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Vitamin A, Retinoids, and Provitamin A Carotenoids

Other common name(s): none

Scientific/medical name(s): Retinol, retinoic acid, retinyl palmitate, retinoids, Vitamin A, beta carotene, alpha carotene, beta-cryptoxanthin

Description

Vitamin A is a nutrient that is vital to growth and development. Vitamin A is obtained in 2 ways:

  • As vitamin A from animal sources such as liver, fish oils, egg yolks, and dairy products
  • As pro-vitamin A carotenoids (such as beta carotene, alpha carotene, and others) from many colorful fruits and vegetables, like carrots, squash, broccoli, sweet potatoes, apricots, and leafy greens. The body converts these compounds to retinol (a type of vitamin A) in the small intestine

Vitamin A is stored in the liver until needed by the body. Vitamin A and closely related molecules (naturally occurring and synthetic or man-made) are also known as retinoids.

Beta carotene is the best known carotenoid (carotenoids are yellow, orange, and red pigmented compounds in plants). More than 40 different carotenoids can be found in the fruits and vegetables we eat, only some of which can be converted to vitamin A. Those that can be converted are called provitamin A carotenoids. Most carotenoids are antioxidants and have other health benefits. See our document Lycopene.

Overview

Vitamin A and pro-vitamin A carotenoid supplements have not been proven to prevent cancer in humans. High doses of vitamin A are toxic, and long-term use of high-dose beta carotene supplements may increase the risk of lung cancer among current and former smokers. Laboratory and clinical studies continue to explore the role of vitamin A and other retinoids in cancer prevention and treatment.

How is it promoted for use?

Vitamin A is essential for normal growth, bone development, reproduction, and vision. It is used to help maintain healthy skin and mucous membranes, like the ones that line the nose and mouth. This helps protect against infections in the respiratory, digestive, and urinary tracts.

Some research suggests that vitamin A and some other retinoids are able to change cancer cells and can also prevent normal cells from becoming cancer. Retinoids are prescribed as a standard medical treatment for some rare types of cancer or pre-cancerous conditions.

Some alternative healers recommend taking carotenoid supplements as part of a regimen to "cleanse" or "detoxify" the body, especially the liver. Others suggest that beta carotene can be used to treat certain types of cancer.

What does it involve?

Vitamin A is absorbed from foods from animal sources (especially liver, cheese, and eggs), from dietary supplements, and in the form of carotenoids, which are found in many fruits and vegetables and converted to vitamin A by the body. Vitamin A is stored in the liver, so it does not need to be consumed every day.

The best way to get this vitamin is to eat a well-balanced diet. People who eat a balanced diet that includes fruits, vegetables, and low-fat dairy products usually get enough vitamin A and carotene for good health, but supplements are available. The recommended daily allowance (RDA) of vitamin A is 2,310 IU (0.7 milligrams) per day for adult women (more for women who are pregnant or breastfeeding). For adult men, it’s 3,000 IU (0.9 milligrams) per day.

What is the history behind it?

Writings about blindness that could be cured by eating liver have been found in ancient Egypt, among the Assyrians, and in Greece around the time of Hippocrates. Night blindness and blindness due to ulcers on the cornea (the clear part of the eye) were linked together in the 1800’s, but the reason for these 2 problems wasn’t understood. However, there were reports from different parts of the world that one or both types of blindness could be cured by eating liver from mammals or fish.

The discovery of vitamin A dates back to research from the 1920s and 1930s, when test animals on purified diets were found to thrive and grow when butter, milk, liver, or yellow corn was added to their feed. Over the past 30 years, vitamin A has been extensively studied as a cancer-fighting nutrient in laboratory, animal, and studies of large groups of people in various regions.

Several studies based on dietary surveys of large numbers of people have concluded that eating foods rich in vitamin A and carotene is linked to a lower risk of certain types of cancer. But it is not clear whether the protective effect was due to vitamin A or to other helpful substances in these foods.

Researchers have isolated and created other retinoids, many of which are used on the skin to treat acne and other conditions. One of these retinoids has been approved as a cancer treatment drug.

What is the evidence?

Vitamin A deficiency can cause low resistance to infection, poor night vision, blindness due to ulcers on the cornea, poor growth in children, weak bones and teeth, inflamed eyes, diarrhea, and poor appetite. Vitamin A deficiency can lead to death, mainly in children from developing countries. It is rare in developed countries.

Some animal studies have suggested that vitamin A and other retinoids may enhance the immune system, slow tumor growth, shrink tumors, and make some cancer treatments work better. Some laboratory, animal, and human studies have also suggested that certain retinoids may inhibit cancer development.

