Dr S Nayak 1

Micronutrients

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What are Macronutrients and Micronutrients?

The nutrients can be divided into two major groups – “Macronutrients” and “Micronutrients”.

 

Macronutrients are those that are needed in large quantities (tens or hundreds of grams) every day. These are: Carbohydrates, protein and fats/oils.

 

Micronutrients are those that are needed in minute quantities (micrograms or at best milligrams). These are vitamins, minerals and trace elements.

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Vitamins

Vitamins are naturally occurring organic substances.

Their coenzyme forms are active and are essential in metabolic processes.

They serve nearly the same roles in all forms of life. The daily requirement of any vitamin depends on a number of factors and may increase during growth, pregnancy and lactation.

They are essential nutrients of humans, and have various roles in the human body

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Vitamins are either fat-soluble or water-soluble .

• Fat soluble vitamins are vitamins A, D, E and K.

• Water-soluble vitamins are the B-complex vitamins and vitamin C.

• B-complex vitamins are vitamin B1, B2, B6, B12,

niacin, folic acid, biotin and pantothenic acid.

•

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• Soluble vitamins, when taken in excess of body needs, are excreted in urine.

• On the other hand, fat-soluble vitamins, when taken in excess, are stored in the body (particularly liver) for use at times when the intake of these vitamins is inadequate.

• Most vitamins can be derived from liver, fruits, vegetables, legumes and grains.

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Vitamin A

Preformed retinoid is a collective term for retinol,

retinal, and retinoic acid, all of which are biologically

active.

Recommended Dietary Allowance Adult: 5000 IU/day Pregnancy lactation: 4000 IU/day Infants and children: 3000 IU/day

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Functions

1.Role of vitamin A in visionRetina of the eye contains two types of cellsRod cells (Vision in dim light)Cone cells (vision in bright light). Rod cells have a photosensitive pigment called rhodopsin, is a conjugated protein made up of opsin and 11-cis retinal

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2. Retinoic acid form of vitamin A maintains structural and functional integrity of epithelium

3. Retinol form of vitamin A is required for growth and reproductive function.

4. Retinol is also known to require for the formation of

bone and teeth.

Deficiency

Night blindness

Keratomalacia: Dryness of the cornea, corneal

epithelium becomes keratinised and opaque and may

become softened and ulcerated.

Follicular keratosis: Deficiency will affect hair follicles

and causes scaly skin

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Vitamin D

Sources

Fish liver oils, eggs, milk & butter

Sunlight induces synthesis of vit. D in the body from skin

cholesterol.

Required Dietary Allowance Children: 400 IU/day Adults: 400 IU/day Pregnancy and lactation: 400 IU/day Vitamin D2 or D3 are not active biologically but

converted to active form by hydroxylation [1,25 dihydroxyvitamin D3].

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Functions

Helps in the mineralization of bones by enhancing absorption

of calcium

Deficiency

The deficiency of vitamin D leads to rickets in children

Signs and symptoms are bowlegs, knock knee, pigeon

Chest, hypocalcemia and hypophosphatemia

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Vitamin E

SourcesVegetable oils, germinated whole-grain cereals

Required Dietary Allowance Adult male : 30 IU /day Female : 25 IU/day Children : 10-20 IU/day

Functions

1.Potent physiological antioxidant: Protects membranes with lipids from oxidative damage.

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2. Vitamin E, which is present in cell membranes, prevents the destructive non-enzymatic oxidation of polyunsaturated fatty acids (PUFA) by molecular oxygen, and it maintains the membrane integrity.

3.Protects erythrocytes from hemolysis by oxidizing agents (H2O2)

4. Required for normal reproduction in animals.5. Prevents liver necrosis and muscular dystrophy

Deficiency

Hemolysis of erythrocytes which may leads to anemia

Muscular weakness, fragile RBCs.

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 Vitamin K

Phylloquinone, menaquinone and menadione are the

three forms of vitamin K

Sources Green leafy vegetables and Tomato, It is also synthesized by microorganisms in the

intestinal tract

Functions

Required for the maintenance of normal concentration

of blood clotting factors.

Deficiency

Excessive bleeding

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Vitamin C

Sources Citrus fruits (Orange, lemon), Tomatoes Strawberries Green vegetables Guava fruit

Required Dietary Allowance Adults: 60 mg/day Children: 40 mg/day.

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Functions

1. Collagen synthesis. Vitamin c is involved in the hydroxylation of proline and lysine residues, which are the collagen precursors.

2. It helps in the absorption of iron.

4. Acts as an antioxidant, scavenging the free radicals and reduces the nitrosamine formation.

5. The conversion of dopa to dopamine and dopamine to nor adrenaline requires vitamin C as an activator.

Deficiency Scurvy

Spongy gums , loose teeth, fragile blood vessels ,aching

swollen joints and delayed wound healing.

