vitamin A has been most well known as a cure for night
blindness. In fact, night blindness is a symptom of
vitamin A deficiency, which can be alleviated by taking
sufficient amounts of that vitamin. Symptoms of night
blindness were first recognized in ancient Egypt around
1500 B.C. Although at the time the problem was not
linked to a dietary deficiency of any kind, the symptoms
were treated by placing roasted or fried liver over
the eyes. Later, Hippocrates suggested eating beef
liver, a rich source of vitamin A, as a cure for night
blindness. Today we known that vitamin A serves several
other important functions in the body, and chemical
derivatives of vitamin A have important medical benefits,
particularly in the area of treatment of skin conditions
and in cancer treatment. We also know that vitamin
A deficiencies lead to a higher risk for some cancers.
Including lung cancer in smokers.
Several compounds with similar chemical structures
in nature have vitamin A activity. In animal - derived
foods, most vitamin A exists as retinol or retinal.
Vitamin A from plants is in the form of carotenoids.
Carotenoids are considered "provitamins"
because they must be metabolized in the body before
they can act as a vitamin. Alone, however, they may
serve as free-radical scavengers and quenchers of
singlet oxygen. There are many carotenoids in plants,
but not all have vitamin A activity. Beta carotene
is the most common, and it has the most potent vitamin
All compounds with vitamin A activity are fat-soluble;
like all fats, they are absorbed from the intestinal
tract with the help of bile.
A in essential to a variety of biochemical and physiological
processes, the vitamin must undergo a minor chemical
change to allow it to participate in that function.
Vitamin A, as retinal, is a part of the pigment called
rhodopsin, found in the retina of the eye. Rhodospin
in sensitive to small amounts of light and is essential
for night vision because it allows us to discern objects
in very low light. To function in this way, the retina
of the eye must contain a large concentration of vitamin
Retinoic acid is present in very small amounts, yet
it has an important function in promoting cell growth
and cell differentiation. Skin cells and the cornea
of the eye are especially affected by vitamin A deficiency.
The skin turns rough and scaly, and hair follicles
become obstructed. Vitamin A, as retinoic acid, probably
plays an important role in preventing cancer because
of its ability to regulate cell division and differentiation.
Vitamin A, as retinol, is needed for reproduction.
Rats deprived of vitamin A cannot reproduce. Retinoic
acid will not cure the infertility.
Vitamin A is also important in maintaining a normal
immune system. Vitamin A deficiency results in an
increased susceptibility to infections, and it has
been called the "anti-infective vitamin".
In recent years it has been recognized that measles
occurring in vitamin A - deficient children is very
severe, often resulting in death. A program started
by the World Health Organization gives occasional
high oral doses of vitamin A to children in certain
developing countries that have a high death rate from
measles and other infections. The association between
very severe measles requiring hospitalization and
low vitamin A status has been made even in United
States, and a call has been made to pay more attention
to vitamin A intake in children. Some have suggested
that all hospitalized children with measles be given
a high-dose vitamin A supplement.
Beta carotene, the most potent plant - derived precursor
of retinol, retinal, and retinoic acid, ahs a biological
activity of its own. It is an excellent free-radical
scavenger, and it neutralizes reactive singlet oxygen.
However, other plant carotenoids may be even more
important in protecting us against the damaging effects
strength of vitamin A can be expressed in terms of
a measure of biological activity, international units,
or as retinol equivalent, which indicates the amount
of retinol to which the substance can be converted
in the body. The use of IU is older and has been mostly
replaced in nutrition tables by the use of RE values.
Commercial vitamin products, however, still use the
old IU system and the older U.S. RDA values, which
are in IU. To convert between system, simply remember
that 1 RE of vitamin A equals 3.3 IU.
The adult RDA for vitamin A is 1,000 RE for men and
800 RE for women. Pregnant or breast-feeding women
need an additional 200 and 400 RE, respectively. The
U.S. RDA value for adults is 5,000 IU. The RDA for
infants and children is smaller than that for adults,
but when compared on a pound-for-pound basis, it is
considerably larger because of the need for vitamin
A in normal processes of growth and development.
