Fat soluble vitamins are absorbed by the intestinal tract following the same metabolism as used with fat. Any condition that interferes with the absorption of fats will also interfere with the absorption of fat-soluble vitamins. Fat-soluble vitamins are stored in the liver, fatty tissues and muscle and remain in the body longer than water-soluble vitamins. Fat-soluble vitamins are excreted slowly in urine.
Hint to remember: ADEK = addicted to fat are fat soluble vitamins. The following are fat-soluble vitamins.
Vitamin A (Acon, Aquasol) helps to maintain epithelial tissue, eyes, hair and bone growth. It is also used for treatment of skin disorders such as acne. Vitamin A has a toxic effect if taken in excess. For example, birth defects can occur if the patient takes greater than 6000 international units (IU) during pregnancy. It is important to keep in mind that Vitamin A is stored in the liver for up to two years, which can result in inadvertent toxicity if the patient is administered large doses of Vitamin A.
Vitamin D, absorbed in the small intestine with the assistance of bile salts, is necessary for the intestines to absorb calcium. Vitamin D plays a major role in regulating the metabolism of calcium and phosphorus. There are two forms of Vitamin D: D2, called ergocalciferol; and D3, called cholecalciferol. D2 is a synthetic fortified form of Vitamin D. D3 is the natural form of Vitamin D that is produced in the skin by ultraviolet sunlight. Once absorbed, Vitamin D is converted into calcifediol in the liver and then converted to an activated form of calcifediol in the kidneys. The active form is a hormone that combines with parathyroid hormone (PTH) and calcitonin to regulate calcium and phosphorus metabolism in the body and stimulate the reabsorption of calcium and phosphorus by bone. When serum levels of calcium are low, more Vitamin D is used to create the active form of calcifediol. Low serum levels of calcium cause a decrease in the creation of the active form of calcifediol. Excess Vitamin D is then excreted in bile and a small amount is excreted in urine.
Vitamin E protects the heart and arteries and cellular components from being oxidized and prevents red blood cells from hemolysis (rupture). If there is a sufficient balance of salts, pancreatic secretion, and fat, Vitamin E is absorbed from the GI tract and stored in all tissues, especially in the liver, muscle, and fatty tissues. Seventy-five percent of excess Vitamin E is excreted in the bile and the remainder is excreted in urine.
Vitamin K comes from dietary sources such as leafy green vegetables, liver, cheese, and egg yolk and is synthesized by intestinal flora. Vitamin K is required to synthesize prothrombin and clotting factors VII, IX, and X and is an antidote for oral overdose of the anticoagulant Coumadin (Warfarin). There are four forms of Vitamin K: K1 (phytonadione), which is the active form; K2 (menaquinone), which is synthesized by intestinal flora, but not commercially available; K3 (menadione) and K4 (menadiol), both of which are produced synthetically. K1 and K2 are absorbed in the presence of bile salts. K3 and K4 are absorbed without bile salts. Vitamin K1 prevents hemorrhage and is available as Mephyton, AquaMEPHYTON, and Konakion. Vitamin K4 is available as Synkayvite. Vitamin K is absorbed in the intestines and is stored in the liver and in other tissues.