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Thiamin [Vitamin B1]

SourcesWhole grains (unpolished rice, wheat), legumes (Beans, peas) Meat.

Required Dietary Allowance Children: 1.2 mg/day Adults: 1.5 mg/day Pregnancy and lactation – 2.0 mg/day.

FunctionsThe coenzyme form of thiamine is Thiamin pyrophosphate (TPP)Helps to release energy from nutrients supports normal appetite and nerve function

TPP is required as coenzyme for Pyruvate dehydrogenasecomplex, α-ketoglutarate dehydrogenase complex,Transketolase etc.

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Deficiency

Cause:alcoholism and malnutrition

The overall picture of this vitamin deficiency including

neurological, cardiovascular and gastrointestinal

disorders is referred to as Beriberi

Beriberi is of four types Dry beriberi (peripheral neuritis) Wet beriberi (cardiac manifestation) Cerebral beriberi (Wernicke-Korsakoff’s syndrome) Infantile beriberi

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Sources Animal liver, yeast, green leafy vegetables, milk & eggs

Required Dietary Allowance Adults: 2.0 mg/day Children: 1.2 mg/day Pregnancy and lactation: 2.0 mg/day

The riboflavin has two coenzyme forms they are flavin mononucleotide (FMN). Flavin adenine dinucleotide (FAD) Some enzymes have FMN and FAD as their integral part. Such enzymes are called flavoproteins

Riboflavin[B2]

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Functions

Helps release energy from nutrients; supports health FMN is required for:

1. L-amino acid oxidase

2. Cytochrome C reductase.

FAD is required as coenzyme for:

1. Succinate dehydrogenase,

2. Pyruvate dehydrogenase complex,

3. α -ketoglutarate dehydrogenase complex,

4. Xanthine oxidase.

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Deficiency seen in: Malabsorption, malnutrition, and chronic alcoholism

Ariboflavinosis It is the medical condition caused by deficiency of

riboflavin. It is often associated with protein energy malnutrition and alcoholism.

Characterized by: Glossitis (Magenta colored tongue) Cheilosis (Fissuring of the lips) Fissuring at the corners of mouth, Seborrheic dermatitis, corneal vascularization are the

symptoms of riboflavin deficiency.

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Niacin [B3]

Sources Lean meats (liver) Legumes, peanuts (ground nuts) Green vegetables Whole grains. Amino acid tryptophan can be converted to the

coenzyme NAD. About 60 mg of tryptophan yields 1 mg of niacin.

Required Dietary Allowance Adults: 16-20 mg/day. Children: 9-16 mg/day Infants: 5-8 mg/day

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The coenzyme forms of niacin are Nicotinamide Adenine Dinucleotide (NAD) Nicotinamide Adenine Dinucleotide Phosphate (NADP).

FunctionsHelps release energy from nutrients; supports skin, nervousand digestive systemsNAD is required as a coenzyme for PDH complex, α-ketoglutarate dehydrogenase complex to mediate the reactions. NADP is required for glucose-6-phosphate dehydrogenase and 6-phosphate gluconate dehydrogenase mediated reactions.

Deficiency Pellagra which Involves skin, gastrointestinal tract and

central nervous system.

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Pyridoxine [B6]

Sources Whole grains, Poultry fish Potatoes Organ meats, Eggs Legumes.

Required Dietary Allowance Adults: 2.2 mg/day Children: 1.2 mg/day Infants: 3.0 mg/day

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Functions

Helps to make red blood cells

Helps in amino acid and fatty acid metabolism Coenzyme form of pyridoxine is pyridoxal

phosphate (PLP) PLP is required as coenzyme for the enzymes like Transaminases, Decarboxylases, Kynureninase, Cystathionine α-synthase, Cystathionine gamma-lyase and ALA synthase.

Deficiency Hypochromic microcytic anemia Glossitis Pigmented scaly dermatitis similar to pellagra

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Biotin [B7]

Sources Egg yolk Organ meats (liver, kidney) Milk Legumes Nuts

Required Dietary Allowance Adults: 0.3 mg/day. The intestinal bacteria also synthesize biotin to some

extent.

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Functions

Biotin itself functions as coenzyme in the reactions

involving fixation of CO2.

Helps release energy from carbohydrates; aids in fat

synthesis  Pyruvate carboxylase Propionyl CoA carboxylase Acetyl CoA carboxylase

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Pantothenic acid [B5]

Sources Eggs, Animal liver,Meat , Milk, Vegetables and Grains.

Required Dietary Allowance Adults: 5-10 mg/day Children: 4-5 mg/day Infants: 1-2 mg/day

Conzyme form: Coenzyme A (CoASH): Required for Pyruvate dehydrogenase complex α-ketoglutarate DH complex Thiokinase  Thiolase

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Sources Fresh green, Vegetables, Liver, Whole grains, Meat

Legumes.

