IMPORTANT GK FOR SSC CGL

vitamins

ü  All living things, plant or animal, need vitamins ~ health, growth, and reproduction.

ü  Vitamins are not a source of calories and do not contribute significantly to body mass. 

ü  Humans uses vitamins as tools in processes that regulate chemical activities in the organism and that use basic food elements—carbohydrates, fats, and proteins—to form tissues and to produce energy.

ü  Vitamins can be used over and over, and only tiny amounts are needed to replace those that are lost. Nevertheless, most vitamins are essential in the diet because the body does not produce enough of them or, in many cases, does not produce them at all.

Daily Requirements

ü  With a few exceptions, the body is unable to make vitamins; they must be supplied in the daily diet or through supplements.

ü  One exception is vitamin D, which can be produced in the skin when the skin is exposed to sunlight.

ü  Another vitamin, vitamin K, is not made by the human body but is formed by microorganisms that normally flourish in the intestinal tract only when green, leafy vegetables and vegetable oils are ingested.

ü  The body's vitamin requirements are expressed in terms of recommended dietary allowances, or RDA. These allowances are the amount of essential nutrients that, if acquired daily, are considered to be sufficient to meet the known nutritional needs of most healthy persons.

ü  Two agencies of the United Nations—the Food and Agriculture Organization and the World Health Organization— develop RDA for different, worldwide population groups.

How Vitamins Work

In the body, proteins, carbohydrates, and fats combine with other substances to yield energy and build tissues. These chemical reactions are catalyzed, or accelerated, by enzymes produced from specific vitamins, and they take place in specific parts of the body.

The vitamins needed by humans are divided into two categories:

1.water-soluble vitamins (the B vitamins and vitamin C)

2.Fat-soluble vitamins (A, D, E, and K).

The water-soluble vitamins ~~absorbed by the intestine and carried by the circulatory system to the specific tissues where they will be put into use. The B vitamins ~~act as coenzymes, compounds that unite with a protein component called an apoenzyme to form an active enzyme.The enzyme then acts as a catalyst in the chemical reactions that transfer energy from the basic food elements to the body. It is not known whether vitamin C acts as a coenzyme.

When a person takes in more water-soluble vitamins than are needed,

v  small amounts ~~` stored in body tissue

v  excess ~~` excreted in urine.

Because water-soluble vitamins are not stored in the body in appreciable amounts, a daily supply is essential to prevent depletion.

Fat-soluble vitamins seem to have highly specialized functions. The intestine absorbs fat-soluble vitamins, and the lymph system carries these vitamins to the different parts of the body. Fat-soluble vitamins are involved in maintaining the structure of cell membranes. It is also believed that fat-soluble vitamins are responsible for the synthesis of certain enzymes.

The body can store larger amounts of fat-soluble vitamins than of water-soluble vitamins. The liver provides the chief storage tissue for vitamins A and D, while vitamin E is stored in body fat and to a lesser extent in reproductive organs. Relatively little vitamin K is stored. Excessive intake of fat-soluble vitamins, particularly vitamins A and D, can lead to toxic levels in the body.

Many vitamins work together to regulate several processes within the body. A lack of vitamins or a diet that does not provide adequate amounts of certain vitamins can upset the body's internal balance or block one or more metabolic reactions.

Sources of Vitamins

Vitamins, though they are available from a variety of sources, are unevenly distributed in natural sources. For example, some vitamins, such as vitamin D, are produced only by animals, whereas other vitamins are found only in plants. (For natural sources of vitamins, see table.) All vitamins can be synthesized, or produced commercially, from foods and other sources, and there is no evidence that natural vitamins are superior to those that are synthetically derived.

Some foods are fortified with vitamins—that is, vitamins that are not normally present in the food, or that have been removed during processing, are added to the food before it is sold. Milk, for example, is fortified with vitamin D, and vitamins that have been lost from flour during processing are often replaced.

Those likely to require such supplements include pregnant women, the elderly, and the chronically ill. Excessive intakes of supplemental vitamins should be avoided, however, because of the possibility of toxicity.

Kinds of Vitamins

Vitamin A

• ~also called retinol~ fat-soluble vitamin ~readily destroyed upon exposure to heat, light, or air.
• direct role in vision and is a component of a pigment present in the retina of the eye
• It is essential for the proper functioning of most body organs and also affects the functioning of the immune system.

Vitamin A deficiency ~various disorders: that most commonly involve the eye and the epithelial tissues—the skin and the mucous membranes lining the internal body surfaces.

early symptom of vitamin A deficiency~ is the development of night blindness

continued deficiency~ eventually results in loss of sight. If deficiency is prolonged, the skin may become dry and rough. Vitamin A deficiency may also result in defective bone and teeth formation.

Excessive intake of vitamin A causes a toxic condition. The symptoms may include nausea, coarsening and loss of hair, drying and scaling of the skin, bone pain, fatigue, and drowsiness. There may also be blurred vision and headache in adults, and growth failure, enlargement of the liver, and nervous irritability in children.

Vitamin B complex

• consists of several vitamins that are grouped together because of the loose similarities in their properties, distribution in natural sources, and physiological functions.
• All the B vitamins are soluble in water.
• Most of the B vitamins have been recognized as coenzymes ~essential in facilitating the metabolic processes of all forms of animal life.

The complex includes:

B₁ (thiamine), B₂ (riboflavin), niacin (nicotinic acid), B₆ (a group of related pyridines), B₁₂ (cyanocobalamin), folic acid, pantothenic acid, and biotin.

