Vitamins E & A and the Skin
Vitamins have not been successfully used in cosmetics until recently, because of the belief that they could not penetrate the skin and because the metabolic activity of the skin was not adequately known.
Now, with a better understanding of the physiology of hair, skin and nails, interest in topically applied vitamins has increased. In terms of beauty and functionality, recent studies have indicated that certain vitamins and their derivatives enhance the performance of cosmetics and toiletries.
Furthermore, laboratory and clinical tests have provided strong evidence that those vitamins, at proper levels, play an important role for the protective, corrective, and renewal processes of hair, skin and nails. Laboratory and clinical studies have indicated a useful role for topically applied vitamins in combating various skin disorders.
Especially to aid in preventing, retarding, or arresting certain degenerative changes associated with the ageing process, such as dry and scaly skin, and the formation of wrinkles. In addition, the naturalness of vitamins has prompted their use in creams and lotions to maintain a soft and smooth skin by "replenishing nature's moisture".
Of popular interest to cosmetic formulators are Vitamins A, C, E, panthenol (pro-vitamin B5) and their derivatives. These vitamins are functional: penetrate skin (panthenol and vitamins E also penetrate hair and nails): and, when used at proper levels, are safe and free of side effects.
Vitamin E - Biological Activity.
Relatively recent research has pointed to the need for Vitamin E in the maintenance of normal body metabolism, and in the protection of body tissues and skin from damage caused by normal body processes. Although the main claim for Vitamin E in cosmetics has been as a "natural moisturiser," extensive studies conducted in the last decade point to significant benefits beyond moisturisation.
In its esterified form, Vitamin E may have anti-inflammatory effects and may provide protection from UVR damage. In nature, Vitamin E appears as Tocopherols, of which the alpha form has the highest biological potency. The unesterfied form is present in oil and other vegetable oils. Unesterified a-tocopherol has antioxidant properties, and is a physiological antioxidant.
In oral administration for therapy against deficiency of this vitamin, a-tocopheryl acetate is used, since this ester is more stable against oxidation than free tocopherol. Gastrointestinal absorption of Vitamin E acetate is similar to that of other fat-soluble vitamins. The ester is first hydrolysed in the intestinal lumen by the bile and pancreatic juice. The tocopherol formed is dispersed by formation micelles with bile salts, then is absorbed from the intestinal tract by passive diffusion.
Absorption through the skin occurs with both the alcohol and acetate. A relatively high proportion of topically applied material has been found in the stratum corneum and in the lower viable skin layers. It has also been shown that the vitamin is absorbed directly into the hair cortex.
Vitamin E is soluble in alcohol, fats and oils. Like vitamin A palmitate, it can be emulsified in aqueous solutions with polysorbate 80. Vitamin E can be added to the oil phases of topical formulations without special precautions. Vitamin E is now considered to be essential for the stabilisation of biological membranes, particularly those containing large amounts of polyunsaturated fatty acids. The oxidation of polyunsaturated fat produce lipid peroxides unsaturated fats production which interfere with the structure and function of biological membranes.
It is now known that Vitamin E acts as an antioxidant, and can inhibit the formation of lipid peroxides. It might thus play a role against ageing- particularly of the skin -since lipid peroxidation in tissues is one of the causes of skin ageing. Vitamin E appears to improve decreased function of the sebaceous gland; it is also expected to ameliorate excessive pigmentation in the skin - a possible cause of decreased elasticity and poor water-retention, which are characteristics of aged skin. For these reasons, it is now recommended that vitamin E be added to cosmetics.
Sunlight is the most important cause of premature ageing of the skin. For many years, it has been recognised that UVR induces production of free radicals in the skin. aTocopherol is an excellent lipid radical scavenger; thus, it is especially useful in terminating lipid radical chain reactions. In these reactions, the stabilised, low energy tocopheroxyl radical is formed. This radical is unable to function by itself as an initiator of new radical chain reactions with membrane lipids, but it can be regenerated by other reducing antioxidants (e.g., Vitamin C).
Often referred to as the "normaliser," Vitamin A is essential not only for normal skin development, but also for growth and maintenance of bones, glands, teeth, nails and hair. This vitamin offers distinct cosmetic advantages to the skin. Vitamin A is absorbed through the skin, helping it remain soft and plump and improves the skin's water barrier properties. The latter renders Vitamin A useful in treating seasonal/environmental problems (dryness, heat, and pollution) and suggests its use in after-sun products for its "normalising" (corrective) properties.
The stimulatory effects of Vit A tend to oppose changes that occur with ageing. Older skin shows a thinned epidermis, the keratin layer is also thin and ill formed in addition the granular layer is reduced to a single layer of cells containing keratohyalin granules. The metabolic activity of the keratinocytes is also reduced, this is shown by reduced activity of respiratory enzymes within the cell.The dendritic cell population (melanocytes) is also depleted or damaged, this may be shown clinically by alterations in the pigmentation of the skin.
All these signs of reduced activity tend to be reversed by the topical application of suitable doses of vitamin A. The skin activated to produce more epidermal protein and to form a thicker epidermis covered by a better-formed keratin layer. There is evidence that this vitamin can also alter or modulate collagen synthesis.
Vitamin A appears necessary for normal reproduction of basal cells. Since all epidermal cells arise from basal cells, the skin becomes thickened and dry when these cells are deprived of this vitamin. The most striking symptom of Vitamin A deficiency is an alteration of the epithelium that is visible as atrophy, proliferation of basal cells and differentiation of new cells into horny epithelium.
Continued deficiency of this vitamin will cause acne-like blackheads as hair follicles and sebaceous glands become plugged. This restriction of sebaceous flow also produces dryness, unmanageability and dullness of hair. In general terms, Vitamin A applied topically can be regarded as an agent which stimulates the skin both mitotically and metabolically. Therefore, it tends to maintain the skin in a more youthful condition.
The generic term for Vitamin A and its derivatives is "retinoid." According to the USP official monograph, the category comprises retinol (vitamin A alcohol) or its esters as well as the free acid, retinoic acid. The role of retinoids in regulation of skin development seems best satisfied by retinoic acid. Thus, activity of retinyl palmitate in skin may depend on its conversion to retinoic acid. This conversion depends on the enzymatic cleavage of the ester bond in retinyl palmitate, and on the skins ability to oxidise retinol to retinoic acid. Non-specific esterase enzyme activity exists within the skin, and it has been demonstrated that skin preparations can indeed convert retinol to retinoic acid.