Characteristics, Functions, Classification, Absorption, Food sources, Deficiency - Vitamins | 12th Nursing : Chapter 5 : Applied Nutrition

Chapter: 12th Nursing : Chapter 5 : Applied Nutrition


Vitamins are essential organic, compounds that are needed in small amounts in the diet both to prevent deficiency diseases and to support optimal health.


Vitamins are essential organic, compounds that are needed in small amounts in the diet both to prevent deficiency diseases and to support optimal health. The term vitamin (vital amines) was coined by Casmir Funk. The term vital denoting essential for life and amines because these compounds contained an amine functional group.


Characteristics of vitamins

·  Vitamins are vital, organic, dietary substance that is necessary in only very small amounts to perform a specific metabolic function or prevent an associated deficiency disease.

·  Vitamins are not synthesized by the body and therefore must be supplied through food.

Table: 7

Functions of Vitamins

Each vitamin has its specific metabolic task. However the general functions are:

·  Function as control agents in cell metabolism

·  Components of body – tissue construction.

·  Prevent specific nutritional deficiency disease, which is considered as a result of their primary role in cell metabolism.


Classification of Vitamins

Thirteen (13) recognized vitamins classified in two groups, based on their solubility in fat or in water are as follows:


1. Fat – soluble vitamins

The four fat – soluble vitamins – vitamins A, D, E and K are often present in the fat portion of foods, they are not easily lost from foods or destroyed by exposure to water, heat, air, or light.


Vitamin A (retinol and beta – carotene)

Vitamin A and carotene can be obtained from either animal or vegetable sources. The animal form is divided between retinol and dehydroretinol whereas the vegetable carotene can be split into four very potent groups– alpha– carotene, beta–carotene, gamma carotene and crypto– carotene.


Vitamin A has a variety of functions in the body. It is required for the synthesis of rhodopsin and other light – receptor pigments in the eye and thus is essential for vision. Vitamin A is needed for normal growth and development to occur in the body, including the formation of bone and cartilage.

Healthy epithelial or skin cells, which line surfaces inside and outside the body, require vitamin A. Vitamin A plays a role in reproduction, metabolism, and immune system function also.

Digestion and absorption

Retinol esters in food are hydrolyzed by pancreatic and intestinal enzymes to form free retinol. After absorption, the retinol, is reesterified and transported to blood.

Carotenes are split in the intestines to form retinaldehyde, which is then reduced to

Table 8: A summary of the fat soluble vitamins

retinol. Some carotene may be absorbed intact and later converted to vitamin ‘A’ in the liver or kidney. Bile is necessary for the absorption of vitamin A and carotene. Vitamin E in the intestinal tract prevents oxidation of the vitamin. Mineral oil hinders absorption since it dissolves the vitamin but is not absorbed.

Food sources

Liver, milk, egg – yolk, carrots, dark green leafy vegetables and yellow fruits are high in vitamin A or beta – carotene.


A diet deficient in vitamin A for several months may lead to night blindness and flaking skin.

A long – term vitamin A deficiency leads Xerophthalmia, major symptom of which is dry, hard cornea. If this condition is left untreated, damage to the cornea progresses, leading to a softening of the cornea and eventually total blindness.

Vitamin A deficiency also affects the skin, causing it to become dry and rough.

If xerophthalmia and the underlying vitamin A deficiency are treated at an early stage, blindness can be prevented.


Vitamin D (Calciferol)

The human body can produce vitamin D from cholesterol present in the skin. This conversion depends on exposure of the skin to the ultraviolet rays in sunlight and yields

inactive pro-vitamin D. Both inactive vitamin D formed in the skin and vitamin D absorbed from dietary sources are transported through the bloodstream to the liver, where they are stored.


·  Vitamin D helps with the absorption, transport and use of calcium.

·  Vitamin D assists in bone growth and the integrity of bone and promotes strong teeth.

·  It also helps to regulate the amount of phosphorus in the body as well as assisting in a healthy heart and nervous system.

Food sources

Vitamin D is present in fatty fish like kipper, sardines, salmon, tuna and mackerel, liver, egg yolk and butter. Smaller amounts are also present in dark leafy vegetables.


Dietary vitamin D is absorbed along with dietary fats in the small intestines and transported to the lymph system. Bile is essential for the absorption of this vitamin Excess vitamin is stored in the body.


Vitamin D deficiency affects the mineralization of bones and teeth.

-Rickets, osteomalacia


Vitamin E (Tocopherol)

Vitamin E is an essential, fat – soluble vitamin that includes eight naturally occurring compounds in two classes designated as tocopherols and tocotrienols.

Vitamin E is an effective chain – breaking, lipid – soluble antioxidant in biological membranes, and aids in membrane stability.


