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B vitamins | Adenine | Retinol | Vitamin C

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Retinol (Vitamin A)
Retinol (Vitamin A)

Vitamins are nutrients required in very small amounts for essential metabolic reactions in the body [1]. The term vitamin does not encompass other essential nutrients such as dietary minerals, essential fatty acids, or essential amino acids. Nor does the term refer to the large number of other nutrients that promote health, but are not strictly essential.

Vitamins act both 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 forms 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 groups (methyl, formyl or methylene) in the cell.

Until the 1900s, vitamins were obtained solely through food intake. Many food sources contain different ratios of vitamins. Therefore, if the only source of vitamins is food, a seasonal, yearly or even daily change in diet also alters the ratio of ingested vitamins. Many vitamins can be stored by the body over a range of dosages and short term deficiencies (e.g. during a particular food growing season), do not always result in disease.

Vitamins have been produced as commodity chemicals and made widely available as inexpensive pills for several decades[2] allowing for consistent supplementation to dietary intake.

Fruits and vegetables are often a good source of vitamins.
Fruits and vegetables are often a good source of vitamins.



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 in which collagen is not properly formed, and is characterized by poor wound healing, bleeding of the gums, and severe pain.[3] In 1753, Lind published his Treatise on the Scurvy, which recommended using lemons and limes to avoid scurvy, which was adopted by the British Royal Navy. This led to the nickname Limey for sailors of that organization. Lind's discovery, however, was not widely accepted by individuals in the Royal Navy's Arctic expeditions in the 19th century, where it was widely believed that scurvy could be prevented by practicing good hygiene, regular exercise, and by maintaining the morale of the crew while on board, rather than by a diet of fresh food.[3] As a result, Arctic expeditions continued to be plagued by scurvy and other deficiency diseases. In the early 20th century, when Robert Falcon Scott made his two expeditions to the Antarctic the prevailing medical theory was that scurvy was caused by "tainted" canned food.[3]

In 1881, Russian surgeon Nikolai Lunin studied the effects of scurvy while at the University of Tartu (in present day Estonia).[4] He fed mice an artificial mixture of all the separate constituents of milk known at that time, namely the proteins, fats, carbohydrates, and salts. The mice that received only the individual constituents died, while the mice fed by milk itself developed normally. He made a conclusion that "a natural food such as milk must therefore contain, besides these known principal ingredients, small quantities of unknown substances essential to life".[4] However, his conclusions were rejected by other researchers when they were unable to reproduce his results. One difference was that he had used table sugar (sucrose), while other researchers had used milk sugar (lactose) which still contained small amounts of vitamin B.

In 1897, Christiaan Eijkman discovered that eating unpolished rice instead of the polished variety helped to prevent the disease beriberi. The following year, Frederick Hopkins postulated that some foods contained "accessory factors"—in addition to proteins, carbohydrates, fats, etc.—that were necessary for the functions of the human body.[3] Hopkins was awarded the 1929 Nobel Prize for Physiology or Medicine, with Christiaan Eijkman, for their discovery of several vitamins.

Kazimierz Funk was the first to isolate the water-soluble complex of micronutrients, whose bioactivity Fletcher had identified, and Funk proposed the complex be named "Vitamine".[5] 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 already 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.

Riboflavin (Vitamin B2)
Riboflavin (Vitamin B2)

Throughout the early 1900s, the use of deprivation studies allowed scientists to isolate and identify a number of vitamins. 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 "vitamin A", the bioactivity of which is now called vitamin D,[6] What we now call "vitamin A" was identified in fish oil because it was inactivated by ultraviolet light.

In 1931, Albert Szent-Györgyi and his research fellow Joseph Svirbely, determined that "hexuronic acid" was actually vitamin C and noted its anti-scorbutic activity, and 1937 Szent-Györgyi was awarded the Nobel Prize for his discovery. In 1943 Edward Adelbert Doisy and Henrik Dam were awarded the Nobel Prize for their discovery of vitamin K and its chemical structure.

