(retinol)

Background

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.

Synonyms

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.

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.

*Key to grades
A: Strong scientific evidence for this use;
B: Good scientific evidence for this use;
C: Unclear scientific evidence for this use;
D: Fair scientific evidence against this use;
F: Strong scientific evidence against this use.

Grading rationale

Uses based on tradition or theory The below uses are based on tradition or scientific theories. They often have not been thoroughly tested in humans, and safety and effectiveness have not always been proven. Some of these conditions are potentially serious, and should be evaluated by a qualified healthcare provider.

Aging, allergic rhinitis, asthma, blurred vision, bronchopulmonary dysplasia in premature infants, burns, candidiasis, cellulite (topical retinal), cold sores, conjunctivitis, Crohn''s disease, cystic fibrosis, deafness, deficiency (protein), diabetes, eczema, fibrocystic breast disease, glaucoma, headache (persistent), heart disease, hyperthyroidism, increasing sperm count, infections, keratosis follicularis (Darier''s disease), kidney stones, leukoplakia, Lichen planus pigmentosus, liver disease, menorrhagia (heavy menstruation), metabolic disorders (Hurler syndrome), neurodegenerative diseases, periodontal disease, pityriasis rubra pilaris, plantar warts, pollutant protection, premenstrual syndrome, psoriasis, rhinitis, sebaceous cysts, sinusitis, skin disorders (ichthyosis), sunburn, tinnitus, ulcers (stress ulcers in severely ill hospitalized patients), urinary tract infections, vaginitis, vision enhancement (nearsightedness).
 

Dosing

The below doses are based on scientific research, publications, traditional use, or expert opinion. Many herbs and supplements have not been thoroughly tested, and safety and effectiveness may not be proven. Brands may be made differently, with variable ingredients, even within the same brand. The below doses may not apply to all products. You should read product labels, and discuss doses with a qualified healthcare provider before starting therapy.

Sources of Vitamin A Vitamin A is found in dairy products, fish, darkly colored fruits and vegetables. Consumption of five servings of fruits and vegetables per day supplies 5-6 milligrams per day of provitamin A carotenoids, which provides about 50-65% of the adult RDA for vitamin A. Adults (over 18 years old) Vitamin A is included in most multivitamins, often in 5,000 IU doses as softgels, capsules, tablets, or liquid. U.S. Recommended Daily Allowance (RDA) for adults have been established by the U.S. Institute of Medicine of the National Academy of Sciences. Recommendations are: 900 micrograms per day (3,000 IU) for men and 700 micrograms per day (2,300 IU) for women. For pregnant women 19 years and older, 770 micrograms per day (2,600 IU) is recommended. For lactating women 19 years and older, 1,300 micrograms per day (4,300 IU) is recommended. For vitamin A deficiency not involving xerophthalmia, 100,000 IU orally or intramuscularly administered daily for three days, followed by 50,000 IU per day for two weeks has been used. A maintenance dose of 10,000 to 20,000 IU per day for two months has been recommended. Supporting care following chemotherapy may include weekly injections of 100,000 IU vitamin A. Patients receiving vitamin A should be observed carefully for liver toxicity. Injections should always be performed by a licensed healthcare provider. Children (under 18 years old) Recommended Dietary Allowances (RDA) have been established by the U.S. Institute of Medicine of the National Academy of Sciences. Recommendations are: for children 1-3 years-old, 300 micrograms per day (1,000 IU); for children 4-8 years-old, 400 micrograms per day (1,300 IU); and for children 9-13 years-old, 600 micrograms per day (2,000 IU). For pregnant women between 14-18 years-old, 750 micrograms per day (2,500 IU) is recommended; for lactating women between 14-18 years-old, 1,200 micrograms per day (4,000 IU) is recommended. The World Health Organization (WHO) has established dosage guidelines for children between 6-11 months old to receive 100,000 IU of vitamin A. This increases to 200,000 IU every six months from 12 to 59 months of age.

Safety

The U.S. Food and Drug Administration does not strictly regulate herbs and supplements. There is no guarantee of strength, purity or safety of products, and effects may vary. You should always read product labels. If you have a medical condition, or are taking other drugs, herbs, or supplements, you should speak with a qualified healthcare provider before starting a new therapy. Consult a healthcare provider immediately if you experience side effects.

