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VITAMIN A (Retinol)

Vidste du at

  • Der findes 2 slags A-vitamin, et fra dyreriget som retinol, og et provitamin fra planteriget, kaldet beta-caroten?
  • Det er fedtopløseligt og deponeres i lever og fedtvæv til senere brug. Dagligt tilskud er derfor ikke nødvendigt.
  • Det er mest kendt som øjets, hudens og slimhindernes vitamin.

Virkning

  • Det styrker hud, tarmslimhinde, luft- og urinveje, og beskytter mod infektioner og de kræfttyper der skyldes direkte påvirkning.
  • Det er nødvendigt for produktion af et farvestof i øjet (synspurpur), der er vigtigt for at kunne se i mørke (skumringssyn).
  • Det er nødvendigt for normal fosterudvikling.

Mangelsymptomer

  • Natblindhed.
  • Tør skældende hud.
  • Tørre, sarte slimhinder med hyppige infektioner (tarm, luft- og urinveje).
  • Reduceret hørelse, lugt og smag.
  • Hår og negle der let knækker.
  • Overhyppighed af kræft i hud, blære, bronkier og mavesæk.

Måleenhed

1 µg retinol=6 µg beta-caroten=5 IE (international enhed).

Dagsdosis

 Forebygge mangler   Langtidsprofylakse  Støttebehandling   Som medicin 
 700 µg   1000 µg   1000 µg  -5000 µg
 Børn: 2-400 µg  3-500 µg  3-500 µg  -700 µg

Tilskud tilrådes

  • Sukkersygepatienter, da de ikke kan omdanne beta-caroten som raske.
  • Mave-tarmsyge med dårlig fordøjelse.
  • Ved dårlig fedtoptagelighed fra tarmen.
  • Rene vegetarer (veganer) og ældre.
  • Alkoholikere har øget behov (kombineret med zink).

Som medicin

  • Kan forsøges mod forskellige former for hudproblemer, fx. uren hud og psoriasis.

Overdosering

  • Ses sjælden, da en akut overdosering først ses ved doser over 100.000-500.000 µg. En kronisk forgiftning opstår først efter flere måneder med doser over flere tusinde µg.
  • Som medicin er doser på 30 000 µg ikke sjældne. Gravide bør ikke overskride doser på 1000 µg.
  • Symptomer: Kraftig hovedpine, tør skællende hud, ledsmerter, forstoppelse, kvalme og opkast. Der er beskrevet forgiftninger hos polarforskere der spiste A-vitaminrig lever.
  • Doser over 3000 µg hos gravide, øger risikoen for misdannelser i centralnervesystemet, brislen og hjertet.

Husk

  • Zink og vitamin A arbejder sammen. Zinkmangel kan svække A-vitamin virkningen og omvendt.
  • Almindelig levertran indeholder A- og D-vitamin. Den bør derfor ikke kombineres med store doser multivitamin, der ligeledes indeholder disse fedtopløselige vitaminer. Det kan give overdosering.
  • P-pillebrugere har mindre behov for vitamin A.
  • Unge, der benytter vitamin A-syre krem mod uren hud, skal undgå A-vitamin.

Findes i

Lever, smør, margarine, ost, æg, makrel, sardiner.

Litteratur:

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Comstock GW et al. Serum concentrations of alpha-tocopherol, beta-carotene, and retinol preceding the diagnosis of rheumatoid arthritis and systemic lupus erythematosus. Ann Rheum Dis 56: 323-5, 1997.

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Goodman DS. Vitamin A and retinoids in heath and disease. N Eng J Med 310: 1023-1031, 1984.

Hayes KC. Retinal degeneration in monkeys induced by deficiencies of vitamin E or A. Invest Ophthalmol Vis Sci 13:7:499-510, 1974.

Honkanen V et al. Vitamins A and E, retinol binding protein and zinc in rheumatoid arthritis. Clin Exp Rheumatol 7: 465-9, 1989.

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Lohle E. The influence of chronic vitamin A deficiency on human and animal ears. Arch Otorhinolaryngol 234:167-73, 1982.

Mckeown LA. Beta carotene lifts CD4 counts. Study reported in Medical Tribune Feb. 25, p. 1. 1993.

Mobarhan S, Bowen P, Andersen B et al. Effects of beta-carotene repletion on beta-carotene absorption, lipid peroxidation, and neutrophil superoxide formation in young men. Nutr Cancer 14: 195-206, 1990.

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