Vitamins

 

Introduction •    Chemically unrelated organic Compounds •    Cannot be synthesized by HUMANs •    Must be supplied by the diet –  as such –  as utilizable precursors •    Small Amounts •    Required for specific cellular functions –  Optimal Growth –  Maintenance of normal health –  Reproduction

Definition

•     Organic compounds required in the diet in small amounts to perform specific biological functions for normal growth, maintenance, and reproduction i.e. for optimal growth and health of organism.

•     They are required for specific cellular functions, e.g. many of water soluble vitamins are precursors of coenzymes for the enzymes of intermediary metabolism.

 

History & Nomenclature •    Hopkins (1912)—Accessory Factors –  Unknown & essential nutrients in natural food •    Funk (1911-12)— Vitamine (Gr. Vita; life) –  Active principle (an amine) from •    rice polishings (to cure polyneuritis in pigeons) •    Later in yeast (to cure beriberi in pigeons) •    It was later realized that only few of them were Amines. •    However it was continued as Vitamin (without the final letter ‘e’)

•    McCollum & Davis (1915) –  Usage of letters A, B , C to Vitamins –  Initially supposed to have two vitamins –  Fat soluble A and water soluble B (antiberiberi) •    Anti scurvy Vitamin was discovered (Vit C) •    Fat soluble A was found to have two components –  that prevents night blindness (Vit A) –  Another anti rickets factor (Vit D) •    Fat soluble factor— (Vit E) –  in the absence of which rats fail to reproduce •    Vitamin concerned with coagulation—(Vit K) 1930s –  It should be given letter F, but preferred to reflect its function (Koagulation)

 

Vitamins Vs Food & Hormones •    Vs Organic Food –  They do not enter into body tissue unlike protein –  Do not undergo degradation for providing energy like CHO –  Several B-complex vitamins serves as Coenzymes in energy transformation reactions in the body. •    Vs Hormones –  Not produced within organisms –  Most of them have to be provided with diet

Vitamers •    Chemically similar substances •    Qualitatively similar vitamin activity •    Examples –  Retinol, retinal and retinoic acid are vitamers of Vitamin A –  Pyridoxine, pyridoxal, and pyridoxamine are vitamers of Vitamin B₆

 

Pro-Vitamins and Pre-formed Vitamins •    Provitamins –  Substances found in foods that are not in a form directly usable by the body –  Converted to the active form once absorbed •    Pre-formed vitamins –  Vitamins found in foods in their active form

Classification of Vitamins •    There are about 13-16 Vitamins essential for humans •    General Classification in two classes –  Fat Soluble Vitamins –  Water soluble Vitamins

	Fat Soluble Vitamins
•	Four vitamins A,D,E & K are known as fat soluble
•	Availability in diet, absorption and transport are associated with fats
•	Soluble in fats, oils and fat solvents (Alcohols etc)
•	Absorbed into the lymph and carried in blood with protein transporters = chylomicrons.
•	All fat soluble vitamins are Isopernoid compounds (isoprene (–CH=C.CH₃–CH=CH–) derivatives)

•     Stored in liver & adipose tissue

•     Perform diverse functions

•     Vit K has a specific coenzyme function

•     Deficiency—Hypovitaminosis— results in sterility, bleeding and skin diseases etc.

•     Excess consumption of these vitamins (particularly A & D)—Hypervitaminosis— leads to their accumulation and toxicity

•     To maintain normal blood level of these vitamins one should take RDA (recommended dietary allowance)

Water Soluble Vitamins •    Heterogeneous group of compounds—chemically different from each others •    9 Vitamins are included in water soluble group – Vitamin B complex, C –  (inositol, PABA and choline are other water soluble vitamins) •    Quickly dissolves in water and carried to the tissue •    Absorbed directly into the blood stream • Water soluble vitamins form coenzymes – Energy generation biochemical pathways –  Hematopoiesis related biochemical pathways

 

•    Readily excreted in urine •    Cannot be stored in the body in large quantities (except B12) so they must be continuously supplied in the diet •    Large consumption may cause toxicity in rare cases •    Hypervitaminosis related to energy metabolism – dermatitis, –  glossitis (red & swollen tongue), –  cheilitis (rupture at the corners of lips) –  diarrhea –  mental confusion –  depression and malaise

•    Generally vitamin deficiencies are multiple rather than individual with overlapping symptoms – Related to their role in metabolism •    Deficiency of Vitamins B₁, B₆, and B₁₂ – Neurological manifestations

 

Comparison of Fat soluble & Water Soluble Vitamins
Feature	Fat-Soluble Vitamins	Water Soluble Vitamins
Solubility in Fat	Soluble	Insoluble
Solubility in Water	Insoluble	Soluble
Absorption	Absorbed with lipids, require bile salts	Absorption is simple
Absorbed into the	Lymph	Blood
Carrier Proteins	Required & Present (Chylomicrons)	Absent & Not Required
Storage	Stored in Liver & Adipose tissue	No considerable storage
Excretion	Not Excreted easily	Excreted readily
Deficiency	Rare and manifest only when stores are empty or depleted	Common and manifest rapidly
Toxicity	Accumulation of Vitamin (Hypervitaminosis)	Unlikely, due to rapid excretion
Treatment of Deficiency	Single large dose may prevent deficiency	Regular dietary supply is needed