Definition

Vitamin B6 is used by the body as a catalyst in reactions
that involve amino acids. Vitamin B6 deficiency is
rare, since most foods eaten contain the vitamin.

Description

Vitamin B6 is a water-soluble vitamin. The recommended
dietary allowance (RDA) for vitamin B6 is 2.0
mg/day for the adult man and 1.6 mg/day for the adult
woman. Vitamin B6 in the diet generally occurs as a form
called pyridoxal phosphate. In this form, it cannot be
absorbed by the body. During the process of digestion,
the phosphate group is removed, and pyridoxal is produced.
However, the body readily absorbs pyridoxal, and
converts it back to the active form of the vitamin (pyridoxal
phosphate).

Poultry, fish, liver, and eggs are good sources of vitamin
B6, comprising about 3-4 mg vitamin/kg food; meat
and milk contain lesser amounts of the vitamin. The vitamin
also occurs, at about half this level, in a variety of
plant foods, including beans, broccoli, cabbage, and
peas. Vitamin B6 tends to be destroyed with prolonged
cooking, with storage, or with exposure to light.
As mentioned, vitamin B6 takes various forms. One
of these forms, called pyridoxine, is relatively stable. For
this reason, pyridoxine is the form of vitamin B6 that is
used in vitamin supplements, or when foods are fortified.
Apples and other fruits are poor sources of the vitamin,
containing only 0.2-0.6 mg vitamin/kg food.

Vitamin B6, used mainly in the body for the processing
of amino acids, performs this task along with certain
enzymes. The enzyme that participates in this type of complex
is aminotransferase. Several types of aminotransferase
exist. With vitamin B6 deficiency, while aminotransferase
continues to occur in the various organs of the body,
there is an abnormally low level of the active vitamin
B6/aminotransferase complex present. Thus, this vitamin
deficiency results in the impairment of a variety of activities
in the body. With supplement correction of the vitamin
B6 deficiency, the aminotransferase then readily forms the
active complex, and normal metabolism is restored.
Vitamin B6 converts certain amino acids (glutamic
acid, aspartic acid, glycine) to energy. This allows the
body to process all dietary protein, even when the dietary
protein is in excess of the body’s needs. Vitamin B6 also
allows the body to synthesize certain amino acids. For
example, if the diet is deficient or low in certain amino
acids, such as glycine or serine, vitamin B6 enables the
body to make them from sugar. Vitamin B6 is used also
for the synthesis of certain hormones, such as adrenaline.

Causes and symptoms

Vitamin B6 deficiency occurs rarely. When it does, it
is usually associated with poor absorption of nutrients in
the gastrointestinal tract (as in alcoholism, or with
chronic diarrhea), the taking of certain drugs (as isoniazid,
hydrolazine, penicillamine) that inactivate the vita-
min, with genetic disorders that inhibit metabolism of the
vitamin, or in cases of starvation.

The symptoms of vitamin B6 deficiency in adults are
only vaguely defined. These include nervousness, irritability,
insomnia, muscle weakness, and difficulty in
walking. Vitamin B6 deficiency may produce fissures and
cracking at the corners of the mouth. The deficiency
occurred in infants fed early versions of commercial
canned infant formula, when the vitamin had been inadvertently
omitted from the formula. This error resulted in
infants failing to grow, in irritability, and in seizures.

Diagnosis

Vitamin B6 status is measured by the transaminase
stimulation test. This test requires extraction of red blood
cells, and placement of the cells in two test tubes. Special
chemicals (reagents) are added to both test tubes to allow
for measurement of aminotransferase. This enzyme
requires pyridoxal phosphate. A known quantity of pure
pyridoxal phosphate is added to one of the test tubes. The
activity level of the enzyme is measured, and compared,
in both test tubes. If the added pyridoxal phosphate did
not stimulate activity, the patient is considered not to be
deficient in vitamin B6. Neither is the patient considered
deficient if only slight stimulation occurred. But if a
stimulation of four-fold or more occurred, a vitamin B6
deficiency is present.

Treatment

Vitamin B6 deficiency can be prevented or treated
with consumption of the recommended dietary allowance,
as supplied by food or by vitamin supplements.

Prognosis

The prognosis for correcting vitamin B6 deficiency
is excellent.

Prevention

Vitamin B6 deficiency is not a major concern for
most people. The deficiency can be prevented with consumption
of a mixed diet that includes poultry, fish, eggs,
meat, vegetables, and grains.