VITAMINS

Description/Definition:

1960's = an organic compound which:

1. is a component of natural foods - different than CHO, fat, protein, minerals and water

2. is present in foods in minute amounts, and has specific functions

3. is essential for development of normal tissues, health, growth, and maintenance

4. when absent from the diet or not properly absorbed or utilized, results in a specific deficiency disease or syndrome

5. can not be synthesized by animal tissue - and must be obtained exclusively from the diet

Flokers, 1969 = added it can be component of enzymes (co-enzymes); some intrinsic biosynthesis (trypsin ® niacin)

Classification:

Originally assigned letters of the alphabet - now they have chemical names, but still retain alphabet designation. Based on chemical properties and solubility in water they are classified as fat or water soluble.

Fat soluble

1. A (retinols)

2. D (calciferols)

3. E (tocopherols)

4. K (quinones) - rumen microbes synthesize in rumen

Water soluble

1. Thiamine (B₁)

2. Riboflavin (B₂)

3. Niacin (nicotinic acid)

4. Pyrodoxine (B₆)

5. Folic Acid

6. Biotin

7. Pantothenic Acid

8. Cobalamine (B₁₂)

9. Ascorbic acid (Vit. C)

Comparing Fat VS Water Soluble Vitamins

Chemical composition

Fat soluble = contain only C, H, O (non-polar ® water insoluble)

Water soluble = also can contain N, S, or Co

Occurrence

Fat soluble = can be in the form of a provitamin in animal tissues

Water soluble = no provitamins known (tryptophan ® Niacin; not considered a provitamin)

Physiological Action

Fat soluble = required for regulation of metabolism

Water soluble = concerned with the transfer of energy (niacin, riboflavin)

Absorption

Fat soluble = absorbed in the presence of fat

Water soluble = simpler process, absorbed constant with water in intestine

Storage

Fat soluble = stored wherever fat is deposited

Water soluble = little storage (all different)

Excretion

Fat soluble = wholly excreted in the feces

Water soluble = feces, mainly following metabolic pathways Þ urine

Synthesis

Fat soluble = Only K can be synthesized by rumen microbes

Water soluble = all can be synthesized by rumen microbes

Vitamin A (the Retinols)

Provitamin: beta-carotene - found only in plants - yellow pigment

Conversion to active form: carotene converted to 2 retinols in GI tract

Functions in the body:

1. Retinol - reproduction, growth promotion, epithelial tissues

2. Retinal - vision; retinal + opsin = rhodopsin (visual purpel)

3. Retinoic acid - growth promotion, epithelial tissue

4. Retinyl palmitate - storage form of Vit. A, in liver

Deficiency symptoms

1. Night blindness

2. Xeropthalmia (unusually dry eye)

3. Reproductive failure

4. susceptibility to infections (decrease tissue integrity)

5. Poor growth

Vitamin D (the calciferols; "sunshine vitamin")

Provitamins: plants = ergosterol (D₂)

Animals = 7-dehydrocholesterol (D₃; in skin)

Conversion to active form: (1,25-(OH)₂- D₃) = fx as hormone

1. 7-dehydrocholesterol ® cholecalciferol (D₃) (UV light in skin)

2. D₃ ® 25(OH)D₃ (Liver)

3. 25(OH)D₃ ® 1,25(OH)₂D₃ (Kidney)

4. 1,25(OH)₂D₃ in S.I. = synthesis of Ca binding protein

5. absorption of Ca & P

Functions (vit. D, Ca, and/or P):

¯ Ca in blood triggers thyroid gland to secrete PTH, which activates hydroxylation in kidney. PTH also mobilization of Ca from bone. 99% body Ca stored in bone; 70-80% body P stored in bone

Soft tissues -	Ca important for blood clotting, neuromuscular activity, cofactor
	P important for high energy phosphate bonds cell membranes (phospholipids)

Deficiency symptoms:

1. Rickets - young animals - bones do not calcify Þ flexible

2. Osteomalacia - adult - demineralization of bones Þ easy to fracture

3. Milk Fever - older/high producing dairy cows - onset of lactation, ¯ Ca in serum