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 neurotransmittersand adrenal
gland hormones; in the response of the
immune systemto 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 scurvyand anaemia.
If the daily dose of vitamin C exceeds
about 1g, it may cause nausea, stomach
cramps, diarrhoea, or kidney stones
(see calculi, urinary tract).
vitamin DThe collective term for a
group of substances that help to regu-
late the balance of phosphate and
calciumin 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
includeliver 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 hypercalcaemiaand abnormal
calcium deposits in the soft tissues,
kidneys, and blood vessel walls. In chil-
dren, it may cause growth retardation.
vitamin EThe 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 KA fat-soluble vitaminthat 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 supplementsA 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,VITAMIN D VITAMIN SUPPLEMENTS
V