VITAMIN D
VITAMIN SUPPLEMENTS
of various
enzymes.
Vitamin C is impor-
tant for the growth and maintenance of
healthy bones, teeth, gums, ligaments,
and blood vessels; in the production of
certain
neurotransmitters
and adrenal
gland hormones; in the response of the
immune system
to infection; in wound
healing; and in the absorption of
iron.
The main dietary sources are fruits
and vegetables. Considerable amounts
of vitamin C are lost when foods are
processed, cooked, or kept warm.
Mild deficiency of vitamin C may re-
sult from a serious injury or burn, major
surgery, the use of
oral contraceptives
,
fever, or continual inhalation of carbon
monoxide (from traffic fumes or tobacco
smoke). It may cause weakness, general
aches, swollen gums, and
nosebleeds
.
More
serious
deficiency
is
usually
caused by a very restricted diet. Severe
deficiency leads to
scurvy
and
anaemia.
If the daily dose of vitamin C exceeds
about
1
g, it may cause nausea, stomach
cramps, diarrhoea, or kidney stones
(see
calculi, urinary tract).
vitamin D The collective term for a
group of substances that help to regu-
late the balance of
phosphate
and
calcium
in the body, aid calcium absorp-
tion in the intestine, and promote strong
bones and teeth.
Good sources include oily fish, liver,
and egg yolk; vitamin D is also added to
margarines. In the body, vitamin D is
synthesized by the action of ultraviolet
light on a particular chemical in the skin.
Deficiency may occur in people with a
poor diet, in premature infants, and in
those deprived of sunlight. It can also
result from
malabsorption
. Other causes
include liver or kidney disorders and
some genetic defects. Prolonged use of
certain drugs, such as
phenytoin
, may
also lead to deficiency. Deficiency in
young children causes
rickets
; long-term
deficiency in adults leads to
osteomalacia
.
Excessive intake of vitamin D may
lead to
hypercalcaemia
and abnormal
calcium deposits in the soft tissues,
kidneys, and blood vessel walls. In chil-
dren, it may cause growth retardation.
vitamin E The collective term for a group
of substances that are essential for nor-
mal cell structure, for maintaining the
activities of certain
enzymes
, and for the
formation of red blood cells. Vitamin E
also protects the lungs and other tissues
from
damage by pollutants and is
believed to slow aging of cells. Sources
include vegetable oils, nuts, meat, green
vegetables, cereals, and egg yolk.
Dietary deficiency is rare; deficiency is
most common in people with
malab-
sorption
, certain liver disorders, and in
premature infants. It leads to the de-
struction of red blood cells, which
eventually leads to
anaemia
. In infants,
deficiency causes irritability and
oedema
.
Prolonged excessive intake of vitamin
E may cause abdominal pain, nausea,
and diarrhoea. It may also reduce intes-
tinal absorption of vitamins A, D, and K.
vitamin K A fat-soluble
vitamin
that is
essential for the formation in the liver
of substances that promote blood clot-
ting. Good sources are green vegetables,
vegetable oils, egg yolk, cheese, pork,
and liver. Vitamin K is also manufac-
tured by bacteria in the intestine.
Dietary deficiency rarely occurs. De-
ficiency may develop in people with
malabsorption
, certain liver disorders, or
chronic diarrhoea. It may also result
from prolonged treatment with
antibi-
otics.
Newborns
lack the
intestinal
bacteria that produce vitamin K and are
routinely given supplements to prevent
deficiency. Vitamin K deficiency may
cause nosebleeds and bleeding from
the gums, intestine, and urinary tract. In
rare, severe cases, brain haemorrhage
may result. Excessive intake of vitamin
K is not known to cause harmful effects.
vitamin supplements A group of diet-
ary preparations containing
1
or more
vitamins
. Most healthy people who have
a balanced diet do not need them. Sup-
plements are used to treat diagnosed
vitamin deficiency. They are also given
to prevent vitamin deficiency in suscep-
tible people, such as those who have
increased requirements (for example,
women who are pregnant or breast-
feeding); those who follow a restricted
diet (in
veganism
, for example); those
with severe
alcohol dependence
; and
people who have
malabsorption
,
liver
disorders
,
kidney disorders
, or another
serious illness or injury. In addition,
V
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