Beta Carotene

Beta-carotene belongs to the carotenoids and is an important part of our physiological non-enzymatic defense mechanisms against radical stress. About 30 to 60% of carotenoids are absorbed in the small intestine; the remainder is excreted (Biesalski et al., 1997). Beta-carotene is the most abundant and most efficient precursor of vitamin A, which is a highly lipidsoluble unsaturated polyene dye and antioxidant found in the plasma. Moreover, vitamin A quenches the free radical singlet oxygen. Lycopene, another carotenoid, has no provitamin A function and is reputed to be more important than beta-carotene in UV-protection (Ribaya-Mercado et al., 1995). Beta-carotene (a synonym to provitamin A) is derived from natural dietary sources such as carrots,

Beta-carotene is the most nutritionally active carotenoid. Gentle cooking generally improves utilization of beta-carotene in foods. It is best absorbed with fat, and further processed as a beta-carotene-lipoprotein-complex. In the gastrointestinal tract beta-carotene is metabolized to retinal by oxidative opening of a double bound by the enzyme 15,15’-Dioxygenase in intestinal cells or liver. Retinal is subsequently reduced to retinol; that is, vitamin A. Bilic acids work as detergents and help stimulate the metabolism of carotenoids. Fortunately, a negative loop in the gut prevents the development of intoxication. Once inside the body, beta-carotene is only partially converted to vitamin A; the rest is stored as beta-carotene. Accordingly, beta-carotene medication never leads to hypervitaminosis A (Raab et al., 1991). Both margarine and fruit drinks are often fortified with beta-carotene. Being an unstable substance, beta-carotene is rarely used in cosmetic formulations (Lupo et al., 2001). Other forms of vitamin A are commonly used in cosmetic formulations, mostly to normalize keratinization. The role of beta-carotene in nutritional uptake and as therapeutic medication continues to be of interest, however, and will be discussed later. Meanwhile, it is evident that in addition to being a safe source of vitamin A, beta-carotene plays important biological roles that are independent of its

It also increases lymphocyte production and T- and Bcell activity (Fuller et al., 1992; Grob et al., 1996; Maxwell et al., 1995; Noonan et al., 1996). By modulating immune defense, beta-carotene might have an impact on carcinogenesis. In addition, beta-carotene may modulate skin carcinogenesis by a reduction of lipid peroxidation in human skin, either as a free radical scavenger or as specific lipoxygenase inhibitor. The substrates of lipoxygenasesare linoleic acid and arachidonic acid; the reaction produces leukotrienes, lipoxins, and physiologically active oxygenated fatty acids. Linoleic acid is one of the major components of membrane phospholipids of living cells that are damaged by reactive oxygen species, leading to pathological events and aging processes. In skin samples, inhibition of metabolites of linoleic acid was achieved using beta-carotene (Bar-Natan et al., 1996; Burton et al., 1984; Fuchs et al., 1994). Cumulative UV exposure results in photoaging and increased risk of epithelial skin cancer. Free radical oxidative stress has been implicated in the pathogenesis of a variety of human diseases, including UV-induced skin cancer (Black et al., 1997; Black et al., 1987; Darr et al., 1994; Jung et al., 1991). Natural antioxidant defense mechanisms have been found to be defective in these patients. Disease progression seems to be retarded by supplementation of