Vitamin A (Retinol)
Vitamin A (Retinol)
Overview
Vitamin A is a fat-soluble vitamin that has several important functions in the body.
- It helps cells reproduce normally, a process called cellular differentiation.
- It is essential for good vision. The first sign of a vitamin A deficiency is often poor sight at night.
- It is needed for the proper development of an embryo and fetus.
Vitamin A helps keep skin and mucous membranes that line the nose, sinuses, and mouth healthy. It also plays a role in:
- Immune system function
- Growth
- Bone formation
- Reproduction
- Wound healing
Vitamin
A comes from two sources. One group, called retinoids, comes from
animal sources and includes retinol. The other group, called
carotenoids, comes from plants and includes beta-carotene. The body
converts beta-carotene to vitamin A. Major carotenoids, including
lycopene, lutein, and zeaxantuin, have important biological properties,
including antioxidant and photoprotective activities.
It is rare in the developed world to have a serious deficiency of vitamin A. Symptoms include:
- Dry eyes
- Night blindness
- Diarrhea
- Skin problems
While
vitamin A is essential for good health, it can be toxic in high doses.
Never take more than the recommended daily allowance without first
talking to your doctor.
Acne, psoriasis, and other skin disorders
Prescription
creams and pills containing retinoids, a synthetic form of vitamin A,
are used to help clear up severe acne and psoriasis. They have also
shown promise for treating other skin disorders, warts, and premature
aging from the sun. Recent studies show that topical forms along with
antioxidants may help minimize the appearance of fine lines and
wrinkles. These medications require close supervision by a doctor.
Isotretinoin (Accutane), an oral medication for acne, can cause very
serious side effects and must not be used by pregnant women or women of
child-bearing age who are not taking birth control.
Eye disorders
Getting
enough vitamin A in your diet is essential for good vision. Research
shows that people who eat more foods with vitamin A are less likely to
develop age-related macular degeneration (AMD). In addition, a large
population study found that people who got high levels of vitamin A
though their diets had a lower risk of developing cataracts. But
researchers don't know whether taking vitamin A supplements would work
the same way. Vitamin A supplements may help slightly slow down the
damage from retinitis pigmentosa, a hereditary disease that causes poor
night vision. However, the study used high doses, which can be toxic.
Measles
For
children who have vitamin A deficiency, supplements can reduce the
severity and complications of measles. Children who are deficient in
vitamin A are more likely to develop infections, including measles. 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 (WHO)
recommends giving vitamin A supplements to children who have measles.
However, vitamin A does not seem to help unless a child has vitamin A
deficiency. Never give a child vitamin A supplements without a doctor's
supervision.
Inflammatory bowel disease (IBD)
People with
IBD, either ulcerative colitis or Crohn disease, may have a hard time
absorbing all the nutrients their bodies need. Doctors often recommend
that people with IBD take a multivitamin, including vitamin A.
Cancer
Whether
vitamin A can reduce the risk of cancer is not clear. People who eat a
healthy diet with enough beta-carotene and other carotenoids from fruits
and vegetables seem to have a lower risk of certain cancers, such as:
- Breast cancer
- Colon Cancer
- Esophageal cancer
- Cervical cancer
- Melanoma
Some laboratory studies suggest that vitamin A and carotenoids may help fight certain types of cancer in test tubes.
Few
studies have shown that taking vitamin A supplements will help prevent
or treat cancer. In fact, there is some evidence that it may be harmful.
Taking beta-carotene or vitamin A supplements has been linked to a
higher risk of lung cancer in people who smoke or drink alcohol.
However, some researchers say more studies are needed to confirm this.
One
preliminary study suggests that a topical form of vitamin A may reduce
abnormal growth of cells on the cervix, called cervical neoplasia.
Researchers
are also investigating retinoids, a synthetic form of vitamin A, for
skin cancer. People with certain types of skin cancer tend to have lower
levels of vitamin A and beta-carotene in the blood. However, studies
that have looked at whether taking higher amounts of vitamin A or
beta-carotene would prevent or treat skin cancer have had mixed results.
Dietary Sources
Vitamin A in the form of retinyl palmitate is found in:
- Beef, calf, and chicken liver
- Eggs
- Fish liver oils
- Dairy products, including whole milk, whole milk yogurt, whole milk cottage cheese, butter, and other cheeses
The
body can also make vitamin A from beta-carotene and other carotenoids,
which are fat-soluble nutrients found in fruits and vegetables that give
them their color. 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, you can increase levels of vitamin A in your
body.
Available Forms
Vitamin A supplements are available as either retinol or retinyl palmitate.
