The Roles of Vitamin C in Skin Health

Abstract

The primary function of the skin is to act as a barrier against insults from the environment, and its unique structure reflects this. The skin is composed of two layers: the epidermal outer layer is highly cellular and provides the barrier function, and the inner dermal layer ensures strength and elasticity and gives nutritional support to the epidermis. Normal skin contains high concentrations of vitamin C, which supports important and well-known functions, stimulating collagen synthesis and assisting in antioxidant protection against UV-induced photodamage. This knowledge is often used as a rationale for the addition of vitamin C to topical applications, but the efficacy of such treatment, as opposed to optimising dietary vitamin C intake, is poorly understood. This review discusses the potential roles for vitamin C in skin health and summarises the in vitro and in vivo research to date. We compare the efficacy of nutritional intake of vitamin C versus topical application, identify the areas where lack of evidence limits our understanding of the potential benefits of vitamin C on skin health, and suggest which skin properties are most likely to benefit from improved nutritional vitamin C intake.

Keywords: UV protection; ascorbate; collagen; dermis; epidermis; skin aging; skin barrier function; vitamin C status; wound healing.

Figure 1

Micrograph of human breast skin sample, showing the full depth of the dermis (pink staining) in comparison to the thin layer of epidermis (purple staining). The scale bar indicates 200 µm. A zoomed-in image is shown within the box. The stratum corneum, the outermost layer of the epidermis, is indicated by the arrows, with its characteristic basket-weave structure. The collagen bundles in the dermis are very clear, as are the scattered purple-stained fibroblasts that generate this structure.

Figure 2

Delivery of nutrients to the skin. The location of the vitamin C transport proteins SVCT1 and SVCT2 are indicated. Red arrows depict nutrient flow from the blood vessels in the dermis to the epidermal layer. Nutrients delivered by topical application would need to penetrate the barrier formed by the stratum corneum.

Figure 3

Structure of the dermis. Higher magnification of H&E-stained dermis, showing the irregular nature of the bundled collagen fibres (pink stained) and sparse presence of the fibroblasts (blue nuclear staining). Vitamin C present in the fibroblasts supports the synthesis of the collagen fibres.

Figure 4

The central role for vitamin C and other antioxidants pertinent to the skin. The interdependence of vitamins E and C, and glutathione, in the scavenging of free radicals and regeneration of the reduced antioxidants, is shown. Vitamin E is in the lipid fraction of the cell, whereas vitamin C and glutathione are water-soluble and present in the cytosol.