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Definition, Classification, Functions, Food Sources, Deficiency | Nutrition - Micronutrients | 11th Home Science : Chapter 5 : Nutrition

Chapter: 11th Home Science : Chapter 5 : Nutrition


Until the middle of the 19th century the importance of minerals and vitamins was not given adequate emphasis.


Until the middle of the 19th century the importance of minerals and vitamins was not given adequate emphasis. It was observed that the macronutrients alone were not sufficient to promote and sustain growth.


This led to the discovery of the micronutrients namely the minerals and vitamins which are essential for growth and maintenance. Macro minerals are those which are present at levels more than 0.05 percent in the human body. Calcium, Phosphorus, magnesium, sodium and potassium belong to this category. Other minerals present at less than 0.05 percent in the human body are defined as micro min-erals. The micro minerals are also known as the trace elements. Some micro miner-als are iron, iodine, zinc, copper, fluorine, selenium, chromium, manganese, cobalt and molybdenum.


1. Minerals

The minerals calcium, phosphorus, iron iodine, sodium and others are found in various foods in combination with organic and inorganic compounds. Minerals are necessary for body building, for building bones, teeth and structural parts of soft tissues.


(i) Calcium


Distribution: Calcium makes up between 1.5 to 2 percent of body weight accounting for 1200-1600 g of the adult male body. Ninety percent of calcium is found in min-eralized tissues such as bones and teeth as calcium phosphate and calcium carbonate. The remaining 1% is found in blood, extracellular fluid (ECF), muscle and tissues.


Functions: The functions of cal-cium in humans are manifold:


•  Bone formation: The import-


ant minerals within bone are calcium phosphate and magne-sium. There is 1 kg of calcium in the adult skeleton as a complete crystalline material with phos-phate.


·        Tooth formation: The enamel and dentin of tooth contain considerable amounts of cal-cium which are dense and are present along with keratin.


Growth:  It  is  required  for growth as it forms an important part of the bones and teeth and proper functioning of every cell in the body.


·        Blood clotting: Calcium con-tributes to clotting of blood.


·        Contraction  of  the muscle:


Calcium ions are bound by the electrostatic forces to the pro-teins inside and outside the cells and to cell membranes. Proteins bound by calcium alter their configuration at the neuro muscular junction by the nerve impulses causing free calcium to be released. The free cal-cium bound to troponin leads to an internal trigger and so the contraction of the muscle takes place


·        Metabolic essentiality: Cal-cium acts as a activator for the enzyme renin present in gastric juice which aids the digestion of milk.


Food sources: Calcium is present in both animal and plant foods. The richest source of calcium among animal foods is milk and among the vegetable sources it is green leafy vegetables. 

Among the green leafy vegetables, amaranth, fenu-greek and drumstick leaves are rich sources of calcium. Ragi among cereals is a rich source of calcium. Small dried fish, nuts and oil seeds like gingelly seeds, betel leaf with slaked lime are also a rich source.




     Factors increasing absorption of calcium: Vitamin D, acidity of digestive mass, lactose, protein and phosphorus are the factors which favor the absorption of calcium.


     Factors decreasing absorption of calcium: Oxalic acid, phytic acid, high fat diets including steatorrhea, emotional instability, increased gastrointestinal mobility, lack of exercise, ageing, caffeine and drugs decrease the absorption of calcium in the body.


Health Problems/ Deficiency:

·        Osteoporosis: This is a condi-tion associated with a loss in bone density and bone mass which literally means “porous bone”. With the ageing process resorption predominates bone formation resulting in osteopo-rosis.


Risk factors for osteoporosis include


·        Females who are fair complexioned are at eight times more at risk


·        Asian Race


·        Family history


·        Prolonged dietary insuf-ficiency


·        Poor absorption and uti-lization of calcium


·        Restricted movement


·        Decreased levels of estro-gen


·        Hyper parathyroidism


·        Vitamin D sufficiency


·        Osteomalacia: It is a condition where the quality of the bone is diminished and the quantity of the bone is not compromised.