·  Vitamin E is a powerful antioxidant.

·  Antioxidant capability helps to prevent degenerative diseases.

·  Vitamin E is also useful in preventing blood clots forming and promotes fertility.

·  An increase in stamina and endurance is also attributed to vitamin E.

·  Vitamin E is also used to great effect for skin treatments.

Deficiency of vitamin E

Deficiency of vitamin E is a not common, and the symptoms not very clear cut, but may include fatigue, inflamed varicose veins, slow wound healing, premature ageing and sub – fertility.


Vitamin K

Vitamin K can be produced in the intestines and this function is improved with the presence of cultured milk, like yogurt, in the diet.


·  The major function of vitamin K is to promote coagulation of blood after injury, thereby preventing haemorrhage.

·  Vitamin K is necessary for the synthesis of prothrombin, an inactive form of thrombin.

·  It is involved in the formation of prothrombin.

It is also involved in bone formation and repair.

Food Source

The best dietary sources of this vitamin are green leafy vegetables, cheese and liver.


Increased tendency to haemorrhage defective blood clotting

Table: 9 Water soluble vitamins

2. Water – soluble vitamins

Water – soluble vitamins are essential of health, and each one has its own function in the body and due to its solubility in water. It is normally easily lost in urine. The water soluble vitamins include vitamin C and 8 B complex vitamins – thiamine, riboflavin, niacin, pyridoxine, folate, cyanocobalamin, biotin and pantothenic acid. Most of these are unstable and thus easily destroyed by exposure to water, heat, air or light.


Vitamin C

Many fruits and vegetables are rich in vitamin C, also known as ascorbic acid. To ensure optimal physiological functioning and to prevent subclinical deficiencies, a person needs to consume a good source of vitamin C every day because the body normally stores only small amounts of Vitamin C.


·  Vitamin C is required in the synthesis of collagen in connective tissue, steroid hormones, carnitine, etc.

·  Vitamin C is required for the conversion of cholesterol to bile acids.

·  It enhances iron bioavailability.

·  Ascorbic acid is a great antioxidant and helps to protect the body against pollutants.

·  Ascorbic acid also promotes healthy cell development.

·  Vitamin C is essential for the formation and maintenance of intercellular cement substances such as bone matrix, cartilage dentine, collagen, connective tissue, etc.

·  Vitamin C is needed for healthy gums and to protect against infection.

Food sources

Good sources of vitamin C are green leafy vegetables, berries, citrus fruits, guavas, tomatoes, melons, papayas, etc.


In infants and children, vitamin C deficiency results in defective bone formation leading to retardation of growth.


B – complex vitamins

The eight B – complex vitamins include thiamine (B1), riboflavin (B2), niacin (B3), pyridoxine (B6), cyanocobalamin (B12), folic acid, biotin (B7), and pantothenic acid. The B vitamins are easily lost in cooking water because they are water soluble. With the exception of niacin, all other B vitamins lose some activity when exposed to heat, oxygen, light, or alkaline conditions.

Thiamine (Vitamin B1)

Thiamine also called B1 is used in many different body functions and deficiencies may have far reaching effects on the body, yet very little of this vitamin is stored in the body and depletion of this vitamin can happen within 14 days. Thiamine is integrally involved as a coenzyme in the catabolism of carbohydrates to yield energy.


·  It is also required for the health of the nervous system.

·  It is used in the manufacture of hydrochloric acid, and therefore plays a part in digestion.

·  In children it is required for good appetite and proper growth.

Food sources

Sunflower seeds, peanuts, wheat bran, beet liver, pork, seafood, egg – yolk, beans whole grains and yeast contain good amounts of thiamine.


Beriberi occurs in two forms, wet beriberi and dry beriberi, whose prominent symptoms differ.

Riboflavin – (Vitamin B2)

Riboflavin is another B – complex vitamin involved as a coenzyme in the metabolism of carbohydrates, as well as of fats and proteins. The adult RDA for riboflavin has been established at a minimum of 1.2 milligrams per day.


·  It is required by the body to use oxygen and the metabolism of amino acids, fatty acids, and carbohydrates.

·  It is a used for red blood cell formation, antibody production, cell respiration, and growth.

·  It may be helpful in the prevention and treatment of cataracts.

Food sources

Organ meats, nuts, cheese, eggs, milk and lean meat are best sources of riboflavin. It is also available in good quantities in green leafy vegetables, fish, legumes, whole grains, and yogurt.


A dietary deficiency of riboflavin leads to ariboflavinosis.

Niacin (B3)

Niacin also called nicotinic acid or niacin amide and can be manufactured by body. Niacin is derived from two compounds – nicotinic acid and niacin amide.


