Studies on the effect of vitamin C supplementation on wound healing have reported somewhat mixed results. Data from laboratory animals and humans show that vitamin C deficiency results in poor wound healing, and vitamin C supplementation in deficient individuals shows significant benefits (31, 59-61). Although vitamin C levels appear to increase collagen synthesis and decrease inflammatory responses at the site of the wound, neither vitamin C supplementation (62-64) or increased plasma vitamin C status (55) increases wound closure time in otherwise healthy individuals. This suggests that vitamin C may only affect specific facets of the wound healing response. Topical ascorbic acid has not been properly evaluated prior to or during wound healing in humans.
Vitamin C is included in oral therapies for pressure ulcers (bed sores) and burns, along with vitamin E, zinc, and other nutritive factors (65-67).
Dry skin
Higher intakes of dietary vitamin C have been correlated with a decreased risk of dry skin (51), suggesting that ascorbic acid may have effects on trans-epidermal water loss (TEWL). In cell culture models, addition of vitamin C promotes the synthesis of barrier lipids, which would establish a functioning stratum corneum with low water permeability (58, 68). One study using topical vitamin C in human subjects correlated its use with decreased skin roughness (21). However, another study suggested vitamin C increased TEWL when applied to the skin (14). Thus, the effects of vitamin C on skin dryness are not clear.
Other functions
Environmental pollutants, such as ozone, can decrease vitamin C levels in the skin and lead to free radical damage (5). Smoking also leads to increased wrinkling and decreased collagen synthesis, which corresponds to a decline in plasma vitamin C levels (55); however, it is unclear if this correlates to lower vitamin C levels in skin. Topical ascorbic acid has not been evaluated against pollution-related damage.
Topical vitamin C may be useful against acne to reduce inflammatory lesions. However, studies have primarily focused on the use of sodium ascorbyl phosphate, a synthetic derivative that may be poorly absorbed by the skin (20, 69). Topical vitamin C may also have mild skin lightening effects that are caused by reductions in melanin production and melanin oxidation (70).
Conclusion
Vitamin C is an essential part of skin health both as a small molecular weight antioxidant and as a critical factor for collagen synthesis. Vitamin C contributes to photoprotection, decreases photodamage, and is needed for adequate wound healing. Oral supplementation with vitamin C may help prevent UV-induced damage, especially in combination with supplemental vitamin E. Dietary vitamin C may also provide photoprotection, but the extent of the protective effects will require additional research. Topical application of vitamin C appears to be an effective route for delivering ascorbic acid to the skin because ascorbic acid appears to be taken up readily at an acidic pH. Despite inconsistencies in vitamin C preparations and study design, the data suggest that vitamin C is most effective in protecting against damage induced by UV light and also has utility in the treatment of photodamage and/or skin wrinkling. Although vitamin C appears to benefit dry skin and may support wound healing, further research is needed to determine the effect of vitamin C on both. Lastly, the greatest effects of vitamin C supplementation are seen when it is combined with other micronutrients, such as vitamin E and zinc.