Source: University of Mayland Medical Center
Also listed as: Retinol
Vitamin A is very important for maintaining good vision. In fact, the
first sign of a vitamin A deficiency is often night blindness. Vitamin
A also contributes to the maintenance of healthy skin and mucous
membranes that line the nose, sinuses, and mouth. Research has shown
that this nutrient is necessary for proper immune system function,
growth, bone formation, reproduction, and wound healing. Animal studies
also suggest that it provides some protection from toxic chemicals such
as dioxins. (Dioxins are released into the air from combustion
processes such as commercial waste incineration and burning fuels like
wood, coal or oil. These chemicals can also be found in cigarette
smoke.)
The liver can store up to a year's supply of vitamin A. However,
these stores become depleted when a person is sick or has an infection.
Research suggests that parasitic infections such as intestinal worms
may deplete the body's vitamin A stores and interfere with its
absorption.
Vitamin A is a fat-soluble vitamin derived primarily from animal-based
foods. However, the body can also make vitamin A from beta-carotene, a
fat-soluble nutrient found in dark green leafy vegetables and the more
brightly colored fruits and vegetables such as carrots, sweet potatoes,
and cantaloupe.
Acne, Psoriasis, and other Skin disorders
Topical and oral preparations containing retinoids (synthetic form
of vitamin A) are helpful in clearing up acne and psoriasis and have
shown promise for treating other skin disorders such as rosacea,
premature aging from the sun, and warts. These are given by
prescription.
Eye Disorders
A number of vision disorders involving the retina and cornea are
associated with vitamin A deficiencies. Night blindness, for example,
and xerophthalmia (characterized by dry eyes) improve with vitamin A
supplementation. A large, population-based study conducted in Australia
showed that vitamin A had a protective effect against cataracts.
Wounds and Burns
The body needs vitamin A, along with several other nutrients, in
order to form new tissue and skin. The body's levels of vitamin A are
low immediately after burn injuries, for example. Supplementation with
beta-carotene helps the body replenish vitamin A stores, strengthen the
immune system, relieve oxidative stress caused by the injury, and aid
the body in forming new tissue.
Immune System
Research has shown that vitamin A boosts the immune system by
stimulating white blood cell function and increasing the activity of
antibodies (proteins that attach to foreign proteins, microorganisms,
or toxins in order to neutralize them). Vitamin A deficiency may be
associated with increased risk of infection and infections tend to
deplete the body's stores of vitamin A.
Vitamin A deficiency, for example, is common among children in many
developing countries who are prone to infections, which often results
in life-threatening diarrhea. Low levels of vitamin A are also
particularly severe among children infected with the human
immunodeficiency virus (HIV). Some studies suggest that vitamin A
supplements may reduce the risk of death in children infected with HIV.
Your doctor will determine whether vitamin A (in addition to standard
treatment) is necessary and appropriate.
Measles
People, particularly children, who are deficient in vitamin A are more
likely to develop infections (including measles). Vitamin A
deficiencies also cause such infections to be more severe, even fatal.
Vitamin A supplements reduce the severity and complications of measles
in children. Vitamin A also reduces the risk of death in infants with
this disease (especially in those who have low levels of the vitamin).
In areas of the world where vitamin A deficiency is widespread or where
at least 1% of those with measles die, the World Health Organization
recommends giving high doses of vitamin A supplements to children with
the infection.
Intestinal Parasites
There is evidence that roundworms such as Ascaris deplete vitamin A stores in people, particularly children, leaving them
less able to fight off infections. At the same time, it appears that
low vitamin A levels can make a person more susceptible to intestinal
parasites. There is not enough scientific evidence at this point,
however, to suggest that taking vitamin A supplements helps prevent or
treat intestinal parasites. More research is underway.
Osteoporosis
An appropriate balance of vitamin A -- not too much and not too
little -- is necessary for normal bone development. Low levels of
vitamin A may contribute to the development of bone loss or
osteoporosis. On the other hand moderately high doses of vitamin A
(exceeding 1,500 mcg or 5,000 IU per day) may lead to bone loss.
Therefore, for prevention or treatment of osteoporosis, it is best to
obtain vitamin A from food sources and not to eat more than the
recommended dietary allowance (RDA).
Inflammatory Bowel Disease (IBD)
Many people with IBD (both ulcerative colitis and Crohn's disease) have
vitamin and mineral deficiencies, including vitamin A. Further research
is needed to determine whether supplementation with vitamin A or other
individual vitamins or minerals may help treat the symptoms of IBD. In
the meantime, healthcare practitioners often recommend a multivitamin
to people with this condition.