Required Dietary Allowance Children - 300 µg/day Adults - 400 µg/day Pregnancy and lactation - 800 µg/day The coenzyme form of folic acid is tetrahydro folic

acid [THF] (FH4) is the active form.

The THF is a carrier of single carbon and it is involved in

single carbon transfer reactions

Folic acid

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Helps in the formation of DNA and new blood cells

including red blood cells

Deficiency• Megaloblastic anemia

The deficiency of folate leads to impairment of the methionine synthase reaction due to which purine ring synthesis is impaired. The impaired synthesis of DNA prevents cell division and formation of the nucleus of new red blood cells.

• Growth failure.

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Vitamin B12 or cobalamin

Sources

Liver,Meat, Fish, Eggs and Milk.

Human beings get small amount of vitamin B12 from

their intestinal flora.

Required Dietary Allowance Children: 2 µg/day Adults: 3 µ g/day Pregnancy and lactation: 4 µg/day.

Active form of Vitamin B12

Methylcobalamin and Deoxyadenosylcobalamin a

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Functions Vitamin B12 along with folic acid is required for the

development of red blood cells beyond megaloblastic stage.

It acts as coenzyme for the mutase enzyme which converts methyl malonyl CoA into succinyl CoA.

Methylcobalamin is required in the conversion of homocysteine to methionine

It is involved in the conversion of ribonucleotides to deoxyribonucleotide.

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Deficiency

Cause: malabsorption.

Pernicious anemia is caused by a deficiency of intrinsic

factor, which leads to impaired absorption of cobalamin. Megaloblastic anemia, Glossitis and inflammation of mouth, Methyl malonic aciduria.

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Minerals are vital to physical and mental development. They also help protect the body against infections.

Meat, fish, milk, cheese, green leafy vegetables and legumes provide most of the minerals needed by the body.

Minerals

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Minerals

Minerals are inorganic chemical elements present throughout the body in varying amounts. Like the vitamins, they cannot be synthesized in the body and must be taken with food.

Minerals act as co-factors of enzymes for metabolism.

Minerals form part of the structure of body tissues, such as bones, teeth and nails, blood, nerves and muscles.

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Calcium

Functions Mineralization of bones and teeth Regulator of many of the body’s biochemical processes Involved in blood clotting Involved in muscle contraction and relaxation Nerve function blood pressure and immune defenses Activates pancreatic lipase in the digestion of fats Serves as a second messenger in the action of

hormones like adrenaline.Serum ionic calcium level is maintained by vitamin D

and hormones like parathyroid hormone (PTH) and calcitonin.

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Action of Vitamin D

a. Increases the absorption of calcium (and phosphate) from the small intestine

b. Causes bone resorption.

Action of PTH on Kidney and Bone

1. PTH increases the activity of 1 α-hydroxylase in

kidney, which increases the synthesis of 1-25-dihydroxy

vitamin D3 and this in turn enhance the absorption of

calcium from intestine.

2. It increases the reabsorption of calcium from

glomerular filtrate in kidneys.

3. It causes the resorption of calcium from bone.

The above process helps maintain normal calcium level

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Hypocalcemia

This provokes a characteristic hyper excitable state of

the nerves and muscles called tetany.

Symptoms are:

• Numbness of extremities

• Emotional irritability

• Tightness and spasm of muscles.

– Hypocalcaemia also occurs in hypoparathyroidism, rickets, osteomalacia, pancreatitis, etc.

Hypercalcemia

Occurs in hyperparathyroidism and hypervitaminosis D.

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Phosphorous

Functions Mineralization of bones and teeth Part of every cell Used in energy transfer and maintenance of acid-base

Balance Helps in the formation of compounds like nucleic

acids,nucleotides like ATP, GTP, ADP It is also required in energy metabolism, synthesis of

phospholipids

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Hypophosphatemia

• Rickets

• Hyperparathyroidism

Clinical symptoms are muscle pain and weakness with

respiratory failure and decreased myocardial output

Hyperphosphatemia

• Seen in hypoparathyroidism

• Hypervitaminosis D

• Renal failure.

Elevated phosphate may cause a decrease in serum

concentration. Therefore it may lead to tetany and

seizures

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Sodium

Sodium (Na+) is the major cation of the extracellular fluid

Functions Maintains normal fluid and electrolyte balance Assists nerve impulse initiation and muscle contraction Helps in the active transport of glucose, galactose

and amino acids across intestinal mucosa and for

Na+/K+ ATPase.