·        Osteopenia: It refers to the bone density that is lower than nor-mal peak density but not low enough to be classified as osteoporosis. The difference between osteopenia and osteoporosis is a matter of severity of the loss of bone density.


·        Tetany: A decrease in serum calcium levels gives rise to a condition called tetany. The symptoms of tetany are severe intermittent spasms of the mus-cles of hands and feet accompa-nied by muscular pain. Twitch-ing of facial muscles occurs.


(ii) Phosphorus


Distribution: It comprises 1 per-cent of total body weight along with calcium. An adult human body contains about 400-700 g of phos-phorus as phosphates. Bones and teeth contain 85 percent of phos-phorus and soft tissues contain15 percent of phosphorus.




·        Formation of bone and teeth along with calcium and magnesium.


·        Formation of phospholipids which are integral parts of cell structure.


·        Constituent of co enzymes like coenzyme I and co – carboxylase.


·        Integral constituent of DNA and RNA (nucleic acids) and nucle-oproteins.


·        Buffering of acid or alkali excesses to maintain normal pH.


·        Temporary storage and transfer of the energy derived from met-abolic fuels.


·        As part of enzymes needed for the metabolism of carbohy-drates, protein and fats.

Food Sources: Phosphorus is widely distributed in foods. Milk and meat are rich in phospho-rus. Whole grain cereals, legumes, nuts, carrots and fish are also rich sources of phosphorus.


Calcium Phosphorus ratio: Nutri-tionists recommend that a Ca:P ratio between 1:1 to 2:1 should be provided by the total diet.


Deficiency: Phosphorus is so ubiquitous in various foods that near total starvation is required to produce dietary phosphorus deficiency. Inadequate phospho-rus intake is expressed as hypo-phosphatemia which manifests in the form of anemia, anorexia, muscle weakness, bone pain, rickets, osteomalacia, general weakness and increased susceptibility to infection.


(iii) Iron


Distribution: Iron content of nor-mal adult man is estimated to be about 4 grams. Iron is distributed as 60% in the circulating hemoglobin, 5% myoglobin, various heme and non heme enzymes (5%). The remaining iron is found in body storage as ferritin (20%) and hemosiderin (10%) the two major iron storage proteins


Forms of dietary iron


·           Heme iron: Heme iron is the iron associated to the protein globin to form hemoglobin and is found in flesh foods only


·        Non heme iron: This form is pres-ent in all plant sources in addition to 60% of animal sources.

·        Absorption: Several factors favor and inhibit iron absorption


Factors favoring absorption of Iron:


·        Body needs,


·        Ascorbic acid,


·        Animal tissues,


·        Pregnancy,

·        Low iron status,


·        Low heam iron intake.


Factors decreasing the absorption of iron:


·        Binding agents like fiber, phos-phates, phytates and oxalates,


·        High calcium intake,


·        Achlorohydria (low gastric acid)


·        Infection


·        Gastrointestinal disease.


Functions: Iron has varied signif-icant functions in human body. They include:


·        Transport and storage of oxygen where each gram of hemoglobin contains about 3.34 mg of iron.


·        As myoglobin iron is required for oxygen storage in muscle.


·        Iron acts as a cofactor of enzymes.


·        It is a component of cell enzyme systems that oxidize glucose and other energy yielding nutrients.


·        Production of immune cells that attack foreign bacteria invading the body.


·        Positive iron balance is neces-sary for continued growth.


·        To build reserves for physio-logic stress during adolescence for both boys and girls.


·        Necessary for brain develop-ment, cognitive function, the synthesis and breakdown of neurotransmitters.


Food sources:


Rich sources of iron are cereals, millets, pulses and green leafy veg-etables. Of the cereal grains and millets bajra and ragi are very good sources of iron. Other sources of plant foods include manathakali leaves, rice flakes, mint, soya bean, cow pea, gingelly seeds and dates. Animal food sources include red meat, and fishes like herring and mackerel





·        Iron Deficiency anemia: When there is an insufficiency of iron for the formation of hemoglobin, the RBC’s become pale and small. The resulting anemia is called hypo-chromic and microcytic anaemia which is the most common form of anaemia throughout the world affecting women mainly in their reproductive years, infants and children.



