## 3 Vitamin A, Its Vitaminoids and Carotenoids' General Profile and Health Benefits
### Vitamin A-Related Bioactive Compounds: Provitamins (Carotenoids)
#### 4.1.3 Other Absorption Pathways of Vitamin A, Its Vitaminoids, and Carotenoids
Vitamin A, along with its derivatives, namely retinoid esters and carotenoids, is consumed via dietary supplements or food, providing a variety of sources that could benefit the general growth and maintenance of the immune system. Retinal, for example, a retinoid aldehyde, is responsible for the normal function of the eyes, while retinoic acid acts as a hormone-like growth factor in cells. Other retinoid esters have anti-aging activity, as they are used in the cosmetic field for treating skin's fine lines and wrinkles [3; 16; 77]. Deficiency of vitamin A is linked with post-natal growth retardation in children, while in adults it can cause problems for the eyes, immune, or reproductive system [121]. On the other hand, carotenoids, such as zeaxanthin and \(\alpha/\beta\)-carotene, have exhibited bio-functional activity against chronic diseases, like diabetes, cardiovascular diseases (CVDs), cancer, and obesity incidents [122]. They can also be photo-protective, as they are experts in protecting the skin from ROS and lipid peroxyl radicals induced by UV radiation A and B (UV\({}_{\text{A}}\) and UV\({}_{\text{B}}\), respectively), species that damage cells when incorporated in the DNA, causing mutations and early aging, wrinkles, skin cancer, melanoma, ichthyosis, acne, and other skin-associated issues [123]. Because the human body cannot produce vitamin A de novo, all needed bioactive compounds are obtained following a diet rich with animal- and marine-sourced products but also comprised of fruits and vegetables. Preformed vitamin A (retinol and retinyl esters) is mostly found in animals, while provvitamin A carotenoids, including \(\alpha\)- and \(\beta\)-carotene, come from colored plants and fruits [69]. In Western countries, a percent bigger than 70% of the daily dose of vitamin A comes from preformed vitamin A in animals, while less than 30% derives from carotenoids in plants, fruits, and vegetables. On the other hand, in developing countries, the opposite prevails [124]. Lately, nutraceuticals, nutricosmetics, and cosmeceuticals have grown an upward interest in providing several bioactive ingredients, like carotenoids and vitamins, as an alternative, healthier way of supplementation instead of drugs for preventing several health conditions, such as skin cancer, or delaying others, like skin aging. The term \"nutraceutical\" was discovered in 1989 by Dr. [PERSON], as a compound from the words \"nutrition\" and \"pharmaceutical\", while the term \"cosmeceutical\" originated from [PERSON] in 1962 but became famous in 1984 from a dermatologist professor named [PERSON], in research of retinoic acid as an anti-aging ingredient [125; 126]. These categories are placed between nutrition/beauty and pharmaceuticals to provide the bioactive ingredients to the consumers for the cure or prevention of several health issues, with no need for synthetic medications and their potent side effects. Carotenoids in nutraceuticals and/or nutricosmetics provide the same effect as in functional foods, presenting an anti-aging and photo-protective role against UV\({}_{\text{R}}\) in the skin. Interestingly, a supplement mixture of \(\alpha\)- and \(\beta\)-carotene as well as lutein has been proven beneficial in photo-protection, while a combination of \(\beta\)-carotene, lutein, and lycopene has been reported as an effective treatment against erythema [125]. However, \(\beta\)-carotene is generally unstable; hence, other vitamin A forms (retinoids) are frequently utilized in cosmetic formulations in the skincare industry. Either applied topically, orally, or systemically, vitamin A, its retinoids, and carotenoids actively participate in protein synthesis, cell division, and cellular metabolism. Normalization of keratinization and plus growth and differentiation control of epithelial cells have been declared as the main advantages of vitamin A (retinol) and its retinoids, including retinyl palmitate, retinyl acetate, retinal, and ATRA, which are widely exploited in the cosmetic field at different concentrations [100,127].