Human vitamins

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.[7]

In humans there are thirteen vitamins, divided into two groups; four fat-soluble vitamins (A, D, E and K), and nine water-soluble vitamins (eight B vitamins and vitamin C).

Vitamin name Chemical name Solubility Deficiency disease Recommended Dietary Allowances
(male, age 19–70)
Upper Intake Level
Vitamin A Retinoids (include: retinol,
retinal, retinoic acid,
3-dehydroretinol and its derivatives)
Fat Night-blindness,
900 µg 3,000 µg
Vitamin B1 Thiamine Water Beriberi 1.2 mg (N/D)[10]
Vitamin B2 Riboflavin Water Ariboflavinosis 1.3 mg N/D
Vitamin B3 Niacin Water Pellagra 16.0 mg 35.0 mg
Vitamin B5 Pantothenic acid Water Paresthesia 5.0 mg [11] N/D
Vitamin B6 Pyridoxine Water Anemia[12] 1.3-1.7 mg 100 mg
Vitamin B7 Biotin Water n/a 30.0 µg N/D
Vitamin B9 Folic acid Water Deficiency during pregnancy is associated with birth defects. 400 µg 1,000 µg
Vitamin B12 Cyanocobalamin Water Megaloblastic anaemia[13] 2.4 µg N/D
Vitamin C Ascorbic acid Water Scurvy 90.0 mg 2,000 mg
Vitamin D2–D4 Lumisterol, Ergocalciferol,
Cholecalciferol, Dihydrotachysterol,
Fat Rickets 5.0 µg-10 µg [14] 50 µg
Vitamin E Tocopherol, Tocotrienol Fat deficiency is very rare, mild hemolytic anemiain newborn infants [15] 15.0 mg 1,000 mg
Vitamin K Naphthoquinone (not to be confused with ketamine) Fat Bleeding diathesis 120 µg N/D

Vitamins in nutrition and disease

Vitamins are essential for normal growth and development. Using the genetic blueprint inherited from its parents, a fetus begins to develop, at the moment of conception, from the nutrients it absorbs.

The developing fetus requires certain vitamins and minerals to be present at certain times. These nutrients facilitate the chemical reactions that produce, among other things, skin, bone, and muscle. If there is serious deficiency in one or more of these nutrients, a child may develop a deficiency disease. Minor deficiencies also have the potential to cause permanent damage, and may be associated with reduced life expectancy.[16]

For the most part, vitamins are obtained through food sources. However, a few vitamins 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. Some vitamins can be obtained from precursors that are obtained in the diet. Examples include vitamin A, which can be produced from beta carotene and niacin from the amino acid tryptophan.[8]

Once growth and development are completed, vitamins remain essential components of the healthy maintenance of the cells, tissues, and organs that make up the human body, and enable the body to efficiently use the calories provided by the food that we eat, and to help process proteins, carbohydrates, and fats.

Vitamin deficiencies

An organism can survive for some time without vitamins, although prolonged vitamin deficits may result in often painful and potentially deadly diseases. Body stores for different vitamins can vary widely; an adult may be deficient in vitamin A and B12 for long periods of time before developing a deficiency condition, while vitamin B3 stores may only last a couple of weeks.[9][15]

Deficiencies of vitamins are classified as either primary or secondary. A primary deficiency occurs when you do not get enough of the vitamin in the food you eat. A secondary deficiency may be due to an underlying disorder that prevents or limits the absorption or use of the vitamin, or due to a “lifestyle factor”, such as smoking, excessive alcohol consumption, or the use of medications that interfere with the absorption or the body's use of the vitamin.[15]

Well-known vitamin deficiencies involve thiamine (beriberi), niacin (pellagra), vitamin C (scurvy) and vitamin D (rickets). In much of the developed world, such deficiencies are rare due to; an adequate supply of food and the addition of vitamins and minerals, often called fortification, to common foods.[8] [15] [17]

Vitamin side effects and overdose

Vitamins are classified as fat-soluble or water-soluble based on how they are absorbed by the body. Vitamins A, D, E, and K are fat soluble, while the water-soluble vitamins include vitamin C and the B-complex vitamins (thiamine (B1), riboflavin (B2), niacin (B3), pantothenic acid (B5), vitamin B6, vitamin B12, biotin and folate.