Bone Marrow Disorders
Results from a carefully conducted 7-year clinical study suggest
that a modest dose of vitamin A (together with chemotherapy) may help
improve survival time in patients with certain bone marrow disorders
such as chronic myelogenous leukemia (CML; considered a
myeloproliferative disorder). Research suggests that retinoids such as
vitamin A have antitumor effects against juvenile CML (which accounts
for 3% to 5% of cases of leukemia in children), as well as certain
cancer cells grown in the laboratory.
Cancer
Vitamin A, beta-carotene, and other carotenoids from foods may be
associated with decreased risk of certain cancers (such as breast,
colon, esophageal, and cervical). In addition, some laboratory studies
suggest that vitamin A and carotenoids may help fight against certain
types of cancer in test tubes. However, there is no proof that these
supplements can help prevent or treat cancer in people. In fact, some
evidence suggests that beta-carotene and, possibly, vitamin A may put
people at increased risk of lung cancer, particularly smokers.
Preliminary evidence suggests that a topical form of vitamin A, applied
to the cervix (the opening to the uterus) with sponges or cervical caps
shows promise for the treatment of cervical cancer. Also, women with
HIV who are deficient in vitamin A may be at greater risk for cervical
cancer (a common occurrence in women with HIV) than those with normal
levels of this vitamin. More research is needed before conclusions can
be drawn about use of vitamin A to treat or prevent cervical cancer or
cervical dysplasia (a precancerous change to the cervix).
Similarly, use of retinoids (a synthetic form of vitamin A) for skin
cancer is currently under scientific investigation. Vitamin A and
beta-carotene levels in the blood tend to be lower in people with
certain types of skin cancer. However, results of studies evaluating
higher amounts of natural forms of vitamin A or beta-carotene for skin
cancer have been mixed.
Tuberculosis
Although early studies showed no improvement in children who took
vitamin A with standard treatment for tuberculosis (TB), a very recent
study found that this vitamin (together with zinc) may enhance the
effects of certain TB drugs. These changes were demonstrated just two
months after starting the vitamin A. More research is warranted. Until
then, your doctor will determine if the addition of vitamin A is
appropriate and safe.
Peritonitis
Although the effects of vitamin A on peritonitis have not been studied
in people, animal studies suggest that this vitamin may prove to be
useful in combination with antibiotic therapy for the treatment of this
condition.
Osteoarthritis
Vitamin A plays an important role in bone formation and also acts as an
antioxidant, so some researchers believe that it may help reduce
symptoms of osteoarthritis. No studies have investigated this
possibility, however.
Food Poisoning
Animal studies suggest that rats who are deficient in vitamin A are more likely to become infected with Salmonella (one type of bacteria that can cause food poisoning). Also, rats
infected with Salmonella tend to eliminate the bacteria from their
bodies faster when treated with vitamin Athan with placebo. They also
gain more weight and have a better immune response than placebo-treated
rats. How this ultimately relates to people is not known at this time,
however.
Alzheimer's Disease
Preliminary studies suggest that levels of vitamin A and its
precursor, beta-carotene, may be significantly lower in people with
Alzheimer's compared to healthy individuals, but the effects of
supplementation have not been studied.
Miscarriage
Vitamin A and beta-carotene levels tend to be lower in women who
have miscarried. These nutrients are generally found in prenatal
vitamins. Your doctor or nutritionist can advise you about the
appropriate amount to look for in a vitamin. The amount of vitamin A
taken should not exceed the recommendation of your healthcare provider
because too much vitamin A can lead to birth defects.
Human Immunodeficiency Virus (HIV)
Vitamin A deficiency is fairly common in those with HIV. In
addition, pregnant women who have HIV are more likely to transmit the
virus to their unborn child if their zinc levels are low compared to
HIV-positive women with normal zinc levels. Although more research is
needed, vitamin A supplements may delay the progression of HIV to
Acquired Immunodeficiency Syndrome (AIDS), diminish symptoms of HIV and
AIDS such as diarrhea, and help to prevent the transmission of the
virus from mother to child.
Other
Additional conditions for which vitamin A may prove useful include
ulcers (crater like lesion of the skin or mucosal membranes) of the
cornea, stomach or small intestines (called peptic ulcer), and legs
(often due to poor circulation or collection of fluid, called stasis
ulcer). Gingivitis (inflammation of the gums) is another condition for
which vitamin A may prove useful. Much more research is needed in each
of these areas.
