What are Vitamins?

Vitamins are organic compounds or essential micronutrients that are found in various types of foods and are necessary for the growth and good health of animals including humans. Vitamin is an essential dietary factor and is only necessary for very small amounts.

Vitamins (A, D, E, B vitamins and vitamin C) Sources with Definition, Classification and Examples

In addition to oxygen, water, proteins, fats, carbohydrates, and certain inorganic salts, vitamin is also necessary for our life. It cannot be produced by our body. Hence, we need to intake foods or supplements that contain various vitamins. However, vitamin D may be supplied in food or may be produced in the skin by irradiation of ultraviolet-visible light from the sun.

Most vitamins do not contain a single molecule but contain a group of related molecules. Therefore, they are called vitamers. For example, eight vitamers are found in vitamin E, four tocopherols, and four tocotrienols. In B6, six related molecules are found.


Vitamins have been arbitrarily classified into two groups, fat-soluble or water-soluble. Four are fat-soluble (A, D, E, and K) and nine are water-soluble (8 B vitamins and vitamin C). Among these, 13 are found in humans.

Fat-Soluble Vitamins

Fat-soluble vitamin is an essential micronutrients soluble in fat and found in many plant and animal foods and dietary supplements. They are absorbed along with fats in our diet and are stored in our body’s fatty tissue and the liver. These may include,

  1. Vitamin A (Retinol)
  2. D (Cholecalciferol, Ergocalciferol)
  3. E (Tocopherols, Tocotrienols)
  4. K (Phylloquinone, Menaquinones)

Water Soluble Vitamin

The nine water-soluble vitamins are found in the human diet. These may include,

  1. Vitamin B1 (thiamine)
  2. Vitamin B2 (riboflavin)
  3. Vitamin B3 (niacin)
  4. Vitamin B5 (pantothenic acid)
  5. Vitamin B6 (pyridoxine, pyridoxamine, pyridoxal)
  6. Vitamin B7 (biotin)
  7. Vitamin B9 (folates, folic acid)
  8. Vitamin B12 (cyanocobalamin, hydroxocobalamin, methylcobalamin, adenosylcobalamin)
  9. Vitamin C (ascorbic acid)

Uses, sources, biological functions, supplements, side effects, and many more about various vitamins are given below the individual topics in this category,

Vitamin C (ascorbic acid) sources in dietary fruits, citrus fruits and vegetables with supplement, uses, deficiency

Vitamin C

What is Vitamin C? Vitamin C (ascorbic acid and ascorbate) is a water-soluble vitamin found in many fruits mainly citrus fruit and vegetable sources. Many...
Vitamin A (retinol, retinal, retinoic acid and beta carotene) with uses, benefits, sources, supplements, deficiency of Vitamin A

Vitamin A

What is vitamin A? Vitamin A referred to a group of organic compounds that includes retinol, retinal, retinoic acid, and several provitamins A carotenoids like...
Pyridoxal 5'-phosphate Active form of Vitamin B6 with Uses, Supplements, Functions and Benefit

Vitamin B6

What is vitamin B6? Vitamin B6 is a water-soluble vitamin or essential nutrient found naturally in various foods and added to foods and supplements. Pyridoxal...
Vitamin B12 also known as cobalamin structure with deficiency, natural food sources, functions

Vitamin B12

What is vitamin B12? Vitamin B12, also known as cobalamin, is a water soluble vitamin containing cobalt in its structure. Like folic acid, vitamin B12 deficiency...
Thiamine or vitamin B1 deficiency causes, sources or foods rich in thiamine supplement, functions, uses, structure


What is thiamine? Thiamine or vitamin B1 is one member of the water soluble vitamin B complex found naturally in some foods or sold as...
Riboflavin structure and formula, sources, functions, deficiency and benefits of vitamin B2 in health


What is riboflavin? Riboflavin, also known as vitamin B2 is a water soluble vitamin that occurs widely in nature and necessary for growth and health....
Folic acid structure and uses of folate or vitamin B9 in anemia or benefit of folic acid in pregnancy

Folic acid (Folate)

What is folic acid? Folic acid and folate are the forms of vitamin B9 that we used for the treatment of certain types of iron...