Beta-carotene oxidation product

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The constituents of cigarette smoke can degrade beta-carotene (71,72), but the conclusion that smoking causes increased carotenoid metabolism demands the demonstration of raised carotenoid oxidation products. Moreover, the consistent observation of subnormal carotenoid concentrations but unchanged alpha-tocopherol concentrations (70) suggests that factors other than oxidative stress contribute to the relative carotenoid deficiency. 

Metabolism—Foods supply vitamin A in the form of vitamin A, vitamin A esters, and carotenes. Almost no absorption of vitamin A occurs in the stomach. In the small intestine, vitamin A and beta-carotene are emulsified with bile salts and products of fat digestion and absorbed in the intestinal mucosa. Here, much of the conversion of beta-carotene to vitamin A (retinol) takes place. There are wide differences in species and individuals as to how well they utilize the carotenoids. Their absorption is affected by several factors, including the presence in the small intestine of bile, dietary fat, and antioxidants. Bile aids emulsification fat must be absorbed simultaneously and antioxidants, such as alpha-tocopherol and lecithin, decrease the oxidation of carotene. Also, the presence of enough protein of good quality enhances the conversion of carotene to vitamin A—a matter of great importance in developing countries where protein is limited in both quantity and quality. 

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