Micronutrients - Vitamins

Micronutrients - vitamins

• In this section we will discuss…

• Introduction

• Classification of vitamins

• RDA of vitamins

• Dietary sources

• Functions

• Absorption, synthesis, metabolism, storage and excretion

• Deficiencies

• Hypervitaminosis

Micronutrients - vitamins

• Introduction

• Vitamins are defined as organic compounds occurring in small quantities in natural food necessary for growth and health

• Required in small quantities so fall in micronutrients category

• Two properties define…..

• It must be vital, organic dietary substance that is not CHO, fat, protein or mineral and is necessary in small amounts for normal health

• It can not be manufactured by the body in sufficient quantities to sustain life

Micronutrients - vitamins

• Introduction

• So far at least 15 different vitamins isolated in pure form from natural foods

• Vitamins do not yield energy but enable the body to use other nutrients

• Vitamins have therapeutic application in prevention and treatment of deficiencies

• Deficiency occurs mainly due to inadequate intake, malabsorption, increased tissue demand, increased excretion, genetic abnormalities and vitamin-drug interactions

Micronutrients - vitamins

• Classification

• Mainly classified in to two groups

• Water soluble and fat soluble

Fat soluble Water soluble

• Vitamin soluble in fat

• Stored in the body for long time and

are able to cause toxicity after ingestion

of large amounts

• Soluble in water

• Not stored in high amounts

• Excess amounts excreted

• No toxicity of over-consumption

Vitamin A and carotene (pro-vitamin A) B complex vitamins

Vitamin DD2 – Calciferol, (artificial vitamin D)

D3 – irradiated dehydro cholesterol (natural)

Thiamin (B1) Riboflavin (B2)

Nicotinic acid (B3) Pyridoxine (B6)

Pantothenic acid (B5) Folic acid (B9)

Biotin (B7) Cobalamine (B12)Vitamin E Vitamin C (ascorbic acid)

Vitamin K

Micronutrients - vitamins

• General Properties

Fat soluble Water soluble

Very stable and not easily destroyed by

normal cooking methods

Comparatively unstable

They are destroyed by rancidity as they

are always associated with fats

Easily affected by factors such as heat,

light oxidation, radiation and metal

contamination

Can cause to hypervitaminosis Affected by cooking practices

Not absorbed in the presence of

mineral oil in intestine

Excess amount usually excreted

Micronutrients - vitamins

• Fat soluble vitamins : vitamin A

• Vitamin A occurs in only animal food

• Pro-vitamin A (carotinoids) from plant sources

• Chemistry

• Vitamin A (retinol) has a beta-inone ring

• side chain contains 4 double bonds and alcoholic group

• Oxidation effects the side chains

• Light exposure also effects side chains

Vitamin A• 3 forms in the body

– retinol

– retinal

– retinoic acid

• collectively known as retinoids

Retinol, the alcohol form Retinal, the aldehyde form Retinoic acid, the acid form

Beta-carotene, a precursor

Cleavage at this point can

yield two molecules of vitamin A*

Vitamin A

• precursor: beta-carotene

– derived from plant foods

– can split and form retinol in

intestine and liver

Micronutrients - vitamins

• Fat soluble vitamins : vitamin A

• Digestion, absorption and storage

• Retinyl esters in food hydrolyzed in intestine to retinol which is absorbed by carrier transport and re esterified

• Retinol ester circulates in chylomicrons and is stored in liver

• Free retinol from liver cells binds with RBP (retinol binding protein) transported to cells

• In cells binds with CRBP (cellular-RBP)

• Liver in adults can store up to 100,000 µg)

Micronutrients - vitamins

• Fat soluble vitamins : vitamin A

• Digestion, absorption and storage• Retinol equivalent (RE) and IU are used to measure

• 1 IU = 0.6 mcg of beta carotene = 0.3 mcg retinol

• 1 RE = 1mcg of retinol (3.3 IU) = 6 mcg of beta carotene (10 IU)

Micronutrients - vitamins

• Fat soluble vitamins : vitamin A

• Digestion, absorption and storage

Micronutrients - vitamins

• Fat soluble vitamins : vitamin A

• Sources

• Vitamin A is widely distributed in animal and plant foods

• Preformed vitamin A (retinol) – in animal food

• Precursor of vitamin A ( caro.) – in plant food

Micronutrients - vitamins

• Fat soluble vitamins : vitamin A

• RDA – Daily intake should be 20,000 IU

• Functions and physiological role

• Visual cycle

• Vitamin A essential for vision in dim light

Micronutrients - vitamins

• Fat soluble vitamins : vitamin A

• Functions and physiological role

• Epithelial tissue – maintains structural integrity, promotes mucus secretion and stops hyper keratinization of lungs, eyes, skin…

• Reproduction – retinol needed for spermatogenesis and fetal development

• Immunity – strengthens immunity by helping proliferation of lymphocytes and antibody production

• Bone – Retinol essential for normal bone formation

Micronutrients - vitamins

• Fat soluble vitamins : vitamin A

• Deficiency

• Deficiency symptoms appear only after long time

• Conjuctival xerosis – conjuctiva is dry, thickened, and wrinkled (hyper keratinization)

• Night blindness

• Bitot’s spot

• Skin hyper keratinization

Bitot’s spot

Hyper keratosis

Micronutrients - vitamins

• Fat soluble vitamins : vitamin A

• Toxicity

• Regular consumption of meats leads to gross excess consumption of vitamin A

• Symptoms – nausea, vomiting, hair loss, bone and joint pains loss of appetite…

• Excess intake of carotenoids does not produce toxicity as there is ceiling on how much carotin is converted in to retinol