Hyponatremia

Causes

• Kidney failure and defect in adrenal cortex

• Vomiting and diarrhea

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Syndrome of inappropriate secretion of antidiuretic

hormone (SIADH)

Hypernatremia

Causes: Hyperactivity of adrenal cortex

When water loss exceeds sodium loss, as occurs with

Dehydration.

Clinical symptoms: high blood pressure, fluid retention

and swelling

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Potassium

Most important cation of intracellular fluid

Functions Intracellular K+ is essential for a number of enzyme-

mediated reactions such as pyruvate kinase, glycogen synthesis and protein synthesis

The extracellular potassium is important for its

influence cardiac muscle

Hypokalemia and Hyperkalemia

Renal causes

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Chloride

Functions

Maintains normal fluid and electrolyte balance

It is involved in maintaining osmotic pressure

Hypochloremia: Metabolic alkalosis

Vomiting diarrhea, diuretics and gastric suction

Hyperchloremia :Metabolic acidosis

Dehydration, decreased renal blood flow, medications

ammonium chloride and Hyperparathyroidism

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Magnesium

Magnesium (Mg2+) is the major intracellular cation

Functions

• It is an essential activator of many enzymes especially those involving transfer of phosphate groups from ATP.

• Examples are hexokinase and phospho fructokinase.

• It also activates a number of enzymes like

– Enolase,

– Glucose-6-P dehydrogenase,

– Pyruvate carboxylase,

– Thiokinase,

– Glucose 6 Phospho gluconate dehydrogenase.

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Iron

Functions Iron is necessary for the synthesis of certain proteins Iron containing proteins in the body are of two types: Heme proteins (Hemoglobin, myoglobin, catalase

and cytochrome) and non-heme proteins (ferritin, transferrin, aconitase and sucinate dehydrogenase).

Essential in the formation of blood Involved in the transport and storage of oxygen in the

blood It is a cofactor bound to several non-heme enzymes

Required for the proper functioning of cells

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Ferritin is the storage form of iron and transferrin is

the transport form

Deficiency

Hypochromic microcytic anemia (microcytic RBC of

reduced size).

Causes: haemorrhage, malabsorption

Iron overload

Haemosiderosis and haemochromatosis

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Copper

Functions

A need for copper is linked to its functional role in

several copper containing enzymes.

1. Ceruloplasmin

2. Cytochrome oxidase

3. Dopamine-oxidase of catecholamine synthetic pathway.

4. Monoamine oxidase and diamine oxidase.

5. Cytoplasmic superoxide dismutase

6. Lysyl oxidase involved in cross-linking process in the conversion of tropocollagen to collagen.

7. Tyrosinase of melanin synthetic pathway is a Cu dependent enzyme.

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Deficiency

Hypochromic microcytic anemia

Wilson’s disease or Hepatolenticular degeneration

It is a fatal inherited disease.

Blood copper level decreases.

There is an excessive storage of copper in the liver,

kidney, brain and cornea

Menkes syndrome or Kinky-hair disease

It is a rare X-linked recessive disorder

Both serum copper and ceruloplasmin and liver copper

content are reduced.

Depigmentation of the skin and hair

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Zinc

Essential for normal growth, development and reproductionIt is required as an activator ion for:• Carbonic anhydrase • Alkaline phosphatase • Liver alcohol dehydrogenase • Carboxyl peptidase A • DNA polymerase• Cytosolic superoxide dismutase

DeficiencyDwarfism Acrodermatitis enteropathica: autosomal recessive disorder

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Manganese

Manganese acts as a cofactor or an activator

for several enzymes Acetyl CoA carboxylase Mitochondrial superoxide dismutase Arginase 6 Phosphate-gluconate dehydrogenase Squalene synthetase Isocitrate dehydrogenase Glutamine synthetase Kinases

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Selenium

It acts as an antioxidant:

It is an integral component of glutathione peroxidase.

This enzyme scavenging the free radicals and protect

the cells and membranes against oxidative damage.

So, this mineral complements the action of vitamin E.

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Iodine

Involved in the synthesis of thyroid hormones, triiodothyronine (T3) and tetraiodothyronine (t4), which influence a large number of metabolic functions.

Deficiency Cretinism in children: Severe iodine deficiency in mothersleads to intrauterine or neonatal hypothyroidism results inCretinism in their children, a condition characterized by mental retardation,dwarfism, slow growth

Endemic goitre in adults: It is an enlarged thyroid withdecreased thyroid hormone production.

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Fluoride

Involved in the formation of dental enamel and prevents

dental caries

Involved in the formation of teeth and skeleton

Inhibits osteoporosis in old age

Deficiency:

Dental caries and osteoporosis.

Excess fluoride causes fluorosis. In this condition there

is mottling of enamel. The mottled enamel is discolored,

corroded and pitted.

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Ref: Essentials of Biochemistry by Dr Nayak

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