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Vitamin A Side Effects, Interactions and Warnings

There is evidence of adverse effects from beta-carotene supplements in current heavy smokers.
- Am J Clin Nutr 1997 Aug;66(2):427-37 -- Vitamins and minerals: efficacy and safety. -- Hathcock JN.

Moreover, in smokers who also consume alcohol, beta-carotene supplementation promotes pulmonary cancer and, possibly, cardiovascular complications. Thus ethanol, while promoting a deficiency of vitamin A also enhances its toxicity as well as that of beta-carotene. This narrowing of the therapeutic window for retinol and beta-carotene must be taken into account when formulating treatments aimed at correcting vitamin A deficiency, especially in drinking populations.
- Am J Clin Nutr 1999 Jun;69(6):1071-85 -- Alcohol, vitamin A, and beta-carotene: adverse interactions, including hepatotoxicity and carcinogenicity. -- Leo MA, Lieber CS.

Toxicity has been associated with abuse of vitamin A supplements and with diets extremely high in preformed vitamin A. Consumption of 25,000-50,000 IU/d for periods of several months or more can produce multiple adverse effects. The lowest reported intakes causing toxicity have occurred in persons with liver function compromised by drugs, viral hepatitis, or protein-energy malnutrition. Certain drugs or other chemicals may markedly potentiate vitamin A toxicity in animals. Especially vulnerable groups include children, with adverse effects occurring with intakes as low as 1,500 IU.kg-1.d-1, and pregnant women, with birth defects being associated with maternal intakes as low as approximately 25,000 IU/d. The maternal dose threshold for birth defects cannot be identified from present data. An identifiable fraction of the population surveyed consumes vitamin A supplements at 25,000 IU/d and a few individuals consume much more. beta-Carotene is much less toxic than vitamin A.
- Am J Clin Nutr 1990 Aug;52(2):183-202 -- Evaluation of vitamin A toxicity. -- Hathcock JN, Hattan DG, Jenkins MY, McDonald JT, Sundaresan PR, Wilkening VL.

Retinol intake was negatively associated with bone mineral density. High dietary intake of retinol seems to be associated with osteoporosis.
- Ann Intern Med 1998 Nov 15;129(10):770-8 -- Excessive dietary intake of vitamin A is associated with reduced bone mineral density and increased risk for hip fracture. -- Melhus H, Michaelsson K, Kindmark A, Bergstrom R, Holmberg L, Mallmin H, Wolk A, Ljunghall S.

Vitamin A and isotretinoin should not be taken together and may increase toxicity of each other.
- Int J Vitam Nutr Res 1998;68(6):411-6 -- Safety of vitamin A: recent results. -- Wiegand UW, Hartmann S, Hummler H.

Patients should be cautioned concerning supplements of vitamin A used chronically or ingested in large quantities because it can interfere with oral anticoagulants.
- J Am Diet Assoc 1995 May;95(5):580-4 -- Interaction of dietary factors with oral anticoagulants: review and applications. -- Harris JE.

Possible adverse interaction between vitamin A and anticonvulsants.
- Life Sci 1995;57(1):53-60 -- Antiepileptic drugs alter endogenous retinoid concentrations: a possible mechanism of teratogenesis of anticonvulsant therapy. -- Nau H, Tzimas G, Mondry M, Plum C, Spohr HL.

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last update: March 2010

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