Fat Soluble Vitamins Fat soluble vitamins include A

Fat Soluble Vitamins • • • Fat soluble vitamins include: A and carotenoids, E, K, D Associated with fat absorption Needed in small amounts Stored in fatty tissues Excess intake has toxic consequences

Retinol and caroteinoids • Lipid-soluble red, orange, and yellow pigments produced by plants • Fewer than 10% have vitamin A activity • B carotene, cryptoxanthin • Others also have physiological importance • Lycopene • Canthaxanthin • Zeaxanthin Fig. 10 -1 a, p. 327

Fig. 10 -1 b, p. 328

70 -90% vitamin A absorption if fat is present <5% to 60% for carotenoids; vitamin E interferes CRBPII = cellular retinol binding protein Specfic protein carrier- vitamin A Passive diffusion - carotenoids LRAT = lecithin retinol acyl transferase Fig. 10 -2, p. 329

‘‘Outer limiting membrane’’ Photoreceptor (rod) cell Müller cell Outer segment Inner segment Capillary Pigment epithelium Nucleus Outer of photoreceptor (rod) cell Segment Functions: Vitamin A • Vision • Cell differentiation, growth, reproduction • Bone development • Immune system Fig. 10 -7, p. 334

Fig. 10 -8, p. 334

Functions: Vitamin A • Vision • Cell differentiation, growth, reproduction • Bone development • Immune system Fig. 10 -9, p. 335

Functions: Vitamin A • Vision • Cell differentiation, growth, reproduction • Bone development • Immune system

Functions: Vitamin A • Vision • Cell differentiation, growth, reproduction • Bone development • Immune system Function: Carotenoids • Antioxidants for singlet oxygen; Lycopene > vitamin E > carotene > cryptoxanthin > zeaxanthin, carotene > lutein (also work better when used together) • Antioxidant for lipid peroxides (works with vitamin E) • Lower incidence of atherosclerosis through prevention of oxidation of LDLs

Interaction with other nutrients: • Vitamins E and K (inversely related; high A, low E and K) • Zinc and iron • Protein Excretion: most in urine as oxoretinoic acid, small amounts in expired air, some in feces Fig. 10 -10, p. 339

Deficiency: • increased morbidity in children under age 5 with no evident clinical signs of deficiency • Signs, when present include xeropthalmia, anorexia, retarded growth, increased susceptibility to infections, enlargement of hair follicle, and keratinization of epithelial (mucous cells) of the skin. Toxicity: • Hypervitaminosis A • Nausea, vomiting, double vision, headache, dizziness, and desquamation of the skin • Teratogen

Vitamin D (a seco-steroid) plants animals Fig. 10 -11, p. 344

Table 10 -2, p. 345

• Dietary Vitamin D is absorbed from a micelle, along with other fats. • About 50% of dietary D 3 is absorbed. Most absorbed in distal small intestine. • Incorporated into chylomicrons • Cholecalciferol from the skin is bound to DBP and travels primarily to the liver, but can be picked up by other tissues as well (muscle and adipose) • Blood is the major storage site; half-life of 10 -21 days • Hydroxylases generate the active form of the vitamin (25 -OH cholecalciferol) • Release by the kidney of active forms; a half -life of 4 -6 hours in the blood Fig. 10 -12, p. 346

Functions: • Acts as a steroid hormone in calcium homeostasis • Intestinal effects • Effects on the kidney • Effects on bone Fig. 10 -13, p. 347

Fig. 10 -14, p. 348

Fig. 10 -15, p. 349

Deficiency: rickets, osteomalacia Interaction with other nutrients: • Calcium, phosphorus, vitamin K Excretion: • Bile > feces > urine Toxicity: • Not possible from excess exposure to sunlight • Few cases; calcification of soft tissues, hypertension, anorexia, renal dysfunction

Only form with biologic activity Fig. 10 -17, p. 353

Digestion and Transport: • Synthetic forms are deesterified • Free alcohol forms are absorbed passively in micelles; non-saturable • 20 -80% absorption; better with fats • Incorporated into chylomicrons in intestinal cell and sent out into lymph • Transfer between chylomicrons, HDLs and LDLs occurs in the blood. HDLs and LDLs contain highest concentration of the vitamin • Half-life of about 48 hrs. • Some stored in adipose, liver, lung, heart, muscle, adrenals Table 10 -3, p. 354

Functions: • Maintenance of membranes - prevents oxidation of unsaturated fatty acids contained in the phospholipids (includes membranes of mitochondria and ER) • Reduced LDL oxidation; decreased plaque formation • Reduction in cataract formation • Reduced oxidation in diabetics • Suppression of activity of HMGco. A reductase (cholesterol synthesis) 1 2 Fig. 10 -18, p. 356

Regeneration Nutrient Interactions: • Function closely linked to selenium (needed for GSH peroxidase), vitamin C, sulfur containing amino acids, • Inhibits carotene absorption and conversion to retinol; may impair vitamin K absorption; may cause vitamin -D dependent bone mineralization problems Deficiency: Rare except in populations with fat malabsorption (cystic fibrosis) myopathy and weakness, croid pigment accumulation, and degenerative neurologic problems Toxicity: one of the least toxic; bleeding problems Fig. 10 -19, p. 356

Vitamin K Absorption: in micelles; incorporated into chylomicrons, then chylomicron remnants, then VLDLs, then HDLs and LDLs. Found mainly in liver and heart. Turnover is once every 2. 5 hrs. Synthetic form From green plants Synthesized by bacteria Fig. 10 -20, p. 361

Table 10 -4, p. 361

Functions: blood clotting and bone mineralization Fig. 10 -21, p. 363

Vitamin K cycle Needed for protein carboxylation Vit. K usually only present in this form in the body Osteocalcin or Bone Gla protein Matrix Gla protein Fig. 10 -23, p. 364

Deficiency: rare in adults; newborns, chronic antibiotic administration, and malabsorption can result in deficiency Bleeding episodes Osteoporosis Toxicity: none known

Table 10 -1, p. 326