Vitamins can either be classified as water soluble, which means they dissolved easily in water or fat soluble, which means they are absorbed through the intestinal tract with the help of fats.
In general, an organism must obtain vitamins or their metabolic precursors from outside the body, most often from the organism's diet. Examples of vitamins that the human body can derive from precursors include vitamin A, which can be produced from beta carotene; niacin from the amino acid, tryptophan; and vitamin D through exposure of skin to ultraviolet light.
The term, vitamin, does not encompass other essential nutrients such as dietary minerals, essential fatty acids or essential amino acids, nor is it used for the large number of other nutrients that are merely health promoting, but not strictly essential.
The word vitamin was coined by the Polish biochemist Casimir Funk in 1912. Vita in Latin is life and the -amin suffix is short for amine; at the time it was thought that all vitamins were amines. Though this is now known to be incorrect, the name has stuck.
History
The value of eating certain foods to maintain health was recognized long before vitamins were identified. The ancient Egyptians knew that feeding a patient liver would help cure night blindness, now known to be caused by a Vitamin A deficiency. In 1747, the Scottish surgeon James Lind discovered that citrus foods helped prevent scurvy, a particularly deadly disease characterized by bleeding and severe pain. In 1753, Lind published his Treatise on the Scurvy.
In 1905, William Fletcher discovered that eating unpolished rice instead of polished helped prevent the disease beriberi. The following year, Frederick Hopkins postulated that foods contained "accessory factors"—in addition to proteins, carbohydrates, fats, etc.—that were necessary to the human body. When Casimir Funk isolated the water-soluble complex of micronutrients whose bioactivity Fletcher had identified, he proposed that it be named "Vitamine". The name soon became synonymous with Hopkins' "accessory factors", and by the time it was shown that not all vitamins were amines, the word was ubiquitous. In 1920, Jack Cecil Drummond proposed that the final "e" be dropped, to deemphasize the "amine" reference, after the discovery that Vitamin C had no amine component, and the name has been "vitamin" ever since.
Throughout the early 1900s, scientists were able to isolate and identify a number of vitamins by depriving animals of them. Initially, lipid from fish oil was used to cure rickets in rats, and the fat-soluble nutrient was called "antirachitic A". The irony here is that the first "vitamin" bioactivity ever isolated, which cured rickets, was initially called vitamine A, this bioactivity is now called vitamin D which is subject to the semantic debate that vitamin D is not truly a vitamin. What we now call "vitamin A" was identified in fish oil because it was inactivated by ultraviolet light. Most of what we now recognize as the water-soluble organic micronutrients were initially referred to as just one entity, "vitamin B".
Human vitamins
In humans, there are thirteen vitamins, divided into two groups, the four fat soluble vitamins (A, D, E and K) and the nine water soluble vitamins (eight B vitamins and vitamin C).
| Vitamin Name | Chemical Name | Solubility | Deficiency Disease | Overdose | Example Estimated Average Daily Requirements (M,19-30) |
|---|---|---|---|---|---|
| Vitamin A | Retinol | Fat | Night-blindness, Keratomalacia | 25,000 IUs | 620µg |
| Vitamin B1 | Thiamine | Water | Beriberi | n/a | 1mg |
| Vitamin B2 | Riboflavin | Water | Ariboflavinosis | n/a | 1.1mg |
| Vitamin B3 | Niacin | Water | Pellagra | 2,500 mg | 12mg |
| Vitamin B5 | Pantothenic acid | Water | Paresthesias | n/a | |
| Vitamin B6 | Pyridoxine | Water | n/a | 400 mg | 1.1 mg |
| Vitamin B7 | Biotin | Water | n/a | n/a | 30 µg |
| Vitamin B9 | Folic acid | Water | n/a | 1,000 µg | 320 µg |
| Vitamin B12 | Cyanocobalamin | Water | Pernicious anemia | n/a | 2 µg |
| Vitamin C | Ascorbic acid | Water | Scurvy | n/a | 75 mg |
| Vitamin D1 | Lamisterol | Fat | Rickets | 50,000 IUs | 2 µg for all Vitamin D |
| Vitamin D2 | Ergocalciferol | Fat | Rickets | See above. | 2 µg for all Vitamin D |
| Vitamin D3 | Calciferol | Fat | Rickets | See above. | 2 µg for all Vitamin D |
| Vitamin D4 | Dihydrotachysterol | Fat | Rickets | See above. | 2 µg for all Vitamin D |
| Vitamin D5 | 7-dehydrositosterol | Fat | Rickets | See above. | 2 µg for All Vitamin D |
| Vitamin E | Tocopherol | Fat | n/a | 50,000 IUs | 12 mg |
| Vitamin K | Naphthoquinone | Fat | n/a | n/a | 75 µg |
Some of the vitamins are known by other names in older literature. Vitamin B2 is also referred to as Vitamin G. Vitamin B7, or Biotin is also referred to as Vitamin H. Vitamin B9, or Folic Acid is also referred to as Vitamin M. Vitamin B3 is also referred to as Vitamin P. Many other essential dietary substances were originally called vitamins and are now classified differently.