Causes: Low iron intake, blood loss, malabsorption chronic dis-eases, obesity



·        Regular consumption of iron rich foods, vitamin C rich foods, seasonal fruits and vegetables can definitely prevent anemia.


(iv) Iodine


Distribution: It is one of the essen-tial micronutrients required for normal growth and development of human brain and body. Human body contains a total of 15-20 mg of iodine. Thyroid gland contains 75% of iodine and is an essential constituent of thyroxine the active principle of thyroid gland


Functions: Iodine though required in small quantities is needed to per-form the following functions


·        Synthesis of thyroxine which regulates growth, development and reproduction.


·        Helps the thyroid hormones to increase and regulate the pro-cesses of brain function


·        Enables the thyroid hormones to regulate the conversion of carotene to active vitamin A.


Food sources:


Marine fish and eggs are good sources of iodine. Based on the dietary pat-tern and analysis of raw foods, iodine content of various regional diets range from 170-300 μg/ day


Deficiency: It covers a collection of disorders at all stages of human growth and development.


·        Goiter: Goiter is the enlargement of thyroid gland which results when iodine is not available in sufficient quantities to produce normal quantity of thyroxine. It also arises from eating foods (goitrogens) that inhibit the synthesis of thyroxine

·        Cretinism: A congenital disease resulting from a lack of iodine and thyroxin secretion characterized by physical deformity, dwarfism, men-tal retardation and often goiters.

·        Dietary improvement: Salt iodiza-tion remains the most cost effec-tive way to deliver iodine to both humans and livestock and is cred-ited with eradicating iodine defi-ciency.


(v) Zinc


Distribution: Zinc is the most important intracellular trace element. An adult human contains 2g of zinc of which 60% is in skele-tal muscle, 30% in bone and 4-6% is present in zinc.


Functions: The functions of zinc include


·        Important constituent of enzymes like alkaline phospha-tase and carbonic anhydrase.


·        Required by protein kinases that participate in gene expression.


·        Also a component of metallo-enzymes.


Food sources: Meat, seafood and liver are good sources of bioavail-able Zinc. In cereals most of the zinc is found in the outer fiber rich part of the kernel.


Deficiency: The clinical manifes-tations of severe zinc deficiency in humans are growth retarda-tion, dermatitis, hair loss, diarro-hea, increased infections, delayed wound healing, loss of appetite, hypoguesia (diminished taste) dys-guesia (altered taste) hyposmia (diminished smell). Decreased zinc intake is associated with increased risk of low birth weight and preterm delivery.


2. Vitamins

Fat soluble vitamins A, D, E and K and also water-soluble vitamins C and B group are found in foods. These are needed for growth, normal function of the body and normal body processes.


2. a. Fat Soluble Vitamins


(a) Vitamin A:

The vitamin A compounds include retinol, retinal and retinoic acid. Because it has a specific function in the retina of the eye and because it is an alcohol it was given the name ret-inol. Beta carotene is precursor of vita-min A and is found in large quantities in vegetables and fruits.


Functions: Vitamin A performs the following functions:


·           Vitamin A is essential for vision in normal and dim light.


·           Formation and maintenance of healthy functioning epithelial tissue.


·           Glycoprotein and mucoprotein synthesis


·           Cancer prevention


·           Prevention of degeneration of myelin sheath


·        Normal bone formation and reproduction.


Food sources: In the animal foods vitamin A is present in the form of retinol which are identified to be liver, cream, butter and egg yolk. Liver oils of fish like cod, halibut and shark are the richest sources of vitamin A. The main contribu-tors of beta carotene are the yellow and green vegetable fruit sources of carotene- carrots, papaya, mango, sweet potatoes, spinach and broccoli.


Deficiency: Decreased Vitamin A intake leads to vision problems


·           Night blindness: People suffering  from  night  blindness cannot see objects in dim light


·           Xerosis Conjunctiva:   The conjunctiva is dry, thickened, wrinkled and pigmented. This is due to the keratinization of the epithelial cells.


