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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.
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.
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 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 type 1
diabetes and some people with type 2 diabetes use insulin. People
with type 2 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 type 1 diabetes 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 type 1 diabetes, 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 type 1 diabetes 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.
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