The Physiology of Vitamin C
Vitamin C (L-Ascorbic Acid) is not synthesized by the body. It must be provided in the diet. Body stores are limited by control mechanism which allow a maximum of 1200 mg to be absorbed daily. The half life of Vitamin C is 10-20 days, so that after three weeks Vitamin C is mostly depleted in the absence of further ingestion. The minimum daily requirement for Vitamin C is 200 mg. (Levine et al., Proc Natl Acad Sci, 1996). Vitamin C is a major antioxidant in the body. In addition, it is important in collagen synthesis. The only form of Vitamin C that the body can recognize and use is L-Ascorbis Acid, In order to work, Vitamin C must first penetrate the skin and be present there in the active form, L0Ascorbic Acid. Typically, the skin a good barrier, protecting outside substances from entering skin, and Vitamin C is inherently unstable at neutral pH.
Vitamin C is an Antioxidant
Antioxidants protect skin by neutralizing reactive oxygen species, the oxidative “bomba” generated when skin is exposed to sunlight – bomba which otherwise would destroy skin and its components (Shindo et al., J Invest Derm, 1994). Antioxidants work by naturalizing a series of oxygen molecular species known as oxygen species are stimulated by ultraviolet light and also occur naturally during normal metabolism in the oxygen atmosphere in which we live. L-Ascorbic Acid neutralizes reactive oxygen species including superoxide anion singlet oxygen and hydroxyl radical (Halliwell and Gutteridge Arch of Biochem & Biophye, 1990).
Ultraviolet Radiation Destroys L-Ascorbic Acid in Skin
When skin is exposed to ultraviolet light measurements show that two0thirds of L-Ascorbic Acid in skin is destroyed. Scientists believe that L-Ascorbic Acid’s role as an antioxidant is essential in protecting skin from oxidative damage produced by ultraviolet light exposure and the associated inflammatory reaction. It is believed that this oxidative insult (generation of oxidative free radicals) results in damage to other skin constituents including collagen, elastic, proteoglycan, as well as cell membranes and nuclear constituents. In time, it is believed that these changes may result in connective tissue breakdown (aging and wrinkles) and skin cancer.
Ultraviolet Radiation and the Ultraviolet Spectrum
Exposure to ultraviolet radiation (UVR) is a well- documented health hazard. If it were not for a multi-layered defensive system, humans would die in the oxygen-rich environment in which they live., the ultraviolet spectrum is divided into the following key regions: UVC (270 – 290 nm), UVB ( 290-320 nm), UVAII (320 – 340 nm), and UVAI (340 – 400 nm).
The ozone layer protects humans from damage against UVC rays
The number 2 and 3 carbons are double-bonded and contain an acid-ignitable hydrogen in the water (pk=4.2). L-Ascorbic Acid also is a moderately strong reducing agent. These properties, which lead to instability in the L-Ascorbic Acid structure are well known and have been burdensome to pharmacologists when attempting to formulate active, stable L-Ascorbic Acid solution. At neutral or higher pH, which is the typical cosmetic formulation, L-Ascorbic Acid becomes the notoriously unstable assorbate anion. For these reasons among others scientists have had difficulty formulating stable solutions of L-Ascorbic Acid which would be beneficial for cosmetic, dermatologic or ophthalmic needs. Nevertheless, because of the many beneficial effects attributed to L-Ascorbic Acid, Numerous attempts have been made to overcome these difficulties. Excessive Sun Exposure is the Most Preventable Causes of Melanoma Formulation. The most important preventable cause of melanoma is excessive sun exposure to UV radiation. Malignant melanoma also has been linked to past sunburns and sun exposure at younger ages. Other possible causes of melanoma include genetic factors and immune system deficiencies.
Topical Vitamin C Prevents UV Immunosuppresion
Undoubtedly the most exciting research to emerge from research studies is that topical Vitamin C prevents UV immunosuppression. (Nakamura T., et al ., J Invest Dermatoll, 1997). This phenomenon, in which the activity of the immune system is stifled following exposures to sunlight, occurs in approximately one-third of humans, but in over 90 percent of individuals who get skin cancer, both melanoma and non melanoma skin cancers (Granstein R Arch Dematol. 1995; Streilein, W., in Gilchrest, B., Photoprotection, 1995).
Topical Vitamin C Controls Inflammation and Promoted Healing
Topical Vitamin C is capable of controlling the inflammatory response associated with ultraviolet light (sunburn). Topical Vitamin C is protective even when it is applied after sun exposure (Darret al ., 1992). It is also helpful in speeding the healing process. It is often recommended as a pre-and post operative regimen for laser resurfacing patients. Dermatologic surgeons recommend using it as long as possible prior to laser resurfacing and beginning again as early as fourteen days following surgery (Alster and West, 1997).