Vitamin A : Health Benefits

by MedlinePlus

Vitamin A is a fat-soluble vitamin which is derived from two sources: preformed retinoids and provitamin carotenoids. Retinoids such as retinal, retinal, and retinoic acid are found in animal sources like liver, kidney, eggs, and dairy produce. Carotenoids like beta-carotene (which has the highest vitamin A activity) are found in plants such as dark or yellow vegetables and carrots.

Natural retinoids are present in all living organisms, either as preformed vitamin A or as carotenoids, and are required for a vast number of biological processes like vision and cellular growth. A major biologic function of vitamin A (as the metabolite retinal) is in the visual cycle. Research also suggests that vitamin A may reduce the mortality rate from measles, prevent some types of cancer, aid in growth and development, and improve immune function.

Recommended daily allowance (RDA) levels for vitamin A oral intake have been established by the U.S. Institute for Medicine of the National Academy of Sciences to prevent deficiencies in vitamin A.At recommended doses, vitamin Ais generally considered non-toxic. Excess dosing may lead to acute or chronic toxicity.

Vitamin A deficiency is rare in industrialized nations but remains a concern in developing countries, particularly in areas where malnutrition is common. Prolonged deficiency can lead to xerophthalmia (dry eye) and ultimately to night blindness or total blindness, as well as to skin disorders, infections (such as measles), diarrhea, and respiratory disorders.

Evidence

These uses have been tested in humans or animals. Safety and effectiveness have not always been proven. Some of these conditions are potentially serious, and should be evaluated by a qualified healthcare provider.

Uses based on scientific evidence

Vitamin A deficiency

Vitamin A deficiency may occur after chronic lack of adequate amounts of vitamin A or beta-carotene. Vitamin A is necessary for vision, and an early sign of vitamin A deficiency is keratomalacia (night blindness). Prolonged deficiency may lead to xerophthalmia (dry eye). Eventually, blindness can occur due to damage to the retina and cornea. Vitamin A is necessary for healthy growth and development, and recommended daily amounts (RDA) should be assured, particularly in children.

Acne

Derivatives of vitamin A, retinoids, are used to treat skin disorders such as acne. Topical and oral prescription medications, such as tretinoin (Avita®, Renova®, Retina-A®, Retin-A Micro®) and isotretinoin (Accutane®), are available for treatment. Isotretinoin may cause severe side effects and should be used only for severe resistant acne. Isotretinoin must not be used in women who are pregnant, plan to become pregnant, or have a chance of being pregnant due to a risk of severe birth defects. These medications should be prescribed and coordinated by a qualified licensed healthcare professional. Vitamin A supplements should not be used simultaneously due to a risk of increased toxicity.

Acute promyelocytic leukemia (All-trans retinoic acid)

The prescription drug All- Trans -Retinoic Acid (ATRA, Vesanoid®) is a vitamin A derivative which is an established treatment for acute promyelocytic leukemia and improves median survival in this disease. Treatment should be under strict medical supervision. Vitamin A supplements should not be used simultaneously with ATRA due to a risk of increased toxicity.

Measles (supportive agent)

Vitamin A should be administered to children diagnosed with measles in areas where vitamin A deficiency may be present. Measles is a viral disease that can lead to serious complications such as diarrhea, pneumonia, and encephalitis. Supplementation with vitamin A in children with measles has been shown to be beneficial, by decreasing the length and impact of the disease. Side effects such as diarrhea, pneumonia, and death have been reduced with the use of vitamin A. Management of measles should be under strict medical supervision.

Xerophthalmia (dry eye)

Oral vitamin A is the treatment of choice for xerophthalmia due to prolonged vitamin A deficiency, and should be given immediately once the disorder is established.

Malaria (supportive agent)

Limited research suggests that vitamin A may reduce fever, morbidity, and parasite blood levels in patients with malaria ( Plasmodium falciparum infection). However, there is no evidence that vitamin A is equivalent or superior to well-established drug therapies used for prevention or treatment of malaria. Patients with malaria or living/traveling in endemic areas should speak with a physician about appropriate measures.

Retinitis pigmentosa

Retinitis pigmentosa is a genetic disorder that affects night vision. Early symptoms include night blindness and progressive loss of vision over time. Based on recent findings, 15,000 IU daily of vitamin A in the palmitate form has been recommended in patients with retinitis pigmentosa.

Antioxidant

The benefits to humans of potential antioxidant activity are not clear.

Breast cancer

Research results are not clear as to whether vitamin A is beneficial in the treatment or prevention of breast cancer. Patients receiving chemotherapy or radiation therapy for cancer should speak with their doctor(s) before taking antioxidants such as vitamin A during treatment, due to possible interference.

Cataract prevention

Vitamin A has been suggested to prevent cataract formation. Carotenoids such as beta-carotene, lutein, and zeaxanthin may decrease the risk of severe cataracts. There is not sufficient evidence to form a clear conclusion at this time.

About the Author

medlineplus.gov
MedlinePlus will direct you to information to help answer health questions. MedlinePlus brings together authoritative information from NLM, the National Institutes of Health (NIH), and other government agencies and health-related organizations. MedlinePlus also has extensive information about drugs, an illustrated medical encyclopedia, interactive patient tutorials, and latest health news.