Fat-soluble vitamins (A, D, E and K) are often stored in the body and can cause toxicity when ingested in excess. With the exception of vitamin B12, which is stored in the liver[13], water-soluble vitamins are not stored in the body. All vitamins have documented side effects. Like side effects from drugs, vitamin side effects increase in severity with increasing dosage. At high enough dosages vitamins can cause extreme side effects such as nausea, diarrhea, and vomiting.[8] Unlike side effects caused by drugs, vitamin side effects rarely cause any permanent harm.[18] When vitamin side effects emerge, full and rapid recovery is accomplished by reducing the supplement dosage. Furthermore, the concentrations of vitamins an individual can tolerate vary widely, and appear to be related to age and state of health.[19]

The likelihood of consuming too much of any vitamin from food is remote, but overdosing from vitamin supplementation does occur. It is for this reason that physicians and scientists carefully review all the clinical data on supplement use in order to determine upper dosage thresholds for each vitamin that can be tolerated as a daily dose by the entire population without side effects. This dosage is known as the tolerable upper intake level (UL).[8]

The supplement controversy

Dietary supplements are often used to ensure that adequate amounts on nutrients are obtained on a daily basis, if the nutrients cannot be obtained through a varied diet. Scientific evidence supporting the benefits of some dietary supplements is well established for certain health conditions, but others need further study.[20] It is also important to note that some supplements include vitamins and minerals, as well as herbs, botanicals and other substances.

Supplements are, as required by law, not intended to treat, diagnose, mitigate, prevent, or cure disease.[20] In some cases, dietary supplements may have unwanted effects, especially if taken before surgery, with other dietary supplements or medicines, or if the taker has certain health conditions.[20] Vitamin supplements may also contain levels of vitamins many times higher, and in different forms, than one may ingest through food.[21] Before taking a supplement, it is important to check with a knowledgeable health care provider, especially when combining or substituting supplements with other foods or medicine.

Governmental regulation of vitamin supplements

Most countries place dietary supplements in a special category under the general umbrella of "foods," not drugs. This necessitates that the manufacturer, and not the government, be responsible for ensuring that its dietary supplement products are safe before they are marketed. Unlike drug products, that must implicitly be proven safe and effective for their intended use before marketing, there are often no provisions to "approve" dietary supplements for safety or effectiveness before they reach the consumer. Also unlike drug products, manufacturers and distributors of dietary supplements are not generally required to report any claims of injuries or illnesses that may be related to the use of their products[22] however, side effects have been reported for several types of supplements.[23]

Names in current and previous nomenclatures

The reason the set of vitamins seems to skip directly from E to the rarely-mentioned K is that the vitamins corresponding to "letters" F-J were either reclassified over time, were discarded as false leads, or were renamed because of their relationship to "vitamin B", which became a "complex" of vitamins. The following table lists chemicals that had previously been classified as vitamins, as well as the earlier names of vitamins that later became part of the B-complex.

