vitamin A (generic name)
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SafetyDISCLAIMER: Many complementary techniques are practiced by healthcare professionals with formal training, in accordance with the standards of national organizations. However, this is not universally the case, and adverse effects are possible. Due to limited research, in some cases only limited safety information is available.
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 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.
Cholestyramine (Questran®) and colestipol (Colestid®) may decrease the effectiveness of vitamin A by reducing absorption of this fat-soluble vitamin. Neomycin 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.
Mineral oil 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. Alcohol, particularly chronic use, may induce vitamin A deficiency.
Orlistat (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 (Achromycin®).
Increased toxicity with concurrent use of vitamin A and chemotherapy may occur.
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.
Zinc deficiency may alter vitamin A status, although the mechanism is unclear.