De veelzijdige werking van vitamine C

Vitamine C is wellicht één van de bekendste vitamines. Dit artikel belicht de functie van deze veelzijdige stof en informeert over diverse vormen, doseringen en therapeutische toepassingen van deze vitamine.

Vitamine C
De veelzijdige werking van vitamine C – Auteur Melissa Albers

Functies en eigenschappen

Vitamine C is betrokken bij veel belangrijke processen in het lichaam waaronder het behoud van een goede weerstand, gezonde tanden, botten, huid en bloedvaten, een goed functionerend zenuwstelsel en optimale energievoorziening voor lichaamscellen. Vitamine C is ook een antioxidant waardoor deze stof (samen met vitamine E) beschermt tegen vrije radicalen. Indirect voorkomt vitamine C op deze manier tot op zekere hoogte (versnelde) celveroudering, want vrije radicalen spelen een rol bij verouderingsprocessen. Daarnaast bevordert vitamine C de opname van ijzer en heeft de stof een antihistamine werking, hetgeen allergieën en astma kan verminderen. Tot slot kan vitamine C helpen bij detoxificatie (ontgifting).

Het lichaam kan vitamine C niet zelf aanmaken of opslaan. Daarom is het van belang om dagelijks voldoende vitamine C binnen te krijgen. De belangrijkste bronnen hiervan zijn groente en fruit. De meeste mensen krijgen hiervan echter te weinig binnen om aan de dagelijkse behoefte te kunnen voldoen, dus is het raadzaam om extra vitamine C te gebruiken in de vorm van een supplement. Echter is niet elk supplement daadwerkelijk geschikt. Alleen de juiste samenstelling en dosering kan een aanzienlijke bijdrage aan de gezondheid leveren.

Samenstelling en opname

Allereerst is de vorm waarin vitamine C wordt aangeboden van belang. Ascorbinezuur, calciumascorbaat (Ester C) en magnesiumascorbaat zijn allen vormen van vitamine C. Magnesiumascorbaat en Ester C zijn hiervan de best opneembare en best verdraagbare soorten. Ascorbinezuur is minder geschikt, omdat deze vorm van vitamine C, vooral in grotere hoeveelheden (>250 mg per dag) vaak maagproblemen geeft. Bovendien kan het lichaam per keer maximaal 500 mg vitamine C opnemen. Een dosering die hoger is dan 500 mg per pil heeft dus eigenlijk geen toegevoegde waarde. De zgn. ‘time-released’ pillen hebben geen aantoonbare effectiviteit, dus deze kunnen beter worden vermeden. Daarnaast kan de aanwezigheid en hoeveelheid hulp- en vulstoffen in het preparaat (bv. bioflavonoïden) de opname van vitamine C bevorderen, terwijl vulstoffen of glansmiddelen (zoals E124 en gehydrogeneerde olie) de opname van de vitamine kunnen remmen en zelfs schadelijk kunnen zijn voor de gezondheid.

De vorm waarin het supplement wordt aangeboden is ook van belang. Kauwtabletten en bruistabletten zijn geen verstandige keuze, omdat deze altijd bestaan uit ongezonde vulstoffen (waaronder zoet- en kleurstoffen). Vitamine C in poedervorm is vaak de zuiverste vorm en, ten opzichte van pillen, het beste te doseren. Natuurlijke vitamine C preparaten met extracten uit acerola of camu camu zijn, met het oog op de relatief lage dosis van deze soorten, alleen geschikt als onderhoudsdosering en alleen indien deze geen vulstoffen bevatten.

De beste vorm van vitamine C, vooral als therapeutische toepassing, is magnesiumascorbaat in poedervorm zonder toegevoegde vulstoffen. Verrijking met bioflavonoïden (in het supplement zelf of apart toegediend) zorgt overigens voor een nog betere opname.

Dosering en therapeutische toepassingen

De officiële aanbevolen dagelijkse hoeveelheid (ADH) vitamine C bedraagt voor volwassenen 75 mg. Dit staat gelijk aan 80 gram broccoli of 8 appels of 1 rode paprika. Deze ADH is echter gebaseerd op een minimale dosis die nodig is om cellen normaal te laten functioneren waarbij alle overige factoren (leefstijl, ziekte, omgeving) niet mee zijn genomen. Daarnaast bevatten de meeste groente en fruitsoorten door verarming van de bodem en het gebruik van kunstmest steeds minder vitamines en mineralen. Hierdoor moet men meer van deze gewassen eten om aan de dagelijkse behoefte aan voedingsstoffen te kunnen voldoen. Bovendien bevatten gewassen tegenwoordig veel chemische stoffen zoals resten van pesticiden en kunstmest die de opname van vitamines afremmen of blokkeren. Ook verontreinigende stoffen uit bewerkte voedingsmiddelen (bv. conserveringsmiddelen, chemische smaakstoffen, etc.), uitlaatgassen, tabak, medicijnen en (elektro)stress verhogen de vitamine C behoefte. Daarom wordt aangeraden om in bovengenoemde gevallen dagelijks minimaal 2000 mg vitamine C te nemen (dit staat ongeveer gelijk aan 25-35 mg vitamine C per kg lichaamsgewicht). Deze dosis is nodig om het lichaam gezond te houden, weerbaar te maken en celschade zoveel mogelijk te kunnen beperken.

Bij tandvleesproblemen, huidaandoeningen, gescheurde mondhoeken, slapeloosheid, bloedingen, chronische (ontstekings)ziekten (bv. artrose, reuma, interstiële cystitis, colitis ulcerosa en ziekte van Crohn), hoge koorts, na operaties en bij kanker worden doses tussen 6000 en 18000 mg per dag aangeraden. Bij dergelijk hoge doseringen is het extra belangrijk de vitamine C inname zo veel mogelijk over de dag te spreiden om een evenwichtige opname te bewerkstelligen.

Uit diverse onderzoeken blijkt dat bij kanker intraveneus toegediende vitamine C het effectiefst werkt, omdat hierdoor hogere concentraties in het bloed en lichaamsweefsels kan worden bereikt dan via orale inname. De hoge concentraties die kunnen worden bereikt door intraveneuze toediening zorgen voor een wisselwerking met ijzer en andere metalen (die zich van nature in het bloed bevinden) waardoor waterstofperoxide ontstaat. Deze stof beschadigt het DNA en de energievoorziening van kankercellen waardoor deze (gedeeltelijk) afsterven.

Bijwerkingen en interacties

Intraveneus en oraal toegediende vitamine C is nooit schadelijk voor gezonde cellen (ongeacht de hoogte van de dosering), omdat de celdodende werking alleen optreedt bij zieke (kanker)cellen. Is de vitamine C inname toch hoger dan het lichaam nodig heeft, dan zal het lichaam deze via de urine uitscheiden. Bij (zeer) hoge orale doseringen kan vitamine C diarree veroorzaken. Zodra de dosering verlaagd wordt, verdwijnt dit verschijnsel. Vitamine C verhoogt (vooral in hogere doseringen) de ijzeropname en kan de opname van koper verlagen. Ook zijn er interacties met (natuur)geneesmiddelen. Raadpleeg daarom voor het gebruik van een vitamine C supplement altijd eerst een deskundige.

Referenties:



Melissa Albers
Author: Melissa Albers
Een gezond, slank en fit lichaam binnen handbereik door persoonlijke coaching en praktische adviezen op maat. Als diëtist, natuurvoedingskundige & Food Coach begeleid ik jou bij veranderingen in je voedingspatroon en leefstijl.

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