Nutrition and Metabolism of Vitamins

This chapter highlights the sources, metabolism, and functions of vitamins. The catabolism of vitamin K₁ in the intestine can generate vitamin K₃, whereas the metabolism of vitamin K₃ in animals can lead to vitamin K₂. Through the metabolism of lipoproteins in the blood, vitamin K-rich chylomicrons are converted into chylomicron remnants, which are taken up by the liver through receptor-mediated mechanisms. In animals, a long-chain vitamin K₂ is the major constituent of the hepatic vitamin K pool, with vitamin K₁ being a minor one. Hemorrhagic disease can occur in newborn infants, who are particularly vulnerable to vitamin K deficiency. Animals fed nutrient-balanced diets do not exhibit abnormal metabolism or physiology when they do not consume dietary bioflavonoids. There is no evidence for nutritional roles of these substances in mammals, birds, or fish. Animals fed nutrient-balanced diets do not exhibit abnormal metabolism or physiology when they do not consume dietary para-aminobenzoic acid.