Fat-soluble vitamins in the intestinal lumen

Fat-soluble vitamins in the intestinal lumen" refers to vitamins A, D, E, and K present in the gut after digestion, prior to their absorption into enterocytes. These vitamins (retinol for A, cholecalciferol/ergocalciferol for D, tocopherols/tocotrienols for E, phylloquinone/menaquinones for K) are emulsified by bile salts, hydrolyzed by pancreatic enzymes, and incorporated into mixed micelles with dietary lipids for uptake primarily in the small intestine. Absorption sites vary: vitamin A mainly in the proximal intestine, D in the median, and E/K in the distal regions, involving passive diffusion, facilitated transport via proteins like SR-BI, CD36, and NPC1L1, and packaging into chylomicrons for lymphatic export. It is not a specific therapeutic target such as a receptor, enzyme, or transporter, but rather a physiological state or compartment in the lipid absorption pathway. Deficiencies arise from malabsorption in conditions like celiac disease, cystic fibrosis, or bile acid deficits, leading to issues such as night blindness (A), rickets/osteomalacia (D), hemolysis/nerve damage (E), or bleeding disorders (K). Competitive interactions occur, e.g., vitamin A inhibits uptake of others, while high-fat diets or micelle formation optimize absorption; no drugs directly target this luminal pool, though supplements consider these dynamics to avoid antagonism. Toxicity risks from excess relate to fat storage rather than intestinal mechanisms.

Other names

Fat-soluble vitamins A, D, E, K in intestinal lumen