaguely "feeling bad" to coma and rarely death. Hypoglycemia can arise from many conditions, and can occur at any age.
Hypoglycemia is usually divided into "reactive hypoglycemia" and "functional hypoglycemia." Reactive hypoglycemia refers to hypoglycemia caused by external influences, like diet and medication use. This type is more amenable to management or cure. Functional hypoglycemia refers to hypoglycemia caused by a malfunction, possibly metabolic, within the sufferer. This type is harder to manage. Functional hypoglycemia is caused by an overproduction of insulin, or a malfunctioning of the body's insulin-management system (insulin resistance. Hypoglycemia is also known as idiopathic if no physical cause for the bloodsugar drop can be discerned.
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 result in dizziness, headache, blurred vision, difficulty concentrating and even more serious neurological symptoms. Hypoglycemia also triggers the release of epinephrine, norepinephrine and other body hormones that work to raise blood-sugar levels. The release of these hormones produces additional symptoms of tremor, sweating, rapid heartbeat, anxiety and hunger.
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. 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.
Hypoglycemia is most common in people with diabetes. In these people, hypoglycemia occurs because of some imbalance between their dose of diabetic medication, usually insulin, and their diet or exercise level. Because insulin and exercise both lower blood sugar and food raises it, hypoglycemia in diabetic patients can be caused by too much insulin, a switch to a new combination of insulins whose effects overlap, too little food, meal skipping, or too much exercise. Although hypoglycemia also can occur with the use of oral hypoglycemic medications that lower blood glucose, especially the sulfonylureas, it is much more common in people who are taking insulin.
Hypoglycemia means low blood sugar (glucose). The blood glucose levels in healthy individuals fluctuate depending greatly on the duration of fasting. The normal range is 70 to 120 mg/dl after an overnight (12 hours) fast. In healthy men, the blood glucose can drop to 55 mg/dl after 24 hours of fasting and to 48 mg/dl after 72 hours of fasting. In healthy women, glucose levels can be as low as 35 mg/dl after only 24 hours of fasting.
Since blood glucose levels can fluctuate widely in healthy subjects, and symptoms of hypoglycemia can be vague and nonspecific, establishing the diagnosis of hypoglycemia as the cause of symptoms is often difficult. When symptoms of hypoglycemia occur together with a documented blood glucose under 45 mg/dl, and the symptoms promptly resolve with the administration of glucose, the diagnosis can be made with more certainty.