Vitamin A
DEFINITION
Vitamin A is a fat-soluble vitamin that is essential for a
variety of functions in the body, including maintaining good vision
and a healthy immune system.
variety of functions in the body, including maintaining good vision
and a healthy immune system.
DESCRIPTION
Vitamin A is an essential dietary vitamin whose main storage
site in the body is in the liver. Vitamin A is available in foods
such as liver, kidney and dairy products, but certain fruits and
vegetables contain very high levels of a substance called
beta-carotene. Beta-carotene is absorbed by the body and is easily
converted into Vitamin A. Vitamin A is converted into a number of
active chemicals that perform different roles in the body. The body
first makes retinol, which can be turned into retinal to be used in
vision and reproduction or retinoic acid to be used in the growth
and development of cells.
site in the body is in the liver. Vitamin A is available in foods
such as liver, kidney and dairy products, but certain fruits and
vegetables contain very high levels of a substance called
beta-carotene. Beta-carotene is absorbed by the body and is easily
converted into Vitamin A. Vitamin A is converted into a number of
active chemicals that perform different roles in the body. The body
first makes retinol, which can be turned into retinal to be used in
vision and reproduction or retinoic acid to be used in the growth
and development of cells.
Vitamin A is important for many functions in the body,
including:
including:
- Vision. Vitamin A is essential for healthy eyes. This vitamin
is particularly important for vision in dim light and Vitamin A
deficiency can cause a condition called night blindness. - Skin Conditions and Membranes. Retinoic acid (an active form of
Vitamin A) slows down the production of a skin protein called
keratin. Excess keratin production can cause skin diseases such as
acne and psoriasis. Vitamin A is also essential for the health of
membrane tissues. Membrane tissues are ‘lining’ tissues that
produce mucus (e.g. the intestines, the urinary tract, the
sinuses). - Wound Healing. A deficiency in Vitamin A can retard the
development of collagen in the body that is required for effective
wound healing. - Immunity Against Infection. Vitamin A deficiency can increase
the chances of infection. An adequate intake of Vitamin A improves
the production of antibodies, which are specialised body proteins
that fight specific infections. - Antioxidant Properties and Tissue Repair. Vitamin A is an
antioxidant, which is a chemical that prevents damage and premature
ageing by destroying toxic chemicals called free radicals. Free
radicals are produced during infection, inflammation, stress and
when toxins such as alcohol have been consumed. Vitamin A is
important for wound healing, as it promotes the growth of the new
tissue that replaces dead and damaged areas of the body. - Cancer Prevention. Free radicals in the body can damage DNA,
thus increasing the risk of cancer. Some forms of Vitamin A may
actually protect the cells of the body against free radical damage
and thus help to protect against certain cancers. - Other Uses. Vitamin A is used by the body in the formation of
sperm and the maintenance of the placenta and is essential for
foetal development.
DEFICIENCY
Vitamin A deficiency can cause serious health problems.
Vitamin A is a fat-soluble vitamin, so diseases that interfere with
the absorption of fats from the gut can cause Vitamin A deficiency.
These conditions include inadequate production of bile fluids,
under-production of digestive enzymes by the pancreas, sprue,
Crohn’s disease and some types of liver cirrhosis. Vitamin A
deficiency can cause night blindness and eye diseases, breathing
problems and an increased risk of respiratory infection, skin
lesions and dry, scaly skin, abnormal production of sperm,
infertility, diarrhoea and an impaired sense of taste and of
smell.
Vitamin A is a fat-soluble vitamin, so diseases that interfere with
the absorption of fats from the gut can cause Vitamin A deficiency.
These conditions include inadequate production of bile fluids,
under-production of digestive enzymes by the pancreas, sprue,
Crohn’s disease and some types of liver cirrhosis. Vitamin A
deficiency can cause night blindness and eye diseases, breathing
problems and an increased risk of respiratory infection, skin
lesions and dry, scaly skin, abnormal production of sperm,
infertility, diarrhoea and an impaired sense of taste and of
smell.
SOURCES
Vitamin A is found in animal products such as liver,
fish-liver oils, eggs and full fat dairy products. Dark-green
vegetables and deep-yellow fruits and vegetables provide Vitamin A
as well as beta-carotene (which is converted into Vitamin A by the
body). The Vitamin A content of foods can be lost during
preparation, cooking or storage procedures. To maximise the amount
of Vitamin A that can be derived from foods, take the following
steps:
fish-liver oils, eggs and full fat dairy products. Dark-green
vegetables and deep-yellow fruits and vegetables provide Vitamin A
as well as beta-carotene (which is converted into Vitamin A by the
body). The Vitamin A content of foods can be lost during
preparation, cooking or storage procedures. To maximise the amount
of Vitamin A that can be derived from foods, take the following
steps:
- Serve fruits and vegetables raw whenever possible.
- Keep vegetables and fruits covered and refrigerated during
storage. - Steam vegetables and braise, bake or broil meats instead of
frying, as some Vitamin A is lost in the fat during the frying
process.
DOSAGE
Vitamin A is deposited in the body’s fat stores, so it can
build up to toxic levels in the body. This is especially important
for pregnant women, as Vitamin A has been shown to cause
spontaneous abortion and birth defects when taken in excess. The
recommended daily intake (RDI) for Vitamin A is 750 Retinol
Equivalents (RE) or 3750 IU for adult men and adult women,
including those that are pregnant. Women who are breastfeeding
require an additional 450 RE per day. Higher dosages are taken for
Vitamin A deficiency and medical problems. Doses higher than the
recommended daily intake should be supervised by a medical
practitioner. Vitamin A toxicity can cause dryness and scaling of
the skin, fatigue, headache, loss of body hair and brittle nails.
If in any doubt ask your health professional for advice.
build up to toxic levels in the body. This is especially important
for pregnant women, as Vitamin A has been shown to cause
spontaneous abortion and birth defects when taken in excess. The
recommended daily intake (RDI) for Vitamin A is 750 Retinol
Equivalents (RE) or 3750 IU for adult men and adult women,
including those that are pregnant. Women who are breastfeeding
require an additional 450 RE per day. Higher dosages are taken for
Vitamin A deficiency and medical problems. Doses higher than the
recommended daily intake should be supervised by a medical
practitioner. Vitamin A toxicity can cause dryness and scaling of
the skin, fatigue, headache, loss of body hair and brittle nails.
If in any doubt ask your health professional for advice.
NOTES
Vitamin A and its related chemical, beta carotene, are thought
to reduce the risks of cancer in most people, however, there is
some evidence to suggest that a high intake of beta carotene in
people who smoke may actually increase the risk of certain cancers.
This may be because the toxic chemicals that are produced by
smoking can damage the beta carotene in the body and convert it
into a chemical that can harm the body. .
to reduce the risks of cancer in most people, however, there is
some evidence to suggest that a high intake of beta carotene in
people who smoke may actually increase the risk of certain cancers.
This may be because the toxic chemicals that are produced by
smoking can damage the beta carotene in the body and convert it
into a chemical that can harm the body. .