Vitamin - B6
deficiency
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 vitamin, 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.
Key Terms
Amino acid
Amino acids are small molecules that
are used as building blocks for all proteins. Some amino acids are also used in
the body for the manufacture of hormones. There are about 20 nutritionally
important amino acids, including glutamic acid, glycine, methionine, lysine,
tryptophan, serine, and glycine.
Fat-soluble vitamins
Fat-soluble vitamins can be dissolved
in oil or in melted fat.
Recommended Dietary Allowance (RDA)
The Recommended Dietary Allowances
(RDAs) are quantities of nutrients in the diet that are required to maintain
good health in people. RDAs are established by the Food and Nutrition Board of
the National Academy of Sciences, and may be revised every few years. A separate
RDA value exists for each nutrient. The RDA values refer to the amount of
nutrient expected to maintain good health in people. The actual amounts of each
nutrient required to maintain good health in specific individuals differ from
person to person.
Water-soluble vitamins
Water-soluble vitamins can be
dissolved in water or juice.
