The Facts
The blood that circulates throughout the body performs a number of critical
functions. It delivers oxygen, removes carbon dioxide, and carries life-sustaining
nutrients. By serving as the vehicle for long-distance messengers such as hormones,
blood helps the various parts of the body communicate with each other. These
important functions are performed by blood cells working in partnership with
the liquid part of the blood (plasma). Most of the cells in it are red
blood cells (erythrocytes). White blood cells (leukocytes) are also present
in smaller numbers. Their role is to defend your body against foreign matter,
including infections, viruses, and fungi.
Anemia is a state that occurs when hemoglobin (an iron-protein compound
in red blood cells that transports oxygen) is diminished and your body has too
few red blood cells. When there are too few red blood cells due to a lack
of vitamin B12, the condition is described as pernicious anemia. The
term pernicious was adopted many years ago when there was no effective
treatment and this condition was inevitably fatal. Today, excellent therapies
are available and most people can lead a normal life with very little adverse
effects.
Pernicious anemia can affect all racial groups, but the incidence is higher
among fair-haired people, especially those whose ancestors came from Scandinavia
or Northern Europe. It usually doesn't appear before the age of 30, although
a juvenile form of the disease can occur in children. About one in every 1,000
people is affected.
Alternative names for pernicious anemia are vitamin B12 deficiency (malabsorption),
Addison's anemia, congenital pernicious anemia, and combined
systems disease.
Causes
Pernicious anemia is caused by a deficiency of vitamin B12, which is needed
for normal production of red blood cells. It is often hereditary. Risk factors
include a history of autoimmune endocrine disorders, a family history
of pernicious anemia, and Scandinavian or Northern European descent.
The meat and dairy products we eat are our primary sources of vitamin B12.
However, except in strict vegetarians, pernicious anemia isn't simply caused
by not eating enough of these foods. Usually, it is because of a failure in
the complex process the digestive tract must go through to absorb vitamin B12.
In order for vitamin B12 to be absorbed by the small intestine, the cells
that line a part of the stomach must produce a substance called intrinsic
factor (IF). This substance attaches itself to vitamin B12, and both
are absorbed in combination into the lowest portion of the small bowel (ileum),
just before the small bowel enters the colon. If the ileum is damaged or removed
in the course of surgery, the intrinsic factor/vitamin B12 combination will
not be absorbed. People with conditions like Crohn's disease, who often have
surgery to remove part of their ileum (the part of the small intestine where
vitamin B12 is absorbed), should be screened for vitamin B12 deficiency and
treated if needed.
Lack of intrinsic factor may also be congenital (present at birth).
This form of pernicious anemia (called juvenile or congenital)
is usually seen before a child is three years old. It is believed that only
one parent needs to carry the gene for this disorder to pass it along to a child.
Less common causes of decreased B12 absorption include chronic pancreatitis,
malabsorption syndromes, certain medications, and, very rarely, increased metabolism
of B12 through long-standing hyperthyroidism. A very common cause of
B12 deficiency in the elderly is inadequate absorption of dietary B12.
Pernicious anemia is often is also seen in combination with some autoimmune
endocrine (gland) diseases such as type 1 diabetes, hypoparathyroidism,
Addison's disease, and testicular dysfunction.