Vitamin B₁, or thiamine, helps the body convert carbohydrates into energy and helps in the metabolism of proteins and fats.

Vitamin B₁ deficiency :affects the functioning of gastrointestinal, cardiovascular, and peripheral nervous systems. Beriberi and Wernicke-Korsakoff syndrome (often seen in alcoholics) are the primary diseases related to thiamine deficiency. General symptoms of beriberi include loss of appetite and overall lassitude, digestive irregularities, and a feeling of numbness and weakness in the limbs and extremities.

Vitamin B₂, or riboflavin, is required to complete several reactions in the energy cycle. Reddening of the lips with cracks at the corners of the mouth, inflammation of the tongue, and a greasy, scaly inflammation of the skin are common symptoms of deficiency.

Niacin, or nicotinic acid, helps the metabolism of carbohydrates. Prolonged deprivation leads to pellagra, a disease characterized by skin lesions, gastrointestinal disturbance, and nervous symptoms.

A form of Vitamin B₆ is a coenzyme for several enzyme systems involved in the metabolism of proteins, carbohydrates, and fats. No human disease has been found to be caused by a deficiency of this vitamin. Chronic use of large doses of vitamin B₆ can create dependency and cause complications in the peripheral nervous system.

Vitamin B₁₂, or cyanocobalamin, is a complex crystalline compound that functions in all cells, but especially in those of the gastrointestinal tract, the nervous system, and the bone marrow. It is known to aid in the development of red blood cells in higher animals. Deficiency most commonly results in pernicious anemia.

Folic acid is necessary for the synthesis of nucleic acids and the formation of red blood cells. Folic-acid deficiency most commonly causes folic-acid-deficiency anemia. Symptoms include gastrointestinal problems, such as sore tongue, cracks at the corners of the mouth, diarrhea, and ulceration of the stomach and intestines. Large doses of folic acid can cause convulsions and other nervous-system problems.

Pantothenic acid promotes a large number of metabolic reactions essential for the growth and well- being of animals. Deficiency in experimental animals leads to growth failure, skin lesions, and graying of the hair. A dietary deficiency severe enough to lead to clear-cut disease has not been described in humans.

Biotin plays a role in metabolic processes that lead to the formation of fats and the utilization of carbon dioxide. Biotin deficiency results in anorexia, nausea, vomiting, inflammation of the tongue, pallor, depression, and dermatitis.

Vitamin C

• or ascorbic acid,
• is water-soluble and easily destroyed.  
• essential in wound healing and in the formation of collagen, a protein important in the formation of healthy skin, tendons, bones, and supportive tissues.
• Deficiency results in defective collagen formation and is marked by joint pains, irritability, growth retardation, anemia, shortness of breath, and increased susceptibility to infection.
• Scurvy is the classic disease related to deficiency. Symptoms peculiar to infantile scurvy include swelling of the lower extremities, pain upon flexing them, and bone lesions.
• Excessive ascorbic-acid intake can cause kidney stones, gastrointestinal disturbances, and red-blood-cell destruction.

Vitamin D

• is a fat-soluble compound
• essential for calcium metabolism in animals and therefore important for normal mineralization of bone and cartilage.
• Formation:The skin forms vitamin D when exposed to sunlight, but in some circumstances sunlight may lack sufficient amounts of ultraviolet rays to bring about adequate production of the vitamin.
• Deficiencies :cause many biochemical and physiological imbalances. If uncorrected, faulty mineralization of bones and teeth causes rickets in growing children and osteomalacia (progressive loss of calcium and phosphorus from the bones) in adults.
• Common early symptoms of rickets include restlessness, profuse sweating, lack of muscle tone in the limbs and abdomen, and delay in learning to sit, crawl, and walk. Rickets may produce such conditions as bowlegs and knock-knees. Deficiency may also cause osteoporosis, a bone condition characterized by an increased tendency of the bones to fracture.
• Large doses of vitamin D are toxic, and symptoms include weakness, loss of appetite, nausea, vomiting, diarrhea, excessive thirst, and weight loss.

Vitamin E

• is a fat-soluble compound.
• The metabolic roles of this vitamin are poorly understood. Its primary role appears to be as an inhibitor of oxidation processes in body tissues.
• Deficiency is rare but may impair neuromuscular function.
• serious toxicity large doses of vitamin E, adverse effects have been reported.

Vitamin K

• is fat-soluble
• essential for the synthesis of certain proteins necessary for the clotting of blood.
• Deficiency, though relatively uncommon, results in impaired clotting of the blood and internal bleeding.

Vitamin-like substances

• include a number of compounds that resemble vitamins in their activity but are normally synthesized in the human body in adequate amounts.
• They are often classified with the B vitamins because of similarities in function and distribution in foods. Their status as essential nutrients remains uncertain.
• Choline is found in all living cells and plays a role in nerve function and various metabolic processes.
• Myoinositol is a water-soluble compound; its significance in human nutrition is not established.
• Para-aminobenzoic acid is an integral part of folic acid but its role in human nutrition has not been documented.
• Carnitine has an essential role in the transport of fatty substances.
• Lipoic acid seems to have a coenzyme function similar to that of thiamine; however, because it is synthesized in the human liver and kidneys, it is not considered a vitamin.
• Bioflavinoids are a group of substances that affect the permeability of capillaries but do not normally have to be added to human diets.

Anti-vitamins

• Anti-vitamins are chemical compounds that inhibit the absorption or actions of vitamins.

• avidin is a protein in egg whites that inhibits the absorption of biotin.

• Pyrithiamine is similar to thiamine, vitamin B1, and inhibits the enzymes that use thiamine.