Vitamins are used as a nutrient in very small amounts by the body. A vitamin cannot be synthesized in sufficient quantity by the body and, therefore, has to be consumed through the diet.
However, some vitamins are changed in the human body to the active ingredient. Also, some can be partially synthesized by or in the human body. Vitamin D, for example, is made by the skin under the influence of UV light. Other essential nutrients such as minerals or amino acids are not considered vitamins.
Vitamins are classified by their biological and chemical activity, not by their molecular structure. Therefore, a vitamin can refer to several ingredients that have the same activity but vary in their structure. Vitamin A, for example, contains carotenoids, retinal, and retinol.
Besides for functionality, they can also be classified by fat- or water-solubility. Vitamins A, D, E, and K are fat-soluble, vitamins B and C are water-soluble. The fat-soluble vitamins can be stored in the body and daily consumption is not always necessary. Water-soluble vitamins are easily excreted from the body which makes regular daily consumption important.
Vitamins have a broad range of functions, such as antioxidants (e.g. vitamin E) or hormones (e.g. vitamin D). The largest group of vitamins, the vitamin B complex, function as precursors for enzyme cofactors. When acting as part of a catalyst, vitamins are bound to enzymes. For example, biotin is part of enzymes that create fatty acids. They also act as coenzymes and carry chemical groups between enzymes. For example, folic acid transports various forms of carbon groups – methyl, formyl, and methylene – into cells.
The function to assist enzyme reactions are the best-known role but the other vitamin functions are equally important. Most vitamins have more than one function.
Until the 1900’s, vitamins were consumed only by food intake, and changes in diet would affect vitamin consumption. Since several decades, vitamins have been commercially produced and, therefore, created the possibility for supplementation of diets either by vitamin supplements or fortification of regular foods.
Table: Overview of vitamins
|Vitamin||Chemical name(s) (list not complete)||Solubility||Recommended dietary allowances
(male, age 19–70)
|Vitamin A||carotenoids, retinol, retinoids||Fat||900 µg||Night-blindness and Keratomalacia|
|Vitamin B1||Thiamine||Water||1.2 mg||Beriberi, Wernicke-Korsakoff syndrome|
|Vitamin B2||Riboflavin||Water||1.3 mg||Ariboflavinosis|
|Vitamin B3||Niacin, niacinamide||–||–||–|
|Vitamin B5||Pantothenic acid||Water||5.0 mg||Paresthesia|
|Vitamin B6||Pyridoxamine, Pyridoxal, Pyridoxine||–||–||–|
|Vitamin B7||Biotin||Water||30.0 µg||Dermatitis, enteritis|
|Vitamin B9||Folic acid, Folinic acid||Water||400 µg||Deficiency during pregnancy is associated with birth defects, such as neural tube defects|
|Vitamin B12||Cyanocobalamin, Hydroxycobalamin, Methylcobalamin||Water||2.4 µg||Megaloblastic anemia|
|Vitamin C||Ascorbic acid||Water||90.0 mg||Scurvy|
|Vitamin D||Cholecalciferol, Ergocalciferol||Fat||5.0 µg-10 µg||Rickets and Osteomalacia|
|Vitamin E||Tocopherols, Tocotrienols||Fat||15.0 mg||Deficiency is very rare; mild hemolytic anemia in newborn infants.|
|Vitamin K||Menaquinones, Phylloquinone||Fat||120 µg||Bleeding diathesis|
Intake of excessive quantities can cause vitamin poisoning, often due to overdose of Vitamin A and Vitamin D. However, the most common poisoning with multi-nutrient supplement pills does not involve a vitamin but is rather due to the mineral iron. Due to toxicity, most common vitamins have recommended upper daily intake amounts.
Governmental regulation of vitamin supplements
Most countries place dietary supplements in a special category under the general umbrella of foods, not drugs. The manufacturer is responsible for making sure that its dietary supplement products are safe.
Click here to find suppliers of vitamins.
To read more about vitamins: Wikipedia