Small amounts of vitamin E will increase the capacity
of all body tissues, including the retina and liver,
to store vitamin A. For this reason, people who must
take vitamin A to correct a deficiency state should
also take vitamin A to correct a deficiency state
should also take a modest amount of vitamin E. Most
comprehensive multivitamin formulas have enough vitamin
E in the m to satisfy this need for the vitamin.
is easy to recall which foods are rich in vitamin
A if you remember that retinols dissolve in fat and
carotenes are found in yellow plant pigments. Some
rich animal sources of vitamin A are liver, whole
milk, cream, and butter. Additional good sources are
listed in the accompanying table. Four ounces of beef
liver has more than a seven-day supply of vitamin
A, and fish liver has even more. Cold liver oil was
commonly used as a source of this vitamin and of vitamin
D before purified vitamin A was available. A single
teaspoon of cod liver oil will fulfill the adult RDA
High concentration of carotene are found in dark green
vegetables, where the green of chlorophyll usually
covers the yellow to-orange carotenoid color, and
yellow-orange vegetables such as carrots, pumpkin,
and squash. Other sources are listed in the accompanying
A content of Selected Food
(Average adult RDA is 900 RE, or 4,500 IU)
(IU per 3 oz)
Carotene is converted to retinol in the wall of the
small intestine as it is being absorbed into the blood.
The process of conversion continues only as long as
retinol is needed. Once the need for retinol has been
satisfied, the conversion process stops, so high doses
of beta carotene do not result in toxic levels of
A is sensitive to oxygen. Thus, prolonged beating
in the presence of air will destroy the vitamin A
activity of any food. To minimize this loss while
cooking you food, place a lid on the pot or pan used
to boil such vegetables as squash or carrots, and
use a small pot with just enough water to cover the
vegetables. Acid also destroys A, but most food sources
of this vitamin are nonacidic, so this is not a practical
15 percent of Americans, mostly infants and children,
get less than the RDA value for vitamin A. Fortunately,
the average person has about a two-year supply of
vitamin A in their liver, so you have to eat a vitamin
A - deficient diet for many months before symptoms
vitamin A deficiency may be easily overlooked. Dry,
rough skin is common. Sometimes the skin can crack
and may even become infected. The infection develops
because cracks and rough areas in the skin leave openings
for microorganisms to enter and because vitamin A
is needed for a strong immune response.
The most recognizable sign of vitamin A deficiency
is night blindness. This is followed by further damage
to the cornea in the form of a condition called xerophthalmia.
If left untreated, severe vitamin A deficiency can
lead to permanent blindness. Vitamin A deficiency
is the leading worldwide cause of blindness in childhood
and is an enormous problem is many developing countries.
People who are deficient in vitamin A have an increased
susceptibility to respiratory infections because of
changes in the cells that line the respiratory tract.
Because of their depressed immune response, deficient
children develop more severe forms of common childhood
diseases. And a mentioned earlier, measles can be
lethal in a vitamin A - deficient child.
Other possible effects of vitamin A deficiency include
slow growth, thickening of bone, kidney stone that
originate with changes in some of the cells that line
the kidney tubules, diarrhea, and reduced production
of steroid hormones in the body. Steroids are produced
by the adrenal gland and are a part of your natural
response to stress and your immune function. Failure
to make these important hormones will leave your immune
system in a less-than-ideal state. Damage to hearing,
taste, and smell, nerve damage, and reduced sweat
gland function may also occur.
It is possible to measure vitamin A in your blood,
but the results of this test are difficult to interpret
because of the large amounts that are stored in the
liver. Repeatedly low blood values are a direct indication
of a severe vitamin deficiency that demands immediate
may develop symptoms of vitamin A toxicity after taking
more than 50,000 IU a day for long periods of time
or after taking a single dose of 300,000 IU or more.
Infants given 7,500 to 15,000 RE of vitamin A for
thirty days have developed toxicity symptoms. In children,
vitamin A toxicity has usually been caused by an overzealous
parent giving excessive quantities of supplemental
vitamin A. Infants and children who are given 6,000
RE of vitamin A a day and who are not deficient are
likely to develop overdose symptoms after several
Vitamin A overdose is characterized by vomiting, fatigue,
swelling due to fluid accumulation, hydrocephalus,
and headache. Vitamin A overdose has, in some cases,
been misdiagnosed as a brain tumor. Other symptoms
of overdose are liver and lymph gland enlargement,
difficult sleeping, joint pains, constipation, and
rough skin. The effects of an overdose of vitamin
A will usually reverse themselves after you stop taking
Since the body will convert as much carotenoid to
retinol as it needs, it is possible to have excess
unconverted carotene in the blood. A very high concentration
of unconverted carotenoids in the blood is known as
hypercarotenosis and can cause a yellow discoloration
of the skin. This condition has been confused with
jaundice, but the two are not related. Hypercarotenosis
is unsightly but usually not dangerous.
and Pregnant Women
women taking excess vitamin A risk bearing a child
with birth defects because of the action of the vitamin
on the developing fetus. Some of the possible defects
are urinary tract malformations, hydrocephalus, and
bone deformities. If you are pregnant, do not exceed
your doctor's recommendation for any vitamin or drug,
including vitamin A. Current recommendations are to
take no more than 10,000 IU per day during pregnancy,
and prenatal vitamins contain no more than this amount.
