What Is 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.
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.
Blood Sugar Range
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.
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 Diabetes
The most common cause of hypoglycemia is as a complication of diabetes.
Diabetes occurs when the body cannot use glucose for fuel because either
the pancreas is not able to make enough insulin or the insulin that is
available is not effective. As a result, glucose builds up in the blood
instead of getting into body cells.
The aim of treatment in diabetes is to lower high blood sugar levels.
To do this, people with diabetes may use insulin or oral drugs, depending
on the type of diabetes they have or the severity of their condition.
Hypoglycemia occurs most often in people who use insulin to lower their
blood sugar. All people with insulin-dependent diabetes (IDDM or Type
I) and some people with noninsulin-dependent diabetes (NIDDM or Type II)
use insulin. People with Type II diabetes who take oral drugs called sulfonylureas
are also vulnerable to low blood sugar episodes.
Conditions that can lead to hypoglycemia in people with diabetes include
taking too much medication, missing or delaying a meal, eating too little
food for the amount of insulin taken, exercising too strenuously, drinking
too much alcohol, or any combination of these factors. People who have
diabetes often refer to hypoglycemia as an "insulin reaction."
Managing Hypoglycemia in Diabetes
People with diabetes should consult their health care providers
for individual guidelines on target blood sugar ranges that are best for
them. The lowest safe blood sugar level for an individual varies, depending
on the person's age, medical condition, and ability to sense hypoglycemic
symptoms. A target range that is safe for a young adult with no diabetes
complications, for example, may be too low for a young child or an older
person who may have other medical problems.
Because they are attuned to the symptoms, people with diabetes can usually
recognize when their blood sugar levels are dropping too low. They can
treat the condition quickly by eating or drinking something with sugar
in it such as candy, juice, or nondiet soda. Taking glucose tablets or
gels (available in drug stores) is another convenient and quick way to
treat hypoglycemia.
People with IDDM are most vulnerable to severe insulin reactions, which
can cause loss of consciousness. A few patients with long-standing insulin-dependent
diabetes may develop a condition known as hypoglycemia unawareness, in
which they have difficulty recognizing the symptoms of low blood sugar.
For emergency use in patients with IDDM, physicians often prescribe an
injectable form of the hormone glucagon. A glucagon injection (given by
another person) quickly eases the symptoms of low blood sugar, releasing
a burst of glucose into the blood.
Emergency medical help may be needed if the person does not recover
in a few minutes after treatment for hypoglycemia. A person suffering
a severe insulin reaction may be admitted to the hospital so that blood
sugar can be stabilized.
People with diabetes can reduce or prevent episodes of hypoglycemia
by monitoring their blood sugar levels frequently and learning to recognize
the symptoms of low blood sugar and the situations that may trigger it.
They should consult their health care providers for advice about the best
way to treat low blood sugar. Friends and relatives should know about
the symptoms of hypoglycemia and how to treat it in case of emergency.
Episodes of hypoglycemia in people with IDDM may become more common
now that research has shown that carefully controlled blood sugar helps
prevent the complications of diabetes. Keeping blood sugar in a close-to-normal
range requires multiple injections of insulin each day or use of an insulin
pump, frequent testing of blood glucose, a diet and exercise plan, and
guidance from health care professionals.
Other Causes of Hypoglycemia
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.
Diagnosis
To diagnose hypoglycemia in people who do not have diabetes,
the doctor looks for the following three conditions:
- The patient complains of symptoms of hypoglycemia
- Blood glucose levels are measured while the person is experiencing
those symptoms and found to be 45 mg/dl or less in a woman or 55 mg/dl
or less in a man
- The symptoms are promptly relieved upon ingestion of sugar.
For many years, the oral glucose tolerance test (OGTT) was used to diagnose
hypoglycemia. Experts now realize that the OGTT can actually trigger hypoglycemic
symptoms in people with no signs of the disorder. For a more accurate
diagnosis, experts now recommend that blood sugar be tested at the same
time a person is experiencing hypoglycemic symptoms.
The doctor will also check the patient for health conditions such as
diabetes, obtain a medication history, and assess the degree and severity
of the patient's symptoms. Laboratory tests to measure insulin production
and levels of C-peptide (a substance that the pancreas releases into the
bloodstream in equal amounts to insulin) may be performed.
Reactive Hypoglycemia
A diagnosis of reactive hypoglycemia is considered only after
other possible causes of low blood sugar have been ruled out. Reactive
hypoglycemia with no known cause is a condition in which the symptoms
of low blood sugar appear 2 to 5 hours after eating foods high in glucose.
Ten to 20 years ago, hypoglycemia was a popular diagnosis. However,
studies now show that this condition is actually quite rare. In these
studies, most patients who experienced the symptoms of hypoglycemia after
eating glucose-rich foods consistently had normal levels of blood sugar--above
60 mg/dl. Some researchers have suggested that some people may be extra
sensitive to the body's normal release of the hormone epinephrine after
a meal.
People with symptoms of reactive hypoglycemia unrelated to other medical
conditions or problems are usually advised to follow a healthy eating
plan. The doctor or dietitian may suggest that such a person avoid foods
high in carbohydrates; eat small, frequent meals and snacks throughout
the day; exercise regularly; and eat a variety of foods, including whole
grains, vegetables, and fruits.
Rare Causes of Hypoglycemia
Fasting hypoglycemia occurs when the stomach is empty. It usually
develops in the early morning when a person awakens. As with other forms
of hypoglycemia, the symptoms include headache, lack of energy, and an
inability to concentrate. Fasting hypoglycemia may be caused by a variety
of conditions such as hereditary enzyme or hormone deficiencies, liver
disease, and insulin-producing tumors.
In hereditary fructose intolerance, a disorder usually seen in children,
the body is unable to metabolize the natural sugar fructose. Attacks of
hypoglycemia, marked by seizures, vomiting, and unconsciousness, are treated
by giving glucose and eliminating fructose from the diet.
Galactosemia, a rare genetic disorder, hampers the body's ability to
process the sugar galactose. An infant with this disorder may appear normal
at birth, but after a few days or weeks of drinking milk (which contains
galactose), the child may begin to vomit, lose weight, and develop cataracts.
The liver may fail to release stored glycogen into the blood, triggering
hypoglycemia. Removing milk from the diet is the usual treatment.
A deficiency of growth hormone causes increased sensitivity to insulin.
This sensitivity occurs because growth hormone opposes the action of insulin
on muscle and fat cells. For this reason, children with growth hormone
deficiency sometimes suffer from hypoglycemia, which goes away after treatment.
People with insulin-producing tumors, which arise in the islet cells
of the pancreas, suffer from severe episodes of hypoglycemia.
To diagnose these tumors, called insulinomas, a doctor will put the
patient on a 24- to 72-hour fast while measuring blood levels of glucose,
insulin, and proinsulin. High levels of insulin and proinsulin in the
presence of low levels of glucose strongly suggest an insulin-producing
tumor. These tumors are usually benign and can be surgically removed.
In rare cases, some cancers such as breast cancer and adrenal cancer
may cause hypoglycemia through secretion of a hormone called insulin-like
growth factor II. The treatment is removal of the tumor, if possible.
NIH Publication No. 95-3926
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