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Vitamins

Drug class
B vitamin supplement tablets.jpg
A bottle of high potency B-complex vitamin supplement pills.
Pronunciation /ˈvtəmənis/

A vitamin is an organic compound and a vital nutrient that an organism requires in limited amounts. An organic chemical compound (or related set of compounds) is called a vitamin when the organism cannot synthesize the compound in sufficient quantities, and it must be obtained through the diet; thus, the term "vitamin" is conditional upon the circumstances and the particular organism. For example, ascorbic acid (one form of vitamin C) is a vitamin for humans, but not for most other animal organisms. Supplementation is important for the treatment of certain health problems, but there is little evidence of nutritional benefit when used by otherwise healthy people.

By convention the term vitamin includes neither other essential nutrients, such as dietary minerals, essential fatty acids, or essential amino acids (which are needed in greater amounts than vitamins) nor the great number of other nutrients that promote health, and are required less often to maintain the health of the organism. Thirteen vitamins are universally recognized at present. Vitamins are classified by their biological and chemical activity, not their structure. Thus, each "vitamin" refers to a number of vitamer compounds that all show the biological activity associated with a particular vitamin. Such a set of chemicals is grouped under an alphabetized vitamin "generic descriptor" title, such as "vitamin A", which includes the compounds retinal, retinol, and four known carotenoids. Vitamers by definition are convertible to the active form of the vitamin in the body, and are sometimes inter-convertible to one another, as well.

Vitamins have diverse biochemical functions. Some, such as vitamin D, have hormone-like functions as regulators of mineral metabolism, or regulators of cell and tissue growth and differentiation (such as some forms of vitamin A). Others function as antioxidants (e.g., vitamin E and sometimes vitamin C). The largest number of vitamins, the B complex vitamins, function as enzyme cofactors (coenzymes) or the precursors for them; coenzymes help enzymes in their work as catalysts in metabolism. In this role, vitamins may be tightly bound to enzymes as part of prosthetic groups: For example, biotin is part of enzymes involved in making fatty acids. They may also be less tightly bound to enzyme catalysts as coenzymes, detachable molecules that function to carry chemical groups or electrons between molecules. For example, folic acid may carry methyl, formyl, and methylene groups in the cell. Although these roles in assisting enzyme-substrate reactions are vitamins' best-known function, the other vitamin functions are equally important.