Vitamin deficiency and excess
An organism can survive for some time without vitamins, although prolonged vitamin deficit results in a disease state, often painful and potentially deadly. Body stores for different vitamins can vary widely; an adult may be deficient in Vitamins A or B12 for a year or more before developing a deficiency condition, while Vitamin B1 stores may only last a couple of weeks.
Fat-soluble vitamins may be stored in the body and can cause toxicity when taken in excess. Water-soluble vitamins are not stored in the body, with the exception of Vitamin B12, which is stored in the liver.
Pseudo-vitamins
* Vitamin F was the designation originally given to essential fatty acids that the body cannot manufacture. They were "de-vitaminized" because they are fatty acids. Fatty acids are a major component of fats which, like water, are needed by the body in large quantities and thus do not fit the definition of vitamins which are needed only in trace amounts.
* Although there is no Vitamin S, the suggestion has been made that salicylic acid may qualify for the criteria needed to be defined as a vitamin, and that in this case the designation "Vitamin S" could be used to describe it.
* Herbalists and naturopaths have named various herbs and chemicals "vitamins", even though they are not, including Vitamin T and Vitamin U.
* Some authorities say that Ubiquinone, also called Coenzyme Q10, is a vitamin. Ubiquinone is manufactured in small amounts by the body, like Vitamin D.
* Pangamic acid and the related substance dimethylglycine are sometimes referred to as Vitamin B15.
* Laetrile is sometimes referred to as Vitamin B17. Both pangamic acid and laetrile were first proposed as vitamins by Ernst T. Krebs; neither are recognized by the medical community as vitamins.
* Flavonoids are sometimes called Vitamin P.
* A few substances were once thought to be B-complex vitamins and are referred to as B-vitamins in older literature, including B4 (Adenine) and B8, but are no longer recognized as such.
Colloquial usage of the term
* The sedative Ketamine is often called Vitamin K when used as a recreational drug.
* Vitamin V is a colloquialism for Viagra, Vitamin Z for Zoloft, and Vitamin R for Ritalin, especially when implying that these drugs are overprescribed (or, as a hyperbole, taken as commonly as vitamins).
* Likewise, Vitamin A and Vitamin C are sometimes used as slang terms for alcoholic beverages and caffeine, respectively.
* Ativan an antianxiety agent is often called "Vitamin A" (off the record).
* Antipsychotic drug haldol is sometimes referred to as Vitamin H in psych hospitals (off-the-record, of course).
* Vitamin W is a colloquialism for water.
* Vitamin I is a colloquialism for ibuprofen.
* Colloquially, the word vitamin is often used to refer to vitamin supplements, products, often in pill form, that contain one or more purified vitamins which are used to supplement the vitamin content of a diet.
Non-human vitamins
Different organisms need different trace organic substances. Most mammals need, with few exceptions, the same vitamins as humans. One notable exception is ascorbic acid; most mammals can synthesize this. The less related a species is to mammals, the more different the organisms' requirements become. For example, some bacteria need adenine. Pyrroloquinoline quinone (PQQ) was reported as a vitamin for mice in 2003. Housecats require the nutrient taurine; it is unclear whether this is a vitamin.
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