It’s like comparing oranges and…well, oranges.

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:

Ascorbyl palmitate

Ascorbyl palmitate is not our favorite vitamin C derivative: Proven not as stable as sodium ascorbyl palmitate, magnesium ascorbyl palmitate, or ascorbyl glucoside. Not cool.

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 phosphate

Salt can make all the difference: Sodium ascorbyl palmitate is more stable than ascorbyl palmitate. BUT, it’s still water-soluble, which crosses it off our “favorites” list. (Photo credit: zion fiction)

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

Magnesium ascorbyl palmitate is more stable than ascorbyl palmitate, but is water-soluble.

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.)

Ascorbyl glucoside

Ascorbyl glucoside contains L-ascorbic acid and glucose. It is fat-soluble and breaks down in the skin into L-ascorbic acid and glucose- pretty stellar, in our opinion.

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.

Ascorbyl glucosamine

Ascorbyl glucosamine is a “pass by,” not a “buy”: Studies show 5% ascorbyl glucosamine is not as effective as 20% azelaic acid in lightening spots. And when you consider the major benefit of glucosamine is skin-brightening, not stability, why bother with this in the first place?

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).

Bottom Line

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?