Vitamin B12 Deficiency What Is It? Vitamin B12 is needed to
produce an adequate amount of healthy red blood cells in the
bone marrow. Vitamin B12 is available only in animal foods (meat
and dairy products) or yeast extracts (such as brewer's yeast).
Vitamin B12 deficiency is defined by low levels of stored B12 in
the body that can result in anemia, a lower-than-normal number
of red blood cells. Vitamin B12 deficiency can develop for the
following reasons: - Absence of intrinsic factor, also called
pernicious anemia. Intrinsic factor is a protein secreted by
cells of the stomach lining. Intrinsic factor attaches to
vitamin B12 and takes it to the intestines to be absorbed. An
absence of intrinsic factor is the most common cause of
pernicious anemia. Absent intrinsic factor is often associated
with a condition called atrophic gastritis, a thinning of the
lining of the stomach. Atrophic gastritis is more common in
elderly people of African-American or Northern-European descent.
In these people, pernicious anemia