·           Xerosis  Cornea:  This  man ifests in the form of corneal dryness which gives the cornea a dull hazy and lusterless appearance.


·           Bitot’s spots: These are grey-ish or glistening white plaques occurring in the conjunctiva usually triangular in shape and are found in children.

·           Keratomalacia: When Xerosis of the conjunctiva and cornea is not treated it may develop into the condition called ker-ato malacia which is character-ized by necrosis, ulceration and bacterial invasion of cornea leading to the total destruction of the eyeball and eventually total blindness.


Prevention of vitamin A deficiency

The strategy should be a combina-tion of long term nutrition educa-tion programme, enhanced intake of vitamin A rich food, improve-ment in household food security and availability of vitamin A rich foods and a periodic massive dose of vitamin A.


(b) Vitamin D:

Vitamin D is known to be a prohormone of a sterol type and the synthesis of active form of vitamin D is known as the 1,25 – dihydroxycho-lecalciferol which is accomplished by the combined action of skin, liver and kidneys.




·        Maintains balance with para-thyroid hormone to stimulate the active transport of calcium and phosphorus.


·        Acts on the bones promoting calcification.


·        Facilitates the absorption of calcium and phosphorus from the intestines.


Involved in widespread basic cell processes with targets in brain, kidney, liver, skin, repro-ductive tissues.


Food sources: Vitamin D is pres-ent only in some foods of animal origin. Certain marine fishes and fresh water fishes are known to be good sources of vitamin D. The most important sources are egg yolk, butter, cheese, milk.


Deficiency: Vitamin D deficiency occurs in children who are not ade-quately exposed to sunlight. It is characterized by inadequate min-eralization of the bone. In children the condition is known as rickets and in adults it is called Osteoma-lacia.


Rickets: In rickets there is soft-ening of the skull bones and the head is enlarged, elongated and flattened on the vertex. Softening of the ribs, sinking of the chest, beaded junctions of the ribs with cartilages (rickety rosary), pigeon chest, knock knees and bow legs. Deformities of the long bones spine, pelvis, muscles, and feet are observed. Dentition is delayed.


Osteomalacia: It is the adult counterpart of rickets. It occurs in women of child bearing age and in those who consume poor cereal diets deficient in vitamin D and calcium. 

Besides it is found among those who stay indoors all day and seldom go out in the sun.



(c) Vitamin E:

Vitamin E is the generic name for a group of vitamins, three of which –alpha tocopherol, beta tocopherol and gamma tocopherol display the greatest biologic activity. Of these three, alpha tocopherol is the most significant form of Vitamin E


·        Functions


·        Vitamin E a major antioxidant which reduces the incidence of heart diseases.


·        It is essential for normal repro-duction in man.


·        It acts along with selenium in reducing the body’s require-ment for each other.


·        It plays a vital role in the immune function of the body.


Food sources: Vegetable oils, nuts and whole grams are the richest sources of vitamin E (eg. Wheat germ oil). It is present in small quan-tities in lettuce, grasses and embryos of many seeds. In general, plant foods are richer sources of vitamin E than animal foods.


Deficiency: Vitamin E deficiency has been associated with irritabil-ity, edema and hemolytic anemia among infants. Also Muscular dys-trophy is common to all species in which there is degeneration of skel-etal and cardiac muscle with vita-min E deficiency.


(d) Vitamin K


Vitamin K occurs in two forms.


·        Phylloquinones (vitamin K1) - plant source and dietary form of vitamin K


Menaquinone (vitamin K2) - syn-thesized by intestinal bacterial flora.

Functions: The major functions of Vitamin K though not many are listed as follows:


·        Vitamin K is essential for blood clotting.


·        Required for the synthesis of blood clotting factors by the liver.


·        Vitamin K is vital to maintain normal levels and activation of blood clotting factor like prothrombin,


Food Sources:


The major dietary source of vita-min K is Phyllo Quinone which is present in high concentration in most vegetables like cabbage, spin-ach and cauliflower. Animal food sources include cheese, egg yolk, and liver.

