Vitamin B6
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Pyridoxine
Vitamin B6 is a water-soluble
vitamin. The three major forms
of vitamin B6 are pyridoxine (also known as pyridoxol), pyridoxal,
and pyridoxamine, which are all converted in the
liver to
pyridoxal 5'-phosphate
(PLP) � a cofactor
in many reactions of amino acid
metabolism. PLP also is necessary for the enzymatic reaction governing the release
of glucose from
glycogen.
Contents
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History
Vitamin B6 is a water-soluble compound that was discovered in 1930s during nutrition
studies on rats. The vitamin was named pyridoxine to indicate its structural homology
to pyridine. Later it was shown that vitamin B6 could exist in two other, slightly
different, chemical forms, termed pyridoxal and pyridoxamine. All three forms of
vitamin B6 are precursors of an activated compound known as pyridoxal 5'-phosphate
(PLP), which plays a vital role as the cofactor of a large number of essential enzymes
in the human body.
Enzymes dependent on PLP catalyze a wide variety of chemical reactions mainly
involving amino acids. The reactions carried out by the PLP-dependent enzymes that
act on amino acids include transfer of the amino group, decarboxylation, racemization,
and beta- or gamma-elimination or replacement. Such versatility arises from the
ability of PLP to covalently bind the substrate, and then to act as an electrophilic
catalyst, thereby stabilizing different types of carbanionic reaction intermediates.
Overall, the Enzyme Commission (EC;
http://www.chem.qmul.ac.uk/iubmb/enzyme/)
has catalogued more than 140 PLP-dependent activities, corresponding to ~4% of all
classified activities.
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Sources
The United States
RDA varies between
1.3 mg and 2.0 mg, depending upon age and gender.
Vitamin B6 is prevalent in both animal and vegetable food sources. Liver,
chicken,
fish,
green beans, field
salad,
wheat germ,
nutritional yeast,
sea vegetables and bananas are
particularly good food sources.
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Deficiencies
Pyroluria is one potential
cause of vitamin B6 deficiency. Another cause of vitamin B6 deficiency is the use
of the tuberculostatic medication
isoniazid, and for this reason,
it is recommended to supplement with vitamin B6 when using this drug.
In women, another potential cause for vitamin B6 deficiency is use of
oral contraceptives
and other medications containing estro-progestational hormones (such as those prescribed
as part of Hormone
Replacement Therapy). Other contraceptive medications that may cause vitamin
B6 deficiency include: the patch (Ortho Evra), vaginal ring (Nuvaring), hormonal
IUD (Mirena) and shot (Depo Provera). Specifically, habitual use of estro-progestational
hormones inhibit absorption of vitamin B6 (due to a disturbance of tryptophan metabolism),
necessitating a larger daily doseage of B6 into the bloodstream. Signs of a Vitamin
B6 deficiency include: depression, anxiety, loss of libido, insomnia, water retention,
inability to process glucose (weight loss/gain). Physicians are now beginning to
recommend routine vitamin B6 administation during hormonal contraception/medication.
A meta-analysis of three
databases (MEDLINE,
EMBASE,
and Cochrane Library),
including only double-blind,
randomized controlled trials, found that vitamin B6 has a significant effect compared
to placebos in treating
morning sickness, similar
to that of ginger[1].
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Diagnostic Testing for B6 Deficiency
A positive diagnosis test for pyroxidine deficiency can be assertained by measuring
erythrocyte levels of
aspartate aminotransferase
in serum.
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Overdose
An overdose of pyridoxine can cause a temporary deadening of certain nerves such
as the proprioceptory nerves; causing a feeling of disembodiment common with the
loss of proprioception.
This condition is reversible when supplementation is stopped.[2]
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Increased B6
At least one preliminary study has found that this vitamin may increase
dream vividness or the ability
to recall dreams[3]. It is thought that this effect may
be due to the role this vitamin plays in the conversion of
tryptophan to
serotonin[3].
The intake of vitamin B6, from diet and supplements, could cut the risk of Parkinson�s
disease by half suggests a prospective study from the Netherlands.
[4]
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External links
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References
- ^
Pregnancy
Morning Sickness - Ginger as Effective as Vitamin B6 (open)
Effectiveness
and Safety of Ginger in the Treatment of Pregnancy-Induced Nausea and Vomiting
(subscription), Borrelli et al., Obstetrics & Gynecology, 2005;105:849-856
- ^
Vitamin
and Mineral Supplement Fact Sheets Vitamin B6
- ^ a b
Ebben, M., Lequerica, A., & Spielman A. (2002). Effects of pyridoxine on dreaming:
a preliminary study. Perceptual & Motor Skills, 94(1), 135�140.
- ^
Increased intake of vitamin B6Sheet. Retrieved on
2006-08-11.
Vitamins
All B vitamins |
All D vitamins
Retinol (A) |
Thiamine (B1) |
Riboflavin (B2) |
Niacin (B3) |
Pantothenic acid (B5)
| Pyridoxine (B6) |
Biotin (B7) |
Folic acid (B9) |
Cyanocobalamin (B12)
| Ascorbic acid (C)
| Ergocalciferol (D2)
| Cholecalciferol (D3)
| Tocopherol (E) |
Naphthoquinone (K)
Retrieved from "http://en.wikipedia.org/wiki/Vitamin_B6"
Category:
B vitamins
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