But vitamin supplements containing up to 50,000 IU
per capsule are readily available, so be careful when
selecting a product.
A can interact with corticosteroid - type -drugs,
oral contraceptives, calcium, zinc, and mineral oil.
It can also interfere with certain blood tests.
A supplements may be given to counteract any of the
standard symptoms of vitamin A deficiency reviewed
earlier in the profile. However, such symptoms will
not be alleviated by vitamin A unless they are, in
fact, caused by vitamin deficiency.
carotenoids are excellent free-radical scavengers
and quenchers of singlet oxygen. As such, they play
a role in protecting our cells against oxidative damage
and presumably help protect us from a number of chronic
diseases linke4d to free-radical damage.
discussed earlier, measles can be life-threatening
if the child is deficient in vitamin A. It has been
recommended that the vitamin A status of all seriously
ill patients with measles be checked and a high dose
supplement given if needed. A program of providing
vitamin A supplements to children to some developing
countries has lowered the infant death rate due to
deficient in vitamin A get cancer more often and their
tumors spread more quickly than animals without this
deficiency. There is evidence that the same thing
holds true for people: Those who are deficient in
vitamin A may be at a an increased risk of developing
cancer, and individuals who do get the disease may
find that their cancer spreads more quickly. Low vitamin
A intake from vegetable is directly related to tan
increase in cancer of the lung, bladder, and larynx,.
However, it is not known whether the protective effect
of vitamin A can be attributed to beta carotene, other
plant carotenoids, retinol , or some other component
of green and yellow vegetables. Our best advice is
to eat plenty of vegetables, as high vegetable intake
is consistently associated with a lower risk of cancer.
Retinoic acid is the form of vitamin A required for
normal cell differentiation and thus cancer prevention.
Unfortunately, it is metabolized too quickly and is
too toxic in high doses to be practical for therapeutic
use in cancer treatment. Other synthetic derivatives
of retinoic acid show some promise and are under investigation.
of the symptoms of vitamin A deficiency is an acnelike
condition. The observation led to the use of vitamin
A capsules as an acne treatment in the 1950s and 1960s
and consequently to the discovery that high doses
of vitamin A are toxic. After several decades of using
vitamin A capsules to treat acne, the consensus is
that the treatment is only marginally effective and
carries a significant risk of toxicity.
In the 1970s retinoic acid applied to the skin became
popular as an acne treatment, and it is still used
today. Topical retinoic acid appears to reduce the
plugging of sebaceous glands. Plugged sebaceous glands
can become infected and turn into pimples. Retinoic
acid also mildly irritates the skin and causes peeling,
which also helps to free plugged sebaceous glands.
Retinoic acid cream or lotion is not the ideal treatment.
It can take months for the treatment to begin working,
and it is irritating to the skin. In the search for
more potent and less toxic retinoic acid derivatives,
researches have discovered several that can be taken
by mouth without the usual adverse effects. Isotretinoin,
or 13-cis-retinoic acid, has been of some benefit
to people who suffer from the most severe from of
acne and who have not responded to other forms of
treatment. These retinoic acid derivatives are strong
teratogens, and patients on the drug must take steps
to make sure they do not get pregnant.
retinoic acid derivatives are used with some success
to treat psoriasis. These drugs are available only
by prescription and carry a significant risk for causing
birth defects if taken during pregnancy.
cannot recommend that you take this vitamin to treat
alcoholism, allergies, angina pectoris, arteriosclerosis,
arthritis, asthma, bad breath, broken bones, bronchitis,
canker sores, cataracts, colitis, the common cold,
constipation, cystitis, diabetes, diarrhea, double
vision, ear infections, emphysema, epilepsy, eye strain,
fever, flu, gout, hair problems, hay fever, headache,
heart attack, heart failure, hemorrhoids, hemophilia,
hepatitis, infertility, jaundice, kidney stones, learning
disabilities, liver cirrhosis, meningitis, mononucleosis,
muscular dystrophy, nail problems, osteomalacia, prostate
trouble, psychosis, sinusitis, stroke, swollen glands,
thyroid disease, tuberculosis, vaginitis, varicose
veins, or worms.
its toxicity, vitamin A can be obtained in any strength
without a prescription. Attempts by the FDA to attempt
to limit the doses that can be purchased without a
prescription have been met with fierce opposition
by nutritionally oriented consumer groups.
We do not recommended taking more than 10,000 IU a
day unless you are under the guidance of a licensed
health care professional who is expert in therapy
with vitamin A. This is especially true if you are
or might become pregnant. Do not take vitamin A doses
over 10,000 IU per day if you are pregnant or if there
is any chance you may become pregnant.