Deficiency: It manifests in the form of defective blood clotting. Low levels of prothrombin and hemor-rhage are seen in severe forms of deficiency.



2.b. Water Soluble Vitamins

(a) Thiamin (B1):

Thiamin is the first member of the B complex vitamins which is essential to the body in its coenzyme form.


Functions: The coenzyme of thi-amin is Thiamin Pyro Phosphate (TPP). Thiamin is useful in our body for the following functions


·           It enhances growth in human beings.


·           It plays an important role as a coenzyme in carbohydrate metabolism


·           Maintenance of nerves in nor-mal condition.


Food sources: Good food sources include lean pork, beef, liver, whole or enriched grams and legumes.


Deficiency of thiamin: The dis-covery of thiamin provided the answer to the puzzle of a nutri-tional problem called beri beri. The deficiency of thiamin causes beri beri in human beings. The Philip-pino word beri beri means “I Can’t” refers to the lack of neuromotor coordination in persons with the disease.

Beri Beri is of two types: dry and wet type. In dry beri beri the mus-cles become progressively wasted, weak and walking becomes dif-ficult. If not treated the patient becomes bedridden and will die. In wet beri beri edema is present which involves the face, trunk and serous cavities. Palpitation and breathless-ness are present. The heart becomes weak and death occurs due to heart failure. Infantile beri beri is seen in many South East Asian countries where the diets consist mostly of “polished rice”.


(b) Riboflavin (B2):

Riboflavin is a sta-ble vitamin which is resistant to acid, heat and oxidation. But it is unstable in the presence of alkali and light.




The two coenzymes of Riboflavin Flavin Mono Nucleotide (FMN) and Flavin Adenine Dinucleo-tide (FAD) perform the following functions


·        Formation of red blood cells in the bone marrow.


·        Regulates the functions of hor-mones in carbohydrate metab-olism.


·        Present in the retina in the free form which gets converted to a compound which stimulates the optic nerve.


·        Release of energy from glucose, amino acids and fatty acids.


Food sources: Good sources of riboflavin are milk and milk prod-ucts, eggs, liver, whole or enriched grains and green leafy vegetables.


Deficiency: The deficiency of riboflavin (ariboflavinosis) leads to glossitis (swollen and reddened tongue), swollen lips, cheilosis (inflammation of the corners of the mouth, are some of the com-mon symptoms observed. Further deficiency states are marked by chronic conditions like tubercu-losis, prolonged fevers, malab-sorption, Hyperthyroidism and malignancy.


(c) Niacin:

Niacin formerly known as nic-otinic acid was obtained by the oxida-tion of nicotinic acid. Apart from the food sources, Niacin is also obtained from tryptophan (60mg) an essential amino acid which can be converted into niacin (1mg).


Functions: Two coenzymes of Nia-cin Nicotinamide Adenine Dinu-cleotide (NAD) Nicotinamide Adenine Dinucleotide Phosphate (NADP) are required for:


·        Release of energy from all energy yielding nutrients like carbohydrate, protein and fat.


·        Normal functioning of the skin, intestinal tract and the nervous system.


·        Synthesis of protein and fat for the formation of DNA and RNA.


Food sources: Whole cereals, pulses, nuts and meat are good sources of Niacin. Groundnut is rich in Niacin. Milk is rich in Tryp-tophan the precursor of Niacin in the body.


Deficiency: Deficiency of Niacin causes Pellagra which is the 3D (Dermatitis, diarrohea, dementia or depression) disease leading to the fourth D (Death).

Consumption of diets rich in corn can create amino acid imbalance as corn is rich in leucine and deficient in tryptophan. The typical features of pellagra are loss of weight and increasing weakness. Non- specific signs like anorexia, nausea, diges-tive disturbances and emotional changes like anxiety, irritability and insomnia may be present.


(d) Pyridoxine (B6):

Pyridoxine exists in the body in three forms: Pyridoxal, Pyridoxine and Pyridoxamine. Pyri-doxal 5 phosphate is the co-enzyme form of pyridoxine.


