3,7-dimethyl-9-(2,6,6, trimethyl-1-cyclohexen-1-yl)-2,4,6,8-natetraen-1-ol, 3-dehydroretinol, antixerophthalmic vitamin, Aquasol A®, axerophtholum, beta-carotene oleovitamin A, Palmitate-A®, retinaldehyde (RAL), retinyl acetate, retinyl N-formyl aspartamate, retinyl palmitate, Solatene®, vitamin A, vitamin A1, vitamin A USP, vitaminum A.
Vitamin A is a fat-soluble vitamin that is derived from two sources: preformed retinoids and provitamin carotenoids. Retinoids, such as 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 A is 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.
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 (treatment, All-trans retinoic acid):
The prescription drug All-Trans-Retinoic Acid (ATRA, Vesanoid®) is a vitamin A derivative that 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.
Eye disorders (Bitot's spot):
Vitamin A deficiency can lead to Bitot's spot, or the buildup of keratin debris in the conjunctiva. Bitot's spot is a sign of xerophthalmia, and may be treated with vitamin A supplementation.
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.
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) and Bitot's spot, or the buildup of keratin debris in the conjunctiva. 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.
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 a lack of evidence suggesting that vitamin A is equivalent or superior to well-established drug therapies used for the prevention or treatment of malaria. Patients with malaria or living/traveling in endemic areas should speak with a physician about appropriate measures.
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, vitamin A in the palmitate form has been recommended in patients with retinitis pigmentosa.
The benefits to humans of potential antioxidant activity are not clear.
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.
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.
Vitamin A may reduce the severity and duration of diarrheal episodes in malnourished children but not in well-nourished children. Since diarrhea is a major cause of morbidity and mortality in developing countries, vitamin A supplementation may be considered in undernourished children with diarrhea.
The role of vitamin A in the prevention, transmission, or treatment of HIV is controversial and not well established. A clear conclusion cannot be formed based on the available scientific research.
Vitamin A deficiency may compromise immunity, but there is no clear evidence that additional vitamin A supplementation is beneficial for immune function in patients who are not vitamin A deficient.
There is a limited amount of research in this area, with mixed results. Some evidence suggests possible decreases in infant mortality with vitamin A supplementation, while other research reports no benefits. A clear conclusion cannot be formed based on the available scientific research.
Iron deficiency anemia:
Vitamin A supplementation in combination with iron may have beneficial effects in patients with iron deficiency anemia, including children and pregnant women. It is not clear that there are benefits in individuals who are not vitamin A deficient. This area remains controversial, and further evidence is necessary before a clear conclusion can be drawn.
Vitamin A supplementation has not been shown to improve response to gemcitabine in pancreatic cancer. It is unclear whether vitamin A may provide any benefits in patients with pancreatic cancer. More research is needed in this area.
Parasite infection (Acaris reinfection):
After deworming, children supplemented with vitamin A may be less prone to Ascaris parasite reinfection. These benefits may be less in children with stunted growth.
Photoreactive keratectomy is a type of laser eye surgery used to correct nearsightedness. High-dose vitamin A supplementation in addition to vitamin E has been suggested to help improve ocular healing after surgery and to improve visual acuity, although additional evidence is necessary before a definitive conclusion can be reached.
One study found no effect of a moderate dose of vitamin A supplementation on the duration of uncomplicated pneumonia in underweight or normal-weight children aged younger than five years. However, a beneficial effect was seen in children with high basal serum retinol concentrations.
Maternal vitamin A deficiency is common in developing countries. Beta-carotene may reduce pregnancy-related complications and mortality in such individuals. However, excess intake of vitamin A has been reported to increase the risks of some birth defects. Vitamin A supplementation above the RDA is therefore not recommended in pregnancy.
Skin aging (improving aging skin appearance):
Some studies suggest that topical vitamin A may improve the appearance and integrity of aged skin.
Skin cancer prevention:
It is not clear if vitamin A or beta-carotene, taken by mouth or used on the skin with sunscreen, is beneficial in the prevention or treatment of skin cancers or wrinkles.
Stomach cancer (prevention):
Vitamin supplementation has been proposed to reduce the rate of stomach cancer. However, there is some evidence suggesting that vitamin A does not reduce the rates of gastric cancer or pre-cancerous gastric lesions. More research is needed to examine whether vitamin A has any effects on stomach cancer.
Tumors (polyp prevention):
Alpha-carotene and vitamin A may protect against recurrence of polyps and adenoma in nonsmokers and nondrinkers or be indicative of compliance or another healthy lifestyle factor that reduces risk. Further research is needed before a conclusion can be drawn
Viral infection (Norovirus (NoV) infection):
Vitamin A supplementation has been suggested to help prevent NoV infection in children and reduce the symptoms associated with NoV infections.
Daily vitamin A with calcium has been suggested for weight loss, and in one study an average loss of two pounds was reported after two years of supplementation in young women.
In preliminary study, retinol palmitate significantly reduced rectal symptoms of radiation proctopathy, perhaps because of wound-healing effects. Further research is needed to confirm these results.
Chemotherapy adverse effects:
Vitamin A supplementation does not appear to improve chemotherapy-related side effects including nausea, vomiting, diarrhea, or mouth sores.
Vitamin A has been studied as a possible treatment for lung cancer without evidence of benefits. Available evidence suggests that high-dose Vitamin A and beta-carotene may actually increase the risk of adverse effects, especially among alcohol users and smokers.