While many other cosmetic active agents experience their ups and downs, vitamins continue to be in vogue. They are essential components of natural and of physiological cosmetics.
Vitamins (the term is derived from the Latin word vita = life) are differently structured organic compounds. Already minimal amounts are of vital importance since the human body is not able to synthesize vitamins at all or only in insufficient amounts.
Essential fatty acids, formerly also called vitamin F, and essential amino acids do not pertain to the vitamins. Originally it was assumed that vitamins consist of amines – that is the reason for the second word component “amin”. However, this is no longer applicable for the vitamins known to the present day.
The vitamin needs of humans and animals vary considerably, even the different species have different needs and some of them also can synthesize vitamin C. The lower the evolutionary stage of an organism the more developed is the ability to synthesize vitamins. That is the reason why vegetable food can fully cover the human vitamin needs.
Many of the substances contained in nutritional supplements and described as vitamin-related only are of importance for the marketing of the respective product.
Vitamins control metabolic processes; they have protective and other vital functions and are important for the immune system. Vitamins are ingested with the daily nutrition and partly absorbed via the activity of the intestinal flora.
Besides free vitamins also their derivatives or provitamins are assimilated:
- Derivatives are compounds of vitamins with other substances. Frequently they are esters of acids such as acetic acid and palmitic acid as e.g. Tocopheryl Acetate and Tocopheryl Palmitate (INCI terms). In the cases mentioned, the vitamin already has assumed its final structure and only needs to be released in the tissue by ester hydrolyzing enzymes. Frequently the derivatives are less sensitive in atmospheric conditions. In the form of lipophilic esters they are easier to absorb and their dosage in skin care products, among others, can be reduced.
- Provitamins are the pre-stages of vitamins whose structures are bio- chemically transformed in the body. A typical example here is beta-Carotin that needs several steps in order to form vitamin A and vitamin A acid.
It is the “packaging” that counts in skin care applications. Free vitamin C only has superficial effects on the skin similar to a fruit acid, or may possibly be used as an antioxidant in skin care products. Substantial effects in the skin can only be achieved by derivatives in combination with penetration enhancing substances such as liposomes (hydrophilic) or nanodispersions (lipophilic).
In cosmetic products quite often raw materials can be used that already contain vitamins as natural accompanying substances. In this context, particularly fatty oils such as wheat germ oil, avocado oil or extracts should be mentioned. The skin does not really care whether the vitamins are derived from natural or synthetic sources if the molecules are chemically identical.
This is not the rule, though. While their basic structure remains the same, the number and position of the methyl groups differ in the natural forms of tocopherol (vitamin E), α-, β-, γ- and δ-tocopherol. On the other hand, every single one of the tocopherols can occur in their mirror-imaged d- and l-forms. d-α-tocopherol shows the highest biological efficacy and is denominated as vitamin E in the narrower sense. The synthetic vitamin E frequently is a 1:1 mixture of d-α-tocopherol und l-α-toco- pherol.
As vitamins use up when they fulfil their respective functions in the body, they need to be replenished constantly. This applies for the organism as a whole as well as for the skin in particular. Topical applications are in so far advantageous to the oral systemic application as the dosages basically are low however with regard to the area where they are applied they are relatively high. The topical application of vitamin A for instance allows monitoring the effects of vitamin A acid generated by the epidermal oxidation of the vitamin.
Considering the systemic effects, local over-dosages usually have no impact. As far as vitamin K is concerned, its application was banned in November 2009 as it is supposed to cause sensitizations which definitely rule out its use as pharmaceutical drug in emergencies. This ban however is controversially discussed in expert groups due to the fact that the root cause for said sensitizations has not yet been clearly isolated.
Considerable amounts of anti-oxidative vitamins such as C and E are used as antioxidants in food and cosmetic products.
Vitamin A (retinol) is a diterpene alcohol which abundantly occurs in fish liver and egg yolk.
There is a whole series of derivatives and provitamins:
- Retinyl Acetate, Retinyl Palmitate and Retinyl Propionate are esters of vitamin A. They are enzymatically hydrolysed in the skin.
- Retinal is vitamin A oxidized into andehyde. It occurs in the eyes andissignificant for the vision. Like Retinol, Retinal is oxidized in the skin intotamin A acid (retinoicacid).
- Beta-Carotin (provitamin A), the ring agent of carrots, is enzymatically hydrolyzed into two vitamin Amole-cules. The carotenoid family consists of numerous liposoluble tetraterpenes with a colouring ranging from red via orange to yellow (tomatoes, peppers, rose hips, oranges etc.). Taken in higher dosages for a long time, beta-carotin develops a slight photo-protection, but does not replace UV filter. In foods it is a popular dye.
- 3-Dehydroretinol also occurs in the liver of cold water fish and is referred to as vitamin A2
Retinoids are sensitive to atmospheric oxygen hence cosmetic preparations should not be applied at daytime in blazing sun. The specific effect on the skin primarily results from the conversion of retinoids into vitamin A acid. For many years, vitamin A acid has been banned in skin care products however denominated astretinoin it is licensed in dermatological applications. Isotretinoin differs from tretinoin by another position of the acid group (cis- instead of trans-position).
Retinoids are used to treat:
- hyperkeratosis and scars
- compromised skin and acne caused by cornification disorders on the exits of the sebaceous
- stimulation of cell growth and collagen synthesis in the epithelial tissue
- aging skin: frequently in combination with the antioxidative vitamins E and C
An oral overdose can have teratogenic (harmful to the foetus) effects in pregnant women. This should also be kept in mind in terms of nutrition (liver, innards). A cosmetic treatment does not involve systemically relevant concentrations. At moderate cosmetic application no systemically relevant concentrations are reached. However, the BfR (Federal Institute for Risk Assessment) recommends limiting vitamin A on the face and hand care.
Next article will look at B vitamins and their effect on skin.
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