Still, studies of vitamin A's possible role in cancer prevention have been generally disappointing. Clinical trials have found that vitamin A supplements do not lower the risk for lung cancer in smokers and actually increased their risk for dying of lung cancer and heart disease. Results of studies of vitamin A and other types of cancer have been mixed. There have been no consistent findings showing a lower risk of cancers of the stomach, intestines, skin, breast, cervix, bladder, or prostate due to vitamin A in the diet.

Vitamin A supplements have not been proven to reduce cancer risk in humans. It appears that the combination of micronutrients in fruits, vegetables, legumes, and grains is more likely to be helpful than individual vitamins.

Studies of overall health and longevity found no benefit to taking vitamin A supplements. In fact, a 2007 review of 68 studies of vitamin supplements concluded that people taking beta carotene or vitamin A supplements had a shorter life expectancy than those who did not take these supplements. The US Institute of Medicine does not recommend use of these supplements by the general public, but they do encourage eating carotenoid-rich fruits and vegetables for their health effects. The American Cancer Society Guidelines on Nutrition and Physical Activity for Cancer Prevention recommend getting Vitamin A and (other vitamins) from food sources rather than supplements, unless a person has clinical or laboratory evidence of a vitamin deficiency.

Synthetic retinoids that are more potent than natural vitamin A or beta carotene have shown some ability to reverse pre-cancers in the cervix, mouth, throat, and skin. They also may help prevent new tumors in people who have already been treated for these forms of cancer. But more clinical research is needed. Several clinical trials involving retinoids have been completed and others are still going on.

Retinoids are not currently used as a cancer treatment, with one notable exception. A relatively rare type of leukemia, promyelocytic leukemia, often responds to a combination of retinoic acid (a retinoid) and chemotherapy. Patients with this form of leukemia get high doses of a pure form of retinoic acid (derived from Vitamin A) under medical supervision. Treatment of promyelocytic leukemia does not include use of non-prescription vitamin A supplements or dietary changes intended to increase intake of this vitamin.

Studies of other types of cancer such as lung cancer, head and neck cancer, and melanoma found that vitamin A supplements are not helpful as treatments. Some oncologists are concerned that vitamin A and other vitamins that act as antioxidants may even make chemotherapy and radiation therapy less effective when taken during treatment. This is why many oncologists recommend that their patients not take such antioxidant supplements until their treatment is complete.

Are there any possible problems or complications?

This product is sold as a dietary supplement in the United States. Unlike companies that produce drugs (which must be tested before being sold), the companies that make supplements are not required to prove to the Food and Drug Administration that their supplements are safe or effective, as long as they don't claim the supplements can prevent, treat, or cure any specific disease.
Some such products may not contain the amount of the herb or substance that is on the label, and some may include other substances (contaminants). Actual amounts per dose may vary between brands or even between different batches of the same brand. In 2007, the FDA wrote new rules to improve the quality of manufacturing for dietary supplements and the proper listing of supplement ingredients. But these rules do not address the safety of the ingredients or their effects on health.
Most such supplements have not been tested to find out if they interact with medicines, foods, or other herbs and supplements. Even though some reports of interactions and harmful effects may be published, full studies of interactions and effects are not often available. Because of these limitations, any information on ill effects and interactions below should be considered incomplete.

High doses of vitamin A supplements can cause nausea, vomiting, diarrhea, loss of appetite, tiredness, headaches, dizziness, blurred vision, poor muscle coordination, itchiness and scaling of the skin, bone pain, hair loss, irregular menstruation in women, osteoporosis, and temporary or permanent liver damage. They can also cause birth defects if taken during pregnancy.

Getting too much retinol (Vitamin A) from foods or supplements seems to be linked to a higher risk of bone thinning and broken bones.

Provitamin A carotenoids such as beta carotene are generally considered safe because they are not linked to specific bad health effects. Their conversion to vitamin A slows down when body stores are full. A high intake of provitamin A carotenoids from foods can turn the skin yellow, but this is not thought to be dangerous to health.

Relying on this type of treatment alone and avoiding or delaying conventional medical care for cancer may have serious health consequences.

To learn more

More information from your American Cancer Society

The following information on nutrition as well and complementary and alternative therapies may also be helpful to you. You can find them on our Web site (www.cancer.org) or order a copy at no cost to you from our toll-free number (1-800-227-2345).