Vitamin A, in the form of retinyl palmitate, is found in beef, calf,
chicken liver; eggs, and fish liver oils as well as dairy products
including whole milk, whole milk yogurt, whole milk cottage cheese,
butter, and cheese.
Vitamin A can also be produced in the body from beta-carotene and other
carotenoids (fat-soluble nutrients found in fruits and vegetables).
Most dark-green leafy vegetables and deep yellow/orange vegetables and
fruits (sweet potatoes, carrots, pumpkin and other winter squashes,
cantaloupe, apricots, peaches,and mangoes) contain substantial amounts
of beta-carotene. By eating these beta-carotene rich foods, a person
can increase their supply of vitamin A.
Vitamin A supplements are available as either retinol or retinyl
palmitate. All forms of vitamin A are readily absorbed by the body.
Tablets or capsules are available in 10,000 IU, 25,000 IU, and 50,000
IU doses. A healthcare provider can help determine the appropriate
dosage of vitamin A. Most multivitamins contain the recommended dietary
allowance (RDA) for vitamin A (see How To Take It).
In many cases, taking beta-carotene (a building block of vitamin A,
is a safer alternative to taking vitamin A. Unlike vitamin A,
beta-carotene does not build up in the body, so it can be taken in
larger amounts without the same risk. This makes it a better
alternative for children, adults with liver or kidney disease, and
pregnant women in particular.
Vitamin A is a fat-soluble vitamin and is absorbed along with fat in
the diet. Foods or supplements containing vitamin A should be taken
during or shortly after a meal.
Therapeutic doses have ranged as high as 50,000 IU for adults.
However, any high dose therapy (more than 25,000 IU for an adult or
10,000 IU for a child) should be closely monitored by a healthcare
professional. The effect of such high doses on children is not known.
Daily dietary intakes for vitamin A are listed below.
Pediatric
- Infants birth to 6 months: 400 mcg or 1,333 IU of retinol (AI)
- Infants 7 to 12 months: 500 mcg or 1,667 IU of retinol (AI)
- Children 1 to 3 years: 300 mcg or 1,000 IU of retinol (RDA)
- Children 4 to 8 years: 400 mcg or 1,333 IU of retinol (RDA)
- Children 9 to 13 years: 600 mcg or 2,000 IU of retinol (RDA)
- Males 14 to 18 years: 900 mcg or 3,000 IU of retinol (RDA)
- Females 14 to 18 years: 700 mcg or 2,333 IU of retinol (RDA)
Adult
- Males 19 years and older: 900 mcg or 3,000 IU of retinol (RDA)
- Females 19 years and older: 700 mcg or 2,333 IU of retinol (RDA)
- Pregnant females 14 to 18 years: 750 mcg or 2,500 IU of retinol (RDA)
- Pregnant females 19 years and older: 770 mcg or 2,567 IU of retinol (RDA)
- Breastfeeding females 14 to 18 years: 1,200 mcg or 4,000 IU of retinol (RDA)
- Breastfeeding females 19 years and older: 1,300 mcg or 4,333 IU of retinol (RDA)
Because of the potential for side effects and interactions with
medications, dietary supplements should be taken only under the
supervision of a knowledgeable healthcare provider.
An excess of vitamin A taken during pregnancy can cause birth
defects in the fetus. Because all prenatal vitamins contain some
vitamin A, taking any more during pregnancy can pose potential danger
to the fetus.
Too much vitamin A is toxic to the body and can cause liver failure,
even death. Some of the symptoms of vitamin A toxicity are lasting
headache, fatigue, muscle and joint pain, dry skin and lips, dry or
irritated eyes, nausea or diarrhea, and hair loss. While it is unlikely
that one could get toxic amounts of vitamin A from food sources alone,
it is quite possible to do so with supplements. Consuming more than
25,000 IU of vitamin A per day (adults) and 10,000 IU per day
(children) from either food or supplements or both is known to be
toxic. For those 19 and older, the tolerable upper limit for vitamin A
consumption has been set at 10,000 IU per day. Clearly, it is important
to take vitamin A supplements only under the careful supervision of a
knowledgeable healthcare provider, .
While low levels of vitamin A may contribute to the development of bone
loss or osteoporosis, doses exceeding 1,500 mcg or 5,000 IU per day may
lead to bone loss. Therefore, for prevention or treatment of
osteoporosis, it is best to obtain vitamin A from food sources and not
to eat more than the recommended dietary allowance (RDA).
