VITAMINS DEFINITION & TYPES

 VITAMINS DEFINITION & TYPES

Definition of vitamins

Vitamins may be defined as organic compounds occurring in small quantities in different natural foods and necessary for the growth and maintenance of good health in human beings and in experimental animals. Vitamins are essential food factors, which are required for the proper utilization of the proximate principles of food like carbohydrates, lipids, and proteins. The Discovery of vitamins started from observation of deficiency manifestations, e.g. scurvy, rickets, beriberi, etc. The vitamin theory was suggested by Hopkins in 1912 (Nobel Prize, 1929). The term "vitamin" was coined from the words vital + amine, since the earlier identified ones had amino groups. Later work showed that most of them did not contain amino groups, so the last letter ‘e' was dropped in the modern term of the vitamin. Although vitamins are important nutritionally, their role has been over-emphasized in clinical practice. They are useful to correct deficiencies. But taking higher doses of vitamins will not boost health. All the vitamins are usually available in an ordinary Indian diet.

Types

The vitamins are mainly classified into two: 1. The fat-soluble vitamins are A, D, E, and K 2. Water-soluble vitamins are named as B complex and C. The major differences between these two groups of vitamins in general, deficiency of vitamins may occur due to: a. reduced intake b. impaired absorption c. impaired metabolism d. additional requirements e. increased losses.

Fat-soluble vitamins

The four vitamins, namely vitamin A, D, E, and K are known as fat or lipid-soluble. Their availability in the diet, absorption, and transport are associated with fat. They are soluble in fats and oils and also fat solvents (alcohol, acetone, etc.). Fat-soluble vitamins can be stored in the liver and adipose tissue. They are not readily excreted in the urine. Excess consumption of these vitamins (particularly A and D) leads to their accumulation and toxic effects. All the fat-soluble vitamins are isoprenoid compounds since they are made up of one or more of five carbon units namely isoprene units ( CH C.CH3 CH CH ). Fat-soluble vitamins perform diverse functions. Vitamin K has a specific coenzyme function.

Water-soluble vitamins

The water-soluble vitamins are a heterogeneous group of compounds since they differ chemically from each other. The only common character shared by them is their solubility in water. Most of these vitamins are readily excreted in urine and they are not toxic to the body. Water-soluble vitamins are not stored in the body in large quantities (except B12). For this reason, they must be continuously supplied in the diet. Generally, vitamin deficiencies are multiple rather than individual with overlapping symptoms. It is often difficult to pinpoint the exact biochemical basis for the symptoms. The water-soluble vitamins form coenzymes that participate in a variety of biochemical reactions, related to either energy generation or hematopoiesis. It may be due to this reason that the deficiency of vitamins results in several overlapping symptoms. The common symptoms of the deficiency of one or more vitamins involved in energy metabolism include dermatitis, glossitis (red and swollen tongue), cheilitis (rupture at the corners of lips), diarrhea, mental confusion, depression, and malaise. The deficiency of vitamins B1, B6, and B12 is more closely associated with neurological manifestations.

 Vitamers

The term vitamers represent the chemically similar substances that possess qualitatively similar vitamin activity. Some good examples of vitamers are given below Retinol, retinal and retinoic acid are vitamers of vitamin A. Pyridoxine, pyridoxal, and pyridoxamine are vitamers of vitamin B6.