A vitamin is an organic compound required in tiny amounts for essential metabolic reactions in a living organism.Vitamins are bio-molecules that act as catalysts and substrates in chemical reactions. When acting as a catalyst, vitamins are bound to enzymes and are called cofactors. For example, vitamin K is part of the proteases involved in blood clotting. Vitamins also act as coenzymes to carry chemical groups between enzymes. For example, folic acid carries various forms of carbon group – methyl, formyl and methylene- in the cell.
Vitamins are classified as either water-soluble, meaning that they dissolve easily in water, or fat-soluble, and are absorbed through the intestinal tract with the help of lipids. Each vitamin is typically used in multiple reactions and, therefore, most have multiple functions.
In humans there are 13 vitamins: 4 fat-soluble (A, D, E and K) and 9 water-soluble (8 B vitamins and vitamin C).
Mostly vitamins are obtained with food, but a few are obtained by other means. For example, microorganisms in the intestine - commonly known as “gut flora” - produce vitamin K and biotin, while one form of vitamin D is synthesized in the skin with the help of natural ultraviolet in sunlight. Humans can produce some vitamins from precursors they consume. Examples include vitamin A, produced from beta carotene, and niacin, from the amino acid tryptophan
| Vitamin name |
Chemical name |
Solubility |
Recommended dietary allowances
(male, age 19–70) |
Deficiency disease |
Upper Intake Level
(UL/day) |
|
| Vitamin A |
Retinoids
(retinol, retinoids
and carotenoids) |
Fat |
900 µg |
Night-blindness and
Keratomalacia |
3,000 µg |
|
| Vitamin B1 |
Thiamine |
Water |
1.2 mg |
Beriberi |
N/D |
|
| Vitamin B2 |
Riboflavin |
Water |
1.3 mg |
Ariboflavinosis |
N/D |
|
| Vitamin B3 |
Niacin |
Water |
16.0 mg |
Pellagra |
35.0 mg |
|
| Vitamin B5 |
Pantothenic acid |
Water |
5.0 mg |
Paresthesia |
N/D |
|
| Vitamin B6 |
Pyridoxine |
Water |
1.3-1.7 mg |
Anemia |
100 mg |
|
| Vitamin B7 |
Biotin |
Water |
30.0 µg |
Dermatitis |
N/D |
|
| Vitamin B9 |
Folic acid |
Water |
400 µg |
Deficiency during pregnancy is associated with birth defects, such as neural tube defects |
1,000 µg |
|
| Vitamin B12 |
Cyanocobalamin |
Water |
2.4 µg |
Megaloblastic anaemia |
N/D |
|
| Vitamin C |
Ascorbic acid |
Water |
90.0 mg |
Scurvy |
2,000 mg |
|
| Vitamin D |
Ergocalciferol and
Cholecalciferol |
Fat |
5.0 µg-10 µg |
Rickets and Osteomalacia |
50 µg |
|
| Vitamin E |
Tocopherol and
Tocotrienol |
Fat |
15.0 mg |
Deficiency is very rare; mild hemolytic anemia in newborn infants. |
1,000 mg |
|
| Vitamin K |
Naphthoquinone |
Fat |
120 µg |
Bleeding diathesis |
N/D |
|