Both vitamin A and beta-carotene may increase triglycerides (fatty
deposits in the body that rise after eating) and even increase risk of
death from heart disease, particularly in smokers.
Vitamin A is found in many different types of vitamin formulas. For
example, supplements that say "wellness formula," "immune system
formula," "cold formula," "eye health formula," "healthy skin formula,"
or "acne formula," all tend to contain vitamin A. Those who take a
variety of different formulas could therefore put themselves at risk
for vitamin A toxicity.
Vitamin A supplements should not be taken while using any vitamin A–derived drugs, such as isotretinoin and tretinoin.
In addition, synthetic vitamin A can cause birth defects. For this
reason, this type of vitamin A should not be used by pregnant women or
women who are trying to become pregnant.
If you are currently being treated with any of the following
medications, you should not use vitamin A without first talking to your
healthcare provider.
Antacids
One study suggests that the combination of vitamin A and antacids may be more effective than antacids alone in healing ulcers.
Birth Control Medications
Birth control medications increase the levels of vitamin A in women.
Therefore, it may not be appropriate for women taking birth control
medications to take vitamin A supplements. Again, this is something
that should be discussed with a knowledgeable healthcare provider.
Blood thinning Medications, Anticoagulants
Long-term use of vitamin A or use of high doses may lead to an
increased risk of bleeding for those taking blood-thinning medications,
particularly warfarin. People taking this medication should notify a
doctor before taking vitamin A supplements.
Cholesterol-lowering Medications
The cholesterol-lowering medications cholestyramine and colestipol
(both known as bile acid sequestrants), may reduce the body's ability
to absorb vitamin A.
Another class of cholesterol-lowering medications called HMG-CoA
reductase inhibitors or statins (including atorvastatin, fluvastatin,
and lovastatin, among others) may actually increase vitamin A levels in
the blood.
Doxorubicin
Test tube studies suggest that vitamin A may enhance the action of
doxorubicin, a medication used for cancer. Much more research is
needed, however, to know whether this has any practical application for
people.
Neomycin
This antibiotic may reduce vitamin A absorption, especially when delivered in large doses.
Omeprazole
Omeprazole (used for gastroesophageal reflux disease or "heart burn")
may influence the absorption and effectiveness of beta-carotene
supplements. It is not known whether this medication affects the
absorption of beta-carotene from foods.
Weight Loss Products
Orlistat, a medication used for weight loss and olestra, a substance
added to certain food products, are both intended to bind to fat and
prevent the absorption of fat and the associated calories. Because of
their effects on fat, orlistat and olestra may also prevent the
absorption of fat-soluble vitamins such as vitamin A. Given this
concern and possibility, the Food and Drug Administration (FDA) now
requires that vitamin A and other fat soluble vitamins (namely, D, E,
and K) be added to food products containing olestra. How well vitamin A
from such food products is absorbed and used by the body is not clear.
In addition, physicians who prescribe orlistat add a multivitamin with
fat soluble vitamins to the regimen.
Alcohol
Alcohol can enhance the toxic effects of vitamin A, presumably through
its adverse effects on the liver. It is unwise to take vitamin A if you
drink regularly.
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- Review Date:
4/1/2002
- Reviewed By: Participants in the review process include: Ruth
DeBusk, RD, PhD, Editor, Nutrition in Complementary Care, Tallahassee,
FL; Jacqueline A. Hart, MD, Department of Internal Medicine,
Newton-Wellesley Hospital, Harvard University and Senior Medical Editor
Integrative Medicine, Boston, MA; Gary Kracoff, RPh (Pediatric Dosing
section February 2001), Johnson Drugs, Natick, Ma; Steven Ottariono,
RPh (Pediatric Dosing section February 2001), Veteran's Administrative
Hospital, Londonderry, NH. All interaction sections have also been
reviewed by a team of experts including Joseph Lamb, MD (July 2000),
The Integrative Medicine Works, Alexandria, VA;Enrico Liva, ND, RPh
(August 2000), Vital Nutrients, Middletown, CT; Brian T Sanderoff, PD,
BS in Pharmacy (March 2000), Clinical Assistant Professor, University of Mayland School of Pharmacy; President, Your Prescription for
Health, Owings Mills, MD; Ira Zunin, MD, MPH, MBA (July 2000),
President and Chairman, Hawaii State Consortium for Integrative
Medicine, Honolulu, HI.
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