The Role of Vitamin C in Skin Health

Introduction

The skin is a multi-functional organ, the largest in the body, and its appearance generally reflects the health and efficacy of its underlying structures. Being in constant contact with the external environment, the skin is subject to more insults than most of our other organs, and is where the first visible signs of ageing occur.

The skin is composed of two main layers with quite different underlying structures—the outermost epidermis and the deeper dermis. The epidermis fulfils most of the barrier functions of the skin and is predominantly made up of cells, mostly keratinocytes. In contract, the dermal layer provides strength and elasticity, and includes the vascular, lymphatic and neuronal systems. It is relatively acellular and is primarily made up of complex extracellular matrix proteins, being particularly rich in collagen fibres, which make up ~75% of the dermis dry weight. The major cell type present in the dermis is fibroblasts, which are heavily involved in synthesis of many of the ECM components.

Between the two main layers, is the dermal-epidermal junction, a specialised basement membrane that fixes the epidermis to the dermis.

Role of Nutrition in Skin Health

Nutritional status is vital for maintaining normal functioning of the skin during collagen synthesis and keratinocyte differentiation. Additionally, many of the components of our antioxidant defences such as vitamins C and E and selenium are obtained from the diet, and these are likely to be important for protection against UV-induced damage. The epidermis is a challenged environment for nutrient delivery, as it lacks the blood vessels that normally deliver nutrients to cells and dietary nutrients are not easily able to reach the cells in the outermost layers of the epidermis, so these cells receive little nutrient support.

The skin can be targeted for nutrient delivery through topical application, however the stratum corneum functions as a barrier and prevents the passage of many substances, although some lipid-soluble molecules can pass through the surface layer, it is unlikely that topical nutrients would penetrate into the lower layers of the dermis, therefore the dermal layers are best supported by nutrients delivered via the bloodstream.

Vitamin C in Skin

Healthy skin contains high levels of vitamin C in the intracellular compartments, it is transported into cells via the blood vessels. Vitamin C levels are lower in aged or photodamaged skin and exposure to UV, oxidant stress and pollutants is associated with depleted vitamin C levels in the epidermis. More vitamin C is found is the epidermal layer than in the dermis, however the high concentration of vitamin C in the skin indicates that is has a number of important biological functions which include:

• Collagen formation

• Antioxidant protection

• Decrease melanin synthesis

• Cell signalling

• Wound healing

• Barrier and lipid function

• Anti-inflammatory

The most compelling argument for a role of vitamin C in protecting skin function comes from observations that deficiency causes obvious skin problems—early signs of scurvy, for example, include skin fragility, corkscrew hairs and poor wound healing.

Conclusion

The following information is available as a result of research into the role of vitamin C in skin health:

• Skin fibroblasts have an absolute dependence on vitamin C for the synthesis of collagen, and for the regulation of the collagen/elastin balance in the dermis. There is ample in vitro data with cultured cells demonstrating this dependency. In addition, vitamin C supplementation of animals has shown improved collagen synthesis in vivo.

• Skin keratinocytes have the capacity to accumulate high concentrations of vitamin C, and this in association with vitamin E affords protection against UV irradiation. This information is available from in vitro studies with cultured cells, with supportive information from animal and human studies.

• Analysis of keratinocytes in culture has shown that vitamin C influences gene expression of antioxidant enzymes, the organisation and accumulation of phospholipids, and promotes the formation of the stratum corneum and the differentiation of the epithelium in general.

• Delivery of vitamin C into the skin via topical application remains challenging. Although some human studies have suggested a beneficial effect with respect to UV irradiation protection, most effective formulations contain both vitamins C and E, plus a delivery vehicle.

• Good skin health is positively associated with fruit and vegetable intake in a number of well-executed intervention studies. The active component in the fruit and vegetables responsible for the observed benefit is unidentified, and the effect is likely to be multi-factorial, although vitamin C status is closely aligned with fruit and vegetable intake.

• Signs of aging in human skin can be ameliorated through the provision of vitamin C. A number of studies support this, although measurement of skin changes is difficult. Some studies include objective measures of collagen deposition and wrinkle depth.

• The provision of vitamin C to the skin greatly assists wound healing and minimises raised scar formation. This has been demonstrated in numerous clinical studies in humans and animals.

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