Allergies Avoid in individuals with a known hypersensitivity/allergy to vitamin A. Side Effects and Warnings Vitamin A toxicity, or hypervitaminosis A, is rare in the general population. Vitamin A toxicity can occur with excessive amounts of vitamin A taken over short or long periods of time. Consequently, toxicity can be acute or chronic. An infant with acute toxicity can develop a bulging fontalle (the soft spot on the head) and symptoms similar to a brain tumor. Adults experience less specific symptoms such as headache, dizziness, fatigue, malaise, blurry vision, bone pain and swelling, nausea, and/or vomiting. Acute vitamin A toxicity may also lead to increased intracranial pressure, pruritus or itching, and bone problems. Severe toxicity can lead to eye damage, high levels of calcium, and liver damage. Persons with liver disease and high alcohol intake may be at risk for hepatotoxicity from vitamin A supplementation. Smokers who consume alcohol and beta-carotene may be at an increased risk for lung cancer or cardiovascular disease. Vitamin A toxicity may lead to intrahepatic cholestasis, a condition where bile cannot flow from the liver into the intestines. Treatment with ursodeoxycholic acid has been shown to greatly improve the symptoms of cholestasis. Pregnancy and Breastfeeding Vitamin A should only be used within the recommended dietary allowance, because vitamin A excess, as well as deficiency, has been associated with birth defects. Excessive doses of vitamin A have been associated with central nervous system malformations. Vitamin A is excreted in human breast milk. Benefits or dangers to nursing infants are not clearly established.

Interactions

Most herbs and supplements have not been thoroughly tested for interactions with other herbs, supplements, drugs, or foods. The interactions listed below are based on reports in scientific publications, laboratory experiments, or traditional use. You should always read product labels. If you have a medical condition, or are taking other drugs, herbs, or supplements, you should speak with a qualified healthcare provider before starting a new therapy.

Interactions with Drugs Vitamin A supplements should not be taken simultaneously with acitretin (Soriatane®), anticoagulants (blood thinners) such as warfarin (Coumadin®), bexarotene (Targentin®), All- Trans -Retinoic Acid (ATRA, Vesanoid®), etretinate (Tegison®), isotretinoin (Accutane®, Amnesteen®), or tretinoin (Vesabiod®, Avita®, Renova®, Retin-A®, Retin-A® Micro, Altinac®) due to increased risk of vitamin A toxicity. (Questran®) and colestipol (Colestid®) may decrease the effectiveness of vitamin A by reducing absorption of this fat-soluble vitamin. may interfere with the absorption of vitamin A, although this interaction has not been found to be clinically significant. Oral contraceptives (birth control pills) increase plasma vitamin A levels. Vitamin A may reduce seroconversion rates to the measles virus/vaccine, rendering the vaccine less effective. Other vaccines may be enhanced by vitamin A, including the  Haemophilus influenzae  type b vaccine and the diphtheria vaccine. Other vaccines have been demonstrated to be unaffected by vitamin A supplementation. These include the oral polio vaccine (OPV), tetanus toxoid, pertussis, and hepatitis B vaccines. Vitamin A may also alter the immune response to the Bacille Calmette-Guérin (BCG) vaccine, but this interaction is unclear. has been reported to reduce absorption of all fat-soluble vitamins. With occasional use, the effect on vitamin A levels does not appear to be significant. (obesity drug) decreases the absorption of fat-soluble vitamins, although studies suggest that vitamin A is not affected as much by orlistat as other fat-soluble vitamins. Nonetheless, the manufacturer of orlistat recommends that all patients take a multivitamin supplement containing all the fat-soluble vitamins (including vitamins A, D, E, and K unless otherwise contraindicated), separating the dosing time by at least two hours from orlistat. Patients who take tetracyclines, specifically minocycline (Minocin®), plus vitamin A are at a risk for developing benign intracranial hypertension (pseudotumor cerebri), which can occur with tetracyclines and vitamin A intoxication. Therefore, high doses of vitamin A should be avoided in people taking chromic tetracyclines. Other examples of tetracyclines include demeclocycline (Declomycin®) and tetracycline (®). Interactions with Herbs and Dietary Supplements Carob may increase risk of vitamin A toxicity. Vitamin A may improve anemia in people who are deficient in iron and vitamin A. There is likely no benefit in people who are not vitamin A deficient. deficiency may alter vitamin A status, although the mechanism is unclear.

Methodology

This information is based on a systematic review of scientific literature, edited and peer-reviewed by contributors to the Natural Standard Research Collaboration (www.naturalstandard.com): Ethan Basch, MD (Memorial Sloan-Kettering Cancer Center); Dawn Costa, BA, BS (Natural Standard Research Collaboration); Shaina Tanguay-Colucci, BS (Natural Standard Research Collaboration); Catherine Ulbricht, PharmD (Massachusetts College of Pharmacy); Christine Ulbricht, PharmD (University of Massachusetts); Wendy Weissner, BA (Natural Standard Research Collaboration).