|
| Vitamin name | Chemical name | Solubility | Deficiency disease | Overdose disease |
Recommended Dietary Allowances (male, age 19–70)[8] |
Upper Intake
Level (UL/day)[8] |
|---|---|---|---|---|---|---|
| Vitamin A |
Retinoids (retinol, retinoids and carotenoids) |
Fat |
Night-blindness and Keratomalacia[9] |
Hypervitaminosis A | 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 | None identified | ? | 30.0 µg | N/D |
| Vitamin B9 | Folic acid | Water | Deficiency during pregnancy is associated with birth defects, such as neural tube defects | ? | 400 µg | 1,000 µg |
| Vitamin B12 | Cyanocobalamin | Water | Megaloblastic anaemia[13] | ? | 2.4 µg | N/D |
| Vitamin C | Ascorbic acid | Water | Scurvy | (Refer to Vitamin C megadosage) | 90.0 mg | 2,000 mg |
| Vitamin D |
Ergocalciferol and Cholecalciferol |
Fat | Rickets and Osteomalacia | Hypervitaminosis D | 5.0 µg-10 µg[14] | 50 µg |
| Vitamin E |
Tocopherol and Tocotrienol |
Fat | Deficiency is very rare; mild hemolytic anemia in newborn infants.[15] | ? | 15.0 mg | 1,000 mg |
| Vitamin K | Naphthoquinone | Fat | Bleeding diathesis | ? | 120 µg | N/D |
Vitamins
in nutrition and disease
Vitamins are essential for the normal growth and development of a multicellular
organism. 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. Even minor
deficiencies have the potential to cause permanent damage.[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. Humans can produce some vitamins from precursors they
consume. 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 nutrients
for the healthy maintenance of the cells, tissues, and organs that make up a
multicellular organism; they also enable a multicellular life form to
efficiently use chemical energy provided by food eaten, and to help process the
proteins, carbohydrates, and fats required for respiration.
Vitamin deficiencies
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, 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] Individuals who eat a varied diet are unlikely to develop a severe
primary vitamin deficiency. In contrast, restrictive diets have the potential to
cause prolonged vitamin deficits, which may result in often painful and
potentially deadly diseases.
Because humans do not store most vitamins in their bodies, a human must consume
them regularly to avoid deficiency. Human corporeal stores for different
vitamins vary widely; vitamins A, D, and B12 are stored in significant amounts
in the human body, mainly in the liver,[15] and an adult human may be deficient
in vitamin A and B12 for long periods of time before developing a deficiency
condition. Vitamin B3 is not stored in the human body in significant amounts, so
stores may only last a couple of weeks.[9][15]
Well-known human vitamin deficiencies involve thiamine (beriberi), niacin
(pellagra), vitamin C (scurvy) and vitamin D (rickets). In much of the developed
world, such deficiencies are rare; this is due to (1) an adequate supply of
food; and (2) the addition of vitamins and minerals, often called fortification,
to common foods.[8][15]
Vitamin side effects and overdose
In large doses some vitamins have documented side effects. Vitamin side effects
tend to increase in severity with increasing dosage. The likelihood of consuming
too much of any vitamin from food is remote, but overdosing from vitamin
supplementation does occur. At high enough dosages some vitamins cause side
effects, such as nausea, diarrhea, and vomiting.[17][9] Unlike some of the side
effects caused by drugs, vitamin side effects rarely cause any permanent
harm.[18] When vitamin side effects emerge, recovery is often accomplished by
reducing the dosage. Furthermore, the concentrations of vitamins an individual
can tolerate vary widely, and appear to be related to age and state of
health.[19] In the United States, overdose exposure to all formulations of
vitamins was reported by 62,562 individuals in 2004 (nearly 80% of these
exposures were in children under the age of 6), leading to 53 “major”
life-threatening outcomes and 3 deaths[20]-- a small number in comparison to the
19,250 people who died of unintentional poisoning of all kinds in the U.S. in
the same year (2004).[21]
It
is for these reasons that physicians and scientists carefully review 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]
Supplements
Dietary supplements, often containing vitamins, are used to ensure that adequate
amounts of nutrients are obtained on a daily basis, if optimal amounts of 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.[22]
Supplements are, as required by law, not intended to treat, diagnose, mitigate,
prevent, or cure disease.[22] In some cases, dietary supplements may have
unwanted effects, especially if taken before surgery, with other dietary
supplements or medicines, or if the person taking them has certain health
conditions.[22] Vitamin supplements may also contain levels of vitamins many
times higher, and in different forms, than one may ingest through food.[23]
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[24] however, side effects have been reported for several types of
vitamin supplements.[25]
Names in current and previous nomenclatures
The reason the set of vitamins seems to skip directly from E to K is that the
vitamins corresponding to "letters" F-J were either reclassified over time,
discarded as false leads, or renamed because of their relationship to "vitamin
B", which became a "complex" of vitamins. The German-speaking scientists who
isolated and described vitamin K (in addition to naming it as such) did so
because the vitamin is intimately involved in the 'Koagulation' of blood
following wounding. At the time, most (but not all) of the letters from F
through I were already designated, so the use of the letter K was considered
quite reasonable. 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 name[26][27] | Chemical name[26][27] | Reason for name change[26] |
|---|---|---|
| Vitamin B4 | Adenine | No longer classified as a vitamin |
| Vitamin B8 | Adenylic acid | No longer classified as a vitamin |
| 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 | No longer classified as a vitamin |
| Vitamin L1 | Anthranilic acid | No longer classified as a vitamin |
| Vitamin L2 | Adenylthiomethylpentose | No longer classified as a vitamin |
| Vitamin M | Folic acid | Reclassified as Vitamin B9 |
| Vitamin O | Carnitine | No longer classified as a vitamin |
| Vitamin P | Flavonoids | No longer classified as a vitamin |
| Vitamin PP | Niacin | Reclassified as Vitamin B3 |
| Vitamin U | S-Methylmethionine | No longer classified as a vitamin |
General References Include:
| Stedman's Medical Dictionary. Ed. Maureen Barlow Pugh et.al. 27th ed. Baltimore: Lippincott Williams & Wilkins, 2000. | |
| Donatelle, Rebecca J. Health: The Basics. 6th ed. San Francisco: Pearson Education, Inc. 2005. |
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