Tablets
or capsules are available in a variety of doses. The tolerable upper
limit, or safe upper limit, is 10,000 IU. For any dose close to that
amount, a doctor should help you determine the amount to take. Most
multivitamins contain the recommended dietary allowance (RDA) for
vitamin A.
Unlike vitamin A, beta-carotene does not build up in
the body. However, there is some evidence that high doses of
beta-carotene can carry some risk. Talk to your doctor before taking
more than the recommended amount.
How to Take It
Vitamin A is absorbed along with fat in the diet. Take it with food.
Studies
often use high doses of vitamin A. However, such high doses can be
toxic. A doctor should monitor any high-dose therapy (any dose
approaching the level of 10,000 IU for an adult, or above the
recommended daily allowance for a child).
Daily dietary intakes for vitamin A are:
Pediatric
- Infants, birth to 6 months: 400 mcg
- Infants, 7 to 12 months: 500 mcg
- Children, 1 to 3 years: 300 mcg
- Children, 4 to 8 years: 400 mcg
- Children, 9 to 13 years: 600 mcg
- Boys, 14 to 18 years: 900 mcg
- Girls, 14 to 18 years: 700 mcg
Adult
- Men, 19 years and older: 900 mcg
- Women, 19 years and older: 700 mcg
- Pregnant women, 14 to 18 years: 750 mcg
- Pregnant women, 19 years and older: 770 mcg
- Breastfeeding women, 14 to 18 years: 1,200 mcg
- Breastfeeding women, 19 years and older: 1,300 mcg
Precautions
Because
of the potential for side effects and interactions with medications,
you should take dietary supplements only under the supervision of a
knowledgeable health care provider.
Taking too much vitamin A when
you are pregnant can cause serious birth defects. Because all prenatal
vitamins contain some vitamin A, you should not take a separate vitamin A
supplement.
Synthetic vitamin A can cause birth defects. Women
who are pregnant or trying to become pregnant shouldn't take this form
of vitamin A.
Too much vitamin A is toxic and can cause liver failure, even death. Symptoms of vitamin A toxicity include:
- Headache
- Fatigue
- Muscle and joint pain
- Dry skin and lips
- Dry or irritated
- Nausea or diarrhea
- Hair loss
Vitamin
A from foods is considered safe. But you can get too much from
supplements. For adults, 19 and older, the tolerable upper limit for
vitamin A is 10,000 IU per day. Talk to your doctor before taking any
dose close to that amount.
People who have liver disease or diabetes should not take vitamin A supplements without their doctor's supervision.
Smokers and people who drink heavy amounts of alcohol should not take beta-carotene supplements.
Both
vitamin A and beta-carotene may increase triglycerides, which are fats
in the blood. They may even increase the risk of death from heart
disease, particularly in smokers.
Vitamin A is found in many
different vitamin formulas. 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. If you
take a variety of different formulas, you could be at risk for too much
vitamin A.
If you take large doses of vitamin A, you may want to
avoid eating carob. It increases the amount of vitamin A available in
your body.
Possible Interactions
If you are
being treated with any of the following medications, you should not take
vitamin A without first talking to your health care provider:
Tetracycline antibiotics:
People who take a type of antibiotic called tetracyclines and also take
high doses of vitamin A may be at risk for a condition called
intracranial hypertension, which is a rise in the pressure of brain
fluid. Tetracyclines include:
- Demeclocycline (Declomycin)
- Minocycline (Minocin)
- Tetracycline (Achromycin)
Antacids: One study suggests that the combination of vitamin A and antacids may be more effective than antacids alone in healing ulcers.
Anticoagulants (blood thinners):
Long-term use of vitamin A or taking high doses may increase the risk
of bleeding for those taking blood-thinning medications, particularly
warfarin (Coumadin). Talk to your doctor before taking vitamin A.
Cholesterol-lowering medications (bile acid sequestrants):
The medications cholestyramine (Questram) and colestipol (Colestid) may
reduce your ability to absorb vitamin A and lead to lower levels in
your body. A water-soluble form of vitamin A may help. Another class of
cholesterol-lowering medications called statins may actually raise
vitamin A levels in your blood.
Doxorubicin:
Doxorubicin is a medication used to treat cancer. Test tube studies
suggest that vitamin A may make the action of doxorubicin stronger. More
research is needed to understand the effect. If you are undergoing
treatment for cancer, ask your oncologist before taking vitamin A or any
supplement.
Medications processed by the liver:
Taking high doses of vitamin A along with some other medications that
are processed by the liver may cause liver damage or even liver failure.
Some examples of medications processed by the liver include
acetaminophen (Tylenol), carbamazepine (Tegretol), isoniazid, and
methotrexate. If you are taking any prescription medications, ask your
doctor before taking vitamin A.
