Introduction

All living things, plant or animal, need vitamins for health, growth, and reproduction. Yet vitamins are not a source of calories and do not contribute significantly to body mass. Organisms that use the basic food elements (carbohydrates, fats, and proteins) use vitamins in the processes that regulate chemical activities to form tissues and to produce energy.
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.
Thirteen different vitamins have been identified by nutritionists: A, eight B-complex vitamins, C, D, E, and K. Some substances, such as carnitine and choline, behave like vitamins but are made in adequate amounts in the human body.
Vitamins act primarily as catalysts in chemical reactions and without them we would be unable to utilise the other nutrients that we ingest.
They are play an important role in energy release, tissue building and for regulation of our metabolism.
Vitamins are divided into two categories, either fat-soluble or water-soluble.
Vitamins A, D, E and K are fat-soluble and are absorbed into the body bound to fats. Vitamin C and B complex are water-soluble and are absorbed by the body with the aid of water.

Further Reading : -

Daily Requirements and How Vitamins Work
Sources of vitamins and the Recommended Daily Allowances (RDA)
Types of vitamins - Vitamin A, Vitamin B Complex, Vitamin B1, or thiamine, Vitamin B2, Niacin, Vitamin B6, Vitamin B12, Folic acid, Pantothenic acid, Biotin, Vitamin C, Vitamin D, Vitamin E, Vitamin K