Functions: Pyridoxal 5 phosphate acts as a coenzyme in protein metabolism. Its functions include

·        Amino acid transport.


·        Essential for the growth of infants.


Food sources: Good food sources include grains, seeds, liver, kidney and other meats.


Deficiency: Clinical Symptoms of pyridoxine deficiency have not been clearly defined. Some types of angular stomatitis (cracking at the corners of the lips) and cer-tain types of anaemia have been reported due to decreased intake of pyridoxine.


(e) Folic acid:

The term folic acid was coined to as it was first extracted from dark green leafy vegetables such as spinach.


Functions: The different func-tions of folate include:


·        Normal growth and division of all cells.


·        Maturation of red blood cells.


·        Vital role in the metabolism of some amino acids.


Food sources: The rich sources of folate are fish, mutton, liver, egg, chicken, green leafy vegetables and pulses.


Deficiency: Deficiency of folic acid causes megaloblastic anae-mia. Megaloblasts appear in bone marrow and peripheral blood. Poor dietary intake of folic acid, low absorption, increased losses, increased requirements, infes-tation, infection and drugs also cause folic acid deficiency. Symp-toms include weakness, tiredness, dyspnea, sore tongue, headache and palpitation. Folate deficiency during pregnancy can result in neural tube defects like spina bifida and anencephaly.


(f) Cyanocobalamin (B12):

The vitamin is named as cyanocobalamin because of the presence of cobalt and cyanide in its structure. It can be absorbed in the body only in the presence of Intrinsic Factor (IF).


Functions: Physiological func-tions and biochemical functions of cyanocobalmin are:


·        Maturation of erythrocytes


·        Synthesis of myelin (white sheath of lipoprotein) that sur-rounds many nerve fibres.


·        Increase in White Blood Corpus-cle (WBC) count and platelet.


·        Stimulation of appetite and general wellbeing of the people.


·        Cures neurological symptoms of pernicious anemia.


Food sources: Cyanocobalmin is synthesized by bacteria and is found in foods of animal origin. Liver is the richest source of cya-nocobalmin. Meat, fish, kidney, brain and eggs are good sources of cyanocobalmin.


Deficiency: Inability to produce the intrinsic factor which binds cyanocobalmin leads to perni-cious anemia. The red blood cells are macrocytic and the count is often less than 2.5 million. Symp-toms include soreness and inflam-mation of the tongue, paresthesia (numbness and tingling) in fingers and toes, demyelination of the white fibres of the spinal cord and in severe cases degeneration of the spinal cord.


Other B complex vitamins include biotin, pantothenic acid which do have their vital functions as coen-zymes in various biochemical func-tions of the body


(g) Vitamin C (Ascorbic acid):

Ascorbic acid is the chemical name of vitamin C which can be synthesized from glu-cose but humans depend on their diet for vitamin C as they do not have an enzyme gulonolactone oxidase which catalyzes the conversion reaction.


Functions: Functions of vitamin C include:


·        Collagen formation of bone, teeth, cartilage, skin and scar tissue.


·        Formation of dentin layer of tooth


·        Wound healing.


·        Activation of calcitonin, gas-trin, oxytocin, thyrotropin, vasopressin.


·        Drug detoxification


·        Regulation of cholesterol, maintenance of the blood ves-sel structure and antioxidant effects.


·        Conversion of inactive form of folic acid into its active form


·        Reducing agent to keep iron in its ferrous form to facilitate iron solubility.


·        Adrenal cortex function.


·        Enhances calcium absorption.


Food Sources: Citrus fruits like orange, lemon, tomatoes, guava, watermelon are good sources of Vitamin C


Deficiency: Scurvy the most severe form of vitamin C deficiency arises mainly due to faulty cooking habits and inadequate intake of fruits and vegetables. The clinical features of scurvy are characterized by gin-givitis (bleeding gums) petechiae (small hemorrhagic spots), arthral-gia (pain in the joint), depression, postural hypotension, delayed wound healing. Main deficiency symptoms in infants include tender bones, cessation of bone growth, anaemia and pyrexia.


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