VITAMIN B COMPLEX
blood cells in bone marrow, in the uti-
lization of folic acid in the diet, and in
the functioning of the nervous system.
Foods
that are
rich in vitamin
B12
include
liver,
kidney,
chicken,
beef,
pork, fish, eggs, and dairy products.
DEFICIENCY
Deficiency is almost always due to in -
ability of the intestine to absorb vitamin
B12, usually because of pernicious anae-
mia (see
a n a e m ia , m e g a lo b la s t ic
) .
Less
commonly, deficiency may result from
g a s t re c to m y
(removal of all or part of the
stomach),
m a la b s o rp t io n
,
or
v e g a n is m
.
The effects of deficiency are megalo-
blastic anaemia, sore mouth and tongue,
and symptoms resulting from damage
to the
s p in a l c o r d
,
such as numbness and
tingling in the limbs. There may also be
depression and loss of memory.
EXCESS
A high intake of vitamin B12 has no
known harmful effects.
v ita m in B c o m p le x
A group of water-soluble
v ita m in s
that
comprise thiamine (vitamin B j), ribo-
flavin (vitamin B2), niacin, pantothenic
acid, pyridoxine
(vitamin B6), biotin
(vitamin H ), and folic acid.
V ita m in B 12
is discussed above.
THIAMINE
Thiamine plays a role in the activities
of various
e n z y m e s
that are involved in
the utilization of
c a rb o h y d ra t e s
and thus
in the functioning of nerves, muscles,
and the heart. Sources include whole-
grain cereals, wholemeal breads, brown
rice,
pasta,
liver,
kidney, pork,
fish,
beans, nuts, and eggs.
Those who are susceptible to defici-
ency include elderly people on a poor
diet, and people w ith
h y p e rt h y ro id is m
(overactivity of the thyroid gland),
m a l-
a b s o r p t io n
,
or severe
a lc o h o l d e p e n d e n c e
.
Deficiency may also occur as a result of
severe illness, surgery, or injury.
M ild deficiency of the vitamins may
cause tiredness, irritability, and loss of
appetite. Severe deficiency may cause
abdominal pain, constipation, depres-
sion, memory impairment, and
b e r ib e r i
;
in alcoholics, it may cause
W e rn ic k e -K o r-
s a k o f f s y n d ro m e
.
Excessive intake is not
known to cause harmful effects.
RIBOFLAVIN
Riboflavin is necessary for the activities
of various enzymes that are involved in
the breakdown and utilization of carbo-
hydrates, fats, and proteins; production
energy in cells; utilization of other B
vitamins; and hormone production by
the adrenal glands. Liver, whole grains,
milk, eggs, and brewer’s yeast are good
sources of these vitamins.
People who are susceptible to ribo-
flavin deficiency include those taking
phenothiazine
a n tip sy c h o tic d r u g s
,
tricyclic
a n t id e p re s s a n t d r u g s
,
or oestrogen-con-
taining
o ra l c o n tra c e p t iv e s
,
and
those
with malabsorption or severe alcohol
dependence. Deficiency may also occur
through serious illness, surgery, or injury.
Prolonged deficiency may cause sore-
ness of the tongue and the corners of the
mouth, and eye disorders such as
a m b ly -
o p ia
and
p h o t o p h o b ia
.
Excessive intake is
not known to have any harmful effects.
NIACIN
Niacin plays an essential role in the
activities of various enzymes involved
in the metabolism of carbohydrates and
fats, the functioning of the nervous and
digestive systems, the manufacture of
sex hormones, and the maintenance of
healthy skin. The main dietary sources
are liver, lean meat, fish, nuts, and dried
beans. Niacin can be made in the body
from tryptophan (an
a m in o a c id
) .
Most cases of deficiency are due to
malabsorption disorders or to severe
alcohol dependence. Prolonged niacin
deficiency
causes
p e lla g r a
,
the
main
symptoms of w hich are soreness and
cracking of the skin, inflammation of
the mouth and tongue, and mental dis-
turbances. Excessive intake of niacin is
not known to cause harmful effects.
PANTOTHENIC ACID
Pantothenic acid is
essential for the
activities of various enzymes that are
involved in carbohydrate and fat metab-
olism, manufacture of
c o rtic o s t e ro id s
and
s e x h o rm o n e s
,
utilization of other vita-
mins, the functioning of the nervous
system and
a d re n a l g la n d s
,
and growth
and development. It is present in almost
all vegetables, cereals, and animal foods.
Deficiency of pantothenic acid usual-
ly occurs as a result of malabsorption or
alcoholism, but may also occur after
severe illness, surgery, or injury. The
effects include fatigue, headache, nau-
sea,
abdominal pain,
numbness
and
tingling, muscle cramps, and suscepti-
bility to respiratory infections. Excessive
intake has no known harmful effects.
PYRIDOXINE
Pyridoxine aids the activities of various
enzymes and hormones involved in the
utilization of carbohydrates, fats, and
proteins, the manufacture of red blood
cells and antibodies, the functioning of
the digestive and nervous systems, and
the maintenance of healthy skin. Diet-
ary sources are liver, chicken, pork, fish,
whole
grains,
wheat-germ,
bananas,
potatoes, and dried beans. Pyridoxine is
also manufactured by intestinal bacteria.
People who are susceptible to a de-
ficiency of pyridoxine include elderly
people who have a poor diet, those with
malabsorption or severe alcohol depen-
dence, or those who are taking certain
drugs (including
p e n ic illa m in e
and
is o -
n ia z id
) .
Deficiency may cause weakness,
irritability, depression, skin disorders,
inflammation of the mouth and tongue,
a n a e m ia
,
and, in infants,
s e iz u r e s
.
In very
large amounts, pyridoxine may cause
n e u r it is
(nerve inflammation).
BIOTIN
Biotin is essential for the activities of
various enzymes involved in the break-
down of fatty acids and carbohydrates
and for the excretion of the waste prod-
ucts of protein breakdown. It is present
in many foods, especially liver, peanuts,
dried
beans,
egg
yolk,
mushrooms,
bananas, grapefruit, and watermelon.
Biotin is also manufactured by bacteria
in the intestines.
Deficiency of biotin may occur dur-
ing prolonged treatment with
a n tib io tic s
or
s u lp h o n a m id e d r u g s
.
Symptoms are
weakness, tiredness, poor appetite, hair
loss, depression, inflammation of the
tongue, and eczema. Excessive intake
has no known harmful effects.
FOLIC ACID
Folic acid is vital for various enzymes
involved in the manufacture of
n u c le ic
a c id s
and consequently for growth and
reproduction, the production of red
blood cells, and the functioning of the
nervous system. Sources of folic acid
include green vegetables, mushrooms,
liver, nuts, dried beans, peas, egg yolk,
and wholemeal bread.
M ild folic acid deficiency is com-
mon, but it can usually be corrected by
increasing dietary intake. More severe
deficiency may occur during pregnancy
or breast-feeding, in premature or low-
birthweight
infants,
in
people
on
d ia ly s is
,
in people with certain blood
disorders, the skin disorder
p s o r ia s is
,
malabsorption, or alcohol dependence,
and in people taking certain drugs.
The main effects include anaemia,
sores around the mouth, and, in chil-
dren, poor growth. Supplements of folic
acid taken just before conception, and
for the first j 2 weeks of pregnancy, have
been shown to reduce the risk of a
n e u r -
a l tu b e d e fe c t
in the baby.
V
795
previous page 794 BMA A Z Family Medical Encyclopedia   2004 read online next page 796 BMA A Z Family Medical Encyclopedia   2004 read online Home Toggle text on/off