Hui Ling, Lau
Phd, MPharm, RPh
While there is no difference in terms of the absorption and bioavailability between natural and synthetic vitamin C, the type of formulation or dosage form in which the vitamin C is delivered to the body may affect its absorption from your gastrointestinal tract into your blood stream. Vitamin C is available as a supplement in the form of capsules, tablets, effervescent tablets, chewable tablets, powders and more recently as liposomal liquid or liquid capsules. Synthetic vitamin C products usually contain ascorbic acid or mineral ascorbates such as calcium ascorbate and sodium ascorbate, or a mixture of all.
This extensive array of vitamin C preparations provide consumers with a wide range of choices but may also cause confusion regarding the selection of the best form suited to their needs. Many consumers believe that solution or liquid supplements are better and more rapidly absorbed by the body than tablets and capsules. In fact, the absorption of vitamin C is similar regardless whether it is taken as regular release tablets, chewable tablets and powder made into oral solutions; but the cost of these different preparations to consumers may vary greatly.
While consumption of vitamin C at doses up to 2000 mg/day have been considered safe, there have been reports of diarrhea, nausea, abdominal bloating and heartburn in those consuming more than 1000 mg/day. Since the absorption of vitamin C into the blood is dependent on saturable transporters, it was observed that ingestion of more than 200 mg of vitamin C in a single dose increases its excretion in the urine compared to lower doses or when the dose is spread throughout the day. However, the various studies comparing sustained-release (slow-release, timed-release) vitamin C formulations to regular release preparations produced inconclusive results.
A newer formulation of vitamin C supplement in the market is perhaps in the form of liposomes or ‘liposomal vitamin C’ where the vitamin C is trapped in a lipid shell such as soya or sunflower lecithin, making it fat-soluble, thus increasing absorption. While a number of studies have shown promising results of improved absorption with liposomal formulations, larger-scaled studies are required for a definitive conclusion.
Chewable tablet on the other hand, is a favorite supplement dosage form especially among children, mainly due to its pleasant taste. Consumption of chewable vitamin C tablets however, has shown to reduce the pH of oral cavity to approximately pH 2 during chewing, leading to demineralization or erosion of tooth enamel. Effervescent ascorbic acid has been found to produce similar effects on teeth. This erosive effect is predominantly observed in those with reduced salivary flow or those who placed tablets in close proximity to teeth for long periods. A simple way to counter this is perhaps to select preparations containing ‘non-acidic vitamin C’ or mineral ascorbate; and to gargle or brush teeth after chewing the tablets.
Having said that, sodium ascorbate contains approximately 113 mg of elemental sodium per 1000 mg of ascorbic acid and thus large quantities may not be suitable for consumers who are on restrictive low-sodium diet (<2500 mg sodium/ day). Nonetheless, do consult your healthcare provider before taking over-the-counter supplements on top of your regular medications.
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