Vitamin B6

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Vitamin B6 is a water-soluble vitamin. Seven forms of this vitamin are known: pyridoxine (PN), pyridoxine 5'-phosphate (PNP), pyridoxal (PL), pyridoxal 5'-phosphate (PLP), pyridoxamine (PM), pyridoxamine 5'-phosphate (PMP), and 4-pyridoxic acid (PA). PN is the form that is given as vitamin B6 supplement, PLP is the metabolically active form and PA is the catabolite which is excreted in the urine . All forms except PA can be interconverted. PLP is 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 1 History 2 Sources 3 Deficiencies 3.1 Diagnostic Testing for B6 Deficiency 4 Overdose 5 Preventive roles and therapeutic uses 6 External links 7 References

[edit] 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.

[edit] 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. Nuts, Liver, chicken, fish, green beans, field salad, wheat germ, nutritional yeast, sea vegetables and bananas are particularly good food sources.

[edit] Deficiencies

• Supporters of a debated medical condition known as Pyroluria believe it may be 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 dosage of B6 into the bloodstream.
• Signs of a Vitamin B6 deficiency include:
  • Depression
  • Anxiety
  • Loss of Libido
  • Insomnia
  • Water Retention
  • Inability to Process Glucose
  • Body weight Loss/Gain

• Physicians are now beginning to recommend routine vitamin B6 administration during hormonal contraception/medication.
• Grumpiness and irritability are also often symptomatic of a deficiency according to "Body, Mind, and the B Vitamins" by Ruth Adams and Frank Murray.
• 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]

[edit] Diagnostic Testing for B6 Deficiency

A positive diagnosis test for pyridoxine deficiency can be assertained by measuring erythrocyte levels of aspartate aminotransferase and transketolase in serum.

[edit] 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]

Because adverse effects have only been documented from vitamin B6 supplements and never from food sources, only the supplemental form of vitamin B6 (pyridoxine) is discussed with respect to safety. Although vitamin B6 is a water-soluble vitamin and is excreted in the urine, very high doses of pyridoxine over long periods of time may result in painful neurological symptoms known as sensory neuropathy. Symptoms include pain and numbness of the extremities, and in severe cases difficulty walking. Sensory neuropathy typically develops at doses of pyridoxine in excess of 1,000 mg per day. However, there have been a few case reports of individuals who developed sensory neuropathies at doses of less than 500 mg daily over a period of months. None of the studies, in which an objective neurological examination was performed, found evidence of sensory nerve damage at intakes of pyridoxine below 200 mg/day (15). In order to prevent sensory neuropathy in virtually all individuals, the Food and Nutrition Board of the Institute of Medicine set the tolerable upper intake level (UL) for pyridoxine at 100 mg/day for adults. Because placebo-controlled studies have generally failed to show therapeutic benefits of high doses of pyridoxine, there is little reason to exceed the UL of 100 mg/day.

[edit] Preventive roles and therapeutic uses

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 either diet or supplements, could cut the risk of Parkinson’s disease by half according to a prospective study from the Netherlands.^[4]

A combination of vitamin B6 and magnesium may be an effective therapy for children with autism. While two small studies showed no effect of combined vitamin B6 and magnesium therapy (Tolbert 1993, Findling 1997), one larger study, alleged to be poorly-controlled^{[citation needed]} showed that the B6-magnesium combination had a positive and significant behavioral effect on children with autism (Martineau 1985). In addition, two designed studies, again alleged to be poorly-designed^{[citation needed]}, found that supplementation with vitamin B6 and magnesium had significant positive effects on behavior in children with autism (Rimland 1978, Lelord 1981).

It is also suggested that ingestion of vitamin B6 can alleviate some of the many symptoms of a alcoholic hangover.

[edit] External links

• Facts about Vitamin B6 from NIH Office of Dietary Supplements
• The B6 database A database of B6-dependent enzymes
• Vitamin B6 Information Sheet from the Linus Pauling Institute
• Vitamin B6 (and magnesium) in the treatment of autism from the Autism Research Institute

[edit] References

1. ^ 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
2. ^ Vitamin and Mineral Supplement Fact Sheets Vitamin B₆
3. ^ ^{a b} Ebben, M., Lequerica, A., & Spielman A. (2002). Effects of pyridoxine on dreaming: a preliminary study. Perceptual & Motor Skills, 94(1), 135–140.
4. ^ Increased intake of vitamin B6Sheet. Retrieved on 2006-08-11.

• Findling, R.L., et al. 1997. "High-dose pyridoxine and magnesium administration in children with autistic disorder: an absence of salutary effects in a double-blind, placebo-controlled study." J Autism Dev Disord. 27(4):467-478.

• Lelord, G., et al. 1981. "Effects of pyridoxine and magnesium on autistic symptoms--initial observations." J Autism Dev Disord. 11(2):219-230.

• Martineau, J., et al. 1985. "Vitamin B6, magnesium, and combined B6-Mg: therapeutic effects in childhood autism." Biol. Psychiatry 20(5):467-478.

• Rimland, B., et al. 1978. "The effect of high doses of vitamin B6 on autistic children: a double-blind crossover study." Am J Psychiatry 135(4):472-475.

• Tolbert, L., et al. 1993. "Brief report: lack of response in an autistic population to a low dose clinical trial of pyridoxine plus magnesium." J Autism Dev Disord. 23(1):193-199.