Vitamin C is a big topic on this blog, and for good reason! It has been proven in numerous studies to:
- Fight future signs of aging (by scavenging free radicals through reaction with the superoxide anion or the hydroxyl radical);
- Reduce sunspots (by inhibiting the enzyme tyrosinase);
- Fight uneven pigmentation (see above);
- Increase skin firmness (by increasing collagen production);
- Enhance sunscreen protection.
However, it seems everyone and their brother nowadays is premiering a “new” form of vitamin C. It’s impossible to know the differences without studying products all day long – but, thankfully, we’ve been doing just that for years now!
One major thing we’re looking for? Fat – not water – solubility. According to studies, “the most stable vitamin C preparations remain anhydrous or completely water-free.” (Cosmetic Dermatology, 2010).
So, here they are:
Benefits: More stable than L-ascorbic acid in the presence of light and air; non-water soluble
Detriments: Less stable than magnesium ascorbyl glucoside and ascorbyl glucoside; Don’t know the concentration of ascorbyl palmitate needed to achieve maximal efficacy, and concentrations are not listed on the bottle(s).
Ascorbyl palmitate is a fat-soluble ester of L-ascorbic acid; it is L-ascorbic acid combined with palmitic acid, a fatty acid. According to a 1997 study, ascorbyl palmitate is more stable than L-ascorbic acid. A 2001 study in the International Journal of Pharmaceutics found that the stability of ascorbyl palmitate was increased further when ascorbyl palmitate was used in high concentrations (1-2%), or placed in water-in-oil emulsions rather than oil-in-water emulsions, due to the relocation of the unstable cyclic ring to the internal aqueous phase in the water-in-oil emulsions. Given that ascorbyl palmitate concentrations are generally 0.05-1%, unless a higher concentration of ascorbyl palmitate is established for a product, sodium ascorbyl palmitate or magnesium ascorbyl palmitate have been found to be more stable in solutions (see below).
Sodium ascorbyl phosphateBenefits: More stable than L-ascorbic acid or ascorbyl palmitate in the presence of light and air
Detriments: Water-soluble (fat soluble is more stable); Don’t know the concentration needed to achieve maximal efficacy, and concentrations are not listed on the bottle(s).
Sodium ascorbyl phosphate is a water-soluble form of L-ascorbic acid; it is L-ascorbic acid combined with palmitic acid, a fatty acid, and – you’ll never guess – sodium. According to a 2001 study in the International Journal of Pharmaceutics, sodium ascorbyl phosphate has greater long-term stability than ascorbyl palmitate when each is used in similar concentrations. Unlike ascorbyl palmitate, sodium ascorbyl phosphate is stable in water-in-oil emulsions and oil-in-water emulsions.
Magnesium ascorbyl phosphate
Benefits: More stable than L-ascorbic acid or ascorbyl palmitate in the presence of light and air
Detriments: Water-soluble; don’t know the concentration needed to achieve maximal efficacy, and concentrations are not listed on the bottle(s).
Magnesium ascorbyl phosphate is a water-soluble form of L-ascorbic acid. According to a 1997 study in the Journal of Pharmaceutical and Biomedical Analysis, magnesium ascorbyl palmitate has greater stability than both L-ascorbic acid and ascorbyl palmitate, like sodium ascorbyl phosphate. (As far as I know, no peer-reviewed published studies have compared the efficacy and stability of magnesium ascorbyl and sodium ascorbyl palmitate.)
Benefits: More stable than L-ascorbic acid, fat-soluble
Detriments: Don’t know the concentration needed to achieve maximal efficacy, and concentrations are not listed on the bottle(s).
Ascorbyl glucoside has a structure in which the C2-hydroxyl group of L-ascorbic acid is masked with glucose. According to the manufacturer, Hayashibara International, once ascorbyl glucoside is selectively permeated through the skin, it is broken down into L-ascorbic acid and glucose by the enzyme alpha-glucosidase. Essentially, because ascorbyl glucoside is broken down into L-ascorbic acid, it has the same functions as L-ascorbic acid! In addition, ascorbyl glucoside has been found to have greater stability in the presence of air, heat, light, and pH changes than L-ascorbic acid.
Benefits: Combines two skin brighteners: vitamin C and glucosamine
Detriments: Found 5% ascorbyl glucosamine not to be as effective as 20% azelaic acid in lightening spots; don’t know the concentration needed to achieve maximal efficacy, and concentrations are not listed on the bottle(s).
Ascorbyl glucosamine is L-ascorbic acid combined with (yes, this is obvious) glucosamine. Although the combination of N-acetyl glucosamine (NAG) and niacinamide was shown to reduce facial hyperpigmentation in Japanese and Caucasian subjects with facial hyperpigmentation in two double-blind, vehicle-controlled, split-face, left-right randomized clinical studies, use of a formulation with 5% ascorbyl glucosamine was shown to be less effective in reducing hyperpigmentation than 20% azelaic acid (source: Dermatology).
Based upon the above, we prefer the following:
- L-ascorbic acid
- Magnesium/sodium ascorbyl phosphate
- Ascorbyl glucoside
What form of vitamin C do you currently use?