Neomycin (Mycifradin): This antibiotic may reduce the body's ability to absorb vitamin A, especially when taken in large doses.
Omeprazole (Prilosec):
Omeprazole, used for gastroesophageal reflux disease or heart burn, may
interact with beta-carotene supplements. Researchers do not know
whether it also affects the absorption of beta-carotene from foods.
Retinoids:
These medications are a synthetic form of vitamin A and are sometimes
prescribed in high doses. People who take retinoids should not take
additional vitamin A supplements. In addition, these drugs can cause
severe birth defects. Women of child-bearing age must have two negative
pregnancy tests and be on two forms of birth control before taking these
medications. Anyone taking retinoids will be monitored closely by their
doctor. Retinoids include:
- Acitretin (Soriatane)
- Bexarotene (Targretin)
- Isotretinoin (Accutane)
- Tazarotene (Avage)
Tretinoin
(Retin-A) is usually prescribed as a skin cream to treat acne or reduce
wrinkles and is not as concentrated as other retinoids. However, you
may still want to avoid taking a vitamin A supplement while using
Retin-A.
Orlistat (Alli) and Olestra: Orlistat, a
medication used for weight loss, and olestra, a substance added to
certain foods, both prevent the body from absorbing fat and calories.
They may also prevent the body from absorbing enough vitamin A. The Food
and Drug Administration (FDA) requires that vitamin A and other
fat-soluble vitamins (vitamins D, E, and K) be added to food products
containing olestra. In addition, people who take either prescription
orlistat or over-the-counter Alli may want to take a multivitamin.
Supporting Research
Alberts
D, Ranger-Moore J, Einspahr J, et al. Safety and efficacy of
dose-intensive oral vitamin A in subjects with sun-damaged skin. Clin Cancer Res. 2004;10:1875-1880.
Antoon AY, Donovan DK. Burn Injuries. In: Behrman RE, Kliegman RM, Jenson HB, eds. Nelson Textbook of Pediatrics. Philadelphia, PA: W.B. Saunders Company; 2000:287-294.
Arora A, Willhite CA, Liebler DC. Interactions of beta-carotene and cigarette smoke in human bronchial epithelial cells. Carcinogenesis. 2001;22(8):1173-1178.
Bershad SV. The modern age of acne therapy: a review of current treatment options. Mt Sinai J Med. 2001;68(4-5):279-286.
Bjelakovic
G, Nikolova D, Simonetti RG, Gluud C. Antioxidant supplements for
prevention of gastrointestinal cancers: a systematic review and
meta-analysis. Lancet. 2004;364:1219-1228.
Cumming RG, Mitchell P, Smith W. Diet and cataract: the Blue Mountains Eye Study.Ophthalmology. 2000;107(3):450-456.
Flood A, Schatzkin A. Colorectal cancer: does it matter if you eat your fruits and vegetables? J Natl Cancer Inst. 2000;92(21):1706-1707.
Fragoso YD, Stoney PN, McCaffery PJ. The evidence for a beneficial role of vitamin A in multiple sclerosis. CNS Drugs. 2014;28(4):291-9.
French
AL, Kirstein LM, Massad LS, et al. Association of vitamin A deficiency
with cervical squamous intraepithelial lesions in human immunodeficiency
virus-infected women. J Infect Dis. 2000;182(4):1084-1089.
Frieling
UM, Schaumberg DA, Kupper TS, Muntwyler J, Hennekens CH. A randomized,
12-year primary-prevention trial of beta carotene supplementation for
nonmelanoma skin cancer in the Physicians' Health Study. Arch Dermatol. 2000;136(2):179-184.
Fulan
H, Changxing J, Baina WY, et al. Retinol, vitamins A, C, and E and
breast cancer risk: a meta-analysis and meta-regression. Cancer Causes Control. 2011;22(10):1383-1396.
Hall JA, Grainger JR, Spencer SP, Belkaid Y. The role of retinoic acid in tolerance and immunity. Immunity. 2011;35(1):13-22.
Institute of Medicine.
Dietary Reference Intakes for Vitamin A, Vitamin K, Arsenic, Boron,
Chromium, Copper, Iodine, Iron, Manganese, Molybdenum, Nickel, Silicon,
Vanadium, and Zinc. Washington, DC: National Academy Press; 2001.
Kang S, Fisher GJ. Voorhees JJ. Photoaging: pathogenesis, prevention, and treatment. Clin Geriatr Med. 2001;17(4):643-659.
Kliegman. Nelson Textbook of Pediatrics. 19th ed. Philadelphia, PA: Elsevier Saunders; 2011.
Jänne PA, Mayer RJ. Chemoprevention of colorectal cancer. N Engl J Med. 2000;342(26):1960-1968.
Michels
KB, Giovannucci E, Joshipura KJ, et al. Prospective study of fruit and
vegetable consumption and incidence of colon and rectal cancers. J Natl Cancer Inst. 2000;92:1740-1752.
National
Institutes of Health, Office of Dietary Supplements. Facts About
Dietary Supplements: Vitamin A and Carotenoids. December 2001.
Patrick L. Beta-carotene: the controversy continues. Altern Med Rev. 2000;5(6):530-545.
Patrick L. Nutrients and HIV:Part 2 -- vitamins A and E, zinc, B-vitamins, and magnesium. Altern Med Rev. 2000;5(1):39-51.
Prakash
P, Krinsky NI, Russell RM. Retinoids, carotenoids, and human breast
cancer cell cultures: a review of differential effects. Nutr Reviews. 2000;58(6):170-176.
Rai
SK, Nakanishi M, Upadhyay MP, et al. Effect of intestinal helminth
infection on retinol and beta-carotene status among rural Nepalese. Nutr Res. 2000;20(1):15-23.
Ribaya-Mercado JD, Blumber JB. Vitamin A: is it a risk factor for osteoporosis and bone fracture? Nutr Rev. 2007;65(10):425-438.
Rock CL, Michael CW, Reynolds RK, Ruffin MT. Prevention of cervix cancer. Crit Rev Oncol Hematol. 2000;33(3):169-185.
SanGiovanni
JP, Chew EY, Clemons TE, Ferris FL, Gensler G, Lindblad AS, Milton RC,
Seddon JM, Sperduto RD. The relationship between dietary carotenoid and
vitamin A, E and C intake with age-related macular degeneration in a
case-control study. Report No. 22. Arch Ophthalmol. 2007;125(9):1225-1232.
Sei H. Vitamin A and sleep regulation. J Med Invest. 2008;55(1-2):1-8.
Sommer A, Vyas K. A global clinical view on vitamin A and carotenoids. Am J Clin Nutr. 2012;96(5):1204S-62.
Sorg
O, Saurat JH. Topical retinoids in skin ageing: a focused update with
reference to sun-induced epidermal vitamin A deficiency. Dermatology. 2014;228(4):314-25.
Steck-Scott
S, Forman MR, Sowell A, et al. Carotenoids, vitamin A and risk of
adenomatous polyp recurrence in the polyp prevention trial. Int J Cancer. 2004;112(2):295-305.
Stratton SP, Dorr RT, Alberts DS. The state-of-the art in chemoprevention of skin cancer. Eur J Cancer. 2000;36(10):1292-1297.
Tafti M, Ghyselinck NB. Functional implication of the vitamin A signaling pathway in the brain. Arch Neurol. 2007;64(12):1706-1711.
Thornquist
MD, Kristal AR, Patterson RE, et al. Olestra consumption does not
predict serum concentrations of carotenoids and fat-soluble vitamins in
free-living humans: early results from the sentinel site of the olestra
post-marketing surveillance study. J Nutr. 2000;130(7):1711-1718.
van Dam RM, Huang Z, Giovannucci E, et al. Diet and basal cell carcinoma of the skin in a prospective cohort of men. Am J Clin Nutr. 2000;71(1):135-141.
van
Zandwijk N, Dalesio O, Pastorino U, de Vries N, van Tinteren H.
EUROSCAN, a randomized trial of vitamin A and N-acetylcysteine in
patients with head and neck cancer or lung cancer. For the European
Organization for Research and Treatment of Cancer Head and Neck and Lung
Cancer Cooperative Groups. J Natl Cancer Inst. 2000;92(12):959-960.
Vetrugno
M, Maino A, Cardia G, et al. A randomised, double masked, clinical
trial of high dose vitamin A and vitamin E supplementation after
photorefractive keratectomy. Br J Ophthalmol. 2001;85(5):537-539.
Villamor E, Fawzi WW. Vitamin A supplementation: implications for morbidity and mortality in children. J Infect Dis. 2000;182 Suppl 1:S122-S133.
Wang A, Han J, Jiang Y, Zhang D. Association of vitamin A and B-carotene with risk for age-related cataract: a meta-analysis. Nutrition. 2014;30(10):1113-21.
Zhang YP, Chu RX, Liu H. Vitamin A intake and risk of melanoma: a meta-analysis. PLoS One. 2014;9(7):e102527.
Zouboulis CC. Retinoids -- which dermatological indications will benefit in the near future? Skin Pharmacol Appl Skin Physiol. 2001;14(5):303-315.
Alternative Names
Retinol