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Vitamin A (retinol)

Vitamin A (retinol)

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  • 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.
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  • Cox SE, Arthur P, Kirkwood BR, et al. Vitamin A supplementation increases ratios of proinflammatory to anti-inflammatory cytokine responses in pregnancy and lactation. Clin Exp Immunol 2006 Jun;144(3):392-400.
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  • Darboe MK, Thurnham DI, Morgan G, et al. Effectiveness of an early supplementation scheme of high-dose vitamin A versus standard WHO protocol in Gambian mothers and infants: a randomised controlled trial. Lancet 2007 Jun 23;369(9579):2088-96.
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  • Diness BR, Fisker AB, Roth A, et al. Effect of high-dose vitamin A supplementation on the immune response to Bacille Calmette-Guerin vaccine. Am J Clin Nutr 2007 Oct;86(4):1152-9.
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  • Kafi R, Kwak HS, Schumacher WE, et al. Improvement of naturally aged skin with vitamin A (retinol). Arch Dermatol 2007 May;143(5):606-12.
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  • Klemm RD, Labrique AB, Christian P, et al. Newborn vitamin A supplementation reduced infant mortality in rural Bangladesh. Pediatrics 2008 Jul;122(1):e242-50.
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  • Long KZ, Rosado JL, DuPont HL, et al. Supplementation with vitamin A reduces watery diarrhoea and respiratory infections in Mexican children. Br J Nutr 2007 Feb;97(2):337-43.
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  • Newton S, Owusu-Agyei S, Ampofo W, et al. Vitamin A supplementation enhances infants' immune responses to hepatitis B vaccine but does not affect responses to Haemophilus influenzae type b vaccine. J Nutr 2007 May;137(5):1272-7.
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  • Payne LG, Koski KG, Ortega-Barria E, et al. Benefit of vitamin A supplementation on ascaris reinfection is less evident in stunted children. J Nutr 2007 Jun;137(6):1455-9.
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  • Saltzman MD, King EC. Central physeal arrests as a manifestation of hypervitaminosis A. J Pediatr Orthop 2007 Apr-May;27(3):351-3.
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