Vitamins are known as organic compound which is used as a nutrient in small amounts in many organisms. The word vitmain emerged from two words that is ‘vital’ and ‘mineral’ . In the same way a compound is called vitamin when the synthesiezed process is done insufficiently in organisms and as a result it is obtained from one’s diet.  So the usage of vitamins depend on both circumstances and on the specific organism like ascorbic acid acts as vitamin C in few animals but are not applicable in certain animals.  In the same way vitamin d and k shows their prescence in human diet depend on the circumstances.  One should understand that the word vitamin doesn’t mean it has everything required by a body but it contains few of them such as  dietary minerals, essential fatty acids, and essential amino acids etc.  One should have information that vitamins are used on the basis of one’s biological and chemical activity and not on one’s structure. Certain vitamins are inter-converted in the body in certain cases.
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rnVitamins  plays an important role in the functioning of human body because of its diverse nature of biochemical functions such as hormones, antioxidants, mediators in cell signalling, helping in regulating the cells of the body, and tissue growth and differentiation etc. Most of the vitamins works as precursors for many enzymes cofactor bio-molicules which acts as catalysts and substrates in metabolism processing in the body. When playing as the role of catalyst vitamins are strained to be like enzymes and termed as prosthetic groups.  It also act as coenzymes for forwarding chemical groups among enzymes.  
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rnIn war times vitamins are given indirectly to soldiers in the form of white rice, meat,fish,barley, and beans. So now should readmore about vitamins to take more advantages of it. In older times disease which used to effect soldiers during war they were used to serve unpolished rice and chicken to prevent from dying as it was highly rich in proteins and vitamins. Now lots of people take vitamins in various forms such as liquid , solid and powder as per one’s need and usages.