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
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
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
B3 Eggs, meat, liver, beans, peas, niacin enriched bread and cereals
B6 Lean meat, leafy green vegetables, Male: 15–19 mg/day pyridoxine whole-grain cereals, yeast, bananas Female: 13–15 mg/day
Pregnancy: 18 mg/day Lactating: 20 mg/day B12 Liver, kidney, fish, milk Male and female: 3 µg/day
Pregnancy: 4 µg/day Folic Acid Leafy green vegetables, yellow Male and female: 400 µg/day
fruits and vegetables, yeast, meats Pregnancy: 600–800 µg/day Lactating: 600–800 3 µg/day Table 9-1. (continued)
Dose for treatment of deficiency 100,000–500,000 IU daily ×3 d; then 50,000 IU ×14 day Maintenance 10,000–20,000 IU q.d. ×60 day
Pregnancy category A; PB: UK; t1/2: weeks–months*
Deficiency conditions Treats vitamin A deficiency, prevents night blindness, treats skin disorders, promotes bone development Side effects Headache, fatigue, drowsiness, irritability, anorexia,
vomiting, diarrhea, dry skin, visual changes
Adverse reactions Evident only with toxicity; leucopenia, aplastic anemia, papilledema, increased intracranial pressure,
hypervitaminosis A (loss of hair and peeling skin).
Excess dose during pregnancy can cause birth defects.
Contraindications Mineral oil, cholestyramine, alcohol, and antilipemic drugs decrease the absorption of vitamin A. It is excreted through the kidneys and feces.
*PB=Protein Binding UK = unknown t1⁄2=1⁄2life Vitamin A
Dose for treatment Mild deficiency: 50–125 µg/dL
of deficiency Moderate to severe: 2.5–7.5 mg/d; 2500–7500 µg Maintenance Male and female: 40–80 µg; 200–400 IU
Pregnancy category A
Deficiency conditions Rickets, deficit of phosphorus and calcium in blood
Side effects None significant
Adverse reactions Excess of 40,000 international units (IU) results in hypervitaminosis D and may cause hypercalcemia (an elevated serum calcium level). Early symptoms of toxicity are anorexia, nausea, and vomiting.
Contraindications Hypercalcemia, hypervitaminosis D, or renal osteodys-trophy with hyperphosphatemia. Use with caution in patients with arteriosclerosis, hyperphosphatemia, hypersensitivity to vitamin D, and renal or cardiac impairment.
Vitamin D
Dose for treatment Malabsorption: 30–100 mg/day
of deficiency Severe deficit: 1–2 mg/kg/d or 50–200 IU/kg/day Maintenance Male: 10 mg/d; 15 IU
Female: 8 mg/d; 12 IU Pregnancy: 10–12 mg/day Pregnancy category A (C if used in doses above RDA) Deficiency conditions Breakdown of red blood cells Side effects None significant
Adverse reactions Large doses may cause fatigue, weakness, nausea, GI upset, headache, breast tenderness, and may prolong the prothrombin time (PT) (clotting time).
Contraindications Patients taking warfarin (anticoagulant) should have their PT monitored closely. Iron and vitamin E should not be taken together because iron can interfere with the body’s absorption and use of vitamin E.
Vitamin E
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. D3is 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 phospho-rus 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
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
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 (mena-dione) and K4(menadiol), both of which are produced synthetically. K1and K2are absorbed in the presence of bile salts. K3and K4are absorbed without bile salts.
Vitamin K1prevents hemorrhage and is available as Mephyton, AquaMEPHYTON, and Konakion. Vitamin K4is available as Synkayvite. Vitamin K is absorbed in the intestines and is stored in the liver and in other tissues.