ABSTRACT
The fat-soluble vitamins include vitamins A, D, E, and K. Although all these compounds are originally derived from isoprenoid building blocks, they possess differing chemical structures and biological functions. They are all nonpolar lipids with extremely low solubilities in aqueous media. It is customary to consider them together when examining the mechanisms involved in their absorption. The elucidation of the absorption of the fat-soluble vitamins has contributed significantly to the understanding of the absorption of fatty acids, monoacylglycerols, cholesterol, and other lipid-soluble compounds. An accurate determination of the absorption of the fat-soluble vitamins requires effective methods for their isolation, precise identification, and quantitation. The fat-soluble vitamins in the diet are believed to be dissolved in the dietary fats, which consist largely of triacylglycerols and glycerophospholipids, with smaller amounts of free fatty acids, steryl esters, and free sterols. An interesting aspect of intestinal uptake of lipid-soluble vitamins concerns the absorption efficiency.
