Keys to Unlocking the Benefits of Vitamin C
By: Lawrence Samuels, MD
Posted: November 29, 2012, from the December 2012 issue of Skin Inc. magazine.
Vitamin C is an essential vitamin for maintaining a healthy body and healthy skin. Yet, the body cannot synthesize vitamin C from glucose, because it lacks the enzyme required for this reaction. As a result, humans rely on dietary intake for their supply of vitamin C in the body, which can be ingested from food sources, such as citrus fruits and dark-green leafy vegetables. Unfortunately, ingested vitamin C cannot deliver an adequate amount of L-ascorbic acid to the skin. If antioxidants could be delivered in high concentration through the stratum corneum into the skin, then the antioxidant protective reservoir could be increased, and photoprotection and skin cell repair could be enhanced. More importantly, skin cell rejuvenation and collagen synthesis could be increased.1
The skin relies on antioxidants for protection against such environmental insults as ultraviolet (UV) rays, cigarette smoke and pollutants that can cause free radicals and photoaging of the skin. Free radicals damage DNA, proteins and lipids, which cause skin cells to die. Since the skin receives the most intense free-radical assault from UV light exposure, replenishing and increasing the antioxidant defense of the skin becomes an attractive strategy for photo protection and photo repair. Studies show that, when applied to the skin, L-ascorbic acid stimulates collagen synthesis, provides sun protection and protects the skin by reducing free radicals that would otherwise destroy skin cells and their components. Topical vitamin C has also been shown to improve skin texture and tone, reduce brown spots, decrease the appearance of fine lines and wrinkles, and help prevent their formation.2
Biologic antioxidant
L-ascorbic acid is one of the most abundant and most powerful antioxidants in the skin and body. It is the primary water-soluble, nonenzymatic biologic antioxidant in human tissue that protects the body from oxidative stress. It is important to note that water-soluble antioxidants act as a first defense against free radicals generated in plasma, but they cannot scavenge lipophilic (fat-soluble) free radicals within the membranes. Lipophilic antioxidants—particularly vitamin E—suppress oxidative damage efficiently in membranes. In addition to its direct antioxidant effects, L-ascorbic acid is known to be the primary replenisher of vitamin E, the most efficient inhibitor of lipid peroxidation in cell membranes.3
Formulation characteristics are critical for the delivery and penetration of L-ascorbic acid into the skin to restore and enhance its natural antioxidant activity. The major formulation characteristics are related to the following:
- Molecular structure of the vitamin C;
- Concentration of the L-ascorbic acid;
- The pH of the L-ascorbic acid serum; and
- The proper packaging of the L-ascorbic acid.
Molecular structure and concentration
Available scientific data has allowed the production of oral vitamin C in appropriate amounts to supplement the diet to maintain serum L-ascorbic acid levels for normal systemic metabolic function.4 However, the challenge to determine the appropriate chemical form of vitamin C, the appropriate pH and concentration of vitamin C, and the appropriate preparation has been elusive until the past few years. A study published by the American Society for Dermatologic Surgery demonstrated that L-ascorbic acid, which is true vitamin C, is the chemical derivative of vitamin C that is chemically reactive and bioavailable. Other derivatives of vitamin C, including magnesium ascorbyl phosphate, ascorbyl-6-palmitate and dehydroascorbic acid, did not increase skin levels of L-ascorbic acid. These are vitamin C-related molecules that moisturize the skin, but have not been shown to penetrate the skin and do not increase L-ascorbic levels in the skin. In this study, Sheldon Pinnell, MD, demonstrated that free L-ascorbic acid is the only molecular structure proven to penetrate into the skin and neutralize those damaging free radicals. Therefore, simply because a vitamin C derivative is in a product does not mean it is effective—unless it is L-ascorbic acid. This highlights and magnifies just one of the problems of vitamin C products on the market today.5, 6