ABSTRACT
Because humans are unable to synthesize vitamin A de novo, they must consume diets with preformed vitamin A, predominantly as retinyl esters, or provitamin A carotenoids, such as β-carotene and carotenoids containing an unsubstituted β-ionone ring [1,2]. β-Carotene constitutes the main provitamin A source with a daily consumption of around 1-3 mg and is the most suitable and important precursor for vitamin A due to its symmetrical structure [3-5]. However, a number of factors such as the food matrix, the nutrient status of the host, and genetic factors can affect the utilization of β-carotene in humans and are summarized by the mnemonic SLAMENGHI (reviewed by Castenmiller and West [6]).