Vitamin generic
descriptor name
Vitamer chemical name(s) (list not complete) Solubility United States Recommended dietary allowances
(male, age 19–70)
Deficiency disease Upper Intake Level
(UL/day)
Overdose disease Food sources
Vitamin A Retinol, retinal, and
four carotenoids
including beta carotene
Fat 900 µg Night blindness, hyperkeratosis, and keratomalacia 3,000 µg Hypervitaminosis A Liver, orange, ripe yellow fruits, leafy vegetables, carrots, pumpkin, squash, spinach, fish, soya milk, milk
Vitamin B1 Thiamine Water 1.2 mg Beriberi, Wernicke-Korsakoff syndrome N/D Drowsiness or muscle relaxation with large doses. Pork, oatmeal, brown rice, vegetables, potatoes, liver, eggs
Vitamin B2 Riboflavin Water 1.3 mg Ariboflavinosis, glossitis, angular stomatitis N/D Dairy products, bananas, popcorn, green beans, asparagus
Vitamin B3 Niacin, niacinamide Water 16.0 mg Pellagra 35.0 mg Liver damage (doses > 2g/day) and other problems Meat, fish, eggs, many vegetables, mushrooms, tree nuts
Vitamin B5 Pantothenic acid Water 5.0 mg Paresthesia N/D Diarrhea; possibly nausea and heartburn. Meat, broccoli, avocados
Vitamin B6 Pyridoxine, pyridoxamine, pyridoxal Water 1.3–1.7 mg Anemiaperipheral neuropathy 100 mg Impairment of proprioception, nerve damage (doses > 100 mg/day) Meat, vegetables, tree nuts, bananas
Vitamin B7 Biotin Water 30.0 µg Dermatitis, enteritis N/D Raw egg yolk, liver, peanuts, leafy green vegetables
Vitamin B9 Folic acid, folinic acid Water 400 µg Megaloblastic anemia and deficiency during pregnancy is associated with birth defects, such as neural tube defects 1,000 µg May mask symptoms of vitamin B12 deficiency; other effects. Leafy vegetables, pasta, bread, cereal, liver
Vitamin B12 Cyanocobalamin, hydroxocobalamin, methylcobalamin Water 2.4 µg Megaloblastic anemia N/D Acne-like rash [causality is not conclusively established]. Meat, poultry, fish, eggs, milk
Vitamin C Ascorbic acid Water 90.0 mg Scurvy 2,000 mg Vitamin C megadosage Many fruits and vegetables, liver
Vitamin D Cholecalciferol (D3), Ergocalciferol (D2) Fat 10 µg Rickets and osteomalacia 50 µg Hypervitaminosis D Fish, eggs, liver, mushrooms
Vitamin E , Fat 15.0 mg Deficiency is very rare; sterility in males and abortions in females, mild hemolytic anemia in newborn infants 1,000 mg Increased congestive heart failure seen in one large randomized study. Many fruits and vegetables, nuts and seeds
Vitamin K phylloquinone, menaquinones Fat 120 µg Bleeding diathesis N/D Increases coagulation in patients taking warfarin. Leafy green vegetables such as spinach, egg yolks, liver
Vitamin Soluble in Water Exposure to Air Exposure to Light Exposure to Heat
Vitamin A no partially partially relatively stable
Vitamin C very unstable yes yes yes
Vitamin D no no no no
Vitamin E no yes yes no
Vitamin K no no yes no
Thiamine (B1) highly no  ? > 100 °C
Riboflavin (B2) slightly no in solution no
Niacin (B3) yes no no no
Pantothenic Acid (B5) quite stable  ? no yes
Vitamin B6 yes  ? yes  ?
Biotin (B7) somewhat  ?  ? no
Folic Acid (B9) yes  ? when dry at high temp
Vitamin B12 yes  ? yes no
The discovery dates of the vitamins and their sources
Year of discovery Vitamin Food source
1913 Vitamin A (Retinol) Cod liver oil
1910 Vitamin B1 (Thiamine) Rice bran
1920 Vitamin C (Ascorbic acid) Citrus, most fresh foods
1920 Vitamin D (Calciferol) Cod liver oil
1920 Vitamin B2 (Riboflavin) Meat, dairy products, eggs
1922 (Vitamin E) () Wheat germ oil,
unrefined vegetable oils
1926 Vitamin B12 (Cobalamins) Liver, eggs, animal products
1929 Vitamin K1 (Phylloquinone) Leaf vegetables
1931 Vitamin B5 (Pantothenic acid) Meat, whole grains,
in many foods
1931 Vitamin B7 (Biotin) Meat, dairy products, eggs
1934 Vitamin B6 (Pyridoxine) Meat, dairy products
1936 Vitamin B3 (Niacin) Meat, grains
1941 Vitamin B9 (Folic acid) Leaf vegetables
Nomenclature of reclassified vitamins
Previous name Chemical name Reason for name change
Vitamin B4 Adenine DNA metabolite; synthesized in body
Vitamin B8 Adenylic acid DNA metabolite; synthesized in body
Vitamin F Essential fatty acids Needed in large quantities (does
not fit the definition of a vitamin).
Vitamin G Riboflavin Reclassified as Vitamin B2
Vitamin H Biotin Reclassified as Vitamin B7
Vitamin J Catechol, Flavin Catechol nonessential; flavin reclassified as Vitamin B2
Vitamin L1 Anthranilic acid Non essential
Vitamin L2 Adenylthiomethylpentose RNA metabolite; synthesized in body
Vitamin M Folic acid Reclassified as Vitamin B9
Vitamin O Carnitine Synthesized in body
Vitamin P Flavonoids No longer classified as a vitamin
Vitamin PP Niacin Reclassified as Vitamin B3
Vitamin S Salicylic acid Proposed inclusion of salicylate as an essential micronutrient
Vitamin U S-Methylmethionine Protein metabolite; synthesized in body

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