·  Niacin functions as a coenzyme in nearly all the metabolic pathways yielding energy from carbohydrates, fats, proteins, and alcohol.

·  Niacin also plays a role in tissue respiration.

·  It is involved in the synthesis and breakdown of fats, and helps to maintain healthy skin.

Food sources

Liver, lean meat, fish, nuts, cereals, legumes, asparagus, milk, green leafy vegetables and fish. A cup of coffee also provides 3 milligrams of niacin.


A deficiency of niacin is known as pellagra, which means rough skin (from the Italian words pelle for skin and Agra for rough).

Pyridoxine (Vitamin B6)

Pyridoxine is part of the B group vitamins and is water – soluble and is required for both mental and physical health.


Pyridoxine is required for the balancing of hormonal changes in women.

·  It is essential for the metabolism and proteins, fats and carbohydrates.

·  It assists in the maintenance of serum level of sodium and potassium

·  It helps to promote red blood cell production.

·  It is linked to cancer immunity and fights the formation of the toxic chemical homocysteine.

Food sources

Good sources to obtain pyridoxine are brewer’s yeast, egg, chicken, carrot, fish, liver, kidney, pea, wheat germ and walnuts. Roots and tubers, cabbage, legumes, molasses, whole grains, etc., contain moderate amount of this vitamin.


Irritability, nervousness, insomnia, anemia, general weakness, skin changes such as dermatitis.

Folic acid (Vitamin B9) – folic acid, folacin, folate

Folic acid is also referred to as folacin or folate. Its chemical name is pteroylglutamic acid. This vitamin can be produced by the body and be stored in the liver.


·  Folic acid is required for DNA synthesis and cell growth and is important for red blood cell formation, energy production as well as the forming of amino acids.

·  Folic acid is essential for synthesizing heme, the iron containing substance in hemoglobin, crucial for oxygen transport.

·  Folic acid is very important in the development of the nervous system of a developing fetus.

Food sources

Fresh green vegetable such as spinach and broccoli contains folic acid. It is also found in fruit, starchy vegetables, beans, whole grains, liver, kidney, egg, yeast etc.


A deficiency of folate can lead to macrocytic, megaloblastic anemia, diarrhea, fatigue, depression, and mental confusion.

Cyanocobalamin (Vitamin B12)

Cyanocobalamin also known as cobalamin is referred to as the energy vitamin. It is a very widely researched vitamin, and used in supplementation to a very large degree.


·  Cobalamin is required in the metabolism of fats, proteins and carbohydrates.

·  It is needed in the manufacture of red blood cells and the maintenance of red blood cells.

·  It stimulates appetite and Promotes growth.

Food sources

Liver, organ meat, muscle meat, shellfish, egg, cheese and fish are rich sources of this vitamin. It can be manufactured in the body. Milk contains vitamin B 12 however processing of milk may destroy the vitamin.


Vitamin B12 deficiency results in macrocytic, megaloblastic anemia (pernicious anemia) similar to that occurring with folate deficiency.

Biotin (Vitamin B7)

Biotin is also referred to as anti – egg white injury factor.

Biotin present in foods in not affected by exposure to light. Biotin is also produced by bacteria in the intestine.


Biotin is involved in carbohydrate and lipid metabolism.

·  Biotin is also indicated for healthy hair and skin, healthy sweat glands, nerve tissue, and bone marrow.

·  Biotin is also helps in maintaining a steady blood sugar level.

Food sources

Biotin is widely distributed in both animal and plant foods. Liver, kidney, egg, yolk, milk, tomatoes are rich sources.


Dietary deficiency of biotin is rare. Symptoms of biotin deficiency include lack of appetite, nausea, an enlarged tongue, mental depression, pallor, loss of hair.

Pantothenic acid (vitamin B6)

Pantothenic acid referred to as the “anti – stress vitamin” is part of the B group vitamins. This vitamin can be produced in the body by the intestinal flora.


·  Pantothenic acid plays an important role in the secretion of hormones, such as cortisone because of the role it plays in supporting the adrenal gland.

·  Pantothenic acid is also used in the release of energy as well as the metabolism of fat, protein and carbohydrates.

·  It is used in the synthesis of lipids, neurotransmitters and haemoglobin.

Food sources

Beef, brewer’s yeast, egg, fresh vegetables, kidney, legumes, liver, mushrooms, nuts, pork, royal jelly, saltwater fish, torula yeast, whole rye flour, and whole wheat contain this vitamin.


Symptoms of a pantothenic acid deficiency though rare, may occur in severely malnourished individuals and include fatigue, irritability, low blood pressure upon standing, lack of appetite, constipation, and tingling and numbness in both the feet and hands.


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