Previous vitamin
name [24] [25]
Chemical name[24][25] Current vitamin
Reason for name change[24]
Vitamin B4 Adenine N/A No longer classified as a vitamin
Vitamin B8 Adenylic acid N/A No longer classified as a vitamin
Vitamin F Essential fatty acids N/A Needed in large quantaties,
does not fit definition of vitamin.
Vitamin G Riboflavin Vitamin B2 Reclassified as B-complex
Vitamin H/ Vitamin I Biotin Vitamin B7 Reclassified as B-complex
Vitamin J Catechol, Flavin N/A No longer classified as a vitamin
Vitamin L1 Orthoaminobenzoic acid,
Anthranilic acid
N/A No longer classified as a vitamin
Vitamin L2 Adenyl thiomethylpentose N/A No longer classified as a vitamin
Vitamin M Folic acid Vitamin B9 Reclassified as B-complex
Vitamin P Flavonoids N/A No longer classified as a vitamin
Vitamin PP Niacin Vitamin B3 Reclassified as B-complex
Vitamin R, Vitamin B10 Pteroylmonoglutamic acid N/A No longer classified as a vitamin
Vitamin S, Vitamin B11 Pteroylheptaglutamic acid N/A No longer classified as a vitamin
Vitamin U Allantoine N/A No longer classified as a vitamin

See also


  1. ^ Lieberman, S, Bruning, N (1990). The Real Vitamin & Mineral Book. NY: Avery Group, 3.
  2. ^ Kirk-Othmer (1984). Encyclopedia of Chemical Technology Third Edition. NY: John Wiley and Sons, Vol. 24:104.
  3. ^ a b c d Jack Challem (1997). "The Past, Present and Future of Vitamins"
  4. ^ a b 1929 Nobel lecture
  5. ^ Funk, C. and H. E. Dubin. The Vitamines. Baltimore: Williams and Wilkins Company, 1922.
  6. ^ Bellis, Mary. Vitamins - Production Methods The History of the Vitamins. Retrieved 1 Feb 2005.
  7. ^ Kutsky, R.J. (1973). Handbook of Vitamins and Hormones. New York: Van Nostrand Reinhold.
  8. ^ a b c d e f Dietary Reference Intakes: Vitamins The National Academies, 2001.
  9. ^ a b Vitamin and Mineral Supplement Fact Sheets Vitamin A
  10. ^ N/D= "Amount not determinable due to lack of data of adverse effects. Source of intake should be from food only to prevent high levels of intake"(see Dietary Reference Intakes: Vitamins).
  11. ^ Plain type indicates Adequate Intakes (A/I). "The AI is believed to cover the needs of all individuals, but a lack of data prevent being able to specify with confidence the percentage of individuals covered by this intake" (see Dietary Reference Intakes: Vitamins).
  12. ^ Vitamin and Mineral Supplement Fact Sheets Vitamin B6
  13. ^ a b Vitamin and Mineral Supplement Fact Sheets Vitamin B12
  14. ^ Value represents suggested intake without adequate sunlight exposure (see Dietary Reference Intakes: Vitamins).
  15. ^ a b c d The Merck Manual: Nutritional Disorders: Vitamin Introduction Please select specific vitamins from the list at the top of the page.
  16. ^ Dr. Leonid A. Gavrilov, Pieces of the Puzzle: Aging Research Today and Tomorrow
  17. ^ Vitamin E Fact sheet
  18. ^ Institute of Medicine, Food and Nutrition Board. Dietary Reference Intakes: Calcium, Phosphorus, Magnesium, Vitamin D and Fluoride. National Academy Press, Washington, DC, 1999
  19. ^ Healthier Kids [1]
  20. ^ a b c Use and Safety of Dietary Supplements NIH office of Dietary Supplements.
  21. ^ Jane Higdon Vitamin E recommendations at Linus Pauling Institute's Micronutrient Information Center
  22. ^ Overview of Dietary Supplements
  23. ^ FDA Warnings and Safety information
  24. ^ a b c d Every Vitamin Page All Vitamins and Pseudo-Vitamins. Compiled by David Bennett.
  25. ^ a b Vitamins and minerals - names and facts

General References Include:

  • Stedman's Medical Dictionary. Ed. Maureen Barlow Pugh 27th ed. Baltimore: Lippincott Williams & Wilkins, 2000.
  • Donatelle, Rebecca J. Health: The Basics. 6th ed. San Francisco: Pearson Education, Inc. 2005.

External links

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This guide is licensed under the GNU Free Documentation License. It uses material from the Wikipedia.

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