Complementary treatments and herbal medicines

American Cancer Society Guidelines on Nutrition and Physical Activity for Cancer Prevention

Complementary and Alternative Methods and Cancer

Dietary Supplements: What Is Safe?

Placebo Effect

The ACS Operational Statement on Complementary and Alternative Methods of Cancer Management

Finding out about new ways to treat and prevent cancer

Learning About New Ways to Treat Cancer

Learning About New Ways to Prevent Cancer

References

Albanes D, Heinonen OP, Taylor PR, et al. Alpha-tocopherol and beta-carotene supplement and lung cancer incidence in the alpha-tocopherol, beta-carotene cancer prevention study: Effects of base-line characteristics and study compliance. J Natl Cancer Inst. 1996;88:1560-1570.

The Alpha-Tocopherol, Beta Carotene Cancer Prevention Study Group. The effect of vitamin E and beta carotene on the incidence of lung cancer and other cancers in male smokers. N Engl J Med. 1994;330:1029-1035.

Bjelakovic G, Nikolova D, Gluud LL, Simonetti RG, Gluud C. Mortality in randomized trials of antioxidant supplements for primary and secondary prevention: systematic review and meta-analysis. JAMA. 2007;297:842-857.

Bjelakovic G, Nikolova D, Simonetti RG, Gluud C. Antioxidant supplements for prevention of gastrointestinal cancers. Cochrane Database Syst Rev. 2008;Issue 3:Art No: CD004183.

Bjelakovic G, Nikolova D, Gluud LL, Simonetti RG, Gluud C. Antioxidant supplements for prevention of mortality in healthy participants and patients with various diseases. Cocnrane Database Syst Rev. 2008;2:Art No: CD007176.

de Klerk NH, Musk AW, Ambrosini GL, et al. Vitamin A and cancer prevention II: comparison of the effects of retinol and beta-carotene. Int J Cancer. 1998;75:362-367.

Lawenda BD, Kelly KM, Ladas EJ, Sagar SM, Vickers A, Blumberg JB. Should supplemental antioxidant administration be avoided during chemotherapy and radiation therapy? J Natl Cancer Inst. 2008;100:773-783.

Memorial Sloan-Kettering Cancer Center. Vitamin A. Accessed at www.mskcc.org/mskcc/html/69410.cfm on January 24, 2012.

Meyskens FL Jr, Liu Py, Sondak VK, et al. Randomized trial of vitamin A versus observation as adjuvant therapy in high-risk primary malignant melanoma: a Southwest Oncology Group study. J Clin Oncol. 1994;12:2060-2065.

National Comprehensive Cancer Network Clinical Practice Guidelines in Oncology – v.2.2011. Acute Myeloid Leukemia. Accessed at www.nccn.org/professionals/physician_gls/PDF/aml.pdf on January 23, 2012.

Office of Dietary Supplements. Dietary Supplement Fact Sheet: Vitamin A and Carotenoids. Accessed at http://ods.od.nih.gov/factsheets/vitamina.asp on January 23, 2012.

Omenn GS, Goodman GE, Thornquist MD, et al. Effects of a combination of beta carotene and vitamin A on lung cancer and cardiovascular disease. N Engl J Med. 1996;334:1150-1155.

Paiva SA, Russell RM. Beta-carotene and other carotenoids as antioxidants. J Am Coll Nutr. 1999 Oct;18(5):426-433.

Pryor WA, Stahl W, Rock CL. Beta carotene: from biochemistry to clinical trials. Nutr Rev. 2000;58:39-53.

Redlich CA, Blaner WS, Van Bennekum AM, et al. Effect of supplementation with beta-carotene and vitamin A on lung nutrient levels. Cancer Epidemiol Biomarkers Prev. 1998;7:211-214.

Soprano DR, Soprano KJ. Pharmacological doses of some synthetic retinoids can modulate both the aryl hydrocarbon receptor and retinoid receptor pathways. J Nutr. 2003 Jan;133(1):277S-281S.

Tsao AS, Kim ES, Hong WK. Chemoprevention of cancer. CA Cancer J Clin. 2004;54:150-180.

Van Zandwijk N, Dalesio O, Pastirino 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;92:977-986.

Wolf G. A history of vitamin A and retinoids. FASEB J. 1996 Jul;10(9):1102-1107.

Note: This information may not cover all possible claims, uses, actions, precautions, side effects or interactions. It is not intended as medical advice, and should not be relied upon as a substitute for consultation with your doctor, who is familiar with your medical situation.


Last Medical Review: 04/02/2012
Last Revised: 05/04/2012