Vitamins are defined as organic compound, which is required in very little amounts for essential metabolic reactions in any living organisms. The term vitamin should not be confused with dietary minerals, essential amino acids or fatty acids. In other words, vitamins are bio-molecules, which act both as substrates and catalysts in bodily chemical reactions.

In olden days, the vitamins were obtained only through food intake but now using the latest technology and researches, vitamins can be produced as commodity chemicals. These are now widely available as pills with the lowest cost that anyone can afford across the world. Essential vitamins are also distributed by governments in their primary health centers in the interest of public health.

For humans, vitamins are divided into two major categories; water soluble that dissolve easily in water and fat soluble, which are absorbed through intestines with the help of fats or lipids. Each vitamin has its own function in the body and is used in multiple reactions.

There are thirteen vitamins in total. This includes four fat soluble vitamins namely A, D, E and K. Another group of vitamins is water soluble vitamins which contains nine water-soluble vitamins namely eight vitamin B and vitamin C.

Vitamins are very important for the normal growth and development of living organism. These vitamins facilitate the chemical reactions within the body. Almost all the enzymes, hormones and bodily secretions are related with vitamins one or the other way. Proper nourishment with vitamins will build body's immunity and will keep body free from various diseases.

Some of the vitamins are produced by body itself and needed very less as outer supplements. For instance, vitamin D is synthesized in the skin with the help of natural sunlight that contains the ultraviolet rays. The gut flora produces the vitamin K and biotin that plays important role in clotting of the blood. Humans can also some vitamins from their precursors they eat as diet. An example for this is vitamin A, which is produced from beta carotene and niacin which is produced by amino acid tryptophan.

On the other hand, even a minor deficiency can cause permanent damage in the body. Human body doesn't store all of the vitamins and hence, they are to be supplied on daily basis. However, some vitamins can be stored in sufficient quantity in some organs. For instance, liver stores vitamin A, D and B12. The deficiency of vitamin A can cause blindness; vitamin B can cause beriberi, vitamin C can cause Scurvy and vitamin D can cause rickets. Other symptoms of the vitamin deficiency includes numbness in limbs, stomatitis and cracking of the lips.

Vitamins are to be supplied in proper dosage recommended by World Health Organization. Larger doses of vitamins can produce side effects and may result in more serious condition. The side effects include nausea, vomiting and diarrhea. Vitamin supplements rarely produce an allergy to human beings because physicians and scientists carefully do the clinical trials and maintain